Effect of Substrate Micro-arc Oxidation Pretreatment on Microstructure and High-Temperature Oxidation Resistance of Si-Cr-Ti-Zr Coating on Ta12W Alloy

Abstract:

To mitigate the impact of interdiffusion reactions between the silicide slurry and Ta12W alloy substrate during vacuum sintering process on the oxidation resistance of the silicide coating, a micro-arc oxidation pretreatment was employed to construct a Ta₂O₅ ceramic layer on the Ta12W alloy surface. Subsequently, a slurry spraying-vacuum sintering method was used to prepare a Si-Cr-Ti-Zr coating on the pretreated substrate. Comparative studies were conducted on the microstructure, phase composition, and isothermal oxidation resistance (at 1600 ℃) of the as-prepared coatings with and without the micro-arc oxidation ceramic layer. The results show that the Ta₂O₅ layer prepared at 400 V is more continuous and has smaller pores than that prepared at 350 V. After micro-arc oxidation pretreatment, the Si-Cr-Ti-Zr coating on Ta12W alloy consists of three distinct layers: an upper layer dominated by Ti₅Si₃, Ta₅Si₃, and ZrSi; a middle layer dominated by TaSi₂; a coating/substrate interfacial reaction layer dominated by Ta₅Si₃. Both the Si-Cr-Ti-Zr coatings with and without the Ta₂O₅ ceramic layer do not fail after isothermal oxidation at 1600 ℃ for 5 h. Notably, the addition of the Ta₂O₅ ceramic layer reduces the high-temperature oxidation rate of the coating.