The Application of the Bifurcation Theory to the Stability of Microstructure and the Improvement of the Superalloys.

当材料受到弹性约束时，最近观察到几个有趣的微观结构形成现象。特别是在析出相粗化过程中的异常行为；颗粒粗化减速和颗粒分裂为小颗粒是典型的例子。这些现象在理论上得到了“分岔理论”的支持。从实际的角度来看，这些现象预示着非过度老化材料的存在。本工作的目的是为这些现象提供更广泛的实验信息，并提供更准确的理论背景。所得结果如下：(1)在Ni-Mo和Fe-Al-Co合金体系中发现了颗粒的分裂现象。而在Fe-Al-Co中，分裂粒子的形状变化速度非常快。(2)本文提出了一种基于连续成分梯度场中微观结构变化观察的材料科学中成分依赖现象的新实验方法。利用该方法，可以通过实验得到不同粒径的析出相/基体界面的平衡组成，从而验证了析出相粗化的基本原理Gibbs-Thomson关系。(3)提出了一种新的非线性扩散方程的计算方法，该方法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。对Fe-Mo二元体系的相分解进行了二维模拟。计算得到的微观组织与实验结果吻合较好，并成功地计算出了应变致显微组织变化的典型特征。少

Several interesting phenomena for the formation of microstructure have recently been observed when the materials are elastically constrained. Particularly, the extraordinary behavior in the precipitate coarsening ; deceleration of particle coarsening and splitting of a particle into small ones are typical examples. These phenomena have theoretically supported by "bifurcation theory". In the practical point of view, these phenomena predict an existence of non-over aging materials. The purpose of the present work is to get more wide range information for these phenomena experimentally, and also to give more accurate theoretical background. The results obtained are as follows.(1) Splitting of a particle was newly recognized in Ni-Mo and Fe-Al-Co alloy systems. However, the shapechanging rate of split particles in Fe-Al-Co was remarkably fast. Results from the energetic estimation for the sequence of the particle splitting, the splitting path experimentally observed was consistent with min … More imum-energy path predicted by the theoretical calculation(2) We proposed a new experimental method to investigate the composition dependent phenomena in materials science based on the observation of microstructure changes in a continuous composition gradient field. Utilizing this new method, the equilibrium compositions at the interface of precipitate/matrix could experimentally be obtained for various particle sizes, and thus the Gibbs-Thomson's relation, which is the fundamental low in the precipitates coarsening, was verified experimentally.(3) A new calculation method for the nonlinear diffusion equation was proposed, where the composition dependencies of atomic interaction energy, elasticity and mobility of atoms were taken into account so as to be able to calculate the phase decomposition in the real alloy system. The two dimensional simulations were performed for the phase decomposition in the Fe-Mo binary system. The microstructures calculated were well coincident with experimental facts, and typical features in the strain-induced microstructure changes were successfully calculated. Less