Effect of electrolyte depletion on characteristics of anodic plasma electrolytic nitrocarburizing

Abstract

This article considers changes in the composition of aqueous electrolytes containing ammonia chloride and urea during plasma electrolytic nitrocarburizing of low-carbon steels. The main purpose is the identification of the transport mechanism of nitrogen and carbon atoms movement from the urea into treated low-carbon steel. The effect of changes in the composition of the electrolyte on treatment temperature and the structure of the modified layer was also evaluated. Urea decomposition to ammonia and carbon monoxide was confirmed. Electrolyte alkalization during treatment was found due to the action of the urea decomposition products. A hypothesis is proposed to explain the observed rise of the electrolyte surface tension near the vapor phase. This accounts for the observed increase in the sample temperature and in the electric current in the process of carburization. It is found that heating brings about an increase in thickness of the inner diffusion layer, but the thickness of the surface nitrocarburized layer remains almost constant.