Microstructure and improved mechanical properties of ultrafine-grainedMo-12Si-8.5B (at.%) alloys with addition of ZrB2

Multi-hierarchical Mo-12Si-8.5B-xZrB₂ (x?=?0, 0.5, 1.0, 1.5, 2.5?wt%) alloys consisting of three ultrafine-grained (UFG, 0.47–0.81?µm) phases of Mo₅SiB₂ (T2), Mo₃Si and Mo solid solution (α-Mo) were prepared by mechanical alloying following hot pressing. Microstructure observations showed that the intermetallic phases (Mo₃Si and T2) distributed dispersedly in the continuous α-Mo matrix associated with the homogeneously embedded nanoscaled particles (10–225?nm) in the grain interiors and at the grain boundaries. The Mo-12Si-8.5B-xZrB₂ alloys exhibited monotonically increasing compressive strength to 3.13?GPa with increasing content of ZrB₂, and the fracture toughness increased about 27% and reached at 11.5?MPa?m^1/2 at 1.0?wt% ZrB₂, rendering the Mo-12Si-8.5B-1.0?wt% ZrB₂ alloy possessing the best combined mechanical properties of high strength and high toughness. The underlying reason for the superior mechanical properties of the Mo-12Si-8.5B-xZrB₂ alloys is that the dispersedly distributed nanosized particles in the UFG multi-phased-matrix can not only effectively block the dislocation motion to increase the strength but also store the dislocations to increase the strain hardening ability during mechanical deformation.