MICROSTRUCTURAL INVESTIGATION ON THE CRYSTALLISATION AND AGEING PROCESSES OF ADVANCED ALLOYS

用高分辨电子显微镜、差示扫描热分析、X射线衍射仪和振动样品磁强计研究了各种先进材料的晶化、相变和时效过程，得到如下结果：(1)Pr-Fe-B和Nd-Fe-Cr-B非晶薄带的晶化过程和磁性能发现，在退火后期，粗大的Nd2Fe&lt；23&gt；B_3粒子分解成粗大的Nd2Fe_&lt；14&gt；B_2粒子，其中含有非常细的α-Fe粒子。这种结构还表现出优异的硬磁性能，这是由于粗大的Nd2Fe14和细小的α-Fe颗粒之间的交换耦合作用而产生的。(2)Al-Mg-Si合金的时效过程证实了有助于沉淀硬化的β“颗粒的结构与Andersen…More提出的模型是一致的，并表明β”析出后的反应不是迄今所认为的β‘棒的形成，而是立方体β颗粒的析出。已经认识到β颗粒与基质之间存在三种不同的取向关系，其中一种在本研究中被发现。这种关系可以用形态、体积弹性能和界面能来解释。(3)Fe-Ni-C贝氏体的结晶学研究虽然贝氏体相变是通过原子-格位对应和晶格不变剪切的扩散晶格变化发生的，但已确认大部分贝氏体随后以扩散方式迁移。因此，界面位错结构不能作为Aaronson等提出的台阶机制的证据。(4)近β钛合金和钛铝合金的相变过程研究了钛合金中ω相颗粒对α马氏体相变的影响，结果表明，ω相析出的初期促进了β→α马氏体的相变，而后期则显著地稳定了相变。在Ti-Al合金中，已经提出了块状γ结构和反相区形成的模型。较少

The crystallisation, phase transformation and ageing processes of various advanced materials have been investigated by means of high resolution transmission electron microscopy, differential scanning thermal analysis, X-ray diffection and vibrating sample magnetometer and the following results were obtained.(1) The crystellisation processes and magnetic properties of Pr-Fe-B and Nd-Fe-Cr-B amorphous ribbonsThe decomposition of coarse Nd_2Fe_<23>B_3 particles into coarse Nd_2Fe_<14>B_2 particles involving very fine α-Fe particles has been found in the later stage of annealing. It has also been found that this structure exhibits excellent hard magnetic properties arising from the exchange coupling interaction between coarse Nd_2Fe_<14>B_2 particles and fine α-Fe particles within them.(2) The ageing process of Al-Mg-Si alloysIn this study, it has been confimed that the structure of β" particle which contributes precipitation hardening is in good keeping with the model proposed by Andersen … More . It was also shown that the reaction following the β" precipitation is not the β' rod formation as has been believed so far but the precipitation of cuboid β particles. The existence of three different orientation relationships betwen β particles and the matrix has been recognised and one of them has been found in this study. Such relationships can be explained by considering the morphology, volume elastic energy and the interfacial energy.(3) Crystallographic study on Fe-Ni-C bainiteAlthough bainite transformation occurs via a diffusional lattice change with atomic-site correspondence and the lattice invariant shear, it has been confimed that me broad fece of bainite migrates subsequently in diffusional mode. Thus, the dislocation structures on the interface cannot be the evidence of the ledge mechanism proposed by Aaronson et al.(4) The transformation processes of near β Ti alloys and Ti-Al alloysIn Ti alloys, the effects of ω phase particles on the α" martensitic transformation has been examined. It has been shown that the initial stage of ω phase precipitation accelerates the β→α" martensitic transformation but the later stage stabilises the martensitic transformation significantly. In Ti-Al alloys, the models of massive γ structure and the anti-phase domain formation have been proposed. Less