Ultra-high temperature oxidation resistance of a MoSi2 composite coating with TaB2 diffusion barrier on tantalum alloy

Abstract

High-temperature elemental inter-diffusion is an important cause of failure for high-temperature antioxidant coatings on tantalum substrate, yet little research has been reported on improving this phenomenon. A new MoSi2 composite coating with TaB2 diffusion barrier was prepared on a tantalum substrate surface by three steps of embedding/slurry sintering/embedding to solve the failure of silicide coating on tantalum substrate due to elemental diffusion under a high-temperature oxidation environment. The composite silicide coating showed excellent oxidation resistance at 1700 ℃, and the protection time was more than 14 h before failure. This may be due to the prevention of diffusion of Si atoms at the initial stage by the TaB2 with many B atoms in a solid solution. The Mo5SiB2 layer with a low diffusion coefficient will be formed with the slow release of B atoms. The diffusion of Si atoms is further hindered by the formation of a new diffusion barrier between the TaB2 phase and the main layer, and thus slowing down the depletion of Si elements in the main coating. In addition, the coating successfully passed 1021 thermal cycles from room temperature to 1700 ℃, which may be because of the alleviation of thermal mismatch between the ceramic coating body and the tantalum substrate by a diffusion layer thus reducing the cracking trend of coating.