Inter-splat boundary effect on cold-sprayed nickel-based alloy coatings through mechanical and corrosion performance

Cold spraying is a prominent solid-state deposition technique for depositing nickel-based alloy coatings without causing microstructural changes due to its lower operating temperatures than other thermal spray processes. However, depositing nickel-based coatings via cold spraying is more challenging than other metals due to their thermo-mechanical behavior. Thermal sensitivity (m), a constant parameter in the Johnson–Cook (JC) plasticity model, is used to estimate the flow stress of plastically deformed materials at higher strain rates. Since nickel-based alloys such as NiCr, IN625, and IN718 alloys exhibit high thermal sensitivity (m>1), their deposition becomes easier at elevated particle temperatures, particularly when air is used as a process gas instead of more expensive gases like nitrogen or helium. In this work, higher particle temperatures were achieved by increasing the stagnation temperature and the nozzle convergent length. In cold-sprayed coatings, corrosion liquids percolate through unbonded inter-splat boundaries, significantly affecting the corrosion rate. These unbonded boundaries also contribute to a reduction in the elastic modulus. Hence, this study examines the effect of particle temperature on the inter-splat bonding percentage of as-sprayed and heat-treated coatings and its impact on oxidation, corrosion resistance, and elastic modulus. The inter-splat bonding is estimated through numerical simulation using ABAQUS explicit code. The results demonstrate that increasing the particle temperature enhances the oxidation resistance for NiCr coatings. The parabolic oxidation rate is constant for coatings deposited using air as the process gas, comparable to that obtained from other thermal spray techniques (such as Arc spray and HVOF). Corrosion resistance is higher and equivalent to the bulk Inconel after the heat treatment of the coating, which is deposited at a higher stagnation temperature. The elastic modulus was estimated through numerical simulation, and nanoindentation was validated. The obtained results demonstrated that the estimated modulus is improved with inter-splat bonding percentage.