Gas Atomization of Ag-28 wt.%Cu Alloy: Numerical Simulations and Experimental Insights into Droplet Breakup and Solidification

A three-dimensional computational fluid dynamics (CFD) model was developed to investigate the droplet breakup mechanisms during the initial stage of gas atomization of Ag–28 wt.%Cu alloy. The model integrates the Volume of Fluid method, Shear Stress Transport k-ω turbulence model, Discrete Phase Model, and Taylor Analogy Breakup model. Five distinct atomization stages were identified: ( i ) stable jet formation, ( ii ) flask-like deformation by gravity, ( iii ) necking and detachment from aerodynamic shear, (iv) fragmentation under high-velocity gas flow, and ( v ) establishment of dynamic equilibrium. Three primary droplet morphologies—elongated (fibrous), spherical, and ligamentous—were observed, along with two secondary breakup mechanisms: coalescence-dissociation and direct fragmentation. Experimental results showed a strong correlation between particle size and solidification behavior. Larger particles (140–180 mesh, ~80–109 μm) underwent surface nucleation, forming mixed divorced and coupled eutectics with pronounced Cu segregation. Smaller particles (250–300 mesh, ~50–61 μm) solidified via homogeneous nucleation, yielding uniform, refined lamellar eutectics. To further analyze solidification behavior, a two-dimensional solidification model was employed using initial conditions from CFD simulations. The results indicated that 50 μm droplets solidified at ~1.25 × 10 4 K/s, significantly faster than 90 μm droplets at ~8.50 × 10 3 K/s, highlighting the critical influence of particle size on solidification kinetics. Overall, this study provides a comprehensive understanding of the breakup and solidification processes in gas atomization of Ag–28 wt.%Cu alloy, offering valuable guidance for optimizing powder production in additive manufacturing and powder metallurgy.