The tribological properties of a gradient layer prepared by plasma-based ion implantation on 2024 aluminum alloy

DLC films can play an important role in tribological properties of Al-alloys. A gradient layer of AlN/Ti/TiN/DLC film has been prepared by plasma-based ion implanted N, followed by Ti, and N and Ti, and finally C on 2024 Al-alloy. Emphasis has been placed on the tribological properties of the gradient layer. Its composition depth profile and chemical structure were characterized using X-ray photoelectron spectroscopy (XPS), the surface C-layer and the wear tracks were analyzed by laser Raman spectroscopy. The morphologies of the C-layer were observed by atomic force microscopy (AFM), the hardness of the gradient layer was measured with the mechanical property microprobe and the dry wear tests against AISI steel ball at different sliding loads were performed with a ball-on-disk wear tester in ambient environment. The results indicate that the gradient layer shows a gradual change in hardness, compact surface appearance and good tribological properties owing to the gradient structure. As the number of the sliding cycles or the load is increasing, the tribological properties decrease due to the graphitization of the DLC films. Meanwhile, the gradient layer can be controlled by PBII processing parameters, thus an optimized gradient layer can be obtained to offer the possibility of making aluminum alloys and other soft alloys qualified candidates for particular engineering applications.