Visualization of the Phase Decomposition Process Based on the Non-liner Diffusion Equation.

基于非线性扩散方程的扩散控制相变数值分析是计算机材料科学领域的主要研究课题之一。在本研究中，我们提出了一种新的非线性扩散方程的分析方法（“离散型扩散方程”），其中考虑了原子相互作用能、原子弹性和原子迁移率的组成依赖性，从而能够计算实际合金体系中的相分解。此外，所提出的计算理论还包含了溶质原子在原子位置上的占据概率信息。该方法不仅可以预测无序相的相分解，还可以预测应力诱导的析出相粗化、有序/无序相转变、有序合金的相分解、粗花呢组织的形成过程等。本研究的主要目的是通过可视化相分解过程来揭示相变的本质。在“离散型非线性扩散方程”的基础上，计算了扩散控制相分解的详细行为。所得结果如下：利用该方法对Fe-Mo、Fe-Cr、Al-Zn和Cu-Co二元合金体系的相分解进行了二维计算机模拟。本模拟采用了这些合金体系的相图热力学数据。理论计算得到的组织与实验结果吻合较好。特别是，成功地计算了应变引起的微观结构变化的典型特征。此外，在计算机模拟的基础上，将计算结果可视化，制作了相变的“介绍视频”。利用VTR分析了相分解的详细行为，这对材料科学和工程领域的教学具有重要的指导意义。少

A numerical analysis of the diffusion controlled phase transformation based on the non-liner diffusion equation is one of the main subjects in the field of the computer materials science. In the present study, we propose a new analyzing method of the nonlinear diffusion equation ("discrete type diffusion equation"), where the composition dependencies of atomic interaction energy, elasticity and mobility of atoms are taken into account so as to be able to calculate the phase decomposition in the real alloy system. Furthermore, the information of the solute atom occupation probability in atom site is also included in the proposed calculation theory. The proposed new method has a capability of predicting not only the phase decomposition in the disordered phases but also the other phase transformations such as the stress-induced precipitates coarsening, order/disorder phase transitions, phase decompositions in ordering alloys, the formation process of tweed structures, and so on. The purpo … More se of the present work is to reveal the nature of the phase transformation by visualizing the phase decomposition process. The detail behavior in diffusion controlled phase decomposition is calculated on the basis of the "discrete type non-linear diffusion equation". The results obtained are as follows.The two dimensional computer simulations were performed for the phase decomposition in the Fe-Mo, Fe-Cr, Al-Zn, and Cu-Co binary alloy systems on the basis of the new method. The thermodynamic data of phase diagram for these alloy systems was used in the present simulation. The microstructures theoretically calculated were well coincident with experimental facts of these alloy systems. Particularly, the typical features in the strain-induced microstructure changes were successfully calculated. Furthermore, we prepared the "Introduction Video" for the phase transformation by visualizing the calculated results based on the computer simulations. The detail behavior of the phase decompositions was presented by using the VTR,and this result will be very useful for the education in the field of materials science and engineering. Less