Modeling gas diffusion into metals with a moving-boundary phase transformation

A fixed-grid, finite-difference model is developed to investigate the moving-boundary phase transformation that occurs during gas charging or discharging from finite specimens. The model is developed in a nondimensional form, and solutions are calculated for plane sheets, cylinders, and spheres. Numerical predictions are compared with existing analytical solutions, as well as experimental data for the beta/alpha transformation of titanium induced by diffusion of oxygen from the surface of a plane sheet. Finally, a parametric study is performed to elucidate the effect of several input parameters on phase transformation kinetics, and simple empirical relations for the transformation time are developed based on this study.