Shape Bifurcation Theory on the Stability of Microstructure and its Applications

该项目涉及弹性约束合金系统中沉淀颗粒粗化的特征行为。所得结果如下：粗化过程中析出物发生分裂，析出物的粗化率极小，对于给定的大尺寸，粗化速度减慢，粒度分布函数f(r，t)随颗粒尺寸和析出物体积分数的变化，这意味着f(r，t)在弹性约束系统中不能再被标度。根据含弹性相互作用能的微结构总能理论给出的分叉图解释了这些事实。实验发现了一种与溶质含量宏观不均匀有关的新型相分解，并从热力学上评价了它在弹性约束体系中的可能性。提出了一种估算包含化学自由能、弹性应变能、界面能等微结构总自由能的新方法，并讨论了预测微结构发展的可能性。此外，还提出了一种新的时间-温度-组成图--T-T-C体系图。用该系统图可以较全面地描述时效过程中的相变顺序和组织演变过程。

This project is concerned with the characteristic behaviours of the precipitate particles coarsening in elastically constrained alloy systems. The results obtained are as follows; splitting of a precipitate during coarsening, extremely small coarsening rate of precipitates, deceleration of coaresening rate for a given large size and the variations of the size distribution function f(r,t) with particle size and also volume fraction of precipitates, which means that f(r,t) can be no longer scaled in the elastically constrained systems. These facts are explained by the Bifurcation diagram theoretically given on the basis of the total energy of microstructure including the elastic interaction energy.A new type of phase decomposition associated with macroscopic non-uniformity of solute content was experimentally found and thermodynamically evaluated to be possible in elastically constrained systems.A new method to estimate the total free energy of the microstructure containing a chemical free energy, an elastic strain energy, an interfacial energy and so on was proposed, and then a possibility of predection to the microstructure development was discussed. Furtheremore a time-temperature-composition diagram named T-t-c system diagram was newly proposed. By using the system diagram the sequence of phase transformation and the microstructural development with progress of ageing can be comprehensively described.