Structure and tribological properties of plasma nitrided surface films on Inconel 718

Inconel 718 specimen was plasma nitrided for microscopic examination and 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 detected in the surface of the nitrided layer by Auger electron spectroscopy. The nitrogen was found to react with Cr to form CrN which was detected in the nitrided layer by X-ray diffraction analysis. Friction and wear coefficients as a function of atmosphere, load, sliding speed, and surface temperature were performed. Exterior film structure varied from columnar or pyramidal with high roughness to a smoother spherical structure after nitriding at a lower temperature. The distribution of nitrogen within the film appeared uniform and there was a sharp boundary between the him and substrate. A maximum microhardness of 1290 HK was reached after prolonged nitriding. Nitrided surfaces showed 4 times lower coefficient of friction than a plain Inconel surface until the nitrided layer was worn away. Coarse lamellar wear particles showing signs of extreme plastic deformation were formed during wear of nitrided inconel.