Mechanical properties of fine-grained, sintered molybdenum alloys with dispersed particles developed by mechanical alloying

In order to develop Mo alloys with improved mechanical properties of low-temperature toughness and room- and high-temperature strengths without any plastic working after consolidation, fine-grained, particle-dispersed Mo alloys were fabricated by hot isostatic pressing (HIP) or spark plasma sintering (SPS) of mechanically alloyed powders of Mo and 0.8mol% ZrC or TaC (designated as ZRC08 and TAC08). The fabricated Mo alloys were subjected to high-temperature annealing for 3.6 ks up to 2470 K, three-point impact bending tests at temperatures from 270 to 470 K at 5 m s(-1) and static tensile tests at temperatures from 300 to 1970 K at initial strain rates from 4.2 x 10(-5) to 8.3 x 10(-2) s(-1). The fabricated alloys exhibited no significant grain growth even after annealing at 2470 K for 3.6 ks due to the pinning effect of the particles against grain boundary migration. The ductile-to-brittle transition temperatures (DBTT) assessed by impact bending were lower and the tensile strengths up to 1770 K were higher for the fabricated alloys than for recrystallized pure Mo. In particular, HIPed TAC08 was superior in low-temperature toughness having the DBTT lower by 30-40 K than recrystallized Mo-La2O3 (TEM) with an elongated coarse-grained microstructure. HIP- or SPS-treated ZRC08 was superior in room- and high-temperature strengths, respectively. Furthermore, HIPed ZRC08 showed a large elongation of 551% at 1770 K. These excellent mechanical properties of the fabricated Mo alloys were obtained for the first time in the as-consolidated state without subsequent plastic working, and are attributable to fine-grained microstructure and grain-boundary strengthening by the fine particles.