Crystallographic study on the precipitation and the phase transformation processes in alloys

(1)钢和亚稳β相钛合金中间组织形成机理用透射电镜分析了低碳镍钢中铁素体与奥氏体的习惯面、铁素体与奥氏体的取向关系、渗碳体薄片的习惯面、上贝氏体中铁素体与渗碳体的取向关系。根据这些结果，提出了一种上贝氏体转变机制模型——剪切辅助扩散转变机制，其中假设从奥氏体到铁素体的晶格变化是通过保持原子-位对应的单个原子跳变而发生的，但由于这种相变引起的弹性应变应该被晶格不变剪切放松。该模型已成功地应用于钛合金中的Widmanstatten α形成。铁铬铬合金中常见的由针状铁素体和碳化物组成的类贝氏体组织绝对不是贝氏体，而是一种共析组织。(2)有色合金中析出物的结晶学分析本文研究了亚稳态β相钛合金中ω相的析出及其对β * α和β * α的影响。此外，还利用HRTEM研究了Al-Li基合金的早期时效过程。利用高分辨率图像的傅里叶变换和反傅里叶变换，表明该合金中发生了同序过程。

(1) Mechanism of intermediate structure formation in steels and metastable beta phase titanium alloysThe habit plane, the orientation relationship between ferrite and austenite, the habit plane of the cementite platelets, the orientation relationship between ferrite and cementite in the upper bainite in low carbon nickel steels have been analysed by means of transmission electron microscopy. From these results, A model of upper bainite transformation mechanism, Shear-assisted Diffusional Transformation Mechanism, where the lattice change from austenite to ferrite is assumed to occur via individual atomic jumps across the phase interface with keeping the atomic-site correspondence but the elastic strain due to this phase change should be relaxed by the lattice invariant shear, has been proposed. This model has been successfully applied to the Widmanstatten alpha formation in the titanium alloy. It has also been shown that the bainite-like structure consisting acicular ferrite and carbide often observed in Fe-Cr-C alloys is definitely not a bainite but a kind of eutectoid structure.(2) Crystallographic analyses for the precipitation processed in non-ferrous alloysThe omega phase precipitation in a metastable beta phase titanium alloy and the effects of it on the beta*alpha and beta*alpha" have been examined. In addition to this, the early stage of ageing in an Al-Li based alloy was also been investigated by means of HRTEM.Using the Fourier and the inverse Fourier Transforms of the high resolution images, it has been shown that the congruent ordering processes occur in this alloy.