Enhancing the Mechanical Properties and Wear Resistance of Stainless Steel/Nitride Coatings through Compositional and Process Modifications

Surface hardening of stainless steel by plasma nitriding has been successful in numerous engineering applications.  Coatings with similar compositions can be deposited by reactive magnetron sputtering and are not limited to stainless steel substrates, therefore having potential for even broader applications.  This study examines the mechanical and tribological properties of stainless steel coatings with colossal nitrogen contents.  Deposition was carried out using reactive magnetron sputtering in mixed Ar/Nitrogen.  One set of coatings was deposited using a 304 stainless steel target and the effect of substrate temperature, bias and nitrogen gas concentration was examined.  Below 450C the coatings were primarily S-phase with nitrogen concentrations between 29 and 37% and a maximum hardness of 2100 kg/mm².  Additional films were deposited by co-depositing films from stainless steel and titanium targets.  Titanium concentrations of up to 15 at.% were obtained, and nitrogen levels in these films were near 50 at.%.  The structure of these films was again primarily the S-phase.  A maximum hardness of 3000 kg/mm² was obtained at a deposition temperature of 150C.  Further analyses of the films by SEM, TEM, XRD and pin-on-disk wear testing have been conducted in order to evaluate the microstructure and wear resistance of the deposited coatings.