Microstructure and mechanical properties of Mo-12Si-8.5B alloy reinforced by layered Mo₂TiAlC₂ MAX phase

Mo-12Si-8.5B alloy with layered Mo₂TiAlC₂ (a new MAX phase) additions, in order to improve its fracture toughness, were prepared by hot pressing. The composition analysis combined with microstructure features revealed that after hot pressing sintering, the Mo₂TiAlC₂ does not decompose but still maintains the layered structure and exhibits a good interface bonding with the matrix. The grain size of Mo-12Si-8.5B alloys was apparently refined by Mo₂TiAlC₂. The mechanical properties suggested that the Mo₂TiAlC₂ phase affects the hardness of Mo-12Si-8.5B alloy mainly through grain refinement. As the amount of Mo₂TiAlC₂ increased, the compressive strength and flexure strength of alloys improved nonlinearly which is caused by the relatively low strength of Mo₂TiAlC₂ and stress release due to its basal plane sliding, the enhanced strength was attributed to the particle strengthening and fine grain strengthening. The Mo₂TiAlC₂ phase exhibits a remarkably toughening effect on Mo-12Si-8.5B alloy. The fracture toughness of Mo-12Si-8.5B-2%Mo₂TiAlC₂ alloy increased by about 52% compared with the Mo₂TiAlC₂ free alloy. Except for the fine-grain toughening caused by Mo₂TiAlC₂ particles, the improvement of fracture toughness of Mo-12Si-8.5B alloy by Mo₂TiAlC₂ is mainly caused by the crack deflection, the steps formed by Mo₂TiAlC₂ fracture and basal plane (0001) sliding of Mo₂TiAlC₂.