Gas atomization of Ag–28 wt.%Cu alloy: numerical simulations and experimental insights into droplet breakup and solidification

Abstract A three-dimensional computational fluid dynamics (CFDs) 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 μ m) underwent surface nucleation, forming mixed divorced and coupled eutectics with pronounced Cu segregation. Smaller particles (250–300 mesh, ∼50–61 μ m) 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 μ m droplets solidified at ∼1.25 × 10 4 K s −1 , significantly faster than 90 μ m droplets at ∼8.50 × 10 3 K s −1 , 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.