Effects of thickness and cycle parameters on fretting wear behavior of CVD diamond coatings on steel substrates

Diamond films have been grown on carbon steel substrates by hot filament chemical vapour deposition (CVD) methods. A Co-containing tungsten-carbide coating prepared by high velocity oxy-fuel spraying was used as an intermediate layer on the steel substrates to minimize the early formation of graphite (and thus growth of low quality diamond films) and to enhance the diamond film adhesion. The effects of thickness and cycle parameters on adhesion, tribological behaviour and electrochemical treatment of the diamond film were investigated. The diamond films exhibit excellent adhesion under Rockwell indentation testing (1500 N load) and in high-speed, high-load, long-time reciprocating dry sliding ball-on-flat wear tests against a Si3N4 counterface in ambient air (500 rpm, 200 N, 300000 cycles). Time modulated CVD (wherein the CH4 fraction in the process gas mixture is cycled in time) is shown to yield diamond films offering an exceptional combination of low friction, high hardness, high wear resistance, as well as promising corrosion resistance.