Microstructural evolution and oxidation resistance at 1250 °C of a slurry-sintered Si–Cr–Mo–Ti multicomponent silicide coating on a high-Al Nb–Si-based alloy

A Si–Cr–Mo–Ti coating was fabricated on a Nb–22Ti–15Si–3Cr–10Al–0.3Y (at.%) substrate by slurry sintering, and its initial microstructural characteristics and oxidation behavior at 1250 °C were systematically investigated. The results show that the as-prepared coating is relatively dense and exhibits a distinct multilayered structure, with the major coating region mainly consisting of multicomponent silicides such as MSi₂ and M₅Si₃ (M = Nb, Ti, and Cr). After oxidation at 1250 °C for 100 h, the coated specimen showed a mass gain of only 1.88 mg/cm², which was 98.78% lower than that of the uncoated substrate, demonstrating that the Si–Cr–Mo–Ti multicomponent silicide coating markedly enhances the high-temperature oxidation resistance of the investigated Nb–22Ti–15Si–3Cr–10Al–0.3Y alloy. During oxidation, Al in the substrate preferentially diffused outward through substrate/coating interdiffusion and, together with Si from the coating, contributed to the formation of Al–Si–O complex oxides. Subsequently, Cr, Ti, and Y progressively participated in the evolution of the oxide scale, ultimately leading to the formation of a multicomponent oxide scale with SiO₂ as the continuous phase. This oxide scale effectively suppressed inward oxygen diffusion and mitigated severe oxidation of the substrate. These results suggest that the outward diffusion of substrate-derived Al and its incorporation into the SiO₂-based scale contribute to the formation of a protective multicomponent oxide scale, providing an effective coating strategy for improving the oxidation resistance of Nb–Si–based alloys.