Microstructure and oxidation behaviour of Mo-Si-B-Hf alloys at 800 °C and 1100 °C

The influences of the microstructure evolution and oxidation behaviour of Hf-modified Mo-12Si-12B alloys were systematically studied at 800 degrees C and 1100 degrees C. Vickers hardness tests show that the Hf addition increases the hardness of Mo-Si-B-Hf alloys. The oxidation experiments were conducted at 800 degrees C and 1100 degrees C for 12 h; the detailed analysis revealed that the formation of HfSiO4 in Mo-12Si-12B-10Hf alloy can effectively decrease the content of oxygen and make the surface of the oxide layer more complete at 800 degrees C. At 1100 degrees C, the distinct difference in the expansion coefficient among the oxide films results in the formation of cracks and holes in Mo-12Si-12B-10Hf alloy, so the Mo-12Si-12B-10Hf alloy shows poor oxidation resistance.