Investigation of Low Temperature Tribological Behavior of Multi-layer a-C:H Coatings Deposited on 5A06 Aluminum Alloy

Abstract In this paper, a multi-layer gradient coating of Cr/CrN/CrNC/CrC/a-C:H was successfully fabricated on the surface of 5A06 aluminum alloy through the application of anodic layer ion beam deposition and medium-frequency pulse magnetron sputtering techniques. The tribological behavior of the coatings was investigated by means of dry reciprocating sliding tests, conducted at temperatures ranging from −100 °C to 25 °C in both air and oxygen atmospheres. The microstructure, mechanical properties, and wear characteristics were analyzed using SEM, EDS, Raman spectroscopy, and indentation testing. The research findings indicate that the tribological performance in ambient air is primarily influenced by the synergistic effects of transfer layer formation and surface graphitization. In oxygen environments, poor initial tribological performance at 25 °C and 0 °C was due to tribochemical reactions that disrupted the passivated C-H bonds. Low temperatures hindered the formation of friction interface transfer layers, graphitization, and chemical reactions at the interface. Nevertheless, the coating demonstrates satisfactory lubricating performance due to the presence of a considerable quantity of sp2 hybridized carbon atoms within the coating itself. In both atmospheres at low temperatures (−50 °C and −100 °C), the steady-state friction coefficient remains below 0.3, and the wear rate is less than 1×10−6 mm3/Nm. Furthermore, the primary cause of abrasive wear is the residual hard oxide formed by the abrasives on the 0Cr18Ni9 stainless steel used as the mating material for the coating.