Low-Temperature Diffusion of Chromium in a Fine-Grained Austenitic Stainless Steel with Varying Dislocation Densities

Abstract

Chromium tracer diffusion in a fine-grain austenitic stainless steel with varying dislocation densities has been analysed using exact solutions to the grain-boundary and dislocation problem. Down to ∼700°C the results could be explained in terms of lattice and grain-boundary diffusion components. The concentration profiles of tracer below 700°C, however, also required a dislocation component. No systematic dependence of the penetration profile on dislocation density was detected. The dislocation component was dominant at short times and led to an apparent enhancement of the lattice diffusion coefficient. Enhanced lattice diffusion by dislocations according to the Hart model was not observed in the temperature range studied even at high dislocation densities. If the accepted value of the dislocation-pipe diameter is assumed then it can be postulated that the lack of enhancement is due to the ratio D _p/D _L not being sufficiently high (i.e. D _p/D _L < 10³). This implies that the dislocation-pipe diffusion coefficient is not similar to the grain-boundary diffusion coefficient as is generally assumed, but is several orders of magnitude lower.