The conventional method for ZrC coating is based on chemical vapor deposition (CVD) , however, it is complex, expensive, time-consuming, and hazardous to the environment. An alternative blow-cost method is chemical vapor infiltration (CVI), however, it has the disadvantage of low efficiency. Both are well developed and widely used to cover the C/C composites by dense ZrC layers, but limit the shape and size of the substrate. Therefore, it is necessary to identify a suitable approach to coat on the C/C composites. Plasma spraying is one of the most promising coating methods because it is economical and can be easily applied on an industrial scale. It is also a suitable technique for depositing carbides with high melting points such as ZrC, HfC, etc. . In the VPS (vacuum plasma spray) process or in other plasma spray processes in the atmosphere, ZrC powder is oxidized to result in the formation of zirconium oxides. Therefore, VPS coatings are especially preferred because of their high purity with low porosity and high deposition rate without the formation of oxides. In VPS, the coating layer is formed by melting the constituent particles at a very high temperature and by colliding them with the base material. Therefore, the inherent properties of both components, i.e., the molten particles and base substrate, are preserved. However, as numerous parameters contribute to the formation of a high-quality coating layer, it is important to determine the optimal process parameters. Among then operational parameters, it is well known that the velocity and temperature of the plasma jet, which can be controlled mainly by the discharge current, are closely associated with the phase change, thickness, and porosity. As mentioned above, although the coating process using VPS has many advantages, few research articles have reported on UHTCs coatings prepared using the VPS technique.
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