Effect of stress and temperature on creep behavior of a (TiB + TiC + Y2O3)/α-Ti composite

Abstract

A (TiB + TiC + Y2O3)/α-Ti composite was prepared by induction skull melting to investigate the microstructure evolution, high temperature tensile properties and the creep behavior. The results show that the original microstructure of the composite is a basket-weave structure with a little equiaxed α phase. The UTS of the composite is 710 MPa at 650 °C and 581 MPa at 700 °C. Stress exponents of the composite are found to 4.5 at 650 °C and 3.9 at 700 °C, respectively, showing the dislocation climbing is the dominant mechanism of the creep process at both temperatures. Reinforcements including TiB, TiC and Y2O3 can effectively impede the movement of dislocations, which contributes to the improvement of creep properties. The formation of equiaxed α phase is promoted by the addition of TiB and can decrease the creep resistance to some extent. Microstructure instabilities occur during creep process, especially the precipitation of silicides, which is strongly associated with the temperature and the stress. At 650 °C, the composite has S2-type silicide with ellipsoid morphology and (Ti, Zr)x(Sn, Si)y type silicide with equiaxed morphology. At 700 °C, the composite has S1-type silicide with rod morphology. The increase of the stress will promote the growth and rearrangement of the silicides. The precipitation of silicides can be observed in the crystal defects region near the TiB and Y2O3 reinforcements. These silicides have strong pinning effect on dislocations and improve the creep resistance.