The effect of heterogeneous nucleation on two dimensional phase transformation kinetics and resultant microstructure

The goal of this thesis is to assess quantitatively the impact of spatially heterogeneous nucleation on the kinetics of a first-order phase transformation and the nature of the associated evolving microstructure. Given the ubiquity of such transformations in important materials processes, we present the results of our studies of a simple two dimensional model system in which we identify important quantities that characterize the spatio-temporal evolution of a phase transformation. In particular we employ computer simulation as a vehicle to generate evolving, transforming, grain structures corresponding to a given set of nucleation and grain growth assumptions. The associated kinetic and microstructural data is then interpreted using various statistical tools.; The work presented here builds on our previous calculations of n-point correlation functions describing nucleation and growth and another study wherein a hilly coalesced microstructure is interrogated. First, analytical expressions for the temporal evolution of perimeter fraction during a phase transformation for both site-saturated nucleation and nucleation at a constant rate are obtained. In the former case, these expressions are then validated by a direct comparison with the results of two-dimensional computer simulations of nucleation and growth to impingement. The role of evolving perimeter fraction on the energetics of a transforming systems is then discussed.; The effect of nucleation conditions on product microstructure is then examined with respect to individual and “mixed” nucleation site types. Where only one type of site is active, the spatial distribution of nucleation sites is quantified in terms of neighbor distributions and pair correlation functions. In the case of multiple types of site potency, maps that reveal important microstructural behavior and trends are constructed. The dimensionality of the subspace of the sites on which nucleation occurs can be described, thereby facilitating the identification of unique bulk, edge, and corner nucleation signatures in the calculated quantities. The results of the simulations allow possible nucleation conditions to be identified.