Tribological behavior of gradient modified layer on 2024 aluminum alloy modified by plasma-based ion implantation

The N-pre-implanted 2024 aluminum alloy was implanted with Ti and N, or implanted with Ti, and then with Ti and N by plasma-based ion implantation (PBII) to form two gradient layers, respectively. The composition depth profiles of the gradient layers were characterized by X-ray photoelectron spectroscopy. A series of ball-on-disk wear experiments have been carried out in ambient air, to investigate the tribological behavior of the gradient layer against steel ball under dry and un-lubricated conditions, employing various applied loads and a constant sliding speed. The results revealed that tribological properties of the gradient layers were improved markedly in contrast with those of the unmodified sample, and strongly dependent on their composition depth profiles. The gradient layer implanted with Ti, and then with Ti and N was much thicker and contains higher N, thus it corresponded to higher hardness which slowly decrease from surface to substrate and the optimal tribological properties including higher load carrying capacity. As load was increasing, the tribological properties decreased, and the adhesive degree increased since the gradient layer became thinner rapidly. Of course, more proper gradient layers will be obtained as the qualified candidates in some particular engineering applications by optimizing PBII parameters.