Effects of plasma carburizing and DLC coating on friction-wear characteristics, mechanical properties and fatigue strength of stainless steel

This study was conducted to investigate the effects of hybrid surface treatment on the friction-wear characteristics, mechanical properties and fatigue strength of austenitic stainless steel JIS SUS316. In hybrid surface treatment, after plasma carburizing as a pre-treatment had been performed at 773 K for 43.2 ks (12 h), DLC (diamond-like carbon) coating was performed. The formed duplex layer had the DLC layer (thickness 1.6–1.8 μm) outermost and the hardened layer (thickness 90 μm) below it. The DLC layer was markedly effective in decreasing the friction coefficient and improving wear resistance. At the same time, the durability of the DLC layer was improved by the existence of the hardened layer. Since no marked change in the microstructure of the substrate occurred through hybrid surface treatment, the mechanical properties were almost unchanged. Furthermore, fatigue strength was greatly improved by hybrid surface treatment (improvement rate 53%) because the generation of fatigue cracks from the surface was strongly suppressed by the duplex layer.