Diamond like carbon film as a protective coating for high strength steel and titanium alloy

Hard chromium plating is currently used to protect the surfaces of wear and fatigue sensitive aircraft parts such as the landing gear, flap tracks etc. At Boeing, this process has been targeted for elimination due to environmental and workplace safety considerations. Our objective is to develop a non-hazardous, non-line of sight (NLOS) dry process replacement for chromium plating that does not adversely affect the engineering properties such as fatigue and wear. In this work, we report the results for Diamond Like Carbon (DLC) coating as a replacement for chrome plating. Excellent adhesion of DLC film to the steel surface is achieved using a variety of surface modification techniques such as in-situ inert ion sputter cleaning and ion implantation or deposition of an intermediate bonding layer between the DLC film and the substrate. Our tests show that DLC coated 4340 M steel exhibit better wear and fatigue characteristics when compared to those of chromium-plated 4340 M. DLC coating improved the wear resistance of Ti-6Al-4V drastically and did not cause any coating induced fatigue degradation in this alloy.