Nucleation and Growth of Solid-State Transformations

这项研究计划旨在通过对马氏体相变的检验来更好地理解一级相变。该程序采用理论和实验方法来解决两个广泛的领域：(A)非均相成核的分布活化动力学；(B)非线性非局部固体中的竞争转变机制。在热弹性和非热弹性马氏体系中，采用声发射和空间测量的形核动力学实验研究了分布激活非均相动力学的一般特征，确定了初始缺陷和自催化缺陷的能量分布。将原理推广到贝氏体相变和凝固。通过理论和实验相结合的方法，在可用非线性非局域连续介质模型描述的模型系统中考察了结构转变的竞争机制，并预测了界面能。实验预测了一种新的相变机制--准马氏体应变调制的行为，这种机制在晶格不稳定附近的条件下与形核和长大竞争。例如，这项分析和实验工作针对的是钢中的马氏体相变，但也适用于金属和陶瓷中的其他相变。

This research program is directed towards improved understanding of first-order phase transformations based on examination of the martensitic phase transformation. The program employs both theoretical and experimental approaches to address two broad areas: (a) the distributed-activation kinetics of heterogeneous nucleation; and (b) competing transformation mechanisms in nonlinear nonlocal solids. General features of distributed- activation heterogeneous kinetics are examined in nucleation kinetic experiments employing acoustic emission and sterological measurements in both thermoelastic and nonthermoelastic martensitic systems, defining potency distributions of initial and autocatalytic defects. principles are extended to bainitic transformations and solidification. Competing mechanisms of structural transformation are examined by combined theory and experiment in model systems describable by nonlinear nonlocal continuum models predicting interfacial energies. Experiments test predicted behavior of a new transformation mechanism, quasimartensitic strain modulation, which competes with nucleation and growth under conditions near a lattice instability. %%% This analytical and experimental work is directed to martensitic transformations found in steels, for instance, but is applicable to other phase transformations in metals and ceramics.