A study of the crystal structure of V-phase is preformed on Zr4Co4Si7 compound by means of various electron microscopic techniques.Results of electron diffraction analysis show that Zr_4Co_4Si_7 has a body -centered tetragonal structure with space group I4/mmm.Images taken by a high resolution transmission electron microscope(HRTEM) reveal the structure in atomic level.Big bright spots in [001] HRTEM image represent Ge-centered square antiprism columns,and the eight small bright spots around them represent Co-centered octahedron columns.Good agreement between the observed and simulated images has been obtained and thus confirmed the results proposed earlier by X-ray diffraction analysis.correspondent:MAO Jian fu,postdoctor,(Laboratory,of Atomic Imaginq of Solidy,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110015)

TEM investigation associated with computer image simulations were conducted to determine the dissociation of superdislocations in the room temperature deformed Ll2-type Al3Ti alloy.It is determined that the a(110) superdislocations dissociated into pairs of a/3(112) superpartials with SISF between them.The theoretical and experimental micrographs are in good agreement under various diffraction conditions.Correspondent:HU Gengxiang,professor,(Department of Materials Science,Shanghai Jiaolong University,Shanghai 200030)

The effect of hydrogen on the bond structures.bond energy and electron distributions of intermetallic compound Fe3Al is investigated by Empirical Electron Theory of Solids and Molecules.The hydrogen embrittlement in Fe3Al is due to dissolving of hydrogen atoms to change the atomic state of Fe3Al resulting from the sharply reduction of lattice electrons,which cause the decrease of local metallicity,and the formation of severely anisotropic bond structures.At the same time,the hydrogen atoms may occupy the interstitial sites in Fe3Al.Correspondent.ZHANG Jianmin,postdoctoral,(Department of Superalloy,Central Iron and Steel ResearchInstitute,Ministry of Metallurgical Industry,Beijing 100081)

The deep undercooling of the Ni-Sn alloy was achieved by means of the cyclic overheating to high temperature and rapid quenching in a mixed inorganic sail flux,so the pseudo-coupled zone of the alloy was obtained.Under deep undercooling,the nucleations of eutectic phases are both in dependent and heterogeneous.although the Ni3Sn phase is easy to grow nuclei.The inherent impurities in Ni-Sn alloy are favourable to nucleation of α-Ni phase.Correspondent.LI(Shunpu,Institute of physics,Chinese Academy of Sciences,Beijing 100080)

A model for relating the primary dendrite arm spacing to the crystalorientation has been developed.An experiment for investigating the primary dendrite arm spacing in single crystal superalloy DD8 has also been carried out.The results indicate that the primary dendrite arm spacing decreases when the preferred orientation of the dendrite deviates from the solidified direction.The influence of the crystal orientation on the primary dendrite arm spacing is much slight with higher thermal gradient and higher solidification rate.The experimental results are consistent with the prediction of the model.Correspondenl:HE Guo,(Naltonal Key Laboratory,of Advanced Melallic Materials,Unirersity of Science and Technology.Beijing,Beijing.100083)

The microstructure and mechanical properties of boron-modified HAl 77-2brass were investigated by XRD,SEM and tension test.The results show that with the increase of boron added to aluminium brass,the grain size of HAl 77-2 brass with and without arsenic decreases,the strength and hardness of boron-modified brass increase.On the basis of experimental results,the optimum amount of boron in HAl 77-2 brass was found.Correspondent:JIANG Hiaoxia,professor,(Institute of Metal Research,Chinese Academy of Sciences,Shen yang 110015)

Experimental studies on effects of minor elements in a cobalt-base superalloy have been carried out to develop newer high-strengh one.It is found that the high temperature stress-rupture properties increase very rapidly with C or B and the mutual effect is shown obviously between them.But Al weatens the properties and Zr has no obvious effects.Compared with X40 alloy,the stress-rupture life of the new alloy can prolong 6 to 8times and the availabe temperature can raise 45℃.Two carbide strengthening machanisms seem to be carbide beazing capacity and precipitate strenghening.The variations of alloy properties result in the changing of the carbide transformation temperature as well as content.type,distribution and morphology of carbide induced by miner dements.Correspondent.YAO Xiangdong,(Institute of Metal Research,Chinese Academy of Sciences.Shenyang 110015)

The dendritic arm spacings and microsegregations of directionally solidified superalloy DZ22 at various solidification rates have been studied with the help of a ZMLMC directional solidification equipment.which has superhigh temperature gradient.The results show that the dendritic arm spacings have been refined highly and the microsegregation has been suppressed seriously with increasing the cooling rate.The primary and secondary dendritic arm spacings.λ1 and λ2.are equal to 28.8 and 8.4 μm respectively.and the microsegregation ratios of elements Na.Ti.Al.Cr.Co and W tend to unity when the solidification rate is equal to 54.2 K·s(-1).Correspondent:LIU Zhongyuan,(associate professor, Faculty No.403,Northwestern Polytechnical University,Hi'an 710072)