Oxidation Behavior of (Mo,Hf)Si₂-Al₂O₃ Coating on Mo-Based Alloy at Elevated Temperature

Abstract

To improve the oxidation resistance of Mo-based alloys, a novel (Mo,Hf)Si2-Al2O3 composite coating was fabricated on a Mo-based alloy by the method of slurry sintering. The isothermal oxidation behavior of the coating was evaluated at 1400 °C. The microstructure evolution and phase composition of the coating before and after oxidation exposure were characterized. The anti-oxidant mechanism for the good performance of the composite coating during high-temperature oxidation was discussed. The coating had a double-layer structure consisting of a MoSi2 inner layer and a (Mo,Hf)Si2-Al2O3 outer composite layer. The composite coating could offer more than 40 h of oxidation-resistant protection at 1400 °C for the Mo-based alloy, and the final weight gain rate was only 6.03 mg/cm2 after oxidation. A SiO2-based oxide scale embedded with Al2O3, HfO2, mullite, and HfSiO4 was formed on the surface of the composite coating during oxidation. The composite oxide scale exhibited high thermal stability, low oxygen permeability, and enhanced thermal mismatch between oxide and coating layers, thus improving the oxidation resistance of the coating.

Keywords

• (Mo,Hf)Si₂-Al₂O₃ composite coating
• multi-layer structure
• oxidation behavior
• phase transformation
• microstructure evolution