Numerical and experimental investigation of close-coupled twin-nozzle gas atomization towards fine high-entropy alloy powder production

Abstract

The close-coupled nozzle is key to controlling the particle diameter and powder defects such as satellite particles during the production of metal powders via vacuum induction melting gas atomization (VIGA). However, new nozzle structures with greatly improved fine particle yields and morphologies are needed. Also, there is a limited understanding of how gas atomization refines particles and forms satellite particles. Therefore, we developed a novel close-coupled twin-nozzle and revealed the effect of different primary and secondary pressures on the gas flow field, melt atomization, and particle characteristics (particle diameter, sphericity, and satellite particles). This approach involved both numerical simulations and experiments during the production of an AlCoCrFeNi2.1 alloy. The results showed that the particle diameter and distribution width decreased under various combinations of process parameters. This was because of the combined actions of the gas recirculation zone in the air, where the vortex was close to the bottom wall of the delivery tube and a gas jet. The yield of fine particles in the ≤ 45 µm range produced by the twin-nozzle increased to 79.25% from 55.55% upon increasing the secondary pressure from 1.0 MPa to 2.0 MPa, achieving up to a 34.12% higher fine particle yield compared with the conventional single-nozzle. In addition, as the secondary pressure of the twin-nozzle was increased, the number of satellite particles decreased, which also affected the proportion of L12/B2 phase within the powder, causing the Vickers microhardness to decrease and then increase as the particle diameter increased.