STRUCTURE AND TRIBOLOGICAL PROPERTIES OF PLASMA-NITRIDED SURFACE-FILMS ON INCONEL-718

Inconel 718 specimen was plasma nitrided for microscopic examination a nd tribological testing. Film structure and composition, depth of film hardness and surface roughness were measured as a function of coating parameters. The film growth rate appears to be diffusion controlled. (i.e. case depth proportional to root treatment time). Nitrogen was de tected in the surface of the nitrided layer by Auger electron spectros copy. The nitrogen was found to react with Cr to form CrN which was de tected in the nitrided layer by X-ray diffraction analysis. Friction a nd wear coefficients as a function of atmosphere, load, sliding speed, and surface temperature were performed. Exterior film structure varie d from columnar or pyramidal with high roughness to a smoother spheric al structure after nitriding at a lower temperature. The distribution of nitrogen within the film appeared uniform and there was a sharp bou ndary between the him and substrate. A maximum microhardness of 1290 H K was reached after prolonged nitriding. Nitrided surfaces showed 4 ti mes lower coefficient of friction than a plain Inconel surface until t he nitrided layer was worn away. Coarse lamellar wear particles showin g signs of extreme plastic deformation were formed during wear of nitr ided inconel.