The effect of the nitrogen potential on the coarsening kinetics of VN precipitates

An Fe-1.06 pct V alloy was used to study the kinetics of coarsening of VN precipitates. Nitriding was carried out at 600 °C in purified NH₃ gas. Nitrided specimens were then annealed at 820 °C in furnace atmospheres of different NH₃/H₂ ratios. The transmission electron microscopy technique was used to measure the precipitate sizes. The data on the precipitate sizes indicate that the coarsening of the plate shaped VN precipitates seems to be diffusion controlled. The precipitate coarsening rate appears to be lowered by the increase in NH₃ content in the furnace atmosphere. The particle size distributions were found to be broader than the predictions of the LSW theory.