A novel invasion percolation model for co -interpenetrating composites

A novel Invasion Percolation model for simulating the reactive metal infiltration of ceramics to form a co-interpenetrating composite is presented. By combining the pore-level dynamics of percolation models with kinetic Monte Carlo methods for simulating surface phase transformation it is possible to simulate both thermodynamic driving forces for infiltration: the applied pressure and the reactive wetting process. In doing so the model describes both the capillary fingering effects that dominate at high pressures and the time evolution of reaction byproduct phases that cause pore space closure at high temperature. At very high temperature and/or low pressure a "core-shell" morphology forms. At very high pressures the assumption of quasi-static flow in discrete pore throats is violated, and viscous channel flow occurs that leaves undesirable levels of residual porosity.;Statistics derived from percolation theory were applied to determine the effective percolation threshold pressure for infiltration and the critical pressure for divergence of the fingerwidth. At pressure intermediate between these two extremes the residual Pore size distribution was found to determine the probability of discrete pore cluster occurrence, which served as a means, in addition to fingerwidth, for quantifying microstructures. This enabled the application of Weibull statistics to determine the 98% probability survival strength and the Weibull shape factor. For analyzing mechanical properties, the pore cluster probability is a better measurement. For analysis of thermal properties, the fingerwidth' should be used.;The adjustable parameters experimented with were the transformation rate, initial transformation contact angle, applied pressure, kinetic growth rate constant, and initial matrix porosity. The Aluminum/Silicon Carbide system was chosen first because of the large volume of wetting data available, but the model is designed to simulate any system were reactive wetting data, kinetic growth rate data, and correlation of surface XRD data with temperature are available. In general, the conditions most favorable for the formation of the most interconnected composites were high transformation rate, low to intermediate pressure, low initial transformation contact angle (low temperature), low kinetic growth rate constant, and low initial matrix porosity. The optimal combinations were presented in the form of Weibull survival probability plots and process maps.