Tribological Properties of Sulfide Layer on High Speed Steel under Dry Sliding

Sulfide layer was made on the surface of high speed steel (W6Mo5Cr4V2) by means of low temperature ion sulfurization. The tribological properties of the sulfide layer under dry sliding were investigated on an MM 200 friction and wear test rig. An atomic force microscope (AFM) and a scanning electron microscope equipped with an energy dispersive spectrometer attachment were adopted to analyze the morphologies and compositions of the original and worn surfaces of the sulfide layer. The phase structure of the sulfide layer was determined by X ray diffraction. The results show that the sulfide layer of W6Mo5Cr4V2 was composed of FeS, WS 2, and MoS 2 which have good solid lubricity. The sulfide layer was porous and contained randomly distributed nano scale sulfide grains in a size of 30 80 nanometers. The sulfide layer with nano structure was liable to oxidize and hence to enhance the formation of the oxide film during dry sliding. This subsequently leads to improved tribological properties in dry sliding.