Effect of ZrO 2 (Y 2 O 3 ) content on mechanical properties of Mo-12Si-8.5B-ZrO 2 (Y 2 O 3 ) composites with bimodal grain-size distribution

Multiphase Mo-12Si-8.5B alloy is a promising high-temperature structural material. In order to further simultaneously improve the strength and toughness of the Mo-12Si-8.5B alloy, the method of strengthening and toughening the bimodal grain size Mo-12Si-8.5B alloy with adding nano-ZrO2 (Y2O3) particles was put out. Nanometer Mo-ZrO2 (Y2O3) composite powders were successfully prepared by sol-gel and high-temperature hydrogen reduction method, and a series of Mo-12Si-8.5B-ZrO2 (Y2O3) composites with a bimodal grain size distribution were fabricated via spark plasma sintering (SPS) using nanometer Mo-ZrO2 (Y2O3) and micrometer Mo powders as raw materials. The results show that the particle size of Mo powders and the relative density of the sintered body decrease with the increase of the ZrO2 (Y2O3) content. When the ZrO2 (Y2O3) content is less than 2.5wt%, the relative density is above 98.1%. As the content of ZrO2 (Y2O3) are 1.5wt% and 2.5wt%, the composites exhibit the high hardness (9.76-9.98 GPa), flexural strength (672-678 MPa) and fracture toughness (12.68-12.82 MPa·m1/2). Grain refinement of the Mo, grain boundary strengthening of the nanometer/micrometer Mo grains and the second-phase strengthening of the nano-ZrO2(Y2O3) particles attribute to the increase of the hardness and flexural strength. The coarse grain Mo and nanometer ZrO2 (Y2O3) in the composites contribute to the improvement of the fracture toughness. The toughening mechanisms of the Mo-12Si-8.5B-ZrO2 (Y2O3) composites are crack deflection and crack bridging.