Nucleation and Growth of Solid-State Transformations

9500122奥尔森，这项研究计划旨在建立一个统一的观点，一级相变的基础上建立在马氏体反应的典型案例的量化原则。这项研究涉及两个大的领域：(A)非均质置换系统中层次结构的动态演化；(B)非线性非局域固体中的竞争变换机制。体视学测量的目的是确定热弹性和非热弹性马氏体系的自催化形核位势分布的普遍形式。数值模型讨论了塑料基质中的生长动力学和多变量结构的自催化相互作用，并扩展到贝氏体反应，作为耦合的位移/扩散转变。以铁-钯的弱一阶立方-四方相变作为可用非线性非局域连续介质模型描述的模型体系，用理论和实验相结合的方法研究了结构相变的竞争机制。小颗粒实验解决了均匀成核和弱缺陷非均相成核行为，而连续介质计算则解决了三维相干均匀成核和二维非均质成核。理论模型还探索了涨落辅助的连续调制作为成核和生长的替代方案，并对比了竞争机制的前驱效应。本文研究的%相变对结构用铁基合金的性能至关重要。***

9500122 Olson This research program is directed toward a unified view of first-order phase transformations based on quantitative principles established in the prototypical case of martensitic reactions. The research addresses two broad areas (a) the dynamical evolution of hierarchical structure in heterogeneous displacive systems, and (b) competing transformation mechanisms in nonlinear nonlocal solids. Stereological measurements are aimed at identifying a universal form of autocatalytic nucleation site potency distribution for both thermoelastic and non-thermoelastic martensitic systems. Numerical models address the dynamics of growth in a plastic matrix and autocatalytic interactions of multivariant structures, with extension to bainitic reactions as coupled displacive/diffusional transformations. Competing mechanisms of structural transformation are examined by combined theory and experiment employing the weakly first-order cubic-tetragonal transformation in iron-palladium as a model system describable by nonlinear nonlocal continuum models. Small particle experiments address homogeneous nucleation and weak-defect heterogeneous nucleation behavior, while continuum calculations address coherent homogeneous nucleation in three dimensions and heterogeneous nucleation in two dimensions. Theoretical modeling also explores fluctuation-assisted continuous modulation as an alternative to nucleation and growth and contrasts precursor effects of the competing mechanisms. %%% Phase transformations under study here are critical to the properties of iron-base alloys used in structural applications. ***