Nucleation and Growth of Solid-State Transformations

9500122 Olson这个研究项目的目的是在马氏体反应原型中建立的定量原理的基础上，建立一阶相变的统一观点。该研究涉及两个广泛的领域(a)非均质置换体系中等级结构的动态演变，以及(b)非线性非局部固体中的竞争转化机制。立体测量的目的是确定热弹性和非热弹性马氏体体系的自催化成核位点效力分布的通用形式。数值模型解决了在塑性基体中生长的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位移/扩散转化。以铁-钯的弱一阶立方-四方相变为模型系统，采用非线性非局部连续体模型对结构转变的竞争机制进行了理论与实验相结合的研究。小颗粒实验研究均质成核和弱缺陷非均质成核行为，而连续介质计算研究三维共格均质成核和二维非均质成核。理论模型还探讨了波动辅助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。本文所研究的相变对用于结构应用的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. ***