Abstract
Cooling rate of metal/alloy droplet is the core factor that influences formation of amorphous powder. The close-coupled gas atomization becomes a feasible way to prepare amorphous powder since it can get high cooling rate of atomized droplets. Therefore, a numerical simulation method for calculating the cooling process of Al droplets in atomizing gas was set up to disclose the basic cooling law of atomized droplets in powder preparation based on close-coupled gas atomization as well as the major influencing factors. Numerical simulation on relevant experiments was carried out. The numerical simulation results of droplet cooling rate are in high accordance with experimental results. On this basis, influences of several key parameters (e.g. droplet diameter (d), relative gas velocity (v) and type of atomizing gases) on droplet cooling rate were analyzed. According to numerical simulation results, nitrogen (N2) was used as the atomizing gas, and v =200 m/s, the cooling rate of droplets with diameters of 15 μm, 25 μm, 50 μm, 100 μm and 150 μm in gas flow field is 104-106K/s and the cooling rate increases by 85.98 %, 192.47 %, 198.48 % and 124.63 % with the reduction of droplet diameter, indicating a significant growth of cooling rate of droplets. Given d =100 μm and N2 as the atomizing gas, cooling rate of droplets in an gas flow field values 104-105K/s under different gas velocities of v =50 m/s, 100 m/s, 150 m/s, 200 m/s and 300 m/s, and with the increase of relative gas velocity, cooling rates are increased by 34.01 %, 19.86 %, 14.12 % and 21.04 %, indicating the limited growth of cooling rate of droplets. When d =100 μm and v =100 m/s, the cooling rates of droplets in the gas flow fields range within 104-105K/s with changes of atomizing gas among argon (Ar), Air, N2 and helium (He). Moreover, the cooling rates are increased by 35.34 %, 7.93 % and 129.15 % with the increase of thermal conductivity of atomizing gas, indicating an obvious growth of cooling rate of droplets. This study can provide references for studying the formation of amorphous powder through cooling of metal/alloy droplets.
Published Version
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