Effect of particle size of Mo powder and Mo/B atomic ratio on microstructure and properties of Mo2FeB2-based cermets
Mo 2 FeB 2 powders with different Mo/B atomic ratios (0.9, 1.0, 1.1) were first prepared under vacuum condition using different-sized Mo powder, as well as FeB and B 4 C powders as raw materials. Based on the prepared Mo 2 FeB 2 powders, Mo 2 FeB 2 -based cermets were synthesized at different sintering temperatures. Results indicated the morphology of the hard phase was closely related to the Mo/B atomic ratio. As the Mo/B atomic ratio increased, the degree of anisotropy of the hard phase decreased significantly, and its grain morphology gradually evolved from elongated to nearly equiaxed shape. When the sintering temperature was 1200 °C, the incomplete diffusion of the liquid phase led to the occurrence of “liquid-filled lakes” in some samples, while this phenomenon became weakened after the temperature was increased. The microstructure uniformity was optimal when Mo/B = 0.9, with the hardness of 1227 HV 30 ; while the fracture toughness and transverse fracture strength were optimal when Mo/B = 1.1, reaching 23.8 MPa m 1/2 and 2125.9 MPa, respectively. Annealing twins were observed in the γ-Fe binder phase of sample D, which effectively improved the fracture toughness of the cermet by altering the crystallographic orientation of the binder phase. The cermets prepared from ultrafine Mo powders exhibited better mechanical properties due to grain refinement and low porosity.
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