Nucleation and Growth of Solid-State Transformations

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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.