Influence of process parameters on properties of DC arc plasma spheroidized molybdenum powder

【Objective】 With the continuous progress of aerospace, nuclear energy and other high-end strategic industries, additive manufacturing and other advanced forming technologies put forward stricter demands for the overall performance of refractory metal raw powder. High-sphericity, good-fluidity and high-apparent-density molybdenum powder is the key foundation for high-quality forming of molybdenum alloy parts. To solve the bottleneck of high-performance spherical molybdenum powder mass preparation, this work aims to adopt DC arc plasma spheroidization technology to modify commercial irregular molybdenum powder, explore the influence rules of key process parameters on powder comprehensive performance, and reveal the intrinsic spheroidization mechanism, so as to provide technical basis for industrial mass production and high-end engineering application of spherical molybdenum powder.
【Method】 Commercial irregular molybdenum powder was selected as the experimental raw material, and DC arc plasma spheroidization equipment was used for powder modification treatment. Focusing on two critical process parameters including powder feeding rate and plasma power, comparative experiments with different parameter combinations were carried out. Multiple testing devices were applied for multi-dimensional characterization: scanning electron microscope was used to observe powder microscopic morphology, X-ray diffraction was adopted to analyze phase composition changes, and special testing instruments were utilized to detect particle size distribution, powder flowability and apparent density of samples before and after spheroidization.
【Result】 DC arc plasma treatment would not change the phase structure of molybdenum powder, and the spheroidized powder still presents single body-centered cubic molybdenum phase without oxide impurities or miscellaneous phases. The optimal process parameters are determined as powder feeding rate of 80 g/min and plasma power of 45 kW. Under this condition, the powder spheroidization rate is over 98%, with smooth particle surface and no obvious agglomeration. Compared with raw powder, the particle size distribution become more uniform, the median particle size decreases from 34.47 μm to 23.56 μm. Meanwhile, the powder flowability and apparent density are greatly improved, among which the flowability is optimized to 11.6 s/50g, and the apparent density increased by 117.9%.
【Conclusion】 DC arc plasma technology is highly applicable and reliable for the spheroidization modification of molybdenum powder. The whole spheroidization process can be summarized as three stages of energy absorption, droplet formation and solidification stabilization. Excessively high plasma power will induce nanoparticle coating on powder surface, which has potential application value in functional modification. The optimized process parameters obtained in this study can effectively improve the sphericity, flowability and bulk density of molybdenum powder, which is conducive to the popularization and application of high-performance spherical molybdenum powder in advanced powder forming fields.