Influence of TiC contents on the microstructure, mechanical properties, and oxidation behavior of Mo-10Si-8B alloys

The microstructure, mechanical properties, and oxidation behavior of Mo-10Si-8B-xTiC (at.%, x = 0,5,10,15) alloys fabricated via oscillatory pressure sintering are studied. The phase constitution of three TiC-added alloys is alpha-Mo + Mo3Si + Mo5SiB2 + Mo2C + TiC; in 15TiC alloy alpha-Mo phase no longer maintains its contiguity as in the other three alloys. With further TiC addition, the microhardness improves by 60-90 % (up to 1500 HV), Young's elastic modulus increases from 328 to 368 GPa, and the fracture toughness decreases from 14.23 to 10.8 MPa m(1/2), accounting for the less-ductile phase and newly introduced brittle phases. Thermogravimetric analysis indicates that the addition of TiC reduces the oxidation resistance. For isothermal oxidation at 800, 1000, and 1200 degrees C, the serious oxidation occurs for all TiC-added alloys except for 15TiC alloy at 1200 degrees C because the oxidation sequence changes to TiC -> Mo5SiB2 -> Mo3Si -> alpha-Mo. The anomalous phenomenon for 15TiC alloy at 1200 degrees C could be attributed to the rapid formation and cover of protective SiO2-TiO2 layer on alloy surface after the transient MoO3 volatilization.