Numerical evaluation of Ni–Al₂O₃ particles deposition during cold spraying

This study investigates the cold spray deposition behavior of a Ni–Al₂O₃ particle blend onto SS304 stainless steel substrates using a hybrid numerical approach that combines smooth particle hydrodynamics and Lagrangian finite element. The model is used to evaluate the complex thermo-mechanical interactions that occur during the impact of Ni and Al₂O₃ particles. The simulations were conducted for a varying range of particle sizes (20–60 μm), morphologies (spherical, rod-like, flake-like, dodecahedron, coated, and hollow), impact velocities (250–100 m/s), and temperatures (300–600K), including both mono- and multi-particle scenarios with concentric, eccentric or mixed impact configurations. Optimum process parameters were used to coat SS304 substrates with a Ni-Al₂O₃ composite layer. The numerical simulation results were validated against the ALE scheme and experimental works. The results indicate strong correlations between deposition parameters and particle deformation characteristics. The flattening ratio of Ni particles increases with increasing impact temperatures, velocities (≤750 m/s), and decreasing diameters, but decline at velocities >750 m/s due to significant embedment into the substrate. High-aspect-ratio particles penetrate deeper into substrate, while coated or hollow ones spread more laterally. Al₂O₃ particles undergoes partial fracturing and exhibit higher penetration depth. Concentric multi-particle impacts yielded Ni flattening ratios up to 0.78, whereas eccentric impacts ranged from 0.4 to 0.43. Experimental results demonstrated limited Al₂O₃ retention due to rebounding and wider variation in embedded particles size due to Al₂O₃ fracturing. However, its presence improved densification, work hardening, and bonding of Ni coating material, resulting in a hard and dense coating layer with better scratch resistance. These findings offer critical insights for optimizing cold spray feedstock and deposition parameters for advanced composite coatings.