Surface modification of aluminum using ion nitriding and barrel nitriding

In this study, an aluminum nitride (AlN) layer was formed on the surface of aluminum in barrel with alumina/aluminum-magnesium alloy powder, and gas and ion nitriding was thus enabled. The influence of process parameters on the film thickness, hardness and constituents of AlN layer was examined. The film thickness was compared for three nitriding methods: firstly, barrel nitriding only; secondly, gas nitriding after barrel nitriding; and thirdly, ion nitriding after barrel nitriding. After nitriding, there are two layers on the substrate, one is the modified layer composed of AlN and the other is a deposited overlayer composed of alumina and AlN. With increase in time in the barrel, the thicknesses of the modified layer and deposited overlayer also increase. In the combined processes, the thickness of the modified layer is greater than that obtained by barrel nitriding alone. In addition, it is possible that the thickness of the deposited overlayer decreases when gas or ion nitriding is used. While hardness of the modified layer combined with gas or ion nitriding is increased, that of the modified layer combined with ion nitriding is the highest.