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

点击翻译按钮获取中文摘要

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