Oxidation Behaviors of Si/Al Pack Cementation Coated Mo–3Si–1B Alloys at Various Temperatures

Abstract

In this study, we tried to improve the oxidation resistance of Mo–3Si–1B (wt%) alloy at intermediate (800 °C) and high temperature (1300 °C) after applying Si/Al pack cementation coatings. In addition, we examined structural changes and phase change in the intermediate and high temperature oxidizing atmospheres to observe oxidation behaviors. The diffusion pack coatings were carried out with an NH4F activator and both Si and Al powder mixtures. Mo–Si–B alloys were subjected to diffusion coatings of Si/Al powders at various temperatures in various time conditions at a temperature of 1100 °C. When the pack coatings were carried out for 48 h, Mo(Si, Al)2 and Mo3Al8 layers together with a T2 (Mo5SiB2) layer were successfully synthesized on the substrate. After oxidation tests, an Al2O3 protective oxide layer was formed by the diffusion of Al in an ambient atmosphere. The Si/Al pack cementation coatings provided excellent oxidation resistance through the formation of an Al2O3 oxide layer. The enhanced oxidation behaviors are discussed in terms of microstructural evolution at high temperatures.