Mathematical models and computer simulation of nitrogen concentration profiles in pulse plasma nitrided layers

Two materials, pure Fe and pure Al, were nitrided in a pulse plasma nitriding facility. The nitrogen profiles in surface layers and the surface phase structures of specimens nitrided at 500°C for 8 h for Fe and for 6 h for Al were measured using the glow discharge spectrometry and an X-ray diffractometer, respectively. XRD results indicate that the compound layer with hcp crystal structure (AlN) is formed on the top of Al substrate. During the nitriding of Fe, the compound layer growth conforms to the parabolic law and the surface nitrogen concentration change little with the increase of the nitriding time. The surface nitrogen content of nitrided Al specimens is less than the theoretical value 34.17 wt pct of AlN. The mathematical models of nitrogen concentration profiles in the surface layer of nitrided Al specimen were established based on the research of the kinetics of pulse plasma nitriding of Fe and the nitrogen concentration profiles were also simulated. Results show that the predicted curves agree basically with the experimental data.