Fatigue behavior of a 316L stainless steel coated with a DLC film deposited by PVD magnetron sputter ion plating

The present investigation has been conducted in order to evaluate the change in fatigue properties of a 316L stainless steel substrate when this material is coated with a hydrogenated, amorphous carbon (a-C:H) solid lubricant of approximately 2 μm in thickness, which has been developed in recent years and is known commercially as Dymon-iC™, a film deposited by means of physical vapor deposition (PVD) closed field unbalanced magnetron sputter ion platting (CFUBMSIP). The fatigue behavior of the uncoated and coated alloy has been evaluated under rotating-bending conditions at maximum alternating stresses in the range of 430–520 MPa, depending if testing was conducted in air or in a 3 wt.% NaCl solution. The results indicate that the presence of the coating provides a significant increase in fatigue properties, particularly under corrosive conditions, an outcome that is believed to be closely associated with the amorphous structure of the film, besides its elevated mechanical strength, a possible existence of a compressive residual stress state and good adhesion to the substrate. The fractographic analysis conducted both on the fracture surfaces of the tested specimens and along sections normal such surfaces clearly shows that fatigue cracks are nucleated on the surface of the coating and that propagate into the substrate once have crossed over the entire coating thickness.