Fretting wear behavior of graphite-like carbon films with bias-graded deposition

摘要

Although graphite-like carbon (GLC) films have been used to protect the engineering components due to their high mechanical properties and low friction coefficients, the poor interfacial bonding strength and high internal stress can lead their rapid failure. In this study, the bias-gradient (30-120 V) as well as the usual constant bias protocols (30, 60 and 120 V) has been adopted to deposit the GLC films on 316 L stainless steel and silicon using unbalanced magnetron sputtering technology. Based upon the microstructure and composition analysis by SEM, AFM, XRD, Raman and XPS, the sp(3) content and compactness of the films are increased with the increase of the deposition bias. Compared to the film at the constant bias of 120 V, the bias-graded film has a comparable hardness but superior adhesive strength. Detailed fretting wear testing under ambient air and dry N-2 atmospheres against 25 mm diameter Si3N4 ball has been carried out. The friction curves disclosed a three-stage evolution feature: the surface working area, the interlayer transition area and the coating failure area. The bias-graded film displayed the lowest friction coefficient and the longest fatigue life. Further the fretting mechanisms at different stages have been elaborated in terms of the chemical composition, microstructure and mechanical properties.