The large single decagonal quasicrystals of 0.8 mm in diameter and 10 mm in length in Al-Cu-Co-Ge alloy have been obtained by controlled unidirectional solidification.In the process of growth, all of the single quasicrystals grew preferentially along uni-orientation of solidification.The centre axis of quasicrystalline prisms is the tenfold rotational symmetry axis. Under the condition of temperature gradient about 95℃/ cm,the segregation will be occurred and the growing interface will be changed from planar structure into cellular and/ or dendritic one with increasing directional solidification rate.and a large number of crystalline phases will be produced. Thus,it seems to be no means of growing required single quasicrystals of high quality.Correspondent:CHEN Lifan, Institute of physics,Chinese Academy of Science, Beijing 100080

The aging process of 18Ni maraging steel have been studied by means of small angle X-ray scattering,Mossbauer spectroscopy and TEM.The spinodal decomposition firstly appears at the early stages of 500℃ aging in 18Ni maraging steel after solution treatment,and then the Ni3(Mo.Ti)intermetallic particles containing Fe precipitate in Ni-Mo-Ti rich regions of the modulated structure by in situ nucleation. With increasing aging time,Ni3Mo and Ni3Ti particles coalesce significantly and may be partly resolved into the matrix, and simultaneously the Fe2Mo particles precipitate and the reversed austenite can be found.Correspondent:YIN Zhongda,pro fessor,Campus Post Box 433,Harbin institute of Technology, Harbin 150001

The solidification of Cu-Zn-AI-Mn-Ni shape memory alloys may be changed by adding Ti.The dendritic X-phase may preferrentially precipitate at the initial stage out from liquid.The orientation of primary dendrite is〈 111〉.The X-phase spheroidizes and the stable Xl-phase precipitates during solid treatment in high temperature β-phase region.TEM observation showed that Xs-phase precipitated from β-phase nuclear-growth and its shape and size related to heat treatment temperature,holding time and cooling rate. By elevating temperature and prolonging time the shape variation of Xs-phase precipitated is in sequence of:globular, cubic,plum-blossom-like and rughy-shaped.Correspondent: CHANG Fenglian, Analytical and Testing Center,Southeasi University,Nanjing 210018

The effects of withdrawal rate on liquid / solid interface morphology, primary arm spacing,precipitation behaviour of (γ＋γ＇) eutectic and γ＇particles as well as microstructure of single crystal Ni-base superalloy have been investigated.With the increase of the withdrawal rate,the morphology of liguid/ solid interface transforms from planar into cellular, then coarse dendritic and at last fine dendritic. The primary arm spacing first increases and then decreases, the amount of (γ＋γ＇) eutectic increases, the size of γ＇particles decrease and the shape of γ＇precipitates tends to be regular. During cellular and dendritic solidification, double-peak curves of γ＇size distribution are presented. Correspondent: CHENG Guohua, engineer, Department No.5, Central Iron and Steel Research Institute, Ministry of Metallurgical industry, Beijing 100081

The dislocation features in FeAl intermetallic compound deformed at 900℃have been investigated by TEM.A large number of sqaure dislocation loops and helical dipoles have been found．The loops are identified to have the Burgers vector[100] and lie on(100)planes due to vacancy condensation. The helices are identified to have the Burgers vector [111] and result from the climb process of screw [111] dislocation at high temperature.One evidences indicate that further climb of the helical dipoles could result in another kind of loop which has the same Burgers vector as the dipoles and lies on the planes perpendicular to the Burgers vector．It is assumed that the climb of dislocation is responsible for the high ductility of FeAl compound at high temperature.correspondent:(LIN Dongliang，professor,Department of Materials Science，Shanghai Jiaotong University，Shanghai 200030)

An improvement of toughness by microalloying of Zn over the steels, from 20% to 200%, may mainly increase both the tearing work during impact rupture. Zn is so bettered the drawing strength of the matrix slip that a remarkable feature of "drawing tongue"occurred on the macrofracture surface of the steels.Correspondent.:(SHI Chongzhe. senior engineer, Department of Materials Science and Engineering, Xi'an Institute of Technology, Xi'an 710032)

Studies were carried out of the low-frequency fatigue(0.5Hz) behaviour of Ti3Al and Ti3Al+Nb in air and distilled water.It is revealed that the fatigue resistance of the two intermetallics decreases in water. The corrosion fatigue crack growth rate increases with increasing stress ratios,in which Kmax is the mechanical controlling factor of this material-environment system.The corrosion fatigue resistance of Ti3Al+Nb is higher than that of Ti3Al.Fractographic analysis shows that the cracking occurs along cleavage planes of α2(R = 0.1) or along interphase boundaries ofα2/ β(R = 0.5).Correspondent: (XING Zhiqiang, associate professor, Division of Advanced Mechanics, Beijing PolytechnicUniversity, Beijing 100022)

The effects of the impurities and Ce on the fracture behaviour of 8090 alloy sheets were experimentally investigated.Test results show that Fe and Si in 8090 alloy sheets decrease the plane stress fracture toughness in all orientations tested and the crack initiation and propagation resistance in 45°orientation. Na and K decrease the fracture properties in all orientations tested except the crack initiation resistance in T-L orientation.Adding 0.09% Ce into 8090 alloy sheets shows the beneficial effect on the plane stress fracture toughness.The fracture properties of 8090 alloy sheets containing more Fe and Si could be improved by adding 0.28% Ce. The reason behind it may be attributed to that Ce dissolved in a matrix could make the recrystallization microstructure of 8090 alloy sheets more uniform and finer,and reduce the compound particles precipitated along the grain boundaries, which is benefitcal to suppress the tendency of brittle fracture.Correspondent:(MENG Liang,associate professor,Department of Materials Science and Engineering.Northwestern Polytechnical University,Hi'an,710072)