Thermal factor effect on phase formation, structure, substructure features, and stress state in ion-plasma nano-crystalline condensates of quasi-binary WC-TiC carbide

Abstract

Using high-angle X-ray diffraction and X-ray fluorescence spectral analysis, the effects of the sputtered material composition and deposition temperature on the phase and elemental composition, structure, substructure features, and stress state in the ion-plasma quasi-binary WC—TiC coatings. The increase in relative titanium atomic content has been established to result in increasing thermal stability of the single-phase state of the ((W,Ti)C solid solution) condensate up to the temperatures exceeding 950°C at the atomic ratio Ti/W≥0.35. At atomic ratios Ti/W≤0.25 and deposition temperatures exceeding 800°C, a multi-phase condensate is formed containing the lower carbide W₂C, the essentially pure α—W phase with the BCC lattice, along with WC and TiC phases formed through (W,Ti)C solid solution decomposition. In the range of the single-phase solid solution formation, the crystallite sizes rise and the micro-strain extent drops as the condensation temperature rises. The transition into the temperature range of the multi-phase coating is followed by the micro-strain increase and the average crystallite size diminution. The carbon content in the (W,Ti)C solid solution has been estimated and the critical deposition temperature established to be 700°C; at higher temperatures, intensive vacancy formation occurs in carbon sublattice of the carbide. Physical reasons for the effects observed and the regularities revealed have been discussed.