Rezumat
CZU 621.785.53; 621 3.035.183
The article considers changes in the composition of aqueous electrolytes containing ammonia chloride and urea in plasma electrolytic nitrocarburizing of low-carbon steels. The main purpose is identification of the transport mechanism of nitrogen and carbon atoms movement from the urea into the treated low-carbon steel. The effect of changes in the composition of the electrolyte on the 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 of the sample temperature and of the electric current in the process of carburization. It is found that the heating brings about an increase of thickness of the inner diffusion layer, but the thickness of the surface nitrocarburized layer remains almost constant.
Keywords: plasma electrolysis, nitrocarburizing, diffusion layers, urea, microhardness.