The main points of view about shear and difusion for the bainitic transformation, which include some important research results and key controversial points,i.e., bainite definition, incomplete phenomenon, solute-drag and solute drag-like effects,the shape, characteristics,nature of the surface relief,crystallography,initial carbon content in bainitic ferrite, the so-called midrib of bainite, source and formation model of lower bainitic carbide,etc., were briefly reviewed.Correspondent: WANG Jiajun, Department of Materials Science and Engineering,(Tsinghua University,Beijing 100084)

The main problems encountered by shear and diffusion controlled ledgewise mechanisms of bainitic transformation have been reviewed. Based on the ledgewise growth theory, a sympathetic-ledgewise mechanism and its transformation model describing bainitic formation in both steels and non-ferrous alloys have been presented. Correspondent: WANG Jiajun,Depantment of Materials Science, Tsinghua Univesity, Beijing 100084）

The mopohology of slip bands for materials with two different slip modes: pure Cu and Cu-Zn alloy after prestraining and cyclic softening has been observed. Both of their double cross slip bands are rather different, and ones in Cu-Zn alloy is corresponding to the dynamic strain aging. Two kinds of slip bands contrast are shown in the cyclic softened Cu-Zn alloy, but mainly the stationary slip bands appeare in pure Cu. These may indicate that the way to accommodate the cyclic strain is different. According to the feature of slip bands,the mechanical behaviour of softening for the two materials has been explained. Correspondent: CHAI Huifen,（professor, Xi'an Jiaotong University, Xi'an 710049）

The tensile deformation mechanism of α_2-phase (DO_(19)) in a Ti-25Al-10Nb-3V-1Mo alloy at 25—700℃ was studied. In accordance with . =0 invisibility criterion, dislocation types and slip systems were analysed in a TEM equipped with a side entry goniometer stage capable of a ± 45°tilt on X- and Y-axis operating under two-beam condition. Experimental results show that the majority of slip systems activated at 25—700℃ are type dislocation on prismatic and basal planes. A few of / 2 type dislocation pairs on pyramidal plane are found at 25℃, so a large amount of twinning found at 400℃.The density of/2 type dislocation pairs decrease with the increase of temperature. No/2 type dislocation pair is found at 700℃, but some type dislocation pairs are activated at 700℃. Correspondent:SUN Fusheng, senior engineer,（Institute of Aeronautical Materials, Beijing 100095）

Effect of B addition on the microstructure and mechanical properties of Fe-28Al-1. 94Cr alloy was investigated. In the alloy containing 0.038at.-%B, some fine (Fe, Cr)_2 B particles were found to precipitate, and these were tending in quantity and size as B content increasing. When B was up to 1. 18 at.-%, (Fe, Cr)_2 B precipitated in the form of network. Addition of B ranged 0.038 to 0.22at.-% into Fe_3Al alloy may remarkably improve the room temperature ductility and strength. The alloy containing 0.038at.-%B makes the increase of its compressive yield strength from 532 to 678 MPa, and its ductility from 15 to 25%. If the alloy is in excess of B, saying 1.18at.-%, not only reduction of ductility but also decrease of strength will be obvious. Less B in the alloy may be beneficial to its ductility at elevated temperature up to 600℃, while more B may improve its high temperature strength. Correspondent:GUO Jianting, professor,（Institute of Metal Research, Chinese Academy of Sciences, Shenyang110015）

Study was made of the mechanical properties at elevated temperatures of the Ni_3Al(B)-Cr base alloy multi-microalloyed by Mg and RE (alloy Ⅱ) or with additive of Zr (alloy Ⅰ). The temperature dependence on strength of the alloy Ⅱ, i.e., microalloyed by Mg and RE, keeps in abnormality. The temperature dependence on elongation of both alloys reveals into 3 regions:to drop slightly, sharply and then stably, which may be controlled by the mechanisms of dislocation barrier, oxygen diffusion and stable oxygen content respectively. The reason why the elongation of alloy Ⅱ falls into shaop drop region at lower temperature than that of alloy Ⅰ,may be that the oxygen diffusion is promoted by segregation of Mg and RE at grain boundaries. Correspondent:CHEN Junming, professor, Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai 200050

A new ordered ternary intermetallic compound(γ1) has been observed in the TiAl alloy containing 20at.-%Nb. The possible crystal structure has been suggested to be tetragonal lattice with a =0.558─0.584 nm, c =0.815—0.845 nm, based on the results from selected area electron diffraction pattern( SADP). The composition of γ1-phase has been obtained by EDS. The supercell reflection spots of Ll_0(TiAl) sructure have also been found in the alloy containing Nb up to 11at.-%. Thus, the transformation from L1_0(TiAl) structure to γ1 is a continuous ordering process with the substitution of Nb atoms for Ti atoms in alloys. Correspondent: WANG Jinguo, Stale Key Laboratory for Advanced Metal Materials,（University of Science and Technology Beijing, Beijing, 100083）