The occurrence of bainitic ferrite transformation units, namely, shear transformation units,in Fe-C alloys was repeatedly confirmed by various observations,and a sketch illustrating their morphology was given.Some martensite-like bainites,such as regular triangular, crossed,"N"- and butterfly-type,were observed in the alloys. The crossed bainite may be further divided into 4 types,i.e.,units of relative glide disjunction,"wasp- waist"formation and exchange growing orientation.The crossing effect reflects directly on movement of bainite units during transformation.The induced crossed stress field is one of the shear stress concentration under shear transformation.The formation of bainite crossing is caused in the shear stress-strain induced bainitic transformation.The compensation value for the driving force of transformation is proportional to the square of true strain of austenite.The extraordinal violence of impingement brought about by the growing bainite plates can only be explained through shear mechanism of bainitic transformation.Correspondent: YU Degang, professor,(Departrnent of Materials Science, Shanghai Jiaotong University,Shanghai 200030)

By electron microscopy and X-ray diffraction techniques, the high temperature intergranular failure of Ni75Al16.6Cr7.84Zr0.45B0.1Mg0.01 alloy has been studied. The content of Mg is about 15-19 at.-%. in the region of grain boundary in the alloy due to segregation after prior exposure at 1180℃, the content of Zr is 28-33 at.-%; and the localized eutectic grain boundary melting in the alloy was observed. The precipitation of CrN inside the grains and Cr2(C,N) along the grain boundaries occurred by solid solution and thermal cycling treatments.Correspondent: DU Guowei, associate professor.(Departement of Materials Physics,University of Science and Technology, Beijing, Beijing 100083)

One-way and two-way shape memory effects of the Ni-34.6at.-% Al thin ribbon were observed. The ribbon of one-way shape memory effect, occuired over 300℃ , has very good shape recovery(100%). A ductile γ′-Ni_3Al phase precipitated out up to 16 v.-%after high temperature annealing. Both ductility and toughness were further improved.Meanwhile, the annealed ribbon has also good one-way and two-way high temperature shape memory effects. It is believed that the Ni-riched NiAI alloy may possibly develop into a new high temperature shape memory alloy.Correspondent: CHENG Tianyi, associate professor, Beijing institute of Technology, Beijing 100081

One way and two way shape memory alloys of Cu-21% Zn-6% Al (wt-%)were studied by differential scanning calorimetry. The profiles of endothermic and exothermic peaks of one way shape memory alloy are different from those of two way shape memory alloy.The former shows smooth peaks while the other shows bumpy peaks. Besides, the heat of martensitic transformation of two way shape memory alloy is about 25% less than that of one way shape memory alloy.Correspondent: TAN Shusong, professor, (Department of Materials, Central South University of Technology,Changsha 410083)

In-situ SEM observations on TA2/A3 explosion cladding interfaces have been performed to examine the microfracture behaviour. The microfracture mechanism of explosion cladding TA2/A3 interface seems that the microcracks initiate inside the swirls or inside the molten material as well as at the boundary between the molten material and the A3 matrix,and penetrate into the nearby A3 matrix in the direction normal to the tensile load direction under the action of the crack-tip stress field. At the same time, the microcracks initiate along the TA2 /A3 interface, and link up under the tensile load. Terminal cleavage fracture takes place mainly in the recrystallized and grain abnormal growth region on the A3 side in the vicinity of TA2/A3 interface.Localized fracture takes place along the interface molten layer.Correspondent: YANG Yang.(Departnient of Materials. Central-South University of Technology.Changsha 410083)

In situ TEM technique was employed to observe the influence of lamellar structure on the crack propagation in duplex TiAl alloy. It has been found that both crack tip blunting and crack propagating have connected with the angle included between crack growth and lamellar direction. Only if the crack growth roughly parallel to lamellar direction ,the microcracks may nucleate ahead of the main crack. So, shear ligaments play an important role in toughening TiAl alloy. When the crack growth is perpendicular to lamellae or between perpendicular and parallel to lamellae, the main reasons of lamellar toughening in TiAl alloy owe to that:(1) the lamellar boundary inhibits crack propagation,and(2)the crack tip blunting is caused by the slip of interlamellar boundary. According to the dislocations theory of microcrack nucleation, these phenomena are explained.Correspondent: LIN Dongliang, professor,(Shanghai Jiaotong University, Shanghai 200030)

The effect of surface rolling on fatiuge strength and fatigue sensitivity to notch of the Mg alloy ZM1 has been studied. Results showed that the increase in smooth or notohed fatigue limit amounts to 57 or 200% respectively. The fatigue sensitivity to notch may be greatly reduced,and so the q value may become negative. During surface rolling of hcp Mg alloy,the plastic deformation and strengthening may be carried out by the way of slip and twin.The high compressive residual stress is favourable to improve the notched fatigue hmit and to modify the fatigue sensitivity to notch. The plastic deformation strengthening may contribute to develop the benificial behaviour of the compressive residual stress.Correspondent: FENG Zhongxin,(Xi'an Jiaotong University,Xi'an 710049)

High temperature fatigue properties of a polycrystalline Ni_3Al(0.6at.-%B) alloy, being brittle at an elevated temperature, were studied. The tension-tension fatigue tests under controlled loading were carried out in air at 450 ℃. By fixing the maximum values of tensile stress in all tests but changing the minimum values of tensile stress in various tests, the effect of cyclic stress amplitude or mean stress and their interaction on the damage of materials may be differentiated. The results of cyclic stress amplitude and mean stress vs fatigue life are plotted as"S" shape and interpreted preliminarily.Correspondent: LI Gang, Institule of Metal Research, (Chinese Academy of Sciences, Shenyang 110015)