Grain boundary diffusion of chromium in polycrystalline nickel studied by SIMS

Abstract

The grain boundary diffusion of chromium in polycrystalline nickel was studied by means of tracer experiments at 346–668 °C. Intensity-depth profiles were recorded by secondary ion mass spectrometry (SIMS), which allowed short diffusion distances, and therefore relatively low temperatures, to be examined. Individual grain boundaries in coarse-grained substrates produced profiles with a variety of shapes, reflecting the variability of diffusivities in a polycrystal, and even within a grain boundary. Average diffusivities were also measured using cold-rolled substrates, which rapidly recrystallized and provided finer microstructures. The simplifying assumptions usually made in processing B regime data were found not to be applicable here, because of the shallow measurement depths. The errors made by using approximate solutions to the diffusion equation are discussed, and a data processing method adapted to the conditions of SIMS measurements is used. A method to study diffusion tails with smooth slope variations is also demonstrated. The measured diffusivities were found to be in agreement with higher temperature data from the literature.