Microstructure and Growth Kinetics of Nitrided Zone in Plasma-nitrided Fe–Cr Alloys

Abstract

Microstructure and growth kinetics of the nitrided zone have been examined in various Fe–Cr binary alloys ranging from 1 to 30 mass% Cr that had been plasma-nitrided at temperatures between 743 and 943 K. CrN precipitates form under all the nitriding conditions. With increasing Cr content or decreasing nitriding temperature, the morphology of CrN precipitates changes drastically from continuous precipitation with a fine disk-shaped morphology to CrN lamellar precipitation. In addition, small amounts of Cr₂N form when the Cr content and the nitriding temperature are high. In spite of the different manners of Cr–nitride precipitation, the thickness of the nitrided zone is approximately proportional to the square root of the nitriding period. Furthermore, in most of the alloys the activation energies for the overall growth kinetics of the nitrided zone are nearly constant.