Preparation and high temperature oxidation behavior of silicide-based coating on molybdenum substrate by molten salt electrodeposition

摘要

Refractory metal molybdenum (Mo) and its alloys are easily oxidized in high temperature aerobic environment, resulting in a sharp decline in mechanical properties, which limits their applications. In order to improve the high temperature oxidation resistance, MoSi2 coating and Mo-Si-B composite coating were prepared on Mo substrate by molten salt electrodeposition method in this study. The phase composition, microstructure and chemical composition of the coatings were characterized by X-ray diffraction ( XRD), scanning electron microscopy ( SEM) and electron probe microanalysis (EPMA), and high temperature oxidation behavior s of the two coatings were compared. The results show ed that MoSi2 coating exhibited excellent oxidation resistance at 873 K and did not experience “pesting” phenomenon. At medium and high temperatures from 1073 K to 1673 K, a continuous and dense SiO 2 layer was formed on the surface of MoSi 2 coating, which could effectively prevent the further oxidation inside the coating. However, the internal diffusion of Si during high temperature oxidation led to the degradation of MoSi2 to Mo5Si3 and Mo3Si with lower Si contents, thus restricting the service life of MoSi 2 coating. Compared with single MoSi2 coating, Mo -Si-B composite coating exhibit ed better oxidation resistance. A continuous and dense SiO 2-B2O3 composite oxide film was formed on the surface of Mo-Si-B composite coating after oxidation at 1273 K, which could effectively block the entry of oxygen. The original boride diffusion barrier layer and Mo 5SiB2 layer formed during oxidation could hinder the internal diffusion of Si and inhibit the degradation of MoSi2.