Investigation of microscopic mechanisms of diffusional phase transformations

本课题组开展了扩散相变的研究，为材料的微观组织控制奠定了实践基础。本课题组针对合金中有序-无序转变和相分离的微观过程--原子扩散和异相界的原子结构--这两个方面控制着母相和相变产物之间的界面迁移率进行了研究。(1)结合点缺陷热力学的理论分析，对L1_2结构的镍基金属间化合物(Ni3Al、Ni3Ge和Ni3Ge)中的原子扩散进行了实验研究。α亚晶格中的空位机制是这类材料中的主要扩散机制。还精确地测定了某些金属玻璃和准晶中各组元的扩散系数。(2)…应力的应用有序度较高的r磁场对FEPD的磁畴结构产生强烈的变化是非常有效的。并从理论上解释了这一现象的产生原因。(3)用高分辨电子显微镜等技术研究了Ni-Mo和Cu-Pt合金的短程有序结构。通过小角散射实验和计算机模拟研究了某些铝基合金相变的初始阶段。根据建立的沉淀硬化合金设计的指导原则，设计并制备了抗拉强度在900 Mpa以上的新型铝合金。(5)用X射线反常散射技术研究了金属玻璃的原子结构(排列)。(6)通过直接观察和浓度分布测量研究了异相界面的原子结构和成分的变化，为讨论这些界面的稳定性奠定了基础。(7)通过研究钢中非均匀形核析出相与母相界面的原子结构及其结晶学关系，建立了高强度、高韧性钢的组织控制方法。较少

This group carried out research on diffusional phase transformations to establish practical basis for microstructure-control of materials, aiming particularly at the two aspects :-the microscopic processes of order-disorder transformation and phase separation in alloys-atomic diffusion and atomic structure of heterophase boundaries, both of which control the mobility of the boundaries between the parent phase and the transformation products.The results of the research can be summarized as follows.(1) Atomic diffusion in nickel-based intermetallic compounds of the L1_2 structure (Ni_3Al, Ni_3Ga and Ni_3Ge) has been investigated experimentally, in parallel with theoretical analyses of the thermodynamics of point-defects. The vacancy mechanism in the α-sublattice has shown to be the dominant mechanism of diffusion in this class of materials. The diffusion coefficients of constituents in some metallic glasses and quasicrystals have also been determined precisely.(2) Application of stress o … More r magnetic field on ordering has been shown to be very effective in producing strong variations in domain structures in FePd. The origin of the phenomenon has been explained theoretically.(3) The short-range order in Ni-Mo and Cu-Pt alloys have been investigated by high-resolution transmission electron microscopy and some other techniques. A systematic account of the microscopic structure and the ordering processes has been given.(4) The initial stage of the phase transformation in some aluminium-based alloys has been studied by small-angle scattering experiments and computer simulation. On the basis of the guiding principle for the design of precipitation-hardened alloys established, a new aluminium alloy has been designed and prepared, which exhibits tensile strength above 900 MPa.(5) The atomic structure (arrangement) in metallic glasses has been studied by the X-ray anomalous scattering technique. The origin of the thermal stability of those materials have been clarified.(6) The atomic structure and the variations in composition of heterophase interfaces have been investigated by direct observations and concentration profile measurements to establish the basis for discussing the stability of those interfaces.(7) By studying the atomic structure of the interfaces between inhomogeneously-nucleated precipitates and the parent phase in steels and their crystallographic relationships, the method of microstructure control for high-strength, high-toughness steels has been estabilished. Less