Effect of Bias Voltage on Fatigue Behavior of CrN Film Deposited on Ti-6Al-4V Alloy

PVD technique incorporating CrN coating was applied to the titanium alloy (Ti-6Al-4V) and its effects on the fatigue life and fatigue strength were studied in this paper to explore the fatigue behavior of Ti-6Al-4V specimens. A CrN film deposited by arc ion plating (AIP) improved the mechanical properties; specially hardness and fatigue life of Ti-6Al-4V specimens. The properties were studied using XRD, hardness and fatigue testers. The fatigue life of CrN-coated Ti-6Al-4V specimens was improved significantly compared to those of uncoated specimens. The enhanced fatigue life can be attributed to the improved hardness of CrN film due to change of bias voltage during the film deposition. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the substrate surface. It has been determined that the fatigue fracture of the substrate-coating composite is dominated by the fracture of the CrN film since fatigue cracks have been observed to form first at the surface of the film and subsequently to propagate towards the substrate. It has also been concluded that the increase in fatigue properties of the coated substrate is associated mainly with the changing of bias voltage during the coating observed in most of the maximum alternating stress range explored in this work.