The texture of γ/γ'-αDS eutectic alloy during aging has been investigated by means of high resolution electron microscopy(HREM) and analytical transmission electron microscopy.It has been found that the products of phase transformation in γphase are different during aging at temperatures of 850 and 650℃.Stick-like orthorhombic Ni3Mo was precipitated inα fibers,the γ-N i3Al with lamella twin structure can also be found to coexist with Ni3Mo.EDAX analysis shows the solid solution of Ni,Al and small amount of V inαfibers.Correspondent:DAI Jiyan,(Institute of Metal Research,Chinese Acadamy of Sciences,Shenyang 110015)

Substitutional solute atoms are believed to difuse by means of solute atom-vacancy complexes.This mechanism could be used to explain some phenomena very well such as:the rule for occurring of non-equilibrium segregation,the anomalously fast diffusion phenomena of solute atoms,the boron's fast diffusion and non-equilibrium segregation of grain-boundary in γ-Fe,the segregation of solute atoms in vacancy-pits on aluminium surface and the precipitation of silicon in the grain-boundary of aluminium.Correspondent:YU Zongsen,professor,(Department of Materials Physics,Universiy of Science and Technology Beijing,Beijing,100083)

Influence of Nd on microstructure,tensile properties,thermal stability and strengthening behaviour of Ti-5.5A1-4.SSn-2Zr-1Mo-0.25Si-Nd alloy was studied,Nd can not only refine the prior β grains and α plates,and especially densify dislocation network subgrain boundaries,but also improves tensile strength and thermal-stability.The strengthening of Nd is superposition of strengthening caused by grain-refinement,particularily the densifying of subgrain boundaries,and weakening caused by depletion of Sn and O2 in matrix phase.Correspondent:SUN Fusheng,senior engineer.Laboratory No.15,(Beijing Institue of Aeronautical Materials,Beijing 100095)

The strength and ductility of Ti-48Al may be improved by adding certain amount of La and approached to optimal values with increasing to 1.0 and 0.2 at.-% La respectively.It seems to be noticeable that the optimal ductility of TiAl alloy containing La is higher beyond twice than that free from La.Observations showed that the improvement may be caused by the La due to homogenize and refine the TiAl microstructure,to form La2O3 particles and to reduce O2 content in matrix. However,excess La addition would result in forming coarse oxide particles and some pores,thus its mechanical properties deteriorate.Correspondent:CHEN Shiqi,lecturer,(Powder Metallurgy Research Institute,Central South University of Technology,Changsha 410083)

The microstructure and microhardness of rapidly solidified binary Al-Cr alloy ststem has been studied.The beginning temperature of the second phase(θ-Al7Cr) precipitated from the supersaturated α-Al solid solution during annealing process seems to be determined by saturation and precipitation.Correspondent:Ml Guofa,(Ph.D student,Posi Box 434,Harbin Institute of Technology,Harbin 150006)

Effect of deformed structure by shot peening on retardation of fatigue crack initiation in Cu or brass has been investigated via separation from residual stress effect and under observation on surface slip band and microsubstructure.The structure of shot peened layer on specimen may retard the dislocation movement by slip outward from the core to surface,and limit the dislocation movement of deformed layer within the cellular dislocation of Cu or paling twins of brass.Thus,the fatigue damage of intrusion and extrusion type caused by the slip band on surface may be effectively reduced.Correspondent:XU Kewei,(professor,National Laboratory.for Mechanical Behaviour of Metallic Materials,Xi'an Jiaotong University,Xi'an,710049)

Stress corrosion cracking(SCC) in the methanol solution containing 0.6MKCI and hydrogen induced cracking(HIC) at room temperature for the titanium aluminide Ti-24Al-llNb were studied.It was found that SCC of the Ti-24Al-llNb alloy in the methanol solution is very sensitive and the normalized threshold stress intensity of SCC for vavious microstructures are Klscc/Kc=0.53-0.69(constant load specimen) and KISCC/Klc-0.61-0.79(WOL constant deflection specimen),respectively.The threshold stress intensity of HIC during dynamic charging at room temperature is close upon that of SCC,but da/dt or fracture time of HIC is one to three orders lower than that of SCC and the fracture surface for HIC is also different to that for SCC.A kind of interphase SCC for the Ti-24Al-llNb alloy in the methanol solution has been found.For the furnace cooled specimens with low KI,SCC initiated and propagated preferentially along the α2/βinterphase boundaries.There are no interphase SCC for the air cooled specimens or for the furnace cooled specimen with high KI.Correspondent:ZHANG Yue,(Department of Materials Physics.University of Science and Techuology Beijing,Beijing 100083)

A study of oxidation kinetics of DS Ni3Al-Mo base alloy(IC-6) have been carried out in thermobalance at 1273 and 1373 K in air for 300 h.The structure and composition of the oxide were examined by EPMA and XPD analyses.The oxide oxidation of IC-6 alloy can be described as a system in which both oxygen inward diffusion of oxidation of IC-6alloy:is in good agreement with experimental data.The volatilization rate constant of MoO3 was calculated qualitatively,as Ks=3.27×10-4mg/cm2·s at 1273 and 1373K respectively.Correspondent:YE Changjiang,(Institute of Corrosion and Protection of Metals,Chinese Academy of Sciences,Shenyang 110015)