High-temperature compression behavior of bimodal α-Mo structured Mo-Si-B alloy

Abstract

Previous study indicated developing a bimodal (micron/submicron) structured α-Mo matrix could improve fracture toughness of the fine-grained Mo-12Si-8.5B-0.57 wt% La2O3 alloy greatly without sacrificing strength dramatically at room temperature. In this work, the effect of bimodal α-Mo structure on the compressive behavior of this alloy at 1000–1400 °C was investigated. At 1000 °C, because micron α-Mo regions weakened grain boundary strengthening effect, the compressive strength and yield strength of bimodal alloy were lower than those of fine-grained alloy. But at 1200 °C and 1400 °C, the compressive strength and yield strength of bimodal alloy were higher since the micron α-Mo regions exhibited less grain boundary sliding deformation. Especially at 1400 °C, the obvious work hardening induced by the large plastic deformation of micron α-Mo regions was an extra contribution to the strength. Additionally, the intragranular and intergranular nano-scale La2O3 particles could strengthen alloy by inhibiting dislocation slip and pinning grain boundaries. Moreover, this bimodal alloy exhibited good dynamic softening resistance at 1200–1400 °C because the micron α-Mo regions preferentially occurred plastic deformation and dynamic recrystallization, and then the occurrence of dynamic recovery and recrystallization of submicron α-Mo, Mo3Si and Mo5SiB2 regions was delayed. With increasing temperature, the occurrence of plastic deformation and dynamic recovery of submicron Mo3Si and Mo5SiB2 regions was easier, and the dynamic recovery and recrystallization of micron α-Mo regions was easier to occur compared to the submicron α-Mo regions in the bimodal alloy.