Cermet Plasma TiC–Cr3C2–NiCr–Mo–C Coatings

Abstract

To determine the possibility of maintaining the maximum possible carbon content in TiC carbide, a powder additionally doped with chromium carbide, molybdenum, and carbon was produced by plasma spraying of the cermets of the TiC–NiCr system. To reduce the effect of gases from the air atmosphere, plasma spraying was carried out using a standard plasmatron, supplemented with a special nozzle. The analysis of the oxygen, nitrogen, and carbon content in the powder manufacturing stages and in the coatings was carried out. The content of O and N is reduced in the sintering step for spraying a powder with respect to the content in the starting components, but increases again during spraying. In the coating, the quantitative distribution of the carbide phases was determined by their size. A change in the phase composition and dimensions of the crystal lattices of the phases in the powder for deposition and coatings was determined. The share of the main hardening TiC phase in the coating decreased by 9.7% with respect to the initial mixture, but taking into account the newly formed carbide phases with the participation of chromium and molybdenum, the proportion of all the carbide phases in the coating increased by 12.7%. The microhardness of the plasma coating at loads of 200 and 20 g on the indenter was 14.9 and 28.7 GPa, respectively. The reasons for the decrease in the actual microhardness of the cermet coating in relation to the theoretically possible one based on the volume fraction of the strengthening phases are analyzed.