Effect of rare earth on kinetics of pulse plasma nitriding of pure aluminum and properties of nitrided layer

Pure aluminum was successfully nitrided in a pulse plasma nitriding facility with rare earth addition. The surface phase structure of the specimen nitrided at 500°C in N₂ gas with and without rare earth addition was measured using an X-ray diffractometer. The XRD results show that the compound layer with hep crystal structures (AlN) was formed on the top of aluminum substrate. The elastic modulus and the nitrogen concentration profiles in the surface layer were detected employing a nanoindenter and the glow discharge spectrometry, respectively. The quantitative relationship between the thermal conductivity and the thickness of AlN layer has been deduced. The results show that the incorporation of rare earth accelerates the kinetics process of pulse plasma nitriding of pure aluminum and increases the elastic modulus of surface layer resulting mainly from a decrease in oxygen content of AlN layer. The decrease of oxygen content has been sidelong proved based on the deduced mathematical model.