Synthesis of a novel MoSS+Mo5SiB2+Mo5Si3 based Mo-Si-B alloy and its enhanced fracture toughness

Mo-Si-B based alloys are promising ultrahigh-temperature structural materials for turbine blades. Different from traditional Mo-SS (Mo solid solution)+Mo5SiB2+Mo3Si based alloy, present paper focuses on a novel non equilibrium Mo-SS + Mo5SiB2+Mo5Si3 based alloy, which shows more potential for excellent comprehensive performance. This alloy was synthesized by SPS (spark plasma sintering) technique using pure Mo and Mo5SiB2+Mo5Si3 powders as raw materials. SEM, EDS, XRD, EPMA, single-edge notched bending and nanoidentation tests were used to reveal the formation mechanism of this alloy and evaluate its fracture toughness. The results showed that this Mo-SS + Mo5SiB2+Mo5Si3 based alloy was composed of Mo-SS, Mo5SiB2, Mo5Si3 and a little Mo3Si. Mo5SiB2+Mo3Si halos were found around the original Mo5SiB2+Mo5Si3 particles as a result of inter-diffusion between Mo and Mo5SiB2+Mo5Si3 during sintering processes. Compared with traditional cast or reaction sintered Mo-SS + Mo5SiB2+Mo3Si based alloy with the same composition, this Mo-SS + Mo5SiB2+Mo5Si3 based alloy showed superior fracture toughness benefiting from its higher Mo-SS content, larger coarseness of Mo-SS and lower Si concentration in Mo-SS.