Establishing Multilayered Coating On Mo-12si-8.5 B Alloy By Si Pack Cementation And Its Oxidation Behavior At 900 Degrees C-1300 Degrees C

A multilayered oxidation protection coating consisting of MoSi2 outer layer, Mo5Si3 internal layer, and Mo5SiB2/MoB inner layer was developed on the surface of Mo-12Si-8.5B 1.0 wt% ZrB2 alloy via Si pack cementation. The multilayered coating significantly enhanced the oxidation resistance of the alloy at 900 degrees C, 1100 degrees C, and 1300 degrees C in the air by exhibiting negligible oxidation recession. MoSi2 outer layer provided admirable oxidation protection for the alloy at high temperatures by forming a thin and protective SiO2-rich glass scale on its surface. This was supplemented by the Mo5Si3 internal layer and Mo5SiB2/MoB inner layer that reduced the thermal expansion mismatch between the MoSi2 outer layer and substrate, and therefore no obvious cracks were found in the MoSi2 outer layer. More importantly, the Mo5SiB2/MoB layer as an in situ barriers of Si interdiffusion ensured the stable existence of MoSi2 and Mo5Si3 layers without obvious thickness change during oxidation at 900 degrees C and 1100 degrees C. Mechanical property test indicated that the formation of the coating layers could not affect the fracture toughness of the alloy.