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.