Oxidation behaviors of electrodeposited MoSi2 coating in a wide temperature range from 773 K to 1673 K

Abstract

In this study, a MoSi2 coating was prepared on the surface of a molybdenum (Mo) substrate using the molten salt electrodeposition method, and the oxidation behavior of the coating over a wide temperature range from 773 K to 1673 K was studied in detail. The phase composition, surface and cross-sectional morphologies of the MoSi2 coatings after oxidation at various temperatures were characterized, and the evolution of the phase and microstructure were analyzed to elucidate the oxidation mechanism. The experimental results showed that the MoSi2 coating exhibited excellent oxidation resistance at lower temperatures (773 K) and did not experience the pesting phenomenon. When exposed to medium and high temperatures, a continuous and dense SiO2 layer was formed on the surface of the MoSi2 coating, which effectively prevented further oxidation inside the coating, thereby protecting the Mo substrate. Meanwhile, at higher temperatures, especially at 1473 K and 1673 K, the solid-phase diffusion of Si towards the substrate gradually transformed the MoSi2 into Mo5Si3 with a lower Si content. Notably, the thickness of the Mo5Si3 layer that was distributed between the original MoSi2 coating and the Mo substrate increased with the oxidation time and temperature. At 1673 K, a Mo3Si layer with a low Si content was formed beneath the Mo5Si3 layer. Thus, the diffusion of Si was an important factor restricting the service life of MoSi2 coating.