Oxidation Behavior of MoSi2-Coated TZM Alloys during Isothermal Exposure at High Temperatures

Coating properties and oxidation behaviors of Si pack cementation-coated TZM (Mo-0.5Ti-0.1Zr-0.02C) alloys were investigated in order to understand the stability of the coating layer at high temperatures up to 1350 degrees C in an ambient atmosphere. After the pack cementation coatings, MoSi2 and Mo5Si3 layers were formed. When MoSi2-coated TZM alloys were oxidized in air at high temperatures, the Si in the outer MoSi2 layer diffused and formed SiO2. Also, due to the diffusion of Si, the MoSi2 layer was transformed into a columnar shaped Mo5Si3 phase. During isothermal oxidation, the Mo5Si3 phase was formed both within the coated MoSi2 layer and between the MoSi2 and the substrate. The coating properties and the oxidation behavior of the Si pack-coated TZM alloys were discussed along with the identification of growth kinetics.