A diffusion model of metal surface modification during plasma nitriding

Abstract

A diffusion model of metal surface modification by plasma nitriding has been developed. This model takes into account the erosion effects at the plasma/solid interface occurring due to the ion bombardment of the surface. For constant sputtering rate, which is the usual situation during plasma nitriding, the growth of the sub-layers is well described 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 the 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 expression for g(t) reduces to the parabolic law. The diffusion zone (substratum) growth does not follow the parabolic law as well. How ever, the deviation occurs after long plasma nitriding time. The model can be used for experimentally determining the effective diffusion coefficients and the erosion rate during plasma nitriding of metal surfaces.