Nucleation and Growth of Solid-State Transformations

9500122奥尔森这个研究计划是针对一个统一的观点，一阶相变的基础上建立的定量原则，在典型的情况下马氏体反应。 研究涉及两个广泛的领域：（a）异质位移系统中等级结构的动力学演化，（B）非线性非局部固体中的竞争变换机制。 体视学测量的目的是确定一个通用的形式的自催化成核位点的效力分布的热弹性和非热弹性马氏体系统。 数值模型解决了动态增长的塑性矩阵和自催化的相互作用的多元结构，与贝氏体反应的耦合位移/扩散变换扩展。 采用非线性非局域连续介质模型描述铁钯中的弱一级ε-四元相变，通过理论和实验相结合的方法研究了结构相变的竞争机制. 小颗粒实验解决均匀成核和弱缺陷异质成核行为，而连续计算解决三维相干均匀成核和二维异质成核。 理论建模还探讨了波动辅助连续调制作为替代成核和生长和对比竞争机制的前体效应。这里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. ***