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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

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

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 Coll. 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

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

Stress Corrosion Crack Growth Behavior of Titanium Alloy/Bioactive Glasses Sandwiches in Simulated Human Physiological Environment

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Journal of mat.rials sci.nce & Technology 2002年第5期18卷 387-391页

作者： DaCHEN J.M.McNaney E.Saiz A.P.Tomsia R.O.Ritchie Dept. of mat. sci. Shanghai Jiaotong Univ. Shanghai 200030 China Dept. of mat. sci. and eng. Univ. of California Berkeley CA 94720 United States mat. sci. div. Lawrence Berkeley Natl. Lab. Berkeley CA 94720 United States

Based on a series of newly developed bioactive glasses having suitable thermo-mechanical properties to allow application as fixation agents between bone and titanium alloy biomedical implants, the stress corrosion crack growth (SCCG) behavior of their interfaces with Ti6AI4V was investigated in simulated body fluid (SBF) with the objective of discerning the salient mechanisms of crack advance and to assess the reliability of the bonds. Results indicated that crack growth rates in Ti6AI4V/glass/Ti6AI4V sandwich specimens were nearly the same as or slightly lower than those in the bulk glasses at comparable stress intensities; indeed, cracks would prefer to propagate off the interface, suggesting that the Ti6AI4V/glass interface has relatively good crack-growth resistance. Mechanistically, interfacial crack growth appears to be controlled by the classic stress corrosion mechanisms for silicate glasses, with no discernible effect of bioactivity on the SCCG behavior being observed.

关键词： Stress corrosion Titanium alloy Bioactive glass Crack growth

Format.on and Characterization of Bone-like Nanoscale Hydroxyapatite in Glass Bone Cement

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Journal of mat.rials sci.nce & Technology 2004年第6期20卷 772-774页

作者： Qiang FU, Nai ZHOU, Wenhai HUANG, Deping WANG and Liying ZHANGSchool of mat.rials sci.nce and eng.neering, Tongji University, Shanghai 200092, China Sch. of mat. sci. and eng. Tongji Univ. Shanghai 200092 China

Glass based bone cement (GBC) was synthesized by mixing CaO-SiO2-P2O5 based glass powder with ammonium phosphate liquid medium. Bone-like hydroxyapatite (HAP, Ca10(PO4)6(OH)2) was found to form after GBC was immersed in simulated body fluid (SBF). HAP crystal grew with an increasing time along c axle and reached about 200 nm in leng.h after 30 days, however, the end plane granularity remained 30-50 nm. The chemical composition, crystal structure and morphology of HAP formed from GBC were proved to have great resemblance with living HAP. It is believed that GBC was a desirabie biomedicai mat.rial with high bioactivity. Furthermore, the high compressive streng.h guaranteed the possibility of GBC in clinical application.

关键词： Bioactivity Bone cement Hydroxyapatite Microstructure

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

Evaluation on Fracture Toughness at Dynamic Loading for Welded Joint Based on the Local Approach

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Journal of mat.rials sci.nce & Technology 2004年第1期20卷 113-117页

作者： Hongyang JING, Lianyong XU, Lixing HUO and Yufeng.ZHANGSchool of mat.rials sci.nce and eng.neering, Tianjin University, Tianjin 300072, China Sch. of mat. sci. and eng. Tianjin Univ. Tianjin 300072 China

The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during the high loading rate, could be employed to describe the constituent relation for the typical structure steel and its weld metal. The dynamic loading effect on the stress/strain fields and the temperature variation in the vicinity of the crack tip was analyzed by the finite element method, the dynamic fracture behavior was evaluated based on the local approach. It has been found that the Weibull stress is an effective fracture parameter, independent of the temperature and the loading rate.

关键词： Fracture toughness Dynamic loading Welded joint