Kinetics of Phase Transformations

这项资助是对材料相变的实验和理论研究的结合。采用基于快速（毫秒）同步加速器的时间分辨x射线散射研究了合金中的旋多分解和有序。初步研究集中在铝锌中的旋多分解和铜金中的有序的经典案例上，并表明Cahn-Hilliard-Cook线性理论及其推广、langer - bar - on - miller非线性理论在没有显著的时间尺度上是有效的。目前的研究重点是应变效应较小的合金（铁铬合金和铁钴合金）、二阶有序转变的合金（铁钴合金和铝铁合金）以及同时有序和相分离的合金（铝铁合金）。在某些情况下，这些快速实验探测相图中两个相都不是真正平衡结构的区域的转变动力学。研究的模拟和理论部分对Ising模型和流体中的旋量分解和连续排序进行了大规模研究，用于短期和长期相互作用。包括对简单流体结晶的研究。在接近混相极限时，采用模拟数据研究了现有成核理论的极限，并观察了理论开始失效的地方。建立了成核和旋量分解的几何模型

This grant is a combined experimental and theoretical examination of phase transformations in materials. Fast (millisecond ) synchrotron-based time resolved X-ray scattering is employed to study spinodal decomposition and ordering in alloys. Preliminary research has concentrated on the classic cases of spinodal decomposition in aluminum-zinc and ordering in copper-gold and showed that there is no significant timescale during which the Cahn-Hilliard-Cook linear theory or its extension, the Langer-Bar-On-Millier nonlinear theory are valid. Now the research is centered on alloys with smaller strain effects (iron-chromium and iron-cobalt), alloys with second-order ordering transitions (iron-cobalt and aluminum-iron), and alloys that undergo simultaneous ordering and phase separation (aluminum-iron). In some of these cases these fast experiments probe transformation kinetics in regions of the phase diagram in which neither phase is the true equilibrium structure. The simulations and theory part of the research pursues large scale studies of spinodal decomposition and continuous ordering in both Ising models and fluids, for short and long range interactions. Included are studies of crystallization in simple fluids. Limits of the present nucleation theories are studied by taking simulation data as the limit of miscibility is approached and seeing where the theory begins to fail. Geometric models are developed for nucleation and spinodal decomposition