Na Wang

The molybdenum-sodium (Mo-Na) alloy was prepared by spark plasma sintering (SPS), and the effects of sintering temperature, pressure, heating rate, and holding time on the relative density of the Mo-Na alloy were investigated. The relative density and microscopic morphology of the Mo-Na alloy were characterized by means of scanning electron microscopy (SEM), density testing equipment, and other detection methods. Meanwhile, the densification process of the molybdenum-sodium alloy prepared by spark plasma sintering was analyzed. The results show that the sintering temperature and pressure are the main factors affecting the relative density of the Mo-Na alloy. The densification process of the Mo-Na alloy consists of four stages, namely, activation and purification of Mo-Na alloy powder particles; occurrence and formation of sintering necks; connection of sintering necks and liquid-phase filling diffusion; spheroidization of grains and uniform filling of the liquid phase. The maximum relative density of the as-sintered Mo-Na alloy is 98.68%, and the average grain size is less than 10 μm.

Mo-Re pre-alloyed powders are crucial raw materials in fabricating Mo-Re alloys, and their properties can significantly impact the properties of the resulting alloys. The powders are usually produced by the co-reduction of a mixture of Mo and Re oxides. However, it remains unclear if the overall characteristics of the produced Mo-Re powders rely on the different combinations of the Mo and Re oxide precursors. Therefore, in this work, a comparative study is conducted on the co-reduction processes of different Mo oxides together with NH₄ReO₄, along with its influence on the size distribution and phase composition of the resulting Mo-10Re pre-alloyed powders. The results show that MoO₃ is more promising than MoO₂ as a precursor material. The powders fabricated using MoO₃, when compared to MoO₂, have a much more uniform size distribution, with a primary particle size ranging from 0.5–4 μm. In addition, it is also beneficial to achieve atomic-scale homogeneous mixing with Mo and Re elements and the formation of a solely Mo(Re) solid solution if MoO₃ is used as a precursor oxide. In contrast, such desirable features were not identified when using the MoO₂ route. The reason for this discrepancy may relate to whether Mo-O-Re metallurgical bonding has formed during the co-reduction process.

Owing to its potential application prospect in novel accident tolerant fuel, molybdenum alloys and their welding technologies have gained great importance in recent years. The challenges of welding molybdenum alloys come from two aspects: one is related to its powder metallurgy manufacturing process, and the other is its inherent characteristics of refractory metal. The welding of powder metallurgy materials has been associated with issues such as porosity, contamination, and inclusions, at levels which tend to degrade the service performances of a welded joint. Refractory metals usually present poor weldability due to embrittlement of the fusion zone as a result of impurities segregation and the grain coarsening in the heat-affected zone. A critical review of the current state of the art of welding Mo alloys components is presented. The advantages and disadvantages of the various methods, i.e., electron-beam welding (EBW), tungsten-arc inert gas (TIG) welding, laser welding (LW), electric resistance welding (ERW), and brazing and friction welding (FW) in joining Mo and Mo alloys, are discussed with a view to imagine future directions. This review suggests that more attention should be paid to high energy density laser welding and the mechanism and technology of welding Mo alloys under hyperbaric environment.