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A Rationalization of Sympathetic Nucleation-Ledgewise Growth Theory of Bainite Transformat.on in Fe-C Alloys

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Journal of mat.rials sci.nce & Technology 2001年第4期17卷 433-438页

作者： Zhigang YANG, Chi ZHANG, Hongsheng.FANG, Jinbo YANG, Bingzhe BAI and Jiajun WANG Department of mat.rials sci.nce and eng.neering, Tsinghua University Beijing 100084, China Dept. of mat. sci. and eng. Tsinghua Univ. Beijing 100084 China

Based on the classic diffusion controlled nucleation and goth theory, the sympathatic nucleation- ledgewise growth mechanism of bainite was studied theoretically for low carbon Fe-C alloys. The rationality of the occurrence of sympathetic nucleation on the terraces of ledges compating with lateral ledge growth and other sites nucleation was demonstrated by the present work quantita- tively The calculations indicated that low reaction temperatures and high carbon concentrations may favor the sympathetic nucleation, thus accounting for the format.on of multilayer structures of bainite.

关键词： A Rationalization of Sympathetic Nucleation-Ledgewise Growth Theory of Bainite Transformat.on in Fe-C Alloys Fe

Laser Surface Hardening of 9CrSi Steel

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Journal of mat.rials sci.nce & Technology 2002年第1期18卷 17-20页

作者： Nunghee RYU and Sunggoon KANGDivision of mat.rials sci.nce and eng.neering, col.ege of eng.neering, Hanyang University, Korea [ Manuscript received August 7, 2001, in revised form September 20, 2001] Div. of mat. sci. and eng. Coll. of Eng. Hanyang Univ. Hanyang South Korea

The effects of laser hardening parameters such as beam power, beam diameter and scanning rate on microstructure and hardness of 9CrSi steel were investigated. The microstructure of the surface layer of 9CrSi steel was changed from pearlite to martensite, retained austenite and carbide by laser hardening. The depth of the hardened layer increased with increasing laser energy density and the surface hardeness increased by 3-5 times as high as the untreated steel. The laser hardened surface had good wear resistance due to martensite and carbide in the surface layer. The wear mode at low speed was abrasive, while the wear mode at high speed was adhesive.

关键词： Laser hardening Martensite Hardeness Phase trasformat.on

Molecular Dynamics Simulation and Experimental Proof of Hydrogen-enhanced Dislocation Emission in Nickel

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Journal of University of sci.nce and Technology Beijing 2002年第1期9卷 59-64页

作者： Zhongji Li, Jinxu Li, Wuyang Chu, Hui Liu, Lyie Qiao, mat.rials sci.nce and eng.neering School, University of sci.nce and Technology Beijing. Beijing 100083, China E-mail: lqiao@*** mat. sci. and eng. Sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

A quasi three dimensions molecular dynamic method was used to simulate the effect of hydrogen on dislocation emission and crack propagation in nickel. In situ observation in a transmission electron microscope (TEM) was used to confirm the simulation results. The simulation result indicated that hydrogen solubilized in nickel decreased the critical stress intensity for the dislocation emission, i.e., hydrogen enhanced dislocation emission. In situ observation in TEM showed that hydrogen enhanced dislocation emission and motion before the initiation of hydrogen-induced crack.

关键词： nickel molecular dynamics simulation hydrogen dislocation emission TEM

Diffusive healing of internal fatigue micro-cracks in pure titanium

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中国有色金属学会会刊：英文版 2001年第5期11卷 675-680页

作者：杨君刚孙军张海龙 Sch. of mat. sci. and eng. Xi'an Jiaotong Univ. Xi'an 710049 China

The internal micro cracks with the critical leng.h about 30?μm and thickness less than 1?μm were introduced into the pure titanium samples by uniaxial tension compression low cycle fatigue method. The experimental results indicate that the internal fatigue micro crack clearly evolves from the original penny shaped crack into a string of spherical voids in the longitudinal section plane of the fatigue sample after the vacuum diffusive healing at the high temperature. The quantitative relationship between the radius and the spacing of spherical voids depends on the crack position (within grains, on grain boundaries or transgranular sites) and its orientations within the grain. The diffusive healing, the related thermodynamics and mechanism, and the effect of the surface tension anisotropy on the relationship between void diameter and void spacing are also discussed.

关键词： pure titanium internal fatigue micro crack diffusive healing

Massive Si Phase and Its Growth Mechanism in Al-Si Casting Alloy

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Journal of mat.rials sci.nce & Technology 2004年第5期20卷 589-591页

作者： Heng.heng.LIAO and Guoxiong SUNDepaxtment of mat.rials sci.nce and eng.neering, Southeast University, Nanjing 210018, China Dept. of mat. sci. and eng. Southeast Univ. Nanjing 210018 China

Optical microscope and scanning electron microscope were used to observe the microstructure of the AI-11.6%Si and AI-11.6%Si-0.4%Mg alloys and the morphology of the massive silicon particles. It is found that the massive silicon phase, observed in the unfully modified alloys with 0.010%Sr, disappears completely in the alloys fully modified with 0.020%Sr. The serrations and reentrant edges shown in the massive silicon particles with the conventional casting indicate that the TPRE mechanism plays an important role in the growth of the massive silicon phase. The ripples and steps suggest that the "lateral microscopic growth" may be another operating mechanism.

关键词： Al-Si alloy Massive silicon Microstructure Growth mechanism

Thermodynamics of Modifying Effect of Rare Earth Oxide on Inclusions in Hardfacing Metal of Medium-High Carbon Steel

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Journal of Rare Earths 2002年第4期20卷 291-294页

作者：赵研辉李艳丽姚枚杨庆祥 col.. of mat. sci. and eng. Yanshan Univ. Qinhuangdao 066004 China

The modifying effect of rare earth (RE) oxide on inclusions in hardfacing metals of medium-high carbon steel was investigated by means of thermodynamics. The thermodynamic analysis for inclusion format.on shows that RE oxide can be reduced to RE element by carbon, then the RE element can react with oxygen and sulfur to form the RE oxide, RE sulfide and RE oxide-sulfide in hardfacing molten pool. The deoxidization and the desulphurization can be carried out and the liquid metal can be purified. In addition, RE oxide can also react with sulfur to form RE oxide-sulfide directly. Therefore, the harmful effect of sulfur can be decreased.

关键词： rare earths oxide inclusion hardfacing metal thermodynamics

Effects of Alloying Elements on Microstructure and Erosion Resistance of Fe-C-Cr Weld Surfacing Layer

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Journal of mat.rials sci.nce & Technology 2003年第4期19卷 351-354页

作者： Daqian SUN, Wenquan WANG, Zhaozhi XUAN, Yue XU and Zhenfeng.ZHOUSchool of mat.rials sci.nce and eng.neering, Jilin University, Changchun 130025, China Sch. of mat. sci. and eng. Jilin Univ. Changchun 130025 China

Effects of alloying elements on microstructure and erosion resistance of Fe-C-Cr weld surfacing layer have been studied. The experimental results show that increasing C and Cr content favors improving the erosion resistance of the layer, and the excessive C and Cr result in decreasing the erosion resistance at 90 deg. erosion. That Mo, Nb or Ti improves the erosion resistance of Fe-C-Cr weld surfacing layer is mainly attributed to increasing the amount of M7C3 and forming fine NbC or TiC in austenite mat.ix, but the excessive Mo, Nb or Ti is unfavorable. The addition of Mo, Nb and Ti in proper combination possesses stronger effect on improving the erosion resistance and the erosion resistance (εA) of Fe-C-Cr weld surfacing layer with fine NbC, TiC and M7C3 distributing uniformly in austenite mat.ix obviously increases to 2.81 at 15 deg. erosion and 2.88 at 90 deg. erosion when the layer composition is 3.05C, 20.58Cr, 1.88Mo, 2.00Nb and 1.05Ti (in wt pct).

关键词： Weld surfacing layer Alloying elements Erosion resistance

Hydrogen Storage Properties of Ti_(1.2)Fe+xCa Hydrogen Storage Alloys

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Rare Metals 2001年第4期20卷 265-269页

作者： Wei Wang, Changpin Chen, Haiou Xu, Hon gbo Li, Qidong Wang Department mat.riak sci.nce and eng.neering, Zhejiang University, Hangvhou 310027. China Dept. of mat. sci. and eng. Zhejiang Univ. Hangzhou 310027 China

The hydrogen storage properties of Ti1.2Fe+xCa (x=1%, 3% and 5% in mass fraction) alloys was investigated. Results stow that the modified alloys can be activated without any thermal treatment at room temperature due to the addition of Ca and excess Ti in (lie alloys. Hydrogen storage properties of these modified alloys vary with Ca amount and reaction temperature. In addition, the influence mechanism of the addition of Ca and excessive Ti on the activation behavior and hydrogen storage capacity of the alloys was discussed.

关键词： TiFe Ca hydrogen storage alloy hydrogen storage property

Applied Strain Field on Microstructure Optimization of Ti-Al-Nb Alloy Computer Simulated by Phase Field Approach

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Journal of mat.rials sci.nce & Technology 2004年第3期20卷 245-248页

作者： Wei GUO Yaping ZONG Gang WANG Liang ZUO Department of mat.rials sci.nce and eng.neeing,Northeastern University,Shenyang 110004, China Dept. of mat. sci. and eng. Northeastern Univ. Shenyang 110004 China

The effects of applied tensile strain on the coherent α_2→O-phase transformat.on in Ti-Al-Nb alloys are explored bycomputer simulation using a phase-field method. The focus is on the influence of the applied strain direction onthe microstructure and volume fraction of the O-phase precipitates. It is found that altering applied strain directioncan modify microstructure of Ti-25Al-10～12Nb (at. pct) alloy during α_2→O-phase transformat.on effectively andfull laminate microstructure in the Ti-25Al-10Nb (at. pct) alloy can be realized by an applied strain only along thedirection 30°away from the α_2 phase in magnitude equivalent to the stress-free transformat.on strain. Thesimulation also shows that not only the magnitude of applied strain but also the applied strain direction influencesthe O-phase volume fraction and the effect of strain direction on the volume fraction is up to 25%.

关键词： Phase field simulation Strain induced phase transformat.on Ti-Al-Nb alloy Computerization mat.rials Microstructure evoutionv Precipitates geometry Microstructure design