Effects of microstructure on high-temperature strength of TiC-added Mo-Si-B alloys

To evaluate the effects of microstructure on the high-temperature strength of TiC-added Mo-Si-B (MoSiBTiC) alloys, high-temperature compressive behavior was investigated for Mo-5.0Si-10.0B-7.5TiC (70Mo) and Mo-5.0Si-10.0B-10.0TiC (65Mo) (at%) alloys produced by arc-melting and tilt-casting. The cast ingots were heat-treated at 1800°C for 24 h. In the stress-strain curves, the flow stress of both the alloys reached a compressive peak stress immediately after yielding and then gradually decreased with increasing strain. The flow-stress deterioration was relatively smaller for 70Mo than for 65Mo over the test temperature range. The strain-rate sensitivity of the peak stress was very small, and slightly increased with temperature from 0.05 at 1300°C to 0.17 at 1500°C for 70Mo and from 0.08 at 1300°C to 0.19 at 1600°C for 65Mo. From microstructure observations, the followings were found: i) there was no cracking in Mo solid solution and (Mo, Ti)2C phases (suggesting good deformability) through all the test conditions, ii) at and below 1400°C, (Ti, Mo) C phase fractured in a large strain region at all the examined strain-rates, and iii) T₂ phase severely cracked even at a small strain depending on temperature and strain-rate. Such differences in the deformation properties of the constituent phases would control the high-temperature mechanical performance of the MoSiBTiC alloys.