Through the determination of the values of activation energy for embrittlement under isothermal and isochronal conditions.the correlation between the ductile-brittle transition and thermally activated motion of atoms of the amorphous alloys in annealing has been revealed. And the character of thermally activated motion of atoms related to the embrittlement has been described. The matching of the values of activation energy for embrittlement determined under different conditions demonstrates that the potential barriers existed in the ductile-brittle transitions of the amorphous alloys in both isothermal and isochronal anneals are the same,and verifies the close relationship between annealing embrittlement and the thermally activated motion of atoms. The continued increase of activation energy for embrittlement during the brittling process and the correspondence of activation energy values with different transition stages characterize the ductile-brittle transition of amorphous alloys,so the transition is not the simple activating process with a constant activation energy.CHE Xiaozhou,post doctor, Shanghai Jiaotong University,Shanghai 200030

The activation energies,the preexponential factors and the corresponding self-diffusion coefficients for a nanocrystalline material in various diffusion conditions were calculated. Based on comparison of the calculated self-diffusions with the experimentally measured one, it is suggested that the diffusion model in nanocrystals is a complex one with the combination of the boundary diffusion by the vacancy mechanism and the internal surface diffusion of atoms along internal surfaces of boundary voids. CHEN Da, professor, Department of Materials Science, Shanghai Jiaotong University, Shanghai 200030

The effects of phosphorus content on solidification process, segregation of elements and formation of η-phase in GH 761 alloy were studied by using metallography and electron microprobe.It was found that phosphorus segregates markedly in interdendritic area and lowers extremely the final solidification temperature of the alloy. It aggravates the segregation of Ti and Ni, and relieves the segregation of Mo, B, S and Si.The results also showed that phosphorus obviously enhances the formation of η-phase,but lowers the precipitated temperature of this phase.SUN Wenru, Institute of Metal Research, Chinese Academy of Sciences,Shenyang 110015

The plastic deformation propagation speeds of steels are determined by using photo-elastic coating and high speed photography method.The results indicate that the plastic deformation propagation speed of metal under cyclic loading is related to not only internal factors of crystal lattice and microstructure etc, but also external factors, such as loading frequency, stress concentration etc. The plastic deformation propagation speed of 1Cr18Ni9Ti stainless steel with face-centred cubic lattice is greatly higher than that of 40Cr steel with body-centred cubic lattice. In essence. critical loading speed effect should be connected with the plastic deformation propagation speed of metal.FENG Zhongxin,associate professor, Xi＇an Jiaotong University, Xi＇an 710049

The structural characteristics of liquid Cu and structural evolution during rapid cooling have been simulated by MD technique. EAM was used as many-body interaction.Bond orientational order parameters and pair analysis technique were applied to detect the microstructure of liquid, supercooled liquid. non- crystalline and crystalline states. It was shown that EAM is able to describe the complicated disorder system. The calculated pair distribution function was almost the same as the experimental result.The calculated critical point of non-crystalline transition was in reasonable agreement with theoretical value.LI Xiaoping,Department of Physical Chemistry, University of Science and Technology Beijing,Beijing 100083

The correlations among nominal threshold.intrinsic threshold, crack closure effect and crack wake of alloys 2090 and 8090 were investigated, and compared with that of alloys 7075 and 2024,respectively. Aluminum-lithium alloys possess a excellent threshold of long fatigue cracks and the stronger short crack effect,due to a higher level of crack closure effect and the dependent mentality of closure effect on crack wake.The growth resistance of microcracks of alloy 2090 is inferior to that for alloy 2024,which is attributed to the lower △Ki.△Ki of alloy 8090 is equal to that of alloy 2024, and its growth resistance of short crack is equal or superior to alloy 2024. Furthermore, influence of minor rare earth element Ce on the growth behavior of physically-short cracks for aluminum-lithium alloys 2090 and 8090was studied. A significant improvement in intrinsic threshold and a certain increase in crack closure effect can be achieved by adding Ce into alloy 2090. As result, the notable increase in the growth resistance of long and short fatigue cracks has been obtained. On the contrary,the intrinsic threshold is decreased by adding Ce into alloy 8090, which results in a harmful influence on the growth resistance of long and short fatigue cracks for this alloy. CHEN Zheng,professor, Laboratory No.401, Northwestern Polytechnical University, Xi＇an 710072

Based on the micro-change of material internal structure of nickel-base single crystal superalloy in the creep condition.a two-state-variable creep damage constitution considering simultaneously material-type damage and void-type damage has been built .Confirmed by the experiments of single crystal DD3 along<001> crystallographic orientation at 760, 850 and 1000℃,the model can predict precisely the steady creep , the tertiary creep and the rupture characteristics.The lasting time of the steady creep and the onset time of the tertiary creep are approximately power law function of creep stresses.As the test temperature increases,the material-type damage and void-type damage increase rapidly.YUE Zhufeng, postdoctor,Post Box No.350, Northwestern Polytechnical University, Xi＇an 710072

A semi-quantitative method was proposed to evaluate hot cracking tendency.Hot cracking experiments were carried out in directional solidification device for Al-Cu alloys with different compositions. Through comparision between theoretical calculation and experiment results,it was proved that the influence of alloy composition on hot cracking tendency is in conformity with the accommodation theory of alloy contraction in solidification process.The prediction was also proved by experiments about the effect of columnar grain structure on the interdendritic bridging.DING Hao,lecturer,Faculty No.403, Northwestern Polytechnical University,Xi＇an 710072