Preparation of Mo–Re powders and alloys doped with different second phases

Molybdenum rhenium (Mo–Re) composite powders and high-density Mo–Re alloys doped with different second phases (ZrO₂, ZrC, and Ti₃AlC₂) were prepared by solid-solid mixing and hydrogen pressureless sintering process. The morphology and phase composition of the composite powders, as well as the microstructure and properties of the Mo–Re alloys, were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that, the average particle size of the Mo–Re composite powders after hydrogen reduction is 640 nm with the oxygen mass fraction of only 0.012%, and the Mo and Re elements form rich Mo solid solution through solid solution formation. The average particle size of ZrO₂ and ZrC reinforced Mo–Re composite powders is 360 nm and 280 nm, respectively. After the addition of Ti₃AlC₂ particles, the large amount of free ultrafine nano powders is adsorbed around the layered structure of the Mo–Re composite powders. The average grain size of the sintered pure Mo–Re alloys is 35.73 μm, which is obviously smaller than that of Mo–Re alloys doped with ZrO₂, ZrC, and Ti₃AlC₂ particles, which is 19.76 μm, 15.68 μm, and 29.57 μm, respectively. Fine ZrO₂ particles in the sintered alloys are dispersed in the grains, which effectively hinders the migration of Mo–Re grain boundaries, reduces the driving force of grain growth, and inhibits grain growth. ZrC particles are reacted with oxygen during high temperature sintering to generate ZrO₂ particles, which purifies grain boundaries. Ti₃AlC₂ particles are sintered in high temperature reducing atmosphere for a long time, and the topological reaction occurs, and the layered AlTi₃ and Ti₅O₉ are generated in situ to enhance the properties of alloys.