WEAR MECHANISMS IN THERMALLY-SPRAYED MO-BASED COATINGS

The successful development of advanced diesel engines relies heavily o n piston ring coating materials which can withstand elevated temperatu res and reduce friction. Traditional hard chrome plating and flame-spr ayed Mo-wire materials have reached their potential in the diesel engi ne environment, and alternatives are needed. Thermally-sprayed Mo-base d alloys and composites are being evaluated for applications as next-g eneration ring-face coatings. The alloy development task of producing complex Mo-based alloy powders for use as thermally-sprayed coating ma terials requires an understanding of their wear resistance under conta ct stress conditions. In this paper, the wear behavior of Mo and Mo NiCrBSi thermally sprayed coatings is examined by pin-on-disc and sing le-point scratch-test methods. Microstructural analysis beneath worn r egions have revealed that fracture of splats and their decohesion cons titute the mode of failure. Improved wear resistance and stability of low friction coefficient was obtained by prealloying Mo with NiCrBSi p rior to thermal spraying.