Optimization of Molybdenum Powder Milling Parameters

Dycková L., Komarov P., Remešová M., Dycka M., Dvorák K., Menelaou M., Celko L. Optimization of molybdenum powder milling parameters. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2018, vol. 20, no. 3, pp. 109–122. doi: 10.17212/1994-6309-2018-20.3-109-122. (In Russian).



Introduction. The refractory materials are of interest for high temperature applications in aerospace, nuclear and military industries, since they possess high melting temperature (> 2000 °C). Molybdenum (Mo) is among these materials of high interest due to its excellent properties such as good thermal conductivity, high strength and toughness. The production of molybdenum is difficult due to its high melting point and the temperature of the ductile-brittle transition, therefore, in the production of this metal, powder metallurgy methods are mainly used. To implement these methods, it is necessary to have high-quality molybdenum powders, in particular, a high degree of purity and homogeneity of particle size distribution. One of the powder processing methods that is used to produce nano- and microsize powders, is the high energy kinetic milling. This cost-effective method is based on the friction and the high-energy collisions between the balls and the powder particles. And therefore, the purpose of the current work is to optimize the parameters of high energy kinetic milling for molybdenum powder. Optimization of processing parameters has a significant influence on the acceleration of the process of product formation, on subsequent sintering and achievement of the best mechanical properties of the final product. Optimization of milling parameters of Mo powder was achieved under different milling parameters including among others the rotation speed, the ball to powder weight ratio (BPR) and the milling time. Initially, the rotational speed was determined; it varied from 600 to 1200 rpm (where rpm are revolutions per minute). After this determination, milling parameters such as the milling time and the BPR were varied. The milling time ranged from 2 to 60 min and the BPR varied from 100:3 to 200:3. After that, influence of variable parameters on morphology and powder particles size distribution was investigated. The initial powder used in these experiments was Mo powder (particle size ~100 µm). The methods of investigation. Scanning electron microscopy and laser diffraction methods were used to estimate the particle size distribution. Results and Discussion. Particle size was decreased from 100 to 4 µm with increasing grinding time from 2 to 60 min. However, in each batch, a number of cold-welded particles measuring 200-400 μm was detected. These cold-welded particles were about 200-400 µm in size. As the result, the optimal milling parameters were: rotation speed of 900 rpm, BPR (200:3) and milling time of 60 minutes.