Enhanced mechanical properties and thermal stability of boron doped molybdenum alloy

Molybdenum alloys with different boron-doping contents (0.0 %, 0.5 %, 1.0 %, and 10.0 %) were fabricated using powder metallurgy. The thermal stability and mechanical properties of molybdenum alloys doped with 1.0 % boron (Mo-1.0B) were studied at various annealing temperatures at 900 °C, 1000 °C, 1100 °C, and 1200 °C. The results show that trace boron doping enhances the densification of the structure. The porosities of sintered Mo-0.5B and Mo-1.0B specimens are 2.46 % and 1.75 %, respectively. The sintered fractures of Mo-0.5B and Mo-1.0B exhibit a mixture of intergranular and transgranular characteristics, whereas the porosity of sintered Mo-10.0B specimens reaches 27.58 %. The sintered fracture morphology of Mo-10.0B exhibits brittle transgranular characteristics. As the annealing temperature increases, Mo-1.0B undergoes partial recrystallization, transitioning from fragmented strip-like grains (2.72 μm at 900 °C) to approximately equiaxed grains (7.12 μm at 1200 °C). Dislocation density and entanglement are significantly reduced. Mo-1.0B exhibits a significant improvement in plasticity after high-temperature annealing. As the annealing temperature increases, the tensile strength of Mo-1.0B decreases from 791.4 MPa to 540 MPa, while its elongation improves from 21.4 % to 66.2 %, resulting in an ultimate strength–plasticity product exceeding 23 GPa·%. By analyzing the contributions of different strengthening mechanisms in Mo-1.0B at various annealing temperatures, it is determined that at 900 °C, strengthening is primarily governed by dislocation and grain boundary strengthening, whereas at 1000 °C, 1100 °C, and 1200 °C, grain boundary and solution strengthening dominate.