Electrolyte-Plasma Nitriding of Austenitic Stainless Steel with Cathodic and Anodic Polarity

Abstract

The results of modifying the surface of austenitic stainless steel by plasma electrolytic nitriding at the anode and cathode polarities of the processed product in an electrolyte based on ammonia (5%) and ammonium chloride (5%) are presented. The morphology and surface roughness, phase composition, and microhardness of diffusion layers, tribological and corrosion properties were studied. The influence of physico-chemical processes during anodic and cathodic treatments on the features of the formation of the modified surface and its operational properties is shown. Smoothing of micro-roughness and reduction of surface roughness during anodic nitriding due to electrochemical dissolution, and the course of surface erosion with increased roughness during cathodic nitriding due to electrical discharges were revealed. An increase in the hardness of the nitrided layers to 1150 HV was found with a twice decrease in roughness after anodic treatment, accompanied by an increase in the wear resistance by 166 times, with a decrease in the friction coefficient by 1.6 times. After cathodic treatment, it is possible to increase the hardness only to 580 HV and the wear resistance by 13.6 times. An increase in surface roughness after the cathodic treat-ment always leads to an increase in the friction coeffi-cient. In both cases, a decrease in the pitting formation in the medium of sodium chloride is shown.