Correlation between particle size, secondary dendrite arm spacing, and local cooling rate in gas-atomized stainless steel powders for additive manufacturing

Additive manufacturing (AM) demands metallic powders with controlled microstructure and morphology to ensure high-performance components, especially in processes like Laser Powder Bed Fusion (PBF-LB). Gas atomization techniques such as Vacuum Inert Gas Atomization (VIGA) and Electrode Inert Gas Atomization (EIGA) are widely employed for producing stainless steel powders tailored for AM applications. In this study, the solidification behavior of such powders is investigated by analyzing the secondary dendrite arm spacing (SDAS) as a function of particle size (15–170 μm). SDAS is used as a microstructural indicator to estimate local cooling rates during atomization. Experimental results reveal that SDAS increases linearly for particles ≤100 μm and exponentially for larger particles, independent of steel composition, atomization gas, or method. Derived cooling rates, ranging from 10⁴ to 10⁷ K s⁻¹, closely align with predictions from dimensionless criteria, affirming the relevance of such models under rapid solidification. Conversely, regressions developed for slower cooling conditions underestimate these values, emphasizing the need for high-fidelity models in atomization contexts. Notably, fine powders (< 25 μm) showed evidence of metastable δ-ferrite formation due to ultrafast cooling, as confirmed by magnetic saturation and XRD analyses. This work strengthens the predictive control of powder solidification behavior, aiding in the design of high-performance AM components.