Updated on 2022/05/15

写真a

 
NAGUMO, Michihiko
 
Affiliation
Faculty of Science and Engineering
Job title
Professor Emeritus

Education

  •  
    -
    1960

    The University of Tokyo  

  •  
    -
    1960

    The University of Tokyo   Graduate School, Division of Mathematical and Physical Science  

  •  
    -
    1955

    The University of Tokyo   Faculty of Science  

  •  
    -
    1955

    The University of Tokyo   Faculty of Science   Physics  

Degree

  • Dr. Sci.

Research Experience

  • 1988
    -
    2003

    Professor, Waseda Univ.

  • 2000
    -
     

    -02 Dir. Lab. Mater. Sci. Tech. Waseda Univ.

  • 1960
    -
    1988

    Nippon Steel Corp.

  • 1985
    -
     

    -87 Dir. First Res. Labs.

Professional Memberships

  •  
     
     

    日本鉄鋼協会

  •  
     
     

    日本金属学会

  •  
     
     

    The Iron and Steel Institute of Japan

  •  
     
     

    The Japan Institute of Metals

  •  
     
     

    The Japan Society for Technology of Plasticity

  •  
     
     

    Metals and Materials Society

  •  
     
     

    The Minerals

  •  
     
     

    The Physical Society of Japan

▼display all

 

Research Areas

  • Material processing and microstructure control

  • Structural materials and functional materials

  • Metallic material properties

Research Interests

  • 構造・機能材料

  • Structural and Functional Materials

Papers

  • Critical Assessment 35: Assessment of the intrinsic susceptibility to hydrogen embrittlement for qualification of steels

    Michihiko Nagumo, Kenichi Takai

    Materials Science and Technology   36 ( 10 ) 1003 - 1011  2020.07  [Refereed]  [Invited]

    Authorship:Lead author, Corresponding author

    DOI

  • The predominant role of strain-induced vacancies in hydrogen embrittlement of steels: Overview

    Michihiko Nagumo, Kenichi Takai

    Acta Materialia   165   722 - 733  2019.02  [Refereed]  [Invited]

    Authorship:Lead author, Corresponding author

    DOI

  • 鋼の新しい耐水素脆化評価法と材料設計にむけて

    南雲道彦, 高井健一

    ふぇらむ   22   442 - 449  2017  [Refereed]  [Invited]

    Authorship:Lead author

  • Promoted generation of damage and premature fracture due to Hydrogen-enhanced creation of strain-induced vacancies

    M. Nagumo, K. Takai

    Materials Performance in Hydrogen Embrittlement,     36 - 44  2017  [Refereed]

    Authorship:Lead author, Corresponding author

  • Hydrogen embrittlement of austenitic stainless steels revealed by deformation microstructures and strain-induced creation of vacancies

    M. Hatano, M. Fujinami, K. Arai, H. Fujii, M. Nagumo

    Acta Materialia   67   342 - 353  2014  [Refereed]

    Authorship:Last author

  • 「破壊現象における水素の機能

    南雲道彦

    まてりあ   50   205 - 211  2011  [Refereed]  [Invited]

    Authorship:Lead author, Corresponding author

  • Ductile crack initiation and growth promoted by hydrogen in steel

    Y. Shimomura, M. Nagumo

    Environment-Induced Cracking of Materials     285 - 294  2008  [Refereed]

    Authorship:Last author

     View Summary

    This chapter examines the effect of hydrogen in successive stages leading to fracture, in a three-point bending test of low-carbon steel to elucidate the mechanism of hydrogen-related failure. The measurement of the crack-opening displacement, detection of ductile cracks initiation by means of an electric potential method, and R-curve analysis of stable ductile crack growth are conducted. Measurement of crack-opening displacement shows that hydrogen suppresses the blunting of the prenotch even prior to the onset of a stable ductile crack that is detected with an electric potential method. Hydrogen promotes the initiation of the ductile crack and reduces ductile crack growth resistance that is evaluated by means of R-curve analysis. Shallowing and features of quasi-cleavage characterizes the fracture surface of the hydrogen-charged steel. Fractographic features suggest that the effect of hydrogen is to reduce plasticity associated with crack growth. Enhanced strain localization by hydrogen associated with the creation of defects in front of the notch and crack is consistent with these results. Hydrogen likely enhances the creation of vacancies during plastic deformation, which would be consistent with the vacancy agglomeration model for the mechanism of hydrogen-related failure. © 2008 Elsevier Ltd All rights reserved.

    DOI

  • Effects of hydrogen on mechanical behavior of steels

    M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   90 ( 10 ) 766 - 775  2004.10  [Refereed]

     View Summary

    Main features of hydrogen effects on mechanical behavior of steels have been reviewed. While the effects on macroscopic tensile properties are not definite, the increase in dislocation mobility by hydrogen appears as an enhanced stress relaxation the extent of which correlating with the susceptibility to failure. Hydrogen enhances the creation of vacancies during plastic deformation. The extent is susceptible to microstructures of steels and correlates with the susceptibility to failure. Flow localization in the presence of hydrogen is substantial, leading to shear instability. Characteristic fractographic features in hydrogen-related failure, such as striations, have been shown to originate in deformation bands in which the density of defects is high. Prominent localization of void nucleation takes place at the advancing crack tip. Amorphization has been observed in front of the crack and just below the fracture surface in a hydrogen-charged steel in accord with flow localization and associated vacancy creation. Hydrogen remarkably reduces the fatigue resistance of steels, and, conversely, prior fatigue treatment increases the susceptibility to delayed fracture. The mechanism has been ascribed to the creation of vacancies during fatigue and interactions between vacancies and hydrogen. Further studies for assessing the susceptibility to hydrogen-related failure have been suggested to be based on the accumulation of damage rather than hydrogen content.

  • Hydrogen related failure of steels – a new aspect

    M. Nagumo

    Materials Science and Technology   20 ( 8 ) 940 - 950  2004.08  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • Accelerated failure in high strength steel by alternating hydrogen-charging potential

    M Nagumo, H Uyama, M Yoshizawa

    SCRIPTA MATERIALIA   44 ( 6 ) 947 - 952  2001.04  [Refereed]

  • Ductile crack growth resistance in hydrogen-charged steels

    M Nagumo, H Yoshida, Y Shimomura, T Kadokura

    MATERIALS TRANSACTIONS JIM   42 ( 1 ) 132 - 137  2001.01  [Refereed]

     View Summary

    The effect of hydrogen on the shear localization and associated crack nucleation has been investigated by means of a three point bending test of hydrogen-charged steels. The ductile crack growth resistance in terms of the slope of R-curve was lowered under the presence of hydrogen, the decrease being more pronounced in the steel with more abundant slip constraint phases along grain boundaries. Enlargement of size and reduction in depth/width ratio of primary dimples, occasionally associated with quasi-cleavage, were observed on the fracture surface of the hydrogen-charged steels. By means of a FEM calculation, the increase of the nucleation void volume fraction localized at the crack tip with strain localization as well was shown to take place in the hydrogen-charged steel in consistent with enhanced shear instablity. It was discussed that the evolution of vacancy-type defects, rather than void nucleation at second phase particles. in the course of plastic straining was enhanced under the presence of hydrogen, reducing the ductile crack growth resistance.

  • Plasma treatment of pitch-based ultra high modulus carbon fibers

    A Fukunaga, T Komami, S Ueda, M Nagumo

    CARBON   37 ( 7 ) 1087 - 1091  1999  [Refereed]

     View Summary

    Pitch-based ultra high modulus carbon fibers were oxygen or argon plasma treated to compare the anodized fibers. As a result, the plasma treated samples obtained much higher adhesive strength to an epoxy resin than did the anodized samples. In order to characterize the surface, the coulostatic method (an electrochemical method) was applied and laser Raman spectroscopy was employed. The specific surface area and active surface area was determined by BET surface area measurement. As a result of the plasma treatment, the double layer capacity of the surface, which was related to the apparent surface area, dramatically increased. The surface crystalline size became smaller, and the active surface area increased. We therefore proposed the following model for plasma treatment mechanism which was quite different from anodic oxidation. The surface layer was peeled and the aromatic bonds in the basal plane were broken, so the number of active sites on the surface greatly increased, thus enabling strong adhesion to epoxy resin. (C) 1999 Elsevier Science Ltd. All rights reserved.

  • Characterizations of mechanically alloyed Ti-Zr-Cu-Ni powders

    XD Liu, M Nagumo, M Umemoto

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   252 ( 2 ) 179 - 187  1998.09  [Refereed]

     View Summary

    Influences of Zr and Ti contents on amorphization of Ti-Zr-Cu-Ni alloy induced by mechanical alloying are studied. It is found that by increasing Zr content, the 100 h-milled Cu58-xZrxTi34Ni8 (at %) alloys change from a single fee solid solution (x = 0) to a partially amorphous state (x = 11) and finally to almost a single amorphous phase (x greater than or equal to 31). By changing Ti content, partial amorphization is confirmed to occur in the Cu47Zr11Ni42-xTix (at.%) alloy with x greater than or equal to 22. Influences of Zr and Ti contents on the thermal stability of the as-milled Cu58-xZrxTi34Ni8 and Cu47Zr11Ni42-xTix alloys are investigated by means of a differential scanning calorimeter and X-ray diffraction. Oxidation of zirconium in the above as-milled alloys upon heating is discussed. (C) 1998 Elsevier Science S.A. All rights reserved.

  • Effect of cyclic stressing on delayed fracture of high strength steel

    K Izutsu, K Takai, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   83 ( 6 ) 371 - 376  1997.06  [Refereed]

     View Summary

    The delayed fracture characteristics of a PC bar steel have been examined under the FIP test. Earlier fracture occurs by applying cyclic stress compared with the constant stress even when the maximum stress is the same. The peak temperature of desorption of hydrogen at thermal desorption analysis is about 473K. Both the amount of diffusible hydrogen and desorption rate at room temperature of specimens just after the FIP test are irrelevant to the stress mode. After annealing the specimens at 473K for 30min after the test and reimmersing in the FTP solution, the total amount of diffusible hydrogen decreases to about 2/3. The effect of cyclic stressing appears as the increase in the reduction of hydrogen released up to 473K. It is discussed that the effect of cyclic stressing on the delayed fracture characteristics is through a dynamical interaction of hydrogen with defects produced by plastic deformation.

  • AGGLOMERATION OF COAL PARTICLES IN FLUIDIZED-BED HEATING

    T KOJIMA, M. NAGUMO

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   79 ( 11 ) 1236 - 1241  1993.11  [Refereed]

     View Summary

    Agglomeration properties of coal in a fluidized bed was investigated to obtain a fundamental information for the design of a rapid heating unit of a newly proposed continuous coke oven.
    The agglomeration causes troubles in the bed. Agglomeration temperature was defined as the temperature at which a steep temperature change was found in the bed. Effects of properties of raw coals, e.g., softening and solidification properties and fluidity, and operational conditions, e.g., heating rate, and fluidizing gas velocity, on the agglomeration temperature were investigated.
    The following results were obtained : (1) Agglomeration temperature rose with decreasing maximum fluidity of coal, increasing coal size, and increasing gas velocity. (2) Agglomeration temperature was higher for the coal treated at high heating rate than that for coal treated at low heating rate. (3)Agglomeration temperature was well correlated with the temperature at which gas (CH4 or H-2) production began.

  • EXAFS STUDY ON CRYSTALLIZATION OF MECHANICALLY PREPARED CU-TI AMORPHOUS ALLOY

    K NAKAMURA, M NAGUMO

    JOURNAL OF NON-CRYSTALLINE SOLIDS   156   575 - 579  1993.05  [Refereed]

     View Summary

    Structures of amorphous Cu-Ti alloys prepared by mechanical alloying (MA) of elemental metal powders and mechanical grinding (MG) of intermetallic compound CuTi were investigated by means of EXAFS after crystallization. From X-ray diffraction spectra, the crystallization products of amorphous Cu50Ti50 produced by MA and MG are different: the former show phase separation into Cu4Ti and CuTi2, while the latter form primarily the nearly equiatomic phases Cu4Ti3 and CuTi. In an EXAFS analysis, the first shell of the Fourier transform of the normalized EXAFS of the crystallized samples shows an asymmetry or shoulder as the milling time increases. Curve fitting of the profile can be successfully performed by introducing a new Cu-Ti bond, and the difference of MA and MG glasses is in the contribution from the new bond. The EXAFS analysis of samples prepared by the two routes shows that crystallization proceeds by the rearrangement of Cu-Ti bonds in case of MA, while the growth of the residual crystalline structures dominates in case of MG.

  • CRYSTALLIZATION KINETICS OF AMORPHOUS CU50TI50 ALLOY PREPARED BY MECHANICAL GRINDING

    K NAKAMURA, K KASAI, M NAGUMO

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   54 ( 12 ) 1320 - 1328  1990.12  [Refereed]

     View Summary

    Crystallization kinetics of amorphous Cu50Ti50 alloy prepared by mechanical grinding of the intermetallic compound powder with a high energy ball mill was studied. Kinetics at the isothermal annealing was well analyzed in terms of the Johnson-Mehl-Avrami equation, giving a velocity exponent of 0.85 and an activation energy of 183 kJ/mol. Both figures are less than the corresponding values of the material prepared by a rapid cooling process. Kinetics at the athermal annealing was analyzed using the Kissinger method and an activation energy of 154 kJ/mol was obtained in accord with the analysis with the JMA equation.
    The amorphous state and the crystallization process were discussed from these results. In an amorphous material prepared by mechanical grinding, the crystalline fraction remains and is likely to act as nuclei of crystallization. Crystallization is likely to proceed two-dimensionally on these nuclei. The number and average size of nuclei were estimated to be 10(24)/m3 and of 10(3) unit cells Cu50Ti50, respectively.
    The activation energy of diffusion estimated by assuming the two-dimensional crystal growth kinetics is 214 kJ/mol and the diffusion of Ti atoms is likely to be rate-controlling. Atom migration necessary for the crystallization is considered to take place in a short range of the order of 5-10 nm.

  • FRACTURE PROCESS OF A CONTROL-ROLLED STEEL IN THE DUCTILE TO BRITTLE TRANSITION-TEMPERATURE REGION

    M NAGUMO, Y SAWANO

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   54 ( 4 ) 420 - 426  1990.04  [Refereed]

  • EFFECT OF CENTRAL SEGREGATION ON DRAWABILITY OF HIGH-CARBON STEEL WIRE ROD MANUFACTURED FROM CONTINUOUSLY CAST BLOOMS

    OCHIAI, I, H OHBA, Y HIDA, M NAGUMO

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   74 ( 8 ) 1625 - 1632  1988.08  [Refereed]

  • DERIVATION OF A KINETICS MODEL FOR SOLUTE CARBON DURING RAPID-COOLING IN CONTINUOUS ANNEALING PROCESS FOR LOW-CARBON, COLD-ROLLED SHEET STEELS

    K KOYAMA, Y KURODA, H KATOH, M NAGUMO

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   71 ( 11 ) 1497 - 1503  1985  [Refereed]

  • MECHANISM OF THE FORMATION OF COLUMNAR STRUCTURE IN LOW-CARBON STEEL WIRES DURING ANNEALING

    OCHIAI, I, H OHBA, Y HIDA, M NAGUMO

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   70 ( 15 ) 2009 - 2016  1984  [Refereed]

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Books and Other Publications

  • Fundamentals of Hydrogen Embrittlement

    NAGUMO Michihiko( Part: Sole author, Materials Science)

    Springer  2016

  • Theories of Hydrogen Embrittlement in Steels

    NAGUMO Michihiko( Part: Sole author, Encyclopedia of Iron, Steel, and Their Alloys)

    Taylor & Francis  2015.03

  • ”水素脆性の力学的機構ー塑性不安定化ー”,水素脆化研究の基盤構築シンポジウム予稿集

    日本鉄鋼協会  2010

  • 水素製造・吸蔵・貯蔵材料と安全化(4.1水素脆化の機構と対策)

    サイエンス&テクノロジー  2010 ISBN: 9784864280044

  • ”水素脆性評価法とその意義”,水素脆化研究の基盤構築シンポジウム予稿集

    日本鉄鋼協会  2009

  • "水素脆性における水素分析の意義",「材料中の水素状態分析標準化の基盤構築」フォーラムシンポジウム予稿集

    日本鉄鋼協会  2008

  • Ductile Crack Initiation and growth Promoted by Hydrogen in Steel, in "Environment-Induced Cracking of Materials Vol.1: Chemistry, Mechanics and Mechanisms"

    Elsevier  2008

  • 水素脆性の基礎

    内田老鶴圃  2008

  • Fundamentals of Hydrogen-Related Failure

    UCHIDA ROKAKUHO Pub.Co.Ltd  2008

  • “Ductile crack initiation and growth promoted by hydrogen in steel”in Environment-Induced Cracking of Materials: Chemistry, Mechanics and Mechanisms, pp. 285-294.

    Elsevier  2008

  • 構造材料の環境脆化における水素の機能に関する研究ーⅤ

    日本鉄鋼協会  2003

  • Functions of Microstructures in Delayed Fracture of Martensitic Steels

    in "Hydrogen Effects on Materials Behavior and Corrosion Deformation Interactions", TMS, pp.999-1008  2003

  • いろいろな破壊形態の統一的理解

    材料破壊の基礎から応用―信頼性の高い材料の開発・応用にむけて,日本金属学会  2002

  • 水素脆化を支配する材質基本因子の抽出と材料設計指針

    構造材料の環境脆化における水素の機能に関する研究―Ⅳ,日本鉄鋼協会  2001

  • 水素脆化感受性を支配する塑性変形誘起欠陥

    日本鉄鋼協会、構造材料の環境脆化における水素の機能に関する研究-(]G0003[)  2001

  • Deformation-Induced Defects Controlling Susceptibility to Hydrogen Embrittlement

    The Iron & Steel Institute of Japan, Function of Hydrogen in Environmental Degradation of Structural Materials-(]G0003[)  2001

  • 水素脆性に対する材料組織因子・合金元素の機能

    構造材料の環境脆化における水素の機能に関する研究-(]G0002[) 日本鉄鋼協会  2000

  • Functions of Microstructures and Alloying Elements on Hydrogen Embrittlement

    Report of Functions of Hydrogen Environmental Degradation of Structural Materials-(]G0002[), Iron and Steel Institute of Japan  2000

  • 金属の水素脆化メカニズム概論

    最新の水素の検出法と水素脆化防止法 日本金属学会  1999

  • 変形誘起欠陥の水素による安定化

    構造材料の環境脆科における水素の機能に関する研究-1、日本鉄鋼協会  1999

  • Mechanism of Hydrogen Embritlement of Steel

    Recent Technologies of Hydrogen Detection and Prevention of Hydrogen Embrittlement Japan Inst. Metals  1999

  • 破壊現象として一般化される鋼の水素脆性機構

    遅れ破壊解明の新展開、日本鉄鋼協会  1997

  • Synthesis and Mechanical Properties of TiAl/Ti2 AlC Fine Composites Prepared by Mechanical Alloying

    Proc. Int. Conf. Recent Advances in Metallurgical Processes/New Age Int. Pub. , New Delhi  1997

  • Mechanism of Hydrogen Embrittlement Generallized as Fracture of Steels

    Advances in Delayed Fracture Solution of High Strength Steels, Iron and Steel Inst. Japan  1997

  • 脆性的微視き裂の核形成過程

    合金におけるヘテロ構造の定量解析と設計・制御プロセス調査報告書  1995

  • メカニカルアロイングによる微細複合材料の可能性

    先端金属材料の創製基礎技術動向調査報告書  1995

  • Nucleation Process of Microcracks in the Burittle Fracture

    Report of Survey on Hetero-Structures in Alloys  1995

  • Potentials of Synthesis of Fine Composites by Mechanical Alloying

    Report of Survey of Fundamental Technologies for Fabrication of Advanced Metallic Materials  1995

  • Synthsis of Nanocomposites by Solid State Reactions of Metal-Ceramics Systems

    New Horizons for Materials  1995

  • 鋼の延性・脆性破壊遷移温度域における脆性破壊発生の支配因子

    不均一性の本質とそれに由来する材料特性に関する研究調査報告書  1994

  • Microstructures Relevant to Brittle Fracture Initiation at Heat Affected Zone of Weldment of a Low Carbon Steel

    Ext. Abstract of Int. Symp. New Aspects of Microstructures in Modern Low Carbon Hith Strength Steels, Tokyo, Iron and Steel Inst. Japan.  1994

  • 金属材料の高強度化と延・靭性低下機構

    日本金属学会「強度と破壊」  1993

  • Mechanism of strengthening and reducing ductility ang toughness of Steels

    1993

  • Fracture Process of A533B Steel at Ductile-Brittle Transition Region

    Strength of Metals and Alloys (Frend Pub. House)  1991

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Misc

  • Conformity between Mechanics and Microscopic Functions of Hydrogen in Failure

    Michihiko Nagumo

    ISIJ INTERNATIONAL   52 ( 2 ) 168 - 173  2012

    Book review, literature introduction, etc.  

     View Summary

    Conformity between macro-mechanics and microscopic functions of hydrogen in failure is reviewed in reference to some models of hydrogen embrittlement (HE), focusing on the role of plasticity. Plastic strain localization, a characteristic feature of HE, is consistent with the hydrogen-enhanced creation of vacancies during plastic deformation. Constitutive relations that take into account the presence of voids describe well the ductile fracture process in HE. The effect of hydrogen on increasing the density of strain-induced vacancies likely promotes plastic instability and decreases ductile crack growth resistance, thus leading to enhanced shear localization and a premature failure.

  • 破壊のメカニズム

    南雲 道彦

    熱処理   50 ( 5 ) 450 - 457  2010

  • 破壊現象としての水素脆性

    南雲道彦

    圧力技術   46 ( 4 ) 190 - 199  2010

    DOI

  • オーステナイト系ステンレス鋼の水素脆性

    南雲道彦

    圧力技術   48 ( 3 ) 154 - 165  2010

    DOI CiNii

  • 鉄鋼の水素脆性

    南雲 道彦

    ふぇらむ   14   222 - 227  2009

  • Lattice defects dominating hydrogen-related failure of metals

    K. Takai, H. Shoda, H. Suzuki, M. Nagumo

    Acta Materialia   56 ( 18 ) 5158 - 5167  2008.10  [Refereed]

    Authorship:Last author

     View Summary

    The factor that plays the essential role in hydrogen-related failure has been examined for Inconel 625 and iron by means of tensile testing with interposed unloading and reloading with/without hydrogen charging. Aging at 30 degrees C or annealing at 200 degrees C was conducted during the unloaded stage in order to diffuse out hydrogen or to anneal out strain-induced defects. Hydrogen thermal desorption analysis was used to evaluate strain-induced defects that act as trapping sites of hydrogen. Fracture strain decreased in the initially hydrogencharged specimens even though hydrogen was absent at the late stage of straining. Annealing at 200 degrees C at the unloaded stage almost completely recovered the decrease in fracture strain. Enhancement of strain-induced defects by hydrogen and their involvement in degradation were revealed by means of hydrogen thermal desorption analysis. The results provide direct evidence of the primary role of vacancies rather than hydrogen itself in hydrogen degradation, and agree well with the hydrogen-enhanced strain-induced vacancy model with respect to the mechanism of hydrogen-related failure. (C) 2008 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

    DOI CiNii

  • Lattice defects dominating hydrogen-related failure of metals

    K. Takai, H. Shoda, H. Suzuki, M. Nagumo

    ACTA MATERIALIA   56 ( 18 ) 5158 - 5167  2008.10

    Authorship:Last author, Corresponding author

     View Summary

    The factor that plays the essential role in hydrogen-related failure has been examined for Inconel 625 and iron by means of tensile testing with interposed unloading and reloading with/without hydrogen charging. Aging at 30 degrees C or annealing at 200 degrees C was conducted during the unloaded stage in order to diffuse out hydrogen or to anneal out strain-induced defects. Hydrogen thermal desorption analysis was used to evaluate strain-induced defects that act as trapping sites of hydrogen. Fracture strain decreased in the initially hydrogencharged specimens even though hydrogen was absent at the late stage of straining. Annealing at 200 degrees C at the unloaded stage almost completely recovered the decrease in fracture strain. Enhancement of strain-induced defects by hydrogen and their involvement in degradation were revealed by means of hydrogen thermal desorption analysis. The results provide direct evidence of the primary role of vacancies rather than hydrogen itself in hydrogen degradation, and agree well with the hydrogen-enhanced strain-induced vacancy model with respect to the mechanism of hydrogen-related failure. (C) 2008 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

    DOI CiNii

  • Hydrogen embrittlement associated with phase transformation (appendix: Assessment of the susceptibility to hydrogen-related failure)

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   57 ( 7 ) 301 - 317  2008.07

     View Summary

    The features and mechanisms of hydrogen embrittlement of metals that undergo hydride formation and martensitic transformation during service are reviewed. Metastable austenitic stainless steels, Nb and V as well as Ti and its alloys are the metals examined. The embrittlement of austenitic stainless steels is susceptible to the stability of austenite, and hydrogen promotes the martensitic transformation forming hydride as a precursor. However, martensite per se is not always the origin of the embrittlement, but.lattice defects associated with dislocation dynamics in the crack front is noted as a factor. In Nb and V, stress-induced hydride formation successively taking place at the crack front supplies a crack path with a reduced resistance for growth. In Ti, the primary role of hydrides is not always the case. In superelastic and shape memory Ni-Ti alloys, the embrittlement appears prominent in the martensitic transformation, and some dynamic process invoking lattice defects is suggested to play a role. In an appendix, the assessment of the susceptibility in terms of the critical hydrogen concentration is critically discussed, and some mechanical response to hydrogen is proposed as new criteria for the susceptibility of materials to hydrogen embrittlement.

    DOI CiNii

  • オーステナイト系ステンレス鋼の水素脆性

    南雲 道彦

    材料とプロセス   21   1265 - 1268  2008

  • 破壊現象としての水素脆性

    南雲道彦

    圧力技術   46 ( 4 ) 190 - 199  2008

    DOI CiNii

  • 水素脆性研究の新しい方向

    南雲道彦

    日本機械学会論文集 A   73 ( 736 ) 1318 - 1324  2008

  • Mechanism of hydrogen-related failure II

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   56 ( 9 ) 382 - 394  2007.09

    Book review, literature introduction, etc.  

     View Summary

    Following the preceding article, a theory that considers the primary role of strain-induced vacancies in hydrogenrelated failure is presented. Detection of lattice defects the creation and agglomeration of which are enhanced by hydrogen is described. As a support of the theory, correlations between the mount of strain-induced vacancies and the susceptibility to hydrogen-related failure are shown with steels of different microstructures. Interaction of fatigue and delayed fracture is shown as another evidence of the theory. The role of hydrogen concentration in the failure is discussed in regard to a time-dependent alteration of defects during delayed fracture test.

    DOI CiNii

  • Mechanism of hydrogen-related failure I

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   56 ( 8 ) 343 - 352  2007.08

     View Summary

    Major models so far proposed on the mechanism of hydrogen embrittlement are critically reviewed. The theories are classified into two streams, brittle or ductile fracture in nature. The theories for brittle fracture are triggering by internal pressure, surface energy reduction and lattice decohesion. The ductile fracture models presented here are hydrogen-assisted cracking, hydrogen-enhanced localized plasticity, adsorption-induced dislocation emission and autocatalytic effect on plastic instability. Interconnections of hydrogen embrittlement and stress corrosion cracking are also presented. Particular attention is paid on experimental conditions and assumptions on which the theories are based.

    DOI CiNii

  • Characteristic features of hydrogen-related failure

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   56 ( 4 ) 132 - 147  2007.04

     View Summary

    Characteristics of hydrogen-related failure are reviewed from mostly experimentally observed features. Comparison with the failure under normal atmospheres is made so as to extract the way by which hydrogen plays a role in the fracture process. Fractographic features associated with plasticity and the promotion of the crack initiation and growth analyzed by means of an R-curve method are presented. Enhanced plastic instability is noted as a precursor of the failure. Effects of hydrogen on stress relaxation and creep are presented as the dislocation dynamics that operate on delayed fracture. Effects of environmental variation of applied stress and external hydrogen potential are also presented.

    DOI CiNii

  • 水素脆性機構 Ⅱ

    材料と環境   56   382 - 394  2007

    DOI

  • 水素脆性機構 Ⅰ

    南雲道彦

    材料と環境   56 ( 8 ) 343 - 352  2007

    DOI

  • 水素が関与する破壊の特徴

    材料と環境   56   172 - 142  2007

  • The effect of hydrogen on vacancy generation in iron by plastic deformation

    K SAKAKI, T KAWASE, M HIRATO, M MIZUNO, H ARAKI, Y SHIRAI, M NAGUMO

    Scripta Materialia   55 ( 11 ) 1031 - 1034  2006.12  [Refereed]

    Authorship:Last author, Corresponding author

     View Summary

    Positron lifetime spectroscopy was applied to examine the synergistic effect of hydrogen and plastic straining on the vacancy generation in iron. Hydrogen enhanced the increase in mean positron lifetime, T., by plastic straining and elevated the recovery temperature of T. on isochronal annealing. Multi-component analyses of positron lifetime spectra showed that the presence of hydrogen enhances the generation of vacancies, rather than of dislocations. These results are consistent with previous interpretations on thermal desorption analysis of hydrogen in deformed steels. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

    DOI CiNii

  • Entry of hydrogen into metals from liquid phase II - Factors affecting hydrogen entry

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   55 ( 10 ) 430 - 440  2006.10

     View Summary

    Environmental factors that affect the entry of hydrogen into materials are briefly summarized with respect to electrochemical reactions on electrode. Effects of promoters, particularly of H 2S, are reviewed concerned with their mechanism. The effects of localized corrosion, such as crevice corrosion and pitting corrosion, and atmospheric corrosion under wet/dry cycles on hydrogen entry are reviewed. Further, interactions between electrochemical reactions on the surface of electrode and plastic deformation, which appear on polarization during stressing, and vice versa, are noticed as phenomena that suggest some surface effects on internal dislocation dynamics.

    DOI CiNii

  • Hydrogen entry into metals from liquid phase I - Basic electrochemical reactions

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   55 ( 9 ) 380 - 389  2006.09

     View Summary

    Basic electrode reactions for the entry of hydrogen into metals under aqueous environment have been reviewed. Some analytical models that determine the parameters in the kinetics of the entry of hydrogen, including the hydrogen surface coverage and absorbed hydrogen concentration, are presented. On corrosion processes, the significance of surface film for the entry of hydrogen is emphasized from both the structure of the electric double layer at the electrode/electrolyte interface and under-potential deposition of hydrogen.

    DOI

  • Adsorption of gaseous hydrogen onto metal surface

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   55 ( 3 ) 92 - 99  2006.03

     View Summary

    Adsorption behavior of gaseous hydrogen on metal surface has been briefly reviewed, focusing on fundamentals for hydrogen entry that causes degradation of mechanical properties. The measurements for the adsorbed sites and states by means of thermal desorption spectroscopy and the work function are presented. Studies on the isotherm and adsorption kinetics are also presented. The effects of alloying elements and impurities on hydrogen coverage are summarized as well as the effects of gas components.

    DOI CiNii

  • Analysis of hydrogen states in materials

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   55 ( 2 ) 42 - 50  2006.02

    Book review, literature introduction, etc.  

     View Summary

    Analytical methods for hydrogen states in materials are reviewed. Principles and characteristics of visualization techniques, such as tritium radioautography, hydrogen microprint technique and scanning secondary ion mass spectroscopy, and thermal desorption analysis are briefly described. Examples of applications to practical cases are presented putting emphasis on the limitations and uncertainties involved in experiments and theories.

    DOI CiNii

  • 液相から金属への水素侵入 Ⅱ~水素侵入に影響する因子~

    南雲道彦

    材料と環境   55 ( 10 ) 430 - 440  2006

    DOI CiNii

  • 液相から金属への水素侵入 Ⅰ~基本電気化学反応~

    南雲 道彦

    材料と環境   55 ( 9 ) 380 - 389  2006

    DOI CiNii

  • 気相水素の金属表面への吸着

    南雲道彦

    材料と環境   55 ( 3 ) 92 - 99  2006

    DOI CiNii

  • Effect of grain size on the susceptibility of martensitic steel to hydrogen-related failure

    H Fuchigami, H Minami, M Nagumo

    PHILOSOPHICAL MAGAZINE LETTERS   86 ( 1 ) 21 - 29  2006.01

     View Summary

    The effect of grain size on the susceptibility of martensitic steels to hydrogen-related failure has been examined with respect to the role of the hydrogen concentration and lattice defects acting as hydrogen trap sites. Plastic straining increased the hydrogen absorption capacity, but annealing at 250 degrees C after straining eliminated the increase, implying the point-defect-like nature of the increased number of trapping sites for hydrogen. Refinement of the prior austenite grain size, by means of repeated induction heating and quenching, increased the hydrogen absorption capacity in as-heat-treated samples as a consequence of the increased boundary area. Grain refinement reduced the susceptibility, as evaluated by means of a slow strain-rate tensile test of hydrogen-precharged specimens. This reduction of susceptibility is analysed to be associated with a smaller strain-induced increase in hydrogen absorption capacity, i.e. in the defect density. Fractographic features showed a decrease in ductile crack growth resistance in the presence of hydrogen, being less pronounced with grain refinement. The present results support the notion that the susceptibility of steels to hydrogen-related failure originates in the response of microstructures to plastic straining, primarily through the creation of vacancies.

    DOI CiNii

  • States of hydrogen in materials III - Trapped states (2)

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   54 ( 7 ) 306 - 316  2005

     View Summary

    The equilibrium distribution of hydrogen at trapping sites is shown putting emphasis on the effect of the binding energy. Trapping effects on hydrogen diffusivity derived from both the solution of diffusion equation and statistical thermodynamics are reviewed. Analytical and experimental estimations of the kinetics of trapping are reviewed. Dislocation transport of hydrogen by moving dislocations is critically examined.

    DOI

  • States of hydrogen in materials II - Trapped states (1)

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   54 ( 6 ) 251 - 261  2005

     View Summary

    Succeeding the hydrogen states in solid solution, interactions of hydrogen with various defects such as dislocations, vacancies, precipitates, grain boundaries and voids have been reviewed. The binding energies of hydrogen with defects are collected with emphasis on experimental methods and assumptions in the theoretical analyses. The origins of the interactions are briefly described in terms of electron theories on the states of hydrogen.

    DOI

  • Analyzing Hydrogen States in Materials

    Michihiko Nagumo

    Corrosion Engineering   54   43 - 61  2005

  • States of Hydrogen in Materials III: Trapped States (2)

    Michihiko Nagumo

    Corrosion Engineering   54   407 - 431  2005

  • States of Hydrogen in Materials II: Trapped States (1)

    Michihiko Nagumo

    Corrosion Engineering   54   331 - 335  2005

  • Intermediate phase in synthesis of TiSi2 by mechanical alloying and annealing

    Y Kaneko, M. NAGUMO

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   375   825 - 828  2004.07

     View Summary

    The alloying process by mechanical milling and subsequent annealing of a 1:2 mole ratio Ti/2Si system has been analyzed from a crystallographic viewpoint. An intermediate phase appeared after prolonged milling or prior to the formation of TiSi2 on annealing. The observed XRD pattern of the intermediate phase was coincident with that of a structure constructed by introducing a stacking fault on the close-packed plane of the hexagonal Ti lattice with partial replacement of Ti by Si atoms. The structure of TiSi2 is formed from the intermediate phase by an interchange of Ti with Si atoms on the close-packed plane, being associated with structural relaxation. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

  • Effect of constituent phase of Ni-Ti shape memory alloy on susceptibility to hydrogen embrittlement

    K Yokoyama, T Eguchi, K Asaoka, M Nagumo

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   374 ( 1-2 ) 177 - 183  2004.06

     View Summary

    The susceptibility of a Ni-Ti shape memory alloy towards hydrogen embrittlement has been examined with respect to the constituent phase of the alloy. Fracture always occurred in the presence of martensite. A steep decrease in fracture stress took place initially with increasing hydrogen content irrespective of the initial phases. The effect of the constituent phase appeared at high hydrogen contents. The work-hardened martensite phase showed the highest susceptibility succeeded by the parent phase that fractured in the course of martensite transformation. The critical stress for the martensite transformation increased at high hydrogen contents. The embrittlement is likely to be enhanced by the interactions between hydrogen and dynamic processes in materials. (C) 2004 Elsevier B.V. All rights reserved.

    DOI

  • Delayed fracture of Ni-Ti superelastic alloys in acidic and neutral fluoride solutions

    K Yokoyama, K Kaneko, K Moriyama, K Asaoka, J Sakai, M Nagumo

    JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A   69A ( 1 ) 105 - 113  2004.04

     View Summary

    Hydrogen-related degradation of the mechanical properties of a Ni-Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni-Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen-related degradation of performance of Ni-Ti superelastic alloys occurs in the presence of fluoride. (C) 2004 Wiley Periodicals, Inc.

    DOI

  • States of hydrogen in materials I - Solid solution

    Michihiko Nagumo

    Zairyo to Kankyo/ Corrosion Engineering   53 ( 12 ) 548 - 553  2004

    Book review, literature introduction, etc.  

     View Summary

    Fundamentals of hydrogen behaviors in materials are reviewed with respect to degradation of mechanical properties. The present article is the first part that deals with the states of hydrogen in solid solution. The temperature dependence of the solubility, permeability and technical problems particularly of electrochemical permeation measurement have been explained. The interstitial site of hydrogen and the symmetry of lattice strain have been examined.

    DOI

  • Effects of hydrogen on mechanical behavior of steels

    Michihiko Nagumo

    Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan   90 ( 10 ) 766 - 775  2004

     View Summary

    Main features of hydrogen effects on mechanical behavior of steels have been reviewed. While the effects on macroscopic tensile properties are not definite, the increase in dislocation mobility by hydrogen appears as an enhanced stress relaxation the extent of which correlating with the susceptibility to failure. Hydrogen enhances the creation of vacancies during plastic deformation. The extent is susceptible to microstructures of steels and correlates with the susceptibility to failure. Flow localization in the presence of hydrogen is substantial, leading to shear instability. Characteristic fractographic features in hydrogen-related failure, such as striations, have been shown to originate in deformation bands in which the density of defects is high. Prominent localization of void nucleation takes place at the advancing crack tip. Amorphization has been observed in front of the crack and just below the fracture surface in a hydrogen-charged steel in accord with flow localization and associated vacancy creation. Hydrogen remarkably reduces the fatigue resistance of steels, and, conversely, prior fatigue treatment increases the susceptibility to delayed fracture. The mechanism has been ascribed to the creation of vacancies during fatigue and interactions between vacancies and hydrogen. Further studies for assessing the susceptibility to hydrogen-related failure have been suggested to be based on the accumulation of damage rather than hydrogen content.

    DOI

  • States of Hydrogen in Metals I: Solid Solution

    Michihiko Nagumo

    Corrosion Engineering   53   619 - 632  2004

  • Fracture associated with hydrogen absorption of sustained tensile-loaded titanium in acid and neutral fluoride solutions

    Ken'ichi Yokoyama, Kazuyuki Kaneko, Youji Miyamoto, Kenzo Asaoka, Jun'ichi Sakai, Michihiko Nagumo

    Journal of Biomedical Materials Research - Part A   68 ( 1 ) 150 - 158  2004.01

     View Summary

    The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600°C. The amount of absorbed hydrogen was &gt
    300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties. © 2003 Wiley Periodicals, Inc.

    DOI PubMed

  • Amorphization associated with crack propagation in hydrogen-charged steel

    M Nagumo, T Ishikawa, T Endoh, Y Inoue

    SCRIPTA MATERIALIA   49 ( 9 ) 837 - 842  2003.11

     View Summary

    Amorphization, following a decrease in the dislocation density and fragmentation of the matrix, has been revealed in a thin layer just below the tensile-fractured surface of a hydrogen-charged ferritic steel. The creation of a high density of vacancies associated with hydrogen is discussed as the origin. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

    DOI

  • Detection of hydrogen trap distribution in steel using a microprint technique

    T Ohmisawa, S Uchiyama, M. NAGUMO

    JOURNAL OF ALLOYS AND COMPOUNDS   356   290 - 294  2003.08

     View Summary

    The distribution of hydrogen trapped at defects has been visualized by means of a hydrogen microprint technique (HMT). A low carbon steel having a ferrite/pearlite structure with second phases along grain boundaries was subjected to notch-tensile and three-point bending tests with/without hydrogen pre-charging. HMT was applied to tested specimens re-charged with hydrogen. Accumulation of hydrogen was confirmed in strain-concentrated areas as well as along grain boundaries and in pearlite. A noteworthy finding was a substantial increase in defects acting as traps of diffusive hydrogen when specimens were deformed in the presence of hydrogen. The increased defects were annealed out at temperatures as low as 150 degreesC, indicating their point defect nature. Another finding was the appearance of a zone denuded of silver precipitation in highly strained areas such as near grain boundaries and the fracture surface, where tritium autoradiography revealed the evolution of defects having high binding energy with hydrogen. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

  • Degradation of tensile strength due to hydrogen absorption of nickel-titanium superelastic alloys in fluoride solution.

    K. Yokoyama, K. Kaneko, K. Moriyama, K. Asaoka, J. Sakai, M. Nagumo

    JOURNAL OF DENTAL RESEARCH   82   B341 - B341  2003.06

    Research paper, summary (international conference)  

  • Delayed fracture of beta titanium alloys in fluoride solutions.

    K. Kaneko, K. Yokoyama, K. Moriyama, K. Asaoka, J. Sakai, M. Nagumo

    JOURNAL OF DENTAL RESEARCH   82   B341 - B341  2003.06

    Research paper, summary (international conference)  

  • Fatigue damage and its interaction with hydrogen in martensitic steels

    M Nagumo, H Shimura, T Chaya, H Hayashi, Ochiai, I

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   348 ( 1-2 ) 192 - 200  2003.05

     View Summary

    Fatigue damage involving creation of point defects has been revealed by means of hydrogen thermal desorption analysis, utilizing hydrogen as a probe of defects. Two types of high-strength martensitic steels were subjected to a rotational bending test for various cycles. The amount of absorbed hydrogen decreased or was almost constant in the early stage of the fatigue process and then began to increase after a substantial number of fatigue cycles. The increase in the final stage was due to the creation of point defects, presumably vacancies, while the decrease in the early stage was ascribed to changes in microstructural constitutions. Hydrogen-precharging drastically reduced the fatigue life, but the effect of hydrogen on the fatigue limit was not significant. The fracture surface of hydrogen-precharged specimens was smooth without cleavage-like crystallographic features. The defect density in fractured specimens in the presence of hydrogen was higher than in specimens fatigued for a similar number of cycles without hydrogen. Involvement of hydrogen in fatigue damage in the crack nucleation and growth stages is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI

  • Hydrogen embrittlement of Ni-Ti superelastic alloy in fluoride solution

    Ken'Ichi Yokoyama, Kazuyuki Kaneko, Keiji Moriyama, Kenzo Asaoka, Jun'Ichi Sakai, Michihiko Nagumo

    Journal of Biomedical Materials Research - Part A   65 ( 2 ) 182 - 187  2003.05

     View Summary

    Hydrogen embrittlement of Ni-Ti superelastic alloy in a fluoride solution (0.2% APF) has been investigated by means of a tensile test (after immersion) and hydrogen thermal desorption analysis. Upon immersion, the tensile strength of the alloy decreased to the critical stress level of martensite transformation. Hydrogen desorption of the immersed specimens appeared with a peak at around 500°C. The amount of absorbed hydrogen in the alloy ranged from 100 to 1000 mass ppm when immersed in the fluoride solution for 2 to 24 h. The immersion in the fluoride solution led to the degradation of mechanical properties due to hydrogen embrittlement. The results of the present study imply that one reason that Ti and its alloys fracture in the oral cavity is the fact that hydrogen is absorbed in a fluoride solution, such as prophylactic agents. © 2003 Wiley Periodicals, Inc.

    DOI PubMed

  • Enhanced susceptibility to delayed fracture in pre-fatigued martensitic steel

    M Nagumo, S Sekiguchi, H Hayashi, K Takai

    Materials Science and Engineering: A   344 ( 1-2 ) 86 - 91  2003.03  [Refereed]

    Authorship:Lead author, Corresponding author

    Article, review, commentary, editorial, etc. (scientific journal)  

    DOI CiNii

  • Enhanced susceptibility to delayed fracture in pre-fatigued martensitic steel

    M Nagumo, S Sekiguchi, H Hayashi, K Takai

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   344 ( 1-2 ) 86 - 91  2003.03

     View Summary

    Interaction between fatigue damage and hydrogen is the concern of the present study. The susceptibility of a high-strength martensitic steel to delayed fracture has been examined using as-heat-treated and pre-fatigued specimens. The pre-fatigued specimens showed a tendency to fail earlier, but annealing the pre-fatigued specimens at 200 degreesC recovered nearly all of the delayed fracture life. Production of point defects during fatigue was detected by means of hydrogen thermal desorption analysis (TDA), using hydrogen as a probe of defects. Hydrogen absorption capacity increased in fatigued specimens, but it was reduced to the level of the as-heat-treated specimens when fatigued specimens were annealed at 200 degreesC, implying that increased hydrogen-trapping defects, presumably vacancies, were produced during fatigue. Hydrogen TDA peak profiles showed alterations that imply agglomeration of vacancies associated with an increase in fatigue cycles. The involvement of vacancies created during fatigue in the enhanced delayed fracture is consistent with a model that proposes strain-induced vacancies and their agglomeration are the primary mechanism of hydrogen-related failure. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI

  • 鉄鋼の水素脆性解明の新展開

    ふぇらむ(日本鉄鋼協会)   vol.8、pp.800-806  2003

  • SUS304熱延板の加工誘起変態マルテンサイトの新しいエッチング法

    鉄と鋼   vol.89、pp.79-86  2003

  • Degradation of tensile strength of Ni-Ti superelastic alloy due to hydrogen absorption in methanol solution containing hydrochloric acid

    Mater. Sci. Eng. A   vol.A360, pp.153-159  2003

    DOI

  • Delayed fracture of beta titanium orthodontic wire in fluoride aqueous solutions

    Biomaterials   vol.24, pp.2113-2120  2003

    DOI

  • Simulation of hydrogen thermal desorption under reversible trapping by lattice defects

    T Yamaguchi, M Nagumo

    ISIJ INTERNATIONAL   43 ( 4 ) 514 - 519  2003

     View Summary

    The hydrogen thermal desorption of a martensitic steel has been simulated assuming lattice hydrogen diffusion under a local equilibrium with reversibly trapped hydrogen as the rate-determining process, The calculated desorption curves reproduced the observed shift of the peak temperature associated with the specimen thickness and the heating rate. The calculation method involves a combination of a defect density and a hydrogen/defect binding energy as parameters, The dependence of the peak temperature on the defect density and the binding energy has been quantitatively shown, Assignment of the lattice defect relevant to the desorption curves is discussed. A calculation that took into account the increase in the defect density yielded results consistent with the observed change in the desorption curves associated with plastic strain,

    DOI

  • Susceptibility to delayed fracture of Ni-Ti superelastic alloy

    K Yokoyama, S Watabe, K Hamada, J Sakai, K Asaoka, M Nagumo

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   341 ( 1-2 ) 91 - 97  2003.01

     View Summary

    The susceptibility of Ni-Ti superelastic alloys to hydrogen embrittlement has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. It was found that the time to fracture was drastically reduced when the applied stress exceeded the critical stress for martensite transformation. In the applied stress range lower than the critical stress, the time to fracture lessened in the order of instability of the alloys to undergo reversible martensite transformation. Hydrogen thermal desorption of specimens subjected to delayed-fracture test is classified into two types according to the applied stress level. The amount of desorbed hydrogen was markedly increased when the applied stress was higher than the critical stress. It was concluded that Ni-Ti superelastic alloys transformed to martensite are sensitive to environmental conditions accompanying accelerated hydrogen embrittlement. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI

  • Function of hydrogen in intergranular fracture of martensitic steels

    M Nagumo, H Matsuda

    PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES   82 ( 17-18 ) 3415 - 3425  2002.11

     View Summary

    The mechanism of intergranular-mode fracture in hydrogen-related failure of high-strength martensitic steels has been investigated. Pronounced degradation of tensile properties appeared with increasing manganese content in a slow-elongation-rate test under concurrent hydrogen charging. The fracture mode was intergranular with tear traces along martensite lath boundaries. The tear traces disappeared and the average surface roughness decreased with increasing manganese content. Thermal desorption analysis of hydrogen charged to deformed specimens. It was revealed that the density of point defects increased owing to straining and was more noticeable in steels with a higher manganese content. In common with transgranular-mode fracture, the primary function of hydrogen in intergranular-mode fracture is thought to be one of stabilizing and increasing the density of strain-induced vacancies that lead to the formation of microcracks or microvoids in the vicinity of boundaries. The constraint of plastic deformation at grain boundaries due to boundary phases is likely to determine the susceptibility to hydrogen-related failure induced by strain concentration.

    DOI

  • Hydrogen embrittlement of nickel-titanium alloy in biological environment

    K Asaoka, K Yokoyama, M Nagumo

    METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE   33 ( 3 ) 495 - 501  2002.03

     View Summary

    A nickel-titanium superelastic alloy is susceptible to environmental embrittlement in a corrosive atmosphere. Because a delayed fracture of the alloy is associated with hydrogen absorption and subsequent formation of brittle hydride phases, the diffusion rate of hydrogen is thought to be one of the factors determining its service life. The Ni-Ti alloys subjected to hydrogen charging of I or 10 A/m(2) for 24 or 120 hours, respectively, were arranged using an electrochemical system. Both the hardness numbers in the cross-sectional area of the alloy and the amount of evolved hydrogen were determined. The fracture surface of the alloys, under tension, was observed using a scanning electron microscope (SEM). Theoretical distributions of the hydrogen concentration were computed for an infinite cylinder model using the differential equation of diffusion. The diffusion constant of hydrogen through the alloy is estimated to be 9 x 10(-15) m(2)/s, assuming that the hardness is proportional to the concentration of hydride and/or hydrogen. Experimental results of the hardness measurements and fractography support the estimated diffusion constant. The process of fracture formation in a biological corrosive environment was discussed. It was concluded that galvanic currents and fretting corrosion of the alloy might be effective factors in fracture formation during function.

  • Hydrogen thermal desorption relevant to delayed-fracture susceptibility of high-strength steels

    M Nagumo, M Nakamura, K Takai

    METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE   32 ( 2 ) 339 - 347  2001.02

     View Summary

    The susceptibility to hydrogen embrittlement (HE) of martensitic steels has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. The intensity of a desorption-rate peak around 50 degreesC to 200 degreesC increased when the specimen was preloaded and more remarkably so when it was loaded under the presence of hydrogen. The increment appeared initially at the low-temperature region in the original peak. As hydrogen entry proceeded, the increment then appeared at the high-temperature region, while that in the low-temperature region was reduced. The alteration occurred earlier in steels tempered at lower temperatures, with a higher embrittlement susceptibility. A defect acting as the trap of the desorption in the high-temperature region was assigned to large vacancy clusters that have higher binding energies with hydrogen. Deformation-induced generation of vacancies and their clustering have been considered to be promoted by hydrogen and to play a primary role on the HE susceptibility of high-strength steel.

    DOI CiNii

  • マルテンサイト鋼の細粒化に伴う水素吸蔵と水素脆化特性

    材料とプロセス   Vol.14, p.1311  2001

  • Functions of Hydrogen in Embrittlement of High Strength Steels

    ISIJ, Int.   vol. 41, pp. 590-598.  2001

    DOI

  • Accelerated Embrittlement of High Strength Steels by Cyclic Hydrogen Potential

    Scripta Materialia   44 ( 4 ) 947  2001

  • Ductile crack growth resistance in hydrogen-charged steels

    M. Nagumo, H. Yoshida, Y. Shimomura, T. Kadokura

    Materials Transactions   42 ( 1 ) 132 - 137  2001

     View Summary

    The effect of hydrogen on the shear localization and associated crack nucleation has been investigated by means of a three point bending test of hydrogen-charged steels. The ductile crack growth resistance in terms of the slope of R-curve was lowered under the presence of hydrogen, the decrease being more pronounced in the steel with more abundant slip constraint phases along grain boundaries. Enlargement of size and reduction in depth/width ratio of primary dimples, occasionally associated with quasi-cleavage, were observed on the fracture surface of the hydrogen-charged steels. By means of a FEM calculation, the increase of the nucleation void volume fraction localized at the crack tip with strain localization as well was shown to take place in the hydrogen-charged steel in consistent with enhanced shear instablity. It was discussed that the evolution of vacancy-type defects, rather than void nucleation at second phase particles, in the course of plastic straining was enhanced under the presence of hydrogen, reducing the ductile crack growth resistance.

    DOI CiNii

  • Deformation-induced defects controlling fracture toughness of steel revealed by tritium desorption behaviors

    M Nagumo, T Yagi, H Saitoh

    ACTA MATERIALIA   48 ( 4 ) 943 - 951  2000.02

     View Summary

    Defects induced by plastic deformation have been revealed by means of room temperature desorption and thermal desorption spectroscopy of tritium with regards to the ductile crack growth resistance and brittle fracture initiation in steels in the ductile-to-brittle transition region. Tritium, as a probe for detecting defects, was introduced into non-deformed or deformed samples. Three steels, the microstructures of which are characterized by the constrains factor for slip extension, were employed. The residual tritium in a specimen after three days at room temperature increased to the extent corresponding to the constraint factors when plastic deformation was applied. The thermally desorbed tritium, with a peak desorption rate around 150 degrees C, also increased according to the constraint factors. Referring to the previous analysis of the R-curves, the constraint for the extension of slip across grain boundaries is shown to control both the ductile crack growth resistance and the brittle fracture initiation through the deformation microstructures that evolve vacancy clusters or microvoids. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd All rights reserved.

    DOI CiNii

  • Influence of HNO3 treatments on the early stages of pitting of type 430 stainless steel

    T Hong, M Nagumo, WP Jepson

    CORROSION SCIENCE   42 ( 2 ) 289 - 298  2000.02

     View Summary

    The effect of HNO3 surface treatment on the early stages of pitting of Type 430 stainless steel has been studied by AC impedance method. At a given low potential. the Warburg impedance coefficient sigma, which is calculated from impedance plots, is a maximum after wet polishing, and decreases with increasing HNO3 concentration in the solution of surface treatment. It has been suggested that the surface becomes more passive and the most susceptible sites for pit nucleation are eliminated after HNO3 treatments, and that increasing the HNO3 concentration in treatment solution results in increasing the resistance of the steel to metastable pitting. The critical potential (E-m) at which metastable pit or pits start to grow on the surface of the steel depends on HNO3 concentration in treatment solution. The higher the HNO3 concentration in treatment solution, the higher the E-m values, showing that the nucleated pit or pits proceeding to metastable growth stage becomes more difficult. (C) 2000 Elsevier Science Ltd. All rights reserved.

    DOI CiNii

  • Deformation-induced defects controlling fracture toughness of steel revealed by tritium desorption behaviors

    M Nagumo, T Yagi, H Saitoh

    ACTA MATERIALIA   48 ( 4 ) 943 - 951  2000.02

     View Summary

    Defects induced by plastic deformation have been revealed by means of room temperature desorption and thermal desorption spectroscopy of tritium with regards to the ductile crack growth resistance and brittle fracture initiation in steels in the ductile-to-brittle transition region. Tritium, as a probe for detecting defects, was introduced into non-deformed or deformed samples. Three steels, the microstructures of which are characterized by the constrains factor for slip extension, were employed. The residual tritium in a specimen after three days at room temperature increased to the extent corresponding to the constraint factors when plastic deformation was applied. The thermally desorbed tritium, with a peak desorption rate around 150 degrees C, also increased according to the constraint factors. Referring to the previous analysis of the R-curves, the constraint for the extension of slip across grain boundaries is shown to control both the ductile crack growth resistance and the brittle fracture initiation through the deformation microstructures that evolve vacancy clusters or microvoids. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd All rights reserved.

    DOI CiNii

  • Nature of hydrogen trapping sites in steels induced by plastic deformation

    M Nagumo, K Takai, N Okuda

    JOURNAL OF ALLOYS AND COMPOUNDS   293   310 - 316  1999.12

     View Summary

    Thermal desorption spectroscopy (TDS) has been used to reveal the nature of defects acting as trapping sites of hydrogen. Hydrogen was charged to ferritic and eutectoid steels deformed to various degrees and then given annealing treatment. Desorption with a single peak appeared between roam temperature and 600 K from ferritic steels. Under constant hydrogen charging conditions, the amount of desorption increased with strain. However, when the deformed samples were subjected to annealing at temperatures as low as 500 K, the increase of desorbed hydrogen no longer appeared. Vacancy clusters, which themselves annihilate in the course of TDS measurement, are the probable source of hydrogen desorption. When heavy deformation was given to ferritic steels, a two-step decrease of hydrogen desorption took place with increasing annealing temperature, corresponding to annihilation of vacancy clusters and decrease of dislocation density, respectively. The desorption with a single peak has two origins, one due to the annihilation of the trapping sites themselves and the other to desorption from stable sites. For heavily deformed eutectoid steel, an additional desorption peak centered at around 640 K appeared. The peak likely results from deformation-induced defects within the cementite phase or supersaturated carbon in ferrite. Two types of desorption, one due to the annihilation of trapping sites in the course of measurement and the other due to desorption from stable sites, should be discriminated. TDS using hydrogen as a tracer can be applied as a tool to investigate the various defects induced by plastic deformation. (C) 1999 Elsevier Science S.A. All rights reserved.

    DOI CiNii

  • Synthesis of TiC and Ti/TiC composites by reaction milling followed by hot consolidation of Ti with graphite or heptane

    A Yasukawa, M Nagumo

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   63 ( 7 ) 822 - 827  1999.07

     View Summary

    Synthesis of TIC and Ti/TiC composite has been conducted by mechanical alloying and following Spark-Plasma-Sintering starting from elemental Ti powder with graphite or heptane. From graphite, formation of TiC takes place rapidly after a definite period of milling while it proceeds gradually from heptane. The apparent compositional range of Ti1-xCx is extended to a C/Ti ratio as low as 30/70 when graphite is used, while a mixture of Ti and TiC is obtained at a C/Ti ratio of 32/68 with heptane. Sintering can proceed at substantially lower temperatures compared with the conventional process, the sintering temperature decreasing with lower C/Ti ratios. The lattice parameter of TiC and the density of the compacts decrease with lower C/Ti ratios, but are larger than previously reported ones through conventional methods. The mechanism which causes the differences between graphite and heptane is discussed with respect to the reaction process during milling.

    DOI

  • Microstructural evolution of commercial Ti and Zr powders during mechanical milling

    SP Chen, XD Liu, M Nagumo

    MATERIALS TRANSACTIONS JIM   40 ( 6 ) 529 - 536  1999.06

     View Summary

    Microstructural evolution of commercial Ti and Zr powders upon mechanical milling was characterized by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Evident structural inhomogeneity was observed upon milling the two commercial powders. A partial amorphous state was attained in Zr after 100 h of milling. The possible origins for the amorphous phase formation were discussed.

    DOI

  • Anodic surface oxidation mechanisms of PAN-based and pitch-based carbon fibres

    A Fukunaga, S Ueda, M Nagumo

    JOURNAL OF MATERIALS SCIENCE   34 ( 12 ) 2851 - 2854  1999.06

     View Summary

    In order to clarify the differences in the anodic surface oxidation mechanisms of PAN-based and pitch-based carbon fibres, the fibres were oxidized in an electrolyte and characterized using the coulostatic method, X-ray photoelectron spectroscopy, laser Raman spectroscopy, and X-ray diffraction. The interfacial bonding strength to an epoxy resin was evaluated based on the interlaminar shear strength (ILSS). The results showed a good correlation between the differential double layer capacities, which were measured with the coulostatic method, and the ILSS values of PAN-based high tensile strength carbon fibres (PAN-HTCFs), PAN-based high modulus carbon fibres (PAN-HMCFs), and pitch-based high modulus carbon fibres (pitch-HMCFs). Their morphologies for the anodic oxidation were as follows: PAN-HTCFs are anodized homogeneously; pitch-HMCFs are selectively oxidized and promote crevice etching; and PAN-HMCFs resist crevice etching due to the many defects in the hexagonal network. (C) 1999 Kluwer Academic Publishers.

    DOI CiNii

  • Fracture toughness improvement mechanism of calcium treated steel

    H Yoshida, H Katsumoto, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   85 ( 3 ) 261 - 268  1999.03

     View Summary

    The effect of Ca addition on fracture toughness has been examined by means of the analysis of fracture mechanics and tensile tests together with micro-structural observation. The Ca addition results in the spheroidization and reduction of the number of non-metallic inclusions, while the matrix structure does not show significant changes. Fracture mechanics test in terms of J-integral using a three point bending rest shows the increase in the slope of the R-curve, indicating enhanced increase in the stable crack growth resistance. The dimple morphology on the ductile fracture surface is classified into two types, i.e. primary and secondary dimples. By Ca addition, the depth of the primary dimple and local shear area on the fracture surface increase. It implies that Ca addition causes increased local plastic deformation in the course of stable crack extension, resulting in the improvement of fracture toughness. On the other hand effect of Ca addition does not appear in tensile test. It suggests that the effect of micro-structural factors on mechanical properties depends on the testing methods.

    DOI

  • Synthesis, structure, and superconducting properties of NbC nanorods and nanoparticles

    A Fukunaga, S Chu, ME McHenry, M Nagumo

    MATERIALS TRANSACTIONS JIM   40 ( 2 ) 118 - 122  1999.02

     View Summary

    NbC nanorods and nanoparticles have been synthesized using a vapor-solid reaction path starting with carbon nanotube precursors. Their structures are studied using XRD, TEM, and HRSEM. Their superconducting properties of nanoparticles were also characterized using a SQUID magnetometer. For reactions at lower temperatures, NbC nanorods (10 similar to 20 nm) which replicate the precursor carbon nanotubes are observed. For reactions at higher temperature, coarsened NbC nanoparticles (100 similar to 500 nm) are observed which have spherical or faceted morphologies. A morphological Rayleigh instability can be applied as initiating the transition from NbC nanorod to nanoparticle morphologies. NbC nanoparticles with a little larger lattice parameter show a higher T-c than stoichiometric bulk NbC.

    DOI

  • Hydrogen States and Lattice Defects in Steels

    Michihiko Nagumo

    Shinku/Journal of the Vacuum Society of Japan   42 ( 12 ) 1042 - 1047  1999

    DOI

  • Synthesis of TiC and Ti/TiC composites by reaction milling followed by hot consolidation of Ti with graphite or heptane

    Akiko Yasukawa, Michihiko Nagumo

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   63 ( 7 ) 822 - 827  1999

     View Summary

    Synthesis of TiC and Ti/TiC composite has been conducted by mechanical alloying and following Spark-Plasma-Sintering starting from elemental Ti powder with graphite or heptane. From graphite, formation of TiC takes place rapidly after a definite period of milling while it proceeds gradually from heptane. The apparent compositional range of Ti1-xCx is extended to a C/Ti ratio as low as 30/70 when graphite is used, while a mixture of Ti and TiC is obtained at a C/Ti ratio of 32/68 with heptane. Sintering can proceed at substantially lower temperatures compared with the conventional process, the sintering temperature decreasing with lower C/Ti ratios. The lattice parameter of TiC and the density of the compacts decrease with lower C/Ti ratios, but are larger than previously reported ones through conventional methods. The mechanism which causes the differences between graphite and heptane is discussed with respect to the reaction process during milling.

    DOI

  • Ca添加鋼の靭性改善機構

    鉄と鋼   85   261  1999

    DOI

  • Effect of austenitizing temperature on intergranular proeutectoid ferrite nucleation in a V-N steel

    Pingjian Qiu, Michihiko Nagumo

    Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan   85 ( 1 ) 45 - 51  1999

     View Summary

    Intergranular proeutectoid ferrite nucleation in a V-N steel has been examined at isothermal transformation at 600 °C with respect to the austenitizing temperatures. While substantial grain growth takes place, the number of intergranular ferrite grains per unit grain boundary area decreases with increasing austenitizing temperatures. Non-stationary increasing rate with time is observed. Overall transformation during isothermal transformation delays after austenitizing at higher temperatures and follows the Johnson-Mehl-Avrami formula for the case of fast grain boundary nucleation. It is discussed that the decrease in the intergranular ferrite nucleation rate associated with higher austenitizing temperatures is partially due to grain boundary structures, not merely to the decrease in the nucleation sites associated with grain growth. Use of high austenitizing temperature is requisite for the intragranular ferrite precipitation.

    DOI

  • Hydrogen States and Lattice Defects in Steels

    J.Vac.Sci.Jpn   42   1042  1999

  • Air-oxidation and anodization of pitch-based carbon fibers

    A Fukunaga, S Ueda, M Nagumo

    CARBON   37 ( 7 ) 1081 - 1085  1999

     View Summary

    Pitch-based high modulus carbon fibers were oxidized in air and characterized using the coulostatic method in order to compare them with anodized fibers. The interfacial shear strength (IFSS) of these fibers to an epoxy resin was evaluated by a micro debonding test. The results showed a good correlation between the differential double layer capacities, Cd, which were measured by the coulostatic method, and the IFSS values for air-oxidized and anodized fibers. In order to investigate the variation of the air-oxidation and anodization in the tow, the coefficients of variation for the Cd and polarization resistance (Rp) by the mono-filament coulostatic method were compared. As a result, the variation of oxidation in the tow of air-oxidized fiber seemed to be slightly larger than that of anodized fiber. (C) 1999 Elsevier Science Ltd. All rights reserved.

    DOI CiNii

  • Deformation induced defects in iron revealed by thermal desorption spectroscopy of tritium

    M Nagumo, K Ohta, H Saitoh

    SCRIPTA MATERIALIA   40 ( 3 ) 313 - 319  1999.01

    DOI CiNii

  • Effect of austenitizing temperature on intergranular proeutectoid ferrite nucleation in a V-N steel

    PJ Qiu, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   85 ( 1 ) 45 - 51  1999.01

     View Summary

    Intergranular proeutectoid ferrite nucleation in a V-N steel has been examined at isothermal transformation at 600 degrees C with respect to the austenitizing temperatures. While substantial grain growth takes place, the number of intergranular ferrite grains per unit grain boundary area decreases with increasing austenitizing temperatures. Non-stationary increasing rate with time is observed. Overall transformation during isothermal transformation delays after austenitizing at higher temperatures and follows the Johnson-Mehl-Avrami formula for the case of fast grain boundary nucleation. It is discussed that the decrease in the intergranular ferrite nucleation rate associated with higher austenitizing temperatures is partially due to grain boundary structures, not merely to the decrease in the nucleation sites associated with grain growth. Use of high austenitizing temperature is requisite for the intragranular ferrite precipitation.

    DOI

  • Effect of thermal cycles on toughness of heat affected zone of a Ti-killed steel

    K Yokoyama, H Ishikawa, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   84 ( 10 ) 740 - 746  1998.10

     View Summary

    Toughness and related characteristics of microstructures are examined on heat affected zone (HAZ) of weldments of Ti-killed steel given single- or double-heat cycle treatment, Brit-tie fracture initiation and stable crack propagation behavior are examined from fracture toughness rest, observation of tensile deformation microstructures and local strain distributions, It is revealed that resistance for the stable crack propagation of Ti-killed steel is hardly affected by the simulated thermal cycle conditions. However, the ductile-brittle fracture transition temperature increases in double-hear cycled specimens compared with single-heat cycled specimens. It is also revealed that higher strain concentration takes place at the prior austenite grain boundary in a double-heat cycled specimen. It is discussed that strain localization leads to the brittle crack nucleation.

  • Effect of isothermal holding in austenite region on proeutectoid ferrite growth rate in a V-C-N steel

    PJ Qiu, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   84 ( 8 ) 592 - 597  1998.08

     View Summary

    The mechanism of retarded growth rate of intergranular proeutectoid ferrite in a V-C-N steel has been investigated by examining the effect of holding in austenite region during cooling from the solutioning prior to the isothermal transformation at 600 degrees C. The growth rare increases and the transformation start time decreases by increasing the holding temperature, while a C-curve behaviors appears. The growth rare can be ascribed to the supersaturation of C at the transformation interface, THERMO-CALC calculation indicates that substantial precipitation of V(C, N) takes place in the V-C-N steel and the fraction of C in the precipitate decreases with the increasing holding temperature. Analysis of the transformation kinetics in terms of the Johnson-Mehl-Avrami equation shows a two-step process, suggesting decrease in the ferrite nucleation rate by the holding. It is concluded that absorption of C into the precipitate during the incubation period decreases the supersaturation of C at the transformation interface.

    DOI

  • Structure evolution upon heating of mechanically alloyed Ti34Zr11Cu47Ni8 powders

    XD Liu, M Nagumo

    MATERIALS TRANSACTIONS JIM   39 ( 8 ) 795 - 801  1998.08

     View Summary

    (A) quaternary Ti(34)Z(11)Cu(47)Ni(8) alloy is subjected to mechanical alloying on a low energy ball mill. The structure evolution of the as-milled powers upon heating is investigated by means of thermal analysis and X-ray diffraction. An unknown metastable phase is formed by heat treating the 25 h-milled sample which retains the crystalline state. Amorphization is clearly confirmed in the 100 h-milled Ti34Zr11Cu47Ni8 alloy. Thermal crystallization of the as-milled amorphous phase proceeds via two separate steps corresponding respectively to crystallization of NiTi and Cu51Zr11 intermetallic compounds, respectively. The influences of chemical composition and milling time on amorphization and thermal crystallization of the Ti34Zr11Cu47Ni8 alloy are discussed.

    DOI

  • Growth kinetics of intergranular allotriomorph ferrite in V-containing steel

    PJ Qiu, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   84 ( 5 ) 375 - 380  1998.05

     View Summary

    Growth kinetics of intergranular ferrite in a V-N steel has been investigated from the measurement of isothermal transformation kinetics. When compared with a v-C steel, the start of intergranular ferrite transformation starts earlier on isothermal transformation in the V-N steel, whereas irs growth is retarded. The growth rates of the intergranular ferrite are under the parabolic rate rule for both steels with a smaller rate constant for the V-N steel. When the rate constants are ascribed to the supersaturation of carbon at the ferrite/austenite interface, the carbon concentrations are estimated to be 0.29 and 0.35 mass% for the V-N and V-C steels, respectively. Johnson-Mehi-Avrami plot of the transformation kinetics indicates that the ferrite nucleation rate is larger for the V-N steel. II is discussed that the precipitation of intragranular ferrite in the V-N steel is facilitated owing to the retardation of the intergranular ferrite growth in the steel.

  • Mechanical milling of pure Ti and pure Zr

    XD Liu, M Nagumo, M Umemoto

    MATERIALS TRANSACTIONS JIM   39 ( 4 ) 463 - 468  1998.04

     View Summary

    Pure elemental Ti and Zr powders are respectively subjected to mechanical milling. It is discovered that after milling for 100 h, amorphization occurs in Zr while only nanocrystallization is achieved in Ti. Further thermal analysis and electron microscope observations verify amorphization in the 100 h-milled Zr sample. The crystallization peak temperature of the 100 h-milled Zr sample is determined to be 875 K by using a differential scanning calorimeter at a heating rate of 40 K/min. The above experimental results are discussed.

    DOI

  • Amorphization tendency of Ti34Zr11Cu47Ni8 and Ti37Zr17Cu42Ni4 during mechanical alloying

    XD Liu, M Nagumo, M Umemoto

    MATERIALS TRANSACTIONS JIM   39 ( 3 ) 343 - 350  1998.03

     View Summary

    Pure elemental powders of Ti, Zr, Cu and Ti corresponding to the compositions of Ti34Zr11Cu47Ni8 and Ti37Zr17Cu42Ni4 (at%) were subjected to mechanical alloying on a low energy milling machine in the present work. The premixed powders of the above two compositions underwent the following transformations during mechanical alloying up to 100 h: mu m-sized (Ti, Zr, Cu, Ni)-->nm-sized (Ti, Zr, Cu, Ni)-->amorphous+ a small amount of nm-sized crystallites. The 100-h milled Ti34Zr11Cu47Ni8 sample was found to exhibit an excellent thermal stability against crystallization with the crystallization temperature of about 200 K higher than that of the as-quenched amorphous counterpart. Contrary to the previous rapid quenching result, amorphous phase is easier to occur in Ti37Zr17Cu42Ni4 than in Ti34Zr11Cu47Ni8 by MA, indicating that the glass forming ability by rapid quenching is different from that by MA.

    DOI

  • Hydrogen trapping characteristics of cold-drawn pure iron and eutectoid steel evaluated by thermal desorption spectrometry

    K Takai, G Yamauchi, M Nakamura, M Nagumo

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   62 ( 3 ) 267 - 275  1998.03

     View Summary

    Hydrogen absorption characteristics of pure iron and eutectoid steel fabricated by cold drawing have been evaluated by thermal desorption spectrometry (TDS). The pure iron specimens with ferrite (alpha) structure and the eutectoid steel specimens with alpha and Fe3C structures, were produced under various degrees of reduction and also under various heat treatment conditions. These amount of hydrogen absorbed in specimens dipped in 20 mass%NH4SCN solution were measured using TDS. TDS analysis showed that hydrogen evolution rate of pure iron has only one peak, while that of eutectoid steel has two peaks. From transmission electron microscopy and TDS analysis, the lower temperature peak was attributed to hydrogen released from the trapping sites such as point defects, clustered defects, and dislocations in alpha. The higher temperature peak was found to correspond to hydrogen released from the trapping sites such as defects in Fe3C, and/or such as the disordered interface between alpha and Fe3C.

    DOI

  • V-C-N鋼の初析粒界フェライト成長速度に及ぼすオーステナイト域等温保定処理の効果

    鉄と鋼   84   592  1998

    DOI

  • Ti脱酸低炭素鋼溶接熱影響部の靭性に対する熱履歴の効果

    鉄と鋼   84   740  1998

    DOI

  • V鋼の粒界初析フェライトの成長速度

    鉄と鋼   84 ( 5 ) 375 - 380  1998

  • Hydrogen trapping characteristics of cold-drawn pure iron and eutectoid steel evaluated by thermal desorption spectrometry

    Kenichi Takai, Goro Yamauchi, Mariko Nakamura, Michihiko Nagumo

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   62 ( 3 ) 267 - 275  1998

    Book review, literature introduction, etc.  

     View Summary

    Hydrogen absorption characteristics of pure iron and eutectoid steel fabricated by cold drawing have been evaluated by thermal desorption spectrometry (TDS). The pure iron specimens with ferrite (α) structure and the eutectoid steel specimens with α and Fe3C structures, were produced under various degrees of reduction and also under various heat treatment conditions. These amount of hydrogen absorbed in specimens dipped in 20 mass%NH4SCN solution were measured using TDS. TDS analysis showed that hydrogen evolution rate of pure iron has only one peak, while that of eutectoid steel has two peaks. From transmission electron microscopy and TDS analysis, the lower temperature peak was attributed to hydrogen released from the trapping sites such as point defects, clustered defects, and dislocations in α. The higher temperature peak was found to correspond to hydrogen released from the trapping sites such as defects in Fe3C, and/or such as the disordered interface between α and Fe3C.

    DOI

  • Microstructure and high temperature tensile properties of TiC/Ti5Si3/Ti3SiC2 fine composites prepared by mechanical alloying

    Shigehiro Kawamori, Nobuyuki Sasaki, Fumitaka Ishikawa, Michihiko Nagumo, Tatsushi Okumura, Kei Ameyama

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   62 ( 1 ) 30 - 36  1998

     View Summary

    Microstructure and tensile properties at elevated temperatures of fine composites prepared by mechanical alloying of Ti and SiC powders have been investigated. Mixtures of elemental Ti and SiC powders in the composition of Ti-24 mass%SiC are milled under an Ar atmosphere using an attritor ball mill. After milling for 36 ks, formation of TiC and Ti5Si3 is observed and further milling adding n-heptane for 3.6 ks makes the powder particles finer. Milled powders are consolidated by hot pressing at 1773 K for 10.8 ks under 70 MPa and hot isostatic pressing at 1773 K for 10.8 ks under 196 MPa. The compact consists of mostly equi-axed TiC and Ti5Si3 grains of an average diameter of 0.86 μm partially mixed with plate-like phase of Ti3SiC2. The compact shows elongation of 130% at tensile test at 1773 K with an initial strain rate of 4.0 × 10-4 s-1 with the strain rate sensitivity exponent of 0.38. Most grains remain equi-axed after tensile test, while random orientations of plate-like phases of Ti3SiC2 turn parallel along the tensile axis. The large elongation observed above 1773 K is likely due to the superplasticity, while rotation of the plate-like phase accompanies deformation of the surrounding matrix.

    DOI

  • Meaning of Fracture Toughness Test in Steels

    Quartery Report of ANERI   13 ( 4 ) 2 - 5  1998

  • FEM analysis of ductile crack growth in fracture transition region for steels with different void nucleation frequency

    H Yoshida, M Nagumo

    ISIJ INTERNATIONAL   38 ( 2 ) 196 - 202  1998

     View Summary

    Local stress and strain fields in front of a crack have been computed by FEM analysis using a Gurson model which takes into account void nucleation and growth within the material. The original Gurson model has been revised to fit the actual material by introducing experimentally obtained deformation and fractographic data of the material. Calculation has been applied for the ductile-to-brittle transition regions up to the ductile crack growth stage in two steels with different transition behaviors. Higher magnitudes of local stress and strain as well as larger extensions have been shown for a steel which has less nucleated void volume fraction, resulting in higher resistance against the ductile crack growth. Local stress increases with lowering test temperature whereas local strain decreases. Insignificant temperature dependence of R-curves has been understood from the calculated J-integral values because of the cancellation of the stress increase and strain decrease. The calculated R-curves have been shown to be consistent with the experimentally observed ones.

    DOI

  • Brittle Fracture Initiation Associated With Strain Localizationin Heat Affected Zone of a Low Carbon Steel

    Metallur. Mater. Trans. A.   29A ( 2 ) 551 - 558  1998

  • Microstructures controlling the ductile crack growth resistance of low carbon steels

    H Yoshida, M Nagumo

    METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE   29 ( 1 ) 279 - 287  1998.01

     View Summary

    Microstructures controlling the ductile crack growth resistance in the ductile-brittle fracture transition region have been investigated with three low carbon low alloy steels, which showed characteristic differences in the R curves. The crack growth resistance is related to both the primary dimple morphology and the total length of local shear zones appearing on the fracture surface; the latter contribution predominates over the former. The heterogeneity of the microstructures, which constrains slip propagation at the grain boundaries, supplies sites for easy void nucleation and induces local shear and the resulting surface roughness.

  • Microstructure and high temperature tensile properties of TiC/Ti5Si3/Ti3SiC2 fine composites prepared by mechanical alloying

    S Kawamori, N Sasaki, F Ishikawa, M Nagumo, T Okumura, K Ameyama

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   62 ( 1 ) 30 - 36  1998.01

     View Summary

    Microstructure and tensile properties at elevated temperatures of fine composites prepared by mechanical alloying of Ti and SiC powders have been investigated. Mixtures of elemental Ti and SiC powders in the composition of Ti-24 mass%SiC are milled under an Ar atmosphere using an attritor ball mill. After milling for 36 ks, formation of TiC and Ti5Si3 is observed and further milling adding n-heptane for 3.6 ks makes the powder particles finer. Milled powders are consolidated by hot pressing at 1773 K for 10.8 ks under 70 MPa and hot isostatic pressing at 1773 K for 10.8 ks under 196 MPa. The compact consists of mostly equi-axed TIC and Ti5Si3 grains of an average diameter of 0.86 mu m partially mixed with plate-like phase of T3SiC2. The compact shows elongation of 130% at tensile test at 1773 K with an initial strain rate of 4.0 x 10(-4) s(-1) with the strain rate sensitivity exponent of 0.38. Most grains remain equi-axed after tensile test, while random orientations of plate-like phases of Ti3SiC2 turn parallel along the tensile axis. The large elongation observed above 1773 K is likely due to the superplasticity, while rotation of the plate-like phase accompanies deformation of the surrounding matrix.

    DOI

  • Role of microstructures on fracture toughness of heat affected zone of Ti-killed steel

    K Yokoyama, H Ishikawa, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   83 ( 12 ) 803 - 808  1997.12

     View Summary

    Role of microstructures on the improved fracture toughness has been analyzed for the heat affected zone of weldment in Ti-killed steel. A microstructural features of Ti-killed steel is decrease of coarse bainitic ferrite, alpha(B) degrees, and increase of the mixed area of alpha(B) degrees and quasipolygonal ferrite, a(q), besides the presence of intragranular ferrite. The brittle fracture initiation is not from large particles or inclusions, but at the intersections of small alpha(B) degrees grains with different orientations in a mixed area of alpha(B) degrees and alpha(q) in the proximity of boundary between coarse alpha(B) degrees. Ductile crack growth resistance represented by the slop of R-curve is also higher in Ti-killed steel compared with Al-killed steel. Together with observation of deformed microstructures, it is discussed that the decrease of coarse alpha(B) degrees grains in Ti-killed steel suppresses brittle fracture initiation by reducing plastic constraint and the increase in the mixed area of alpha(B) degrees and alpha(q) enhances ductile crack growth resistance by accommodating large strain.

  • Effect of surface roughness on early stages of pitting corrosion of type 301 stainless steel

    T Hong, M Nagumo

    CORROSION SCIENCE   39 ( 9 ) 1665 - 1672  1997.09

     View Summary

    In 0.5 M NaCl solution, the early stages of pitting corrosion of Type 301 stainless steel which is wet-ground on silicon carbide papers ranged from 240 grit to 400, 800, 1000 and 1500 grits have been studied by AC impedance method. It is found that the Warburg impedance coefficient (sigma), which is calculated from Nyquist impedance plots, decreases with increasing grit number of silicon carbide paper for final surface grinding. This is because that the number of metastable pits on a smooth surface is less than that on a rougher surface. The change in E-m (the potential at which metastable pit or pits start to grow on the steel) relates with the change in grit number of silicon carbide paper. The higher the number of the silicon carbide paper, the higher the E-m value. This fact suggests that metastable pit or pits starting to grow on the smoother surfaces is more difficult than that on rougher surfaces. (C) 1997 Elsevier Science Ltd.

    DOI

  • The effect of chromium enrichment in the film formed by surface treatment on the corrosion resistance of Type 430 stainless steel - Reply

    T Hong, T Ogushi, M Nagumo

    CORROSION SCIENCE   39 ( 8 ) 1491 - 1495  1997.08

    Rapid communication, short report, research note, etc. (scientific journal)  

  • Structural relaxation in amorphous Ni-Ti alloys prepared by mechanical alloying

    Y Makifuchi, Y Terunuma, M Nagumo

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   226 ( 226-228 ) 312 - 316  1997.06

     View Summary

    Structural changes in amorphous states during prolonged milling after the completion of amorphization have been investigated through the crystallization behaviors with Ni-Ti alloys of compositions corresponding to the intermetallic compounds. In 33Ni-67Ti, the crystallization to NiTi2 takes place in two steps, a higher crystallization temperature dominating after prolonged milling. In 50Ni-50Ti, structural relaxation leading to the crystallization to NiTi2 and Ni3Ti takes place. In 30Ni-70Ti, which is close to the border of the amorphization range, the initially formed amorphous phase turns into a supersaturated solid solution of Ti in Ni. (C) 1997 Elsevier Science S.A.

  • The effect of SO4(2-) concentration in NaCl solution on the early stages of pitting corrosion of type 430 stainless steel

    T Hong, M Nagumo

    CORROSION SCIENCE   39 ( 5 ) 961 - 967  1997.05

     View Summary

    The early stages of pitting corrosion of Type 430 stainless steel in 0.5 M NaCl solution containing 0, 0.01, 0.05 and 0.1 M Na2SO4 have been studied by an AC impedance method. It is found that the Warburg impedance coefficient (sigma), which is calculated from Nyquist impedance plots, decreases with increasing Na2SO4 in the solution at a given potential in passive region. This is because that increasing SO42- concentration in NaCl solution decreases the total number of surface sites available for metastable pits. The change in E-m (the potential at which metastable pit or pits start to grow on the steel) is a function of SO42- concentration in NaCl solution. The values of E-m in millivolts are linear with logarithm of SO42- concentration in 0.5 M NaCl solution, following the equation, E-m=59 log(SO42-)-114. This fact suggests that increasing SO42- concentration in NaCl solution causes the shift of not only pitting potential but also E-m to more positive potentials. (C) 1997 Elsevier Science Ltd.

    DOI CiNii

  • The load drop phenomenon at the fracture toughness test of the heat affected zone of a low carbon steel

    K Yokoyama, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   83 ( 5 ) 323 - 328  1997.05

     View Summary

    The load drop or pop-in phenomenon at the fracture toughness test of the heat affected zone (HAZ) of a low carbon steel has been investigated. Microstructural features such as the size of the bainitic ferrite were varied with the thermal cycles simulating a double pass welding. It is revealed that the initiation of the load drop is not dependent on test temperatures, whereas the arrest of the load drop decreases with the decrease of the test temperature, thus increasing the amount of the load drop. Fractographic examination has revealed that the amount of the load drop scales with the crack length formed by the local brittle fracture. Also, the size and density of cleavage facets increases with the load drop. It is discussed that the temperature dependent amount of a load drop is determined by the ductile linking of cleavage facets produced at bainitic ferrite grains.

  • Influence of Microstructures on Fracture Toughness of Heat Affected Zone of the Ti-Killed Steel

    YOKOYAMA Ken'ichi

      10 ( 3 ) 591 - 591  1997.03

    CiNii

  • The effect of chloride concentration on early stages of pitting for Type 304 stainless steel revealed by the AC impedance method

    T Hong, M Nagumo

    CORROSION SCIENCE   39 ( 2 ) 285 - 293  1997.02

     View Summary

    The effect of chloride concentration on early stages of pitting for Type 304 stainless steel has been studied by using an AC impedance method. The Warburg impedance coefficient, which is calculated from Bode plots, increases with increasing chloride concentration at low potentials in the passive region when the diffusion process begins to occur at the surface. For a pit which is nucleated under a given potential, there exists a minimum chloride concentration above which the pit on the surface of the steel can be activated into metastable propagation, and below which it cannot. It is also found the effect of chloride concentration is reflected qualitatively in the potential (E(m)) at which the metastable pit or pits start to grow on the surface of Type 304 stainless steel. The values of E(m) in millivolts linearly increases with the logarithm of chloride concentration of solution, following the equation, E(m) = -37 log(C1(-))-212. (C) 1997 Elsevier Science Ltd.

    DOI CiNii

  • Ti脱酸低炭素請鋼の溶接熱影響部の破壊靭性に及ぼす組織の役割

    鉄と鋼   83 ( 12 ) 803  1997

    DOI

  • 鋼中の水素の存在状態と脆化との関係

    金属   67 ( 12 ) 995 - 1002  1997

  • 低炭素鋼溶接熱影響部の靭性試験における荷重低下現象

    鉄と鋼   83   323  1997

    DOI

  • 高強度鋼の遅れ破壊における変動応力の効果

    鉄と鋼   83   371  1997

    DOI

  • Hall-Petch Relationship in Nanocrystalline Materials

    Materials Transactions, JIM   38 ( 12 ) 1033 - 1039  1997

    DOI

  • Relations between Hydrogen Embrittlement and Hydrogen States in Steels

    Metals & Technology KINZOKU   67 ( 12 ) 995 - 1002  1997

  • High-temperature deformation of TiAl/Ti2AlC composites produced by reaction milling

    A Okuno, TS Suzuki, N Sasaki, Y Matsumoto, M Nagumo

    TOWARDS INNOVATION IN SUPERPLASTICITY I   233-2   295 - 302  1997

     View Summary

    Composites of gamma-TiAl intermetallic compound and a complex carbide (Ti2AlC) have been formed by mechanical alloying of Ti-Al-heptane system followed by hot consolidation. The amount of the carbide can be controlled by the milling parameters. The composites have fine microstructures of an average grain size of a few hundreds nm. Mechanical properties at elevated temperatures have been investigated by tensile tests. At 1073K, different deformation behaviors depending on the carbon content are distinct, while the total elongation is still small. The total elongation of specimen tested at 1273K and at a strain rate of 1x10(-3) s(-1) exceeds 300%.

  • Superplastic behavior of composites prepared from mechanically alloyed Ti-Si3N4 powders

    T Namura, M Nagumo, Y Matsumoto, N Sasaki, K Ameyama

    TOWARDS INNOVATION IN SUPERPLASTICITY I   233-2   251 - 259  1997

     View Summary

    In situ synthesis of fine grain composites of TiN and Ti5Si3 has been conducted by the reaction milling of Ti and Si3N4 powder mixtures followed by hot-consolidation. Formation of TiSi2 could be suppressed by increasing the Ti content in the starting powder mixtures to more than 75 wt.%. Full densification was attained at sintering temperature of 1300 degrees C using Hot-Isostatic-Pressing. The mean grain size in the compacts was hundreds nm when HIP treated at 1300 degrees C. Tensile strength at high temperatures was improved by the elimination of TiSi2. Even in this case, substantial plastic deformation appeared at testing temperatures over 1300 degrees C, and the elongation at 1500 degrees C exceeded 100%. The strain rate exponent of the flow stress at 1400 degrees C and at strain of 0.1 was 0.47. It indicates intrinsic superplasticity in this type of ceramics composites.

  • Identification of trapping sites in high-strength steels by secondary ion mass spectrometry for thermally desorbed hydrogen

    K Takai, Y Homma, K Izutsu, M Nagumo

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   60 ( 12 ) 1155 - 1162  1996.12

     View Summary

    The trapping sites of hydrogen detected by Thermal Desorption Spectrometry (TDS) have been identified by Secondary Ion Mass Spectrometry (SIMS). High-strength steel specimens were given applied loads in D2O and 20% NH4SCN solution at 323 K. In SIMS analysis, deuterium ions can be detected with greater sensitivity than hydrogen ions and measurement can be started in a matter of minutes. TDS analysis shows that hydrogen thermal desorption rate has two peaks, corresponding to trap activation energies of 20.1 similar to 22.5 kJ/mol and 82.2 similar to 87.4 kJ/mol for the lower and higher temperature peaks, respectively. These Values are close to 26.8 kJ/mol reported in the literature as the trap activation energy for desorption from dislocations and greater than or equal to 72.3 kJ/mol from the interfaces of inclusions and precipitates. By applying SIMS image-analysis to specimens cooled after the respective peak temperatures, we could identify the trapping sites corresponding to the lower temperature peak as sites within the matrix such as defects including dislocations, and those corresponding to the higher temperature peaks as inclusion interfaces, precipitate interfaces, and segregation bands of phosphorus. These SIMS results confirm the location of the trapping sites to be the same as those estimated from trap activation energy by TDS.

  • Improvement of delayed fracture strength of high strength steels by intergranular ferrite precipitation

    J Watanabe, K Takai, M Nagumo

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   82 ( 11 ) 947 - 952  1996.11

     View Summary

    A new method for improving delayed fracture strength by the precipitation of ferrite along prior austenite grain boundaries has been demonstrated with high strength steels of 1300 MPa in tensile strength. Intergranular fracture which is characteristic to the delayed fracture of tempered martensitic steels is suppressed and is changed to quasi cleavage by the intergranular ferrite precipitation. Hydrogen thermal desorption analysis has revealed that the amount of diffusive hydrogen increases under loading. The mean hydrogen occlusion rate rather than the hydrogen absorption under no loading or the amounts of hydrogen at the time of failure corresponds to the delayed fracture strength levels. The mechanism of the effect of intergranular ferrite on the hydrogen embrittlement based on the accumulation of lattice defects has been discussed.

  • The observation of the early stages of fitting on passivated type 304 stainless steel in a 0.5 M NaCl solution at low potentials in the passive region by using the AC impedance method

    T Hong, GW Walter, M Nagumo

    CORROSION SCIENCE   38 ( 9 ) 1525 - 1533  1996.09

     View Summary

    The changes of electrochemical parameters on the passivated electrode of type 304 stainless steel in a 0.5 M NaCl0 solution at different low potentials ranging From -250 to -100 mV (SCE) in the passive region are studied using the AC impedance method. It is found that the electrode reaction is under metal charge-transfer control at potentials below 200 mV, and the charge-transfer resistance decreases with increasing potential. It is possible that pit nucleation occurs on the passivated stainless steel at this stage. When the potential is above -200 mV, because of the diffusion process appearing in Bode impedance plots, both the metal charge-transfer and diffusion processes occur on the electrode. The metal charge-transfer resistance decreases and the diffusion coefficient increases with increasing potential. The nucleated pits on passivated stainless steel proceed to the stage of metastable growth at the potentials above -200 mV. This potential of -200 mV can be estimated as the level at which metastable pits start to grow on passivated type 304 stainless steel. Copyright (C) 1996 Elsevier Science Ltd

    DOI CiNii

  • Microstructures relevant to brittle fracture initiation at the heat-affected zone of weldment of a low carbon steel

    K Ohya, J Kim, K Yokoyama, M Nagumo

    METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE   27 ( 9 ) 2574 - 2582  1996.09

     View Summary

    Charpy toughness of the heat-affected zone (HAZ) of weldment of a low carbon steel has been investigated by means of an instrumented Charpy test and fractographic analysis. Microstructures were varied with thermal cycles simulating double-pass welding. The ductile-brittle transition temperature is the most deteriorated at an intermediate second-cycle heating temperature. The origin of the difference in the transition temperatures has been analyzed to exist in the brittle fracture initiation stage. Fractographic examination correlating with microstructural features has revealed that the brittle fracture initiation site is associated with the intersection of bainitic ferrite areas with different orientations rather than the martensite-austenite constituents. The role of the constraint of plastic deformation on the brittle fracture initiation is discussed.

    DOI CiNii

  • Effect of chromium enrichment in the film formed by surface treatments on the corrosion resistance of type 430 stainless steel

    T Hong, T Ogushi, M Nagumo

    CORROSION SCIENCE   38 ( 6 ) 881 - 888  1996.06

     View Summary

    The effect of chromium concentration in the surface film formed by surface treatments on the corrosion resistance of Type 430 stainless steel was studied. It was found that the chromium content depends on the surface treatment method. HNO3 treatments result in a significant enrichment of chromium in the surface film on the Type 430 stainless steel, and the chromium enrichment increases with increasing HNO3 concentration. The pitting potential (E(p)), corrosion potential (E(c)) and polarization resistance (R(p)) are changed by the chromium enrichment (S-Cr) in the surface film formed by treatment. The higher the S-Cr value, the higher the E(p), E(c) and R(p) values. Copyright (C) 1996 Elsevier Science Ltd.

    DOI CiNii

  • Detecting stable crack onset at ductile-brittle transition in steels

    Y Fujii, A Kikuchi, M Nagumo

    METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE   27 ( 2 ) 469 - 471  1996.02

  • Identification of trapping sites in high-strength steels by secondary ion mass spectrometry for thermally desorbed hydrogen

    Kenichi Takai, Yoshikazu Homma, Kaori Izutsu, Michihiko Nagumo

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   60 ( 12 ) 1155 - 1162  1996

     View Summary

    The trapping sites of hydrogen detected by Thermal Desorption Spectrometry (TDS) have been identified by Secondary Ion Mass Spectrometry (SIMS). High-strength steel specimens were given applied loads in D2O and 20% NH4SCN solution at 323 K. In SIMS analysis, deuterium ions can be detected with greater sensitivity than hydrogen ions and measurement can be started in a matter of minutes. TDS analysis shows that hydrogen thermal desorption rate has two peaks, corresponding to trap activation energies of 20.7∼22.5 kj/mol and 82.2∼87.4 kj/ mol for the lower and higher temperature peaks, respectively. These values are close to 26.8 kj/mol reported in the literature as the trap activation energy for desorption from dislocations and ≧72.3 kj/mol from the interfaces of inclusions and precipitates. By applying SIMS image-analysis to specimens cooled after the respective peak temperatures, we could identify the trapping sites corresponding to the lower temperature peak as sites within the matrix such as defects including dislocations, and those corresponding to the higher temperature peaks as inclusion interfaces, precipitate interfaces, and segregation bands of phosphorus. These SIMS results confirm the location of the trapping sites to be the same as those estimated from trap activation energy by TDS.

    DOI

  • 粒界フェライト析出による高強度鋼の遅れ破壊強度の改善

    鉄と鋼   82   947  1996

    DOI

  • Metastable states during reaction milling of hcp transition metals with hydrocarbon

    M Nagumo, TS Suzuki, K Tsuchida

    METASTABLE, MECHANICALLY ALLOYED AND NANOCRYSTALLINE MATERIALS, PTS 1 AND 2   225   581 - 586  1996

     View Summary

    The reaction process during milling of Zr and Ti with n-heptane has been investigated. Formation of a metastable intermediate phase characterized by fee-like structure has been revealed at a certain milling time. It disappears upon heating with reversible appearance of the original hcp structure. The amounts of H and C in the metal powders increase with milling time to a constant level at which stabilization of the intermediate phase takes place. The intermediate phase is presumably the stacking fault of hcp structure stabilized by H and C atoms as the precursor of the stable carbides. Dissociation of H from heptane precedes that of C. Site occupation is competitive between H and C, and stabilization of the intermediate phase during milling takes place by the increase of C content excluding H to sites with lower binding energy with H.

  • INCONSISTENCY IN TRANSITION-TEMPERATURE BY TESTING METHODS OF LOW-CARBON STEELS

    T YAGI, M NAGUMO

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   81 ( 11 ) 1103 - 1108  1995.11

     View Summary

    The fracture process at ductile-brittle fracture transition region of low carbon steels has been compared for J-integral tests and instrumented V-notch Charpy tests. Three steels oi ferrite-pearlite structure, A and B, and of mixed structure with bainite, C, were employed. Only differences of the compositions are respective Ni to Mn ratios, and characteristic differences in the ductile-brittle transition behaviors such as the transition temperature, R-curve and brittle fracture initiation stage have been observed. From the analysis of the instrumented test a Charpy energy is decomposed into the energies dissipated in involved fracture processes. On contrary to steel A and B, decreases of the energy transition temperature and of temperature dependence of stretched zone width at Charpy test compared with at the fracture toughness test are observed with steel C. These differences are originated in Region II where blunting of the notch tip proceeds associated with the extension of the stretched zone, Referring to the stress analyses, the estimated local stress at the brittle fracture initiation site of Charpy tests is about a half of that oi J-integral tests. The inconsistency of the transition temperature takes place for steel C which shows pop-in al the J-integral test. It is discussed that the inconsistency of the transition temperature is caused by the suppression of pop-in at Charpy test because of its low local stress.

    DOI

  • STRUCTURAL RELAXATION IN AMORPHOUS NI50TI50 ALLOY PREPARED BY MECHANICAL ALLOYING

    Y TERUNUMA, M NAGUMO

    MATERIALS TRANSACTIONS JIM   36 ( 7 ) 842 - 847  1995.07

     View Summary

    Structural relaxation in amorphous Ni50Ti50 alloy prepared by mechanical alloying has been investigated by differential scanning calorimetry and X-ray diffraction analysis. An exothermic DSC peak originating from structural changes in the amorphous state was observed with alloys milled after completion of amorphization. The peak was characterized by the increase in the intensity with milling time and reduced heating rate, and also with accompanying formation of phases such as NiTi2 and Ni3Ti with compositions different from the original one after crystallization. The kinetics of the reaction taking place at the peak was expressed by the Johnson-Mehl-Avrami equation with the Avrami exponent of 0.57. The origin of the peak was discussed with respect to the free energy diagram of Ni-Ti system. Structural relaxation was considered to take place at the peak to stabilize the configuration in the as-milled alloy, and to enhance phase separation or compositional fluctuation during milling.

    DOI

  • METASTABLE INTERMEDIATE PHASE-FORMATION AT REACTION MILLING OF TITANIUM AND N-HEPTANE

    TS SUZUKI, M NAGUMO

    SCRIPTA METALLURGICA ET MATERIALIA   32 ( 8 ) 1215 - 1220  1995.04

    DOI CiNii

  • RESISTANCE AGAINST THE STABLE CRACK-GROWTH AND BRITTLE-FRACTURE INITIATION SITE CONTROLLING THE DUCTILE-BRITTLE FRACTURE TRANSITION BEHAVIORS OF LOW-CARBON STEELS

    T YAGI, A ITOH, M NAGUMO

    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN   81 ( 3 ) 225 - 230  1995.03

     View Summary

    The fracture process of low carbon steels have been investigated by means of a fracture mechanics test and microscopic observations. Three steels with characteristic differences in the ductile-brittle transition behaviors such as the transition temperature, R-curve and brittle fracture initiation stage are employed. A new microstructural parameter, the constraint factor, is defined to take into account the constraint of plastic deformation by grain boundary carbides. The constraint factor is successfully correlated with the resistance against the stable crack growth. The crack tip field is analyzed in terms of the elastic-plastic analyses in terms of J/delta(y) and COD, and the elastic-plastic analyses are found to be applicable at the ductile-brittle transition region. The brittle fracture initiation is controlled either by the local stress or by the local strain for respective steels. The constraint factor is also correlated with the location of the brittle fracture initiation sites. The estimated local stress at the brittle fracture initiation site shows a unique temperature dependence irrespective of the microstructure of steels. It is suggested that the nucleation of an incipient crack at the brittle initiation site is microstructure dependent through a local deformation behaviors.

  • REACTION MILLING OF METALS WITH HYDROCARBON OR CERAMICS

    M NAGUMO

    MATERIALS TRANSACTIONS JIM   36 ( 2 ) 170 - 181  1995.02

     View Summary

    Recent results on reaction milling have been reviewed focusing on metal-hydrocarbon and metal-ceramics systems. An intermediate metastable phase during the reaction was first revealed with Ti-heptane system. It was shown that stacking faults in Ti introduced by milling is stabilized by C and H which are decomposition products of heptane. Formation of a metastable Ni3C which has a positive heat of formation was revealed at the milling of Ni with SiC. An incubation period for the reaction was observed and related to a threshold value of the stored energy during milling as the driving force of the reaction. The reaction milling of Ti-Al-heptane and Ti-Si3N4, Ti-SiC systems followed by hot consolidation could produce fine composites of TiAl-Ti4Al2C2, TiN-Ti silicides and TiC-Ti silicides. The phases present in the compacts were altered with the process parameters. A kinematical model for the preference of the phases was presented. Improved sinterbility and superplastic-like ductility at elevated temperatures have been demonstrated.

    DOI

  • FRACTURE PROCESS OF A LOW-CARBON LOW-ALLOY STEEL RELEVANT TO CHARPY TOUGHNESS AT DUCTILE-BRITTLE FRACTURE TRANSITION REGION

    T TANI, M NAGUMO

    METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE   26 ( 2 ) 391 - 399  1995.02

     View Summary

    The fracture process that determines the Charpy energy at the ductile-brittle transition region was investigated by means of the instrumented Charpy test and fractographic analysis with a low carbon low alloy steel subjected to different control-rolling conditions. The decomposition of a Charpy energy into the energies dissipated in the course of the notch-tip blunting, stable crack growth, and brittle crack propagation is unique irrespective of the testing temperatures and specimen series. Toughness level can be divided into four regions according to the predominating fracture process. The;temperature dependence of toughness and effects of the anisotropy of a specimen originates in the brittle fracture initiation stage rather than the resistance against the notch-tip blunting or stable crack growth. From fractographic examination referring to the stress analyses, it is discussed that the brittle fracture initiation is controlled by the local deformation microstructures in the plastic zone together with the stress field ahead of the notch or the stable crack front.

    DOI CiNii

  • 低炭素鋼の試験法による破壊遷移温度逆転現象

    鉄と鋼   81   1103 - 1108  1995

    DOI

  • 低炭素鋼の延性脆性破壊遷移挙動を支配する安定き裂伝播抵抗と脆性破壊起点

    鉄と鋼   81   69 - 74  1995

  • Structural relaxation in amorphous Ni50Ti50 alloy prepared by mechanical alloying

    Yuriko Terunuma, Michihiko Nagumo

    Materials Transactions, JIM   36 ( 7 ) 842 - 847  1995

     View Summary

    Structural relaxation in amorphous Ni50Ti50 alloy prepared by mechanical alloying has been investigated by differential scanning calorimetry and X-ray diffraction analysis. An exothermic DSC peak originating from structural changes in the amorphous state was observed with alloys milled after completion of amorphization. The peak was characterized by the increase in the intensity with milling time and reduced heating rate, and also with accompanying formation of phases such as NiTi2 and Ni3Ti with compositions different from the original one after crystallization. The kinetics of the reaction taking place at the peak was expressed by the Johnson-Mehl-Avrami equation with the Avrami exponent of 0.57. The origin of the peak was discussed with respect to the free energy diagram of Ni-Ti system. Structural relaxation was considered to take place at the peak to stabilize the configuration in the as-milled alloy, and to enhance phase separation or compositional fluctuation during milling.

    DOI

  • Synthesis of TiAl-Al2Ti4C2 composite by reaction milling

    TS SUZUKI, M NAGUMO

    MECHANICALLY ALLOYED AND NANOCRYSTALLINE MATERIALS   179- ( 181/ ) 189 - 194  1995

  • DEFORMATION MICROSTRUCTURES OF A LOW-CARBON STEEL CHARACTERIZED BY TRITIUM AUTORADIOGRAPHY AND THERMAL-DESORPTION SPECTROSCOPY

    M AOKI, H SAITO, M MORI, Y ISHIDA, M NAGUMO

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   58 ( 10 ) 1141 - 1148  1994.10

     View Summary

    Deformation microstructures of a low carbon steel with ferrite-pearlite structures have been examined with tritium autoradiography and thermal desorption spectroscopy. The amount of non-diffusible tritium at room temperature increases with strain. When deformed at room temperature which is in the ductile fracture region, the distribution of tritium is fairly uniform within a grain, while it is inhomogeneous when deformed at -80 degrees C which is in the brittle fracture region. In the latter case, the accumulated sites are distributed regularly in arrays and localized as bands. Comparison with slip band traces indicated that the distribution is likely along slip bands. The amount of non-diffusible tritium which desorbs at 180 degrees C is remarkably large when deformed at -80 degrees C. Desorption at 180 degrees C disappears when the deformed sample is annealed at 500 degrees C, suggesting that the defects as the accumulation sites are microdefects presumably point defects or their clusters.

    DOI

  • CHEMICAL SHORT-RANGE ORDER IN AMORPHOUS CU-TI PREPARED BY MECHANICAL ALLOYING

    K NAKAMURA, M NAGUMO

    JOURNAL OF NON-CRYSTALLINE SOLIDS   175 ( 2-3 ) 238 - 243  1994.10

     View Summary

    Chemical short-range order (CSRO) in amorphous CuxTi100-x samples prepared by mechanical alloying of elemental metal powders and mechanical grinding of intermetallic compounds has been examined by EXAFS. Curve fitting for the Fourier filtered first shell of the Fourier transform of EXAFS was conducted to determine the Cu coordination numbers. The Cowley CSRO parameter deduced from the coordination numbers shows a monotonic decrease with increasing Cu concentration. It is positive in the range of x < 68, and negative for x > 68. This behavior is quite different from the results of rapidly quenched Cu-Ti amorphous alloys whose CSRO parameter is negative for all compositions. The ratio of coordination numbers of Cu and Ti atoms, N-Cu/N-Ti, increases linearly for x < 57 and saturates to 2.1 for x > 57. The origin of CSRO in mechanical alloyed samples is probably due to inter-diffusion of Ti into Cu, while CSRO of samples derived from the liquid state is fixed during rapid quenching.

    DOI

  • STRUCTURAL AND MECHANICAL-PROPERTIES OF FINE COMPOSITES PREPARED BY TI-SI3N4 SOLID-STATE REACTIONS

    T KOGA, M MIZUNO, M NAGUMO

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   179   153 - 157  1994.05

     View Summary

    Mechanical alloying of elemental Ti and Si3N4 powders was conducted by high energy ball milling and solid state reactions were observed to take place during milling. An incubation period for the reaction to begin existed which was related to the critical stored energy during milling. Hot compaction of milled powders could be efficiently conducted at lower temperatures than for conventional sintering of Si3N4. The phases formed after sintering varied with the milling time and sintering temperature and a kinematical model has been proposed for the mechanism of phase formation.
    The grain size of samples sintered at 1300-degrees-C was about 100 nm and grain growth took place at increasing sintering temperatures preferentially at Ti5Si3 grains. The Vickers hardness decreased monotonically with increasing test temperature, but the bending strength showed an inverse temperature dependence. Substantial plastic deformation took place at over 900-degrees-C and superplastic behaviour was observed.

    DOI CiNii

  • BRITTLE-FRACTURE INITIATION IN LOW-CARBON STEELS AT THE DUCTILE-BRITTLE TRANSITION-TEMPERATURE REGION

    M KOIDE, A KIKUCHI, T YAGI, M NAGUMO

    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING   176 ( 1-2 ) 171 - 175  1994.03

     View Summary

    The fracture process that determines the temperature dependence of toughness at the ductile-brittle transition was investigated for low carbon steels. It was revealed that the resistance against the stretch zone at the crack tip and the stable crack extensions is temperature independent while it depends on the carbon content. Applicability of elastic-plastic analyses of the crack tip fields was examined in terms of the relationship between J integral value normalized by the flow stress and crack opening displacement. Temperature dependence of toughness is determined primarily by the brittle fracture initiation. Locations of the initiation sites were revealed to coincide with the maximum stress triaxiality rather than the maximum tensile stress. It was suggested that the brittle fracture is caused by the deformation-induced initiation and triaxial stress assisted growth of an incipient crack.

  • 鉄の水素脆性の基本的観点

    日本金属学会報   33   914 - 921  1994

    DOI

  • Deformation microstructures of a low carbon steel characterized by tritium autoradiography and thermal desorption spectroscopy

    Michiko Aoki, Hideo Saito, Minoru Mori, Yoichi Ishida, Michihiko Nagumo

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   58 ( 10 ) 1141 - 1148  1994

     View Summary

    Deformation microstructures of a low carbon steel with ferrite-pearlite structures have been examined with tritium autoradiography and thermal desorption spectroscopy. The amount of non-diffusible tritium at room temperature increases with strain. When deformed at room temperature which is in the ductile fracture region, the distribution of tritium is fairly uniform within a grain, while it is inhomogeneous when deformed at -80°C which is in the brittle fracture region. In the latter case, the accumulated sites are distributed regularly in arrays and localized as bands. Comparison with slip band traces indicated that the distribution is likely along slip bands. The amount of non-diffusible tritium which desorbs at 180°C is remarkably large when deformed at -80°C. Desorption at 180°C disappears when the deformed sample is annealed at 500°C, suggesting that the defects as the accumulation sites are microdefects presumably point defects or their clusters.

    DOI

  • Fundamental Aspects of Hydrogen Embrittlement of Iron

    Bull. Japan Inst. Metals   33 ( 7 ) 914 - 921  1994

    DOI CiNii

  • EFFECT OF NITRIDING CONDITION ON MAGNETIC-PROPERTIES OF MECHANICALLY ALLOYED SM2FE17NX COMPOUNDS

    H SHIRAHATA, T MURASUMI, M NAGUMO

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   57 ( 12 ) 1438 - 1444  1993.12

     View Summary

    Synthesis of Sm2Fe17Nx was conducted by mechanical alloying mixtures of intermetallic compounds Sm2Fe17 and SmFe3. Effects of the mixing ratio and nitriding conditions on the magnetic properties were examined. Milled powders were subjected to a stabilizing treatment followed by annealing and nitriding. The nitriding temperature, holding time and N2 pressure were systematically varied. Milling of mixtures of intermetallic compounds gave an amorphous Sm-Fe alloy and alpha-Fe as in the case of milling of elemental metal powders. Optimum magnetic properties were obtained at a composition Sm15Fe85 at which the precipitation of alpha-Fe, SmO1-xNx and SmFe3 was minimum after nitriding. The increase in the coercivity was parallel to the nitrogen content which increased drastically and then gradually as the nitriding time was extended. It was noted that lattice constants of nitride were constant irrespective of nitrogen content, suggesting that the nitriding conditions affect mainly through the amount of nitride. The optimum nitriding temperature for coercivity was 450-degrees-C. The precipitation of alpha-Fe increased at higher temperatures, while the absorption of nitrogen decreased at lower temperatures. The nitrogen pressure was insensitive to the absorbed nitrogen content. The existence of alpha-Fe together with SmO1-xNx and Sm2O3 may affect the magnetization curve.

    DOI

  • メカニカルアロイング法で作成したSm2Fe17Nxの磁気特性に及ぼす窒化条件の影響

    日本金属学会誌   57 ( 12 ) 1438 - 1444  1993

    DOI

  • EXAFS study on crystallization of Cu-Ti powder prepared by mechanical alloying

    J. Non-Crystalline Solids,   156-158,575-579  1993

  • MECHANOCHEMICAL REACTION OF TI-AL WITH HYDROCARBON DURING MECHANICAL ALLOYING

    T SUZUKI, M NAGUMO

    SCRIPTA METALLURGICA ET MATERIALIA   27 ( 10 ) 1413 - 1418  1992.11

    DOI

  • Selective oxidation in amorphous Cu-Ti powder prepared by mechanical alloying

    Rep. Materials Science & Engineering, Waseda Univ.   43,9-17  1992

  • HIGH HARDNESS TIAL ALLOYS THROUGH REACTION MILLING AND HOT COMPACTION

    T SUZUKI, T INO, M NAGUMO

    MECHANICAL ALLOYING   88   639 - 646  1992

  • 鋼の遷移温度域靭性のばらつきと破壊形態

    鉄と鋼   77 ( 4 )  1991

  • Synthesis of Ceramics Composites by Mechanical Alloying of Ti and Si3N4

    Iwase Yuichi, Koga Tomoaki, Nagumo Michihiko

    journal of the japan society of powder and powder metallurgy   39 ( 3 ) 174 - 178  1991

    DOI

  • Glass Forming Range of Fe-B System by Mechanical Alloying

    Rep. Materials Sci. & Tech. , Waseda Univ.   42  1991

  • 制御圧延鋼の延性・脆性遷移温度域における破壊過程

    日本金属学会誌   54 ( 4 )  1990

    DOI

  • Crystallization kinetics of amorphous Cu50Ti50 alloy prepared by mechanical grinding

    Kuniyasu Nakamura, Kiyoshi Kasai, Michihiko Nagumo

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals   54 ( 12 ) 1320 - 1328  1990

     View Summary

    Crystallization kinetics of amorphous Cu50Ti50 alloy prepared by mechanical grinding of the intermetallic compound powder with a high energy ball mill was studied. Kinetics at the isothermal annealing was analyzed in terms of the Johnson-Mehl-Avrami equation, giving a velocity exponent of 0.85 and an activation energy of 183 kJ/mol. Both figures are less than the corresponding values of material prepared by a rapid cooling process. Kinetics at the athermal annealing was analyzed using the Kissinger method, and an activation energy of 154 kJ/mol was obtained in accord with analysis with the JMA equation. The amorphous state and crystallization process are discussed. In an amorphous material prepared by mechanical grinding, the crystalline fraction remains and is likely to act as nuclei of crystallization. Crystallization is likely to proceed two-dimensionally on these nuclei. The number and average size of nuclei are estimated to be 1024m3 and of 103 unit cells of Cu50Ti50, respectively. The activation energy of diffusion estimated by assuming two-dimensional crystal growth kinetics is 214 kJ/mol and the diffusion of Ti atoms is likely to be rate-controlling. Atom migration necessary for the crystallization is considered to take place in a short range on the order of 5-10 nm.

    DOI

  • A Note on Stochastic Aspect of Fracture Toughness Distribution

    Rep. Materials Sci. & Tech. Waseda Univ.   41  1990

  • Strengthening of Hard Drawn Steel Wire With Improved Ductility

    Wire J. International   13 ( 11 )  1988

  • 鋼の水素脆化における破壊のミクロ過程とその機構

    日本金属学会誌   45  1981

    DOI

▼display all

Awards

  • 日本鉄鋼協会名誉会員

    2005  

  • 日本塑性加工学会功労賞

    1999  

  • 日本塑性加工学会功績賞

    1986  

  • Wire Association International Honorable Mention Award

    1984  

  • Wire Association International Allan Dove Award

    1983  

  • 日本鉄鋼協会西山記念賞

    1983  

  • 日本金属学会論文賞

    1982  

  • 日本塑性加工学会論文賞

    1980  

  • 日本塑性加工学会会田技術奨励賞

    1972  

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Research Projects

  • 構造材料の環境脆化における水素の機能に関する研究

    科学技術振興調整費

    Project Year :

    1998
    -
    2003
     

     View Summary

    高強度構造材料の水素脆化機構の解明と材料設計指針の確立

  • 鉄鋼の延性・脆性破壊遷移現象の機構

    科学研究費補助金

     View Summary

    鉄鋼の延性・脆性破壊遷移を支配する材料因子の作用機構解明

  • メカニカルアロイングによる新材料の合成

  • Synthesis of new materials by mechanical alloying

  • Mechanism of hydrogen embrittlement of high strength materials

  • Mechanism of Ductile-Brittle Fracture Transition of Steels

▼display all

Presentations

  • Hydrogen Effects on Strain-Induced Defects Pertinent to Embrittlement

    International Hydrogen Energy Development Forum 2011 

    Presentation date: 2011

  • Hydrogen Effects on Strain-Induced Defects Pertinent to Embrittlement

    International Hydrogen Energy Development Forum 2011 

    Presentation date: 2011

  • Characterizing Fracture Process in Hydrogen-Related Failure of Steels

    International Hydrogen Energy Development Forum 

    Presentation date: 2010

  • Characterizing Fracture Process in Hydrogen-Related Failure of Steels

    International Hydrogen Energy Development Forum 2010 

    Presentation date: 2010

 

Committee Memberships

  • 1996
    -
    1998

    The Japan Institute of Metals  Editor in Chief(Mater. Trans., JIM)

  • 1991
    -
    1992

    日本金属学会  理事

  • 1989
    -
    1990

    日本鉄鋼協会  理事,評議員

  • 1989
    -
     

    The Iron and Steel Institute of Japan  Chairman of Editorial Board