A DIFFUSION-MODEL OF METAL-SURFACE MODIFICATION DURING PLASMA NITRIDING

A diffusion model of metal surface modification by plasma nitriding ha s been developed. This model takes into account the erosion effects at the plasma/solid interface occurring due to the ion bombardment of th e surface. For constant sputtering rate, which is the usual situation during plasma nitriding, the growth of the sub-layers is well describe d by the analytical expression g(t) = g(0)f(-1)(t/t(0)), where g(t) is the sub-layer thickness at time t, g(0) and t(0) are parameters which depend on the treated material and plasma characteristics, f(-1) is t he inverse of the function - 1n(1 - x) + x), 0 less than or equal to x less than or equal to 1. Under negligible erosion effects, the expres sion for g(t) reduces to the parabolic law. The diffusion zone (substr atum) growth does not follow the parabolic law as well. How ever, the deviation occurs after long plasma nitriding time. The model can be us ed for experimentally determining the effective diffusion coefficients and the erosion rate during plasma nitriding of metal surfaces.