Effects of solidification conditions on microstructural morphologies and crystal characters.and quantitative acquisition of the eutectic symbiotic region at low temperature gradient (G=45℃/cm) in Al-Si alloy were studied by directional solidification and metallography, electron microscopic technique and X-ray preferred orientational analysis.The results show that the morphologies of eutectic symbiotic regions were complicated, as the solidification rate was rised, the region became sliter and sloped to the direction of rich silicon. The complication of symbiotic region relied on the sensibility of microstructures on solidification conditions, while the multiplicity of morphology was decided by crytical characters of eutectic phases. When the interior disturbance or unstablity of exterior condition exist some unusual microstructures and defects appeared in alloy.Correspondent: LI Shunpu, research assistant, Institute of Physics, Chinese Academy of Sciences, Beijing 100080

By means of particle tracking autoradiography (PTA), the diffusion coefficients of B between 900-1200℃ were measured in 04MnNbB steel, 25Mn TiB steel,Ni-B, Fe30% Ni-B and Fe-3% Si-B alloys, and the frequency factor D0 and activation energy Q were obtained respectively. The experimental results indicate that there was an obvious difference between the present result and that obtained by Busby (in 1953). It was found that the B diffusivity in γ-Fe increased as Ni added. The diffusivrty of B in Fe-3% Si-B alloy with bcc structure was much slower than one obtained by Busby in α-Fe(1954), however which was much rapid than the results obtained in γ-Fe(with fcc structure).Correspondent: WANG Wendong, Department of Materials Phvsics, University of Science and TechnologyBeijing, Beijing 100083

The microstructures and mechanical properties of two polycrystalline alloys, a Ni_3Al(0.6 at- %B) alloy and a Ni_3Al(1 .0 at-%B) alloy. are studied. The Ni_3Al(0.6 B)is a single phase alloy whereas the Ni_3Al(1.0 B) consists of few boride eutectic at the grain boundaries. Tensile tests and high cycle fatigue tests at room temperature are carried out in air.The results indicate that the fatigue resistance of the Ni_3Al(0.6B) alloy is higher than that of the Ni_3Al(1.0B) alloy. although, the latter is much higher than the former in tensile strength. The characteristics of fatigue crack initiation and propagation in the two Ni_3Al(B) alloys are different.Correspondent:LI Gang,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110015

JFMS alloy specimens were implanted with hydrogen ion by ion accelerator.and then electron irradiated by HVEM.The results showed that hydrogen implantation promotes the void nucleation under electron irradiation at above 570 K. At 670 K, the void number density in the specimen with hydrogen would be one order of magnitude higher than the specimen without hydrogen. Void swelling would also increase by hydrogen implantation.Correspondent WAN Farong. associate peo fessor,Department of Materials Physics, University of Science andTechnology Beijing, Beijing 100083

The lattice structure of nanocrystalline pure Ni. prepared by high-frequency sputtering, has been investigated. The lattice parameter of nanocrystalline Ni samples with grain sizes ranging from 6 to 15 nm was measured accurately by X-ray diffraction. It was found that the lattice parameter(a) for the nanocrystallie samples is larger than that for the perfect Ni single crystal(ao), and the value of a increases significantly with the decrease of grain size. According to the thermodynamic theory, the lattice expansion in the nanocrystalline sample was explained.Corespondent:LU Ke,professor,Institute of Metal Research. Chinese Academy of Sciences, Shenyang 110015

The grain boundaries in nanocrystalline palladium synthesized by the inert gas condensation and in situ compacting method have ordered and imperfect or disordered regions. Nanovoids are also observed at the interfaces. High density of dislocations are detected inside the grains and at the grain boundaries. Most of the interfaces in nanocrystalline Ti-Ni-Si and Fe-Mo-Si-B alloys produced by the amorphous crystallization have ordered structure. No obvious disordered regions and nanovoids are observed at the interfaces. However, the lattice fringes near the ordered grain boundaries or interfaces regions in the nanocrystalline materials produced by the various process show curved and a little distorted appearance. In comparison with the nanocrystalline palladium, the nanocrystalline alloys obtained from the amorphous crystallization have much lower density of dislocations.Correspondent:PING Dehai,(Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015)

The overall evolution for initiation and propagation of the short fatigue cracks in smooth specimen of the steel 45 was observed under optical microscope by using of the replication short crack initiation life is less than 10% of the failure one. According to the cracking rate. the growth of short cracks may separate into two stages. i.e., micro-crack and physical crack, of which the characteristic values of crack size and the equations of growth rate to identify them are given.Correspondent:XU Hao,professor,(College of Mechanical Engineering, Northeastern University, Shenyang 110006)

The optical microscopy, SEM and TEM have been used to observe the morphological changes at the surface of fatigued Nb monocrystals and the saturated dislocation structure. It reveals that fatigue crack initiation is related to the deformation band at the spcimen surface and cracks initiate easily at the common fold area of the double deformation bands if the slip lines and deformation band are paralled to each other. It is also found that the initiated cracks show the behaviour of cross slips and the steps due to cross slips locate mostly in the vicinity of the initiated cracks. Based on our experimental results, a mechanism.which is the modification of the famous Mott model, is given to theoretically explain the initiation of fatigue cracks. In other words. the experimental results confirm the Mott model in general .Correspondent: WU Jiansheng professor, (Department of Materials Science, Shanghai Jiaotong University.Shanghai 200030)