Kinetics of Phase Transformations

这项资助是对材料中的相变进行实验和理论相结合的检验。用基于同步加速器的快速(毫秒)时间分辨X射线散射研究了合金的调幅分解和有序化。初步研究集中在铝-锌中的调幅分解和铜-金中的有序化这两个经典例子上，结果表明，没有明显的时间尺度来证明Cahn-Hilliard-Cook线性理论或其推广，Langer-Bar-on-Millier非线性理论是有效的。现在的研究集中在应变效应较小的合金(铁-铬和铁-钴)、具有二阶有序转变的合金(铁-钴和铝-铁)以及同时进行有序化和相分离的合金(铝-铁)。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的平衡结构的区域的相变动力学。该研究的模拟和理论部分对Ising模型和流体中的变节分解和连续有序化进行了大规模的研究，包括短程和长程相互作用。包括对简单流体中结晶的研究。研究了现有形核理论的局限性，将模拟数据作为相溶极限的逼近，并观察理论开始失效的地方。建立了形核和调幅分解的几何模型

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