Preparation and oxidation resistance at 1400 ℃ of (WMoCrTa)Si₂ high entropy silicide coatings on tantalum surface

The (WMoCrTa)Si₂ coatings were prepared by two-step process, involving slurry sintering followed by halide-activated pack cementation, with the silicide powders as the raw materials. The oxidation resistance at 1400 ℃ of the coatings on tantalum surface was investigated. In the results, the four-layer structure is present in the final coatings: the porous high-entropy silicide layers, the chromium-tantalum silicide layers, the TaSi₂ interlayers, and the innermost Ta₅Si₃ layers with the overall thickness of 186 μm. Under the static air oxidation at 1400 ℃, the coatings can protect the tantalum substrate for over 14 h, with the mass gain curves showing a three-stage behavior as slow growth, rapid gain, and gradual stabilization. In the initial stage, the dense SiO₂ scale is formed rapidly, Cr is preferentially oxidized to Cr₂O₃, which further reacts with Ta₂O₅ to form CrTaO₄, and the synergy enhances the stability and oxygen-blocking ability of the coatings. In the later stages of oxidation, the protective performance of the coatings finally deteriorates due to the SiO₂ spallation and the internal pore proliferation.