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

Abstract

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 α-Mo + Mo3Si + Mo5SiB2 + Mo2C + TiC; in 15TiC alloy α-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 m1/2, 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 °C, the serious oxidation occurs for all TiC-added alloys except for 15TiC alloy at 1200 °C because the oxidation sequence changes to TiC → Mo5SiB2 → Mo3Si → α-Mo. The anomalous phenomenon for 15TiC alloy at 1200 °C could be attributed to the rapid formation and cover of protective SiO2–TiO2 layer on alloy surface after the transient MoO3 volatilization.