Hardening the surface of metals with WC_1-x coatings deposited by high-speed plasma spraying

The deposition of protective hardening coatings allows increasing the lifetime of important technical materials and pure metals. This work shows the possibility of depositing protective coatings based on cubic tungsten carbide (WC_1-x) on metal substrates using a high-speed (~1 km/s) plasma jet generated by a coaxial magneto-plasma accelerator. In a plasma spraying process, the necessary conditions (high sputtering and crystallization rates) are created for synthesizing the high-temperature WC_1-x phase and stabilizing it in the coating structure. The formation of WC_1-x phase was confirmed by X-ray diffraction and energy dispersive X-ray spectroscopy. The substrate parameters such as linear dimensions and heat dissipation rate were found to directly affect the phase composition (WC_1-x yield) and the structure of the deposited coating. The coatings with a higher WC_1-x content are characterized by an increased hardness. The firstly made direct measurements of a Berkovich hardness (H = 33.0 ± 0.9 GPa) and Young's modulus (E = 401 ± 14 GPa) for bulk WC_1-x grains, exceeding several micrometers in size, confirmed the suggestion about higher mechanical properties of the metastable WC_1-x phase in comparison with hexagonal tungsten carbides WC and W₂C.