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CYCLIC DEFORMATION OF FACE CENTERED CUBIC CRYSTALS AND ITS DISLOCATION INTERACTION MODEL——Ⅱ.DISLOCATION INTERACTION MODEL OF CYCLIC DEFORMATION

JIN Nengyun Shanghai Jiaotong University Jin Nengyun , Department of Materials Science , Shanghai Jiaotong University , Shanghai 200030 , China.Present address:Max-Planck-Institut für Metallforschung , Institut für Physik , 7000 Stuttgart 80 , FRG

金属学报(英文版)

A dislocation interaction model has been proposed for cyclic deformation of fcc crystals.Ac- cording to this model,cyclic stress-strain responses and saturation dislocation structures of a crystal are associated with the modes and intensities of dislocation interactions between slip systems active in the crystal; and,hence,may be predicted by the location of its tensile axis in the crystallographic triangle.This model has successfully explained the different behaviours of double-slip crystals and multi-slip behaviours of some crystals with orientations usually con- sidered as single-slip ones.

关键词: face centered cubic crystal , null , null , null , null

CYCLIC DEFORMATION OF FACE CENTERED CUBIC CRYSTALS AND ITS DISLOCATION INTERACTION MODEL——Ⅰ.CYCLIC DEFORMATION OF COPPER CRYSTALS

JIN Nengyun Shanghai Jiaotong University , Shanghai Jin Nengyun , Department of Materials Science , Shanghai Jiaotong University , Shanghai 200030 , ChinaPresent address:Max-Planck-Institut für Metallforschung-Institut für Physik , Stuttgart 80 , FRG

金属学报(英文版)

Cyclic stress-strain responses and dislocation structure of copper single crystals with various tensile axes were systematically studied and compared with each other.Experimental results reveal that the evolution of microscopic dislocation configurations in a crystal and, accordingly,its macroscopic cyclic behaviours are closely related with its orientation.Re- markable secondary slip has been observed in some crystals with orientations well inside the crystallographic triangle, which are usually considered as single-slip ones.Their cyclio behaviours and dislocation structures at saturation are similar to those of their neighbouring multi-slip crystals.These results have constructed the experimental basis for the newly pro- posed dislocation interaction model Jor cyclic deformation of fee crystals,which will be des- cribed in the second part of this article.

关键词: Copper , null , null , null , null , null , null

THEORETICAL CALCULATION OF POINT DEFECTS IN Ni_3Al

SUN Jian LIN Dongliang Shanghai Jiaotong University , Shanghai , China LIN Dongliang , professor , Department of Materials Science , Shanghai Jiaotong University , Shanghai 200030 , China

金属学报(英文版)

Equilibrium equation of point defects in Ll_2 type intermetallic compounds was established to calculate the relations of the concentration of antisite defects and vacancies and bulk composi- tion in Ni_3Al.The examination of temperature effects on the point defects cleared up the mis. understanding of the properties of the“constitutional point defects”in Ni_3Al.

关键词: intermetallic compound , null , null , null

CREEP CRACK PROPAGATION IN CONVENTIONAL CAST AND DIRECTIONALLY SOLIDIFIED SUPERALLOY RENE 80

SUN Jian ZHANG Yuanhu HU Gengxiang Shanghai Jiaotong University , Shanghai , China SUN Jian , lecturer , Department of Materials Science , Shanghai Jiaotong University , Shanghai 200030 , China

金属学报(英文版)

The creep crack propagation in superalloy René80 of two different microstructures,i.e., equiaxed grain structure by conventional casting and columnar grain by directional solidification,was investigated under static load at 1123 K.The creep crack growth rate, da/dt,seems to be correlated with the stress intensity factor,K.The creep crack growth rate in the directionally solidified alloy is lower than that in the conventional cast alloy,owing to the elimination of transverse grain boundaries.The effect of microstructure on creep crack propagation has also been discussed.

关键词: Superalloy René 80 , null , null , null

THERMODYNAMICS OF MARTENSITIC TRANSFORMATION IN Fe-Mn-C AND Fe-Ni-C ALLOYS

XU Zuyao(T.Y.Hsu) PAN Mu Shanghai Jiaotong University , Shanghai , China Correspondent:XU Zuyao(T.Y.Hsu) Professor , Department of Materials Science , Shanghai Jiaotong University , Shanghai , China

金属学报(英文版)

A Central Atom Model is introduced and the LFG and Hsu models are modified in order to evaluate the driving force for the martensitic transformation in Fe-Mn-C and Fe-Ni-C al- loys.The results show that the relationship between the driving force and the yield strength of austenite at Ms temperature,σ_(0.2)~γ/M_s,fits Hsu's formula;ΔG~=2.1σ_(0.2)~γ/M_s+907 J/mol.The M_s temperatures of Fe-Mn-C and Fe-Ni-C alloys are also calculated.The calculated results are in good agreement with experimental values.

关键词: Fe-Mn-C alloy , null , null

THERMODYNAMICS OF BAINITIC TRANSFORMATION IN Cu-24 at.-% Al ALLOY

XU Zuyao (T.Y.Hsu) ZHOU Xiaowang Shanghai Jiaotong University , China Professor , Department of Materials Science , Shanghai Jiaotong University , Shanghai 200030 , China

金属学报(英文版)

Two driving forces △G~((β_1)+α')and △G~(β_1→β_2+α)for the bainitic transformation have been calcu- lated for Cu-24 at.-% Al alloy.Results reveal △G~(β_1→α')>0 within the transformation tem- perature range 600—750 K.Therefore,the bainitic transformation cannot be initiated by the β_1→α' shearing mechanism.On the other hand,the driving force △G~(β_1→β_2+α)to produce 5% of the α becomes negative only when the composition of the α satisfies x_(Al)~α≤0.204 at 700 K or x_(Al)~α=0.209 at 750 K.So the bainitic transformation can only proceed by β_1→β_2+α diffusional reaction with different diffusion amount at different temperatures.

关键词: Cu-Al alloy , null , null

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