Experimental and numerical investigations of pore formation mechanisms in cold spray

Cold spray (CS) has become an appealing technique for both printing and repairing components. Understanding the formation of a powder track along with the deposition porosity is crucial for producing high-quality structures by CS, unfortunately, very limited resources have been addressed to this direction, especially for the pore formation process. We address this gap by conducting experiments to measure particle properties, print and cut tracks, capture cross-section views, and calculate the deposition porosity. To overcome experimental limitations in observing the coating process, we develop and perform high-fidelity process simulations at the powder-scale using a massively parallel smoothed particle hydrodynamics (SPH) method that incorporates over 10 million discretization points to simulate around 200,000 powder particles for the first time. The high-fidelity SPH simulations of CS exhibit excellent agreement with the experimentally measured data in capturing track profiles, surface roughness and deposition porosity, outperforming the numerical results by current part-scale simulation tools. The present work’s key novelties lie in integrating direct powder measurement data into a large-scale CS process simulation, achieving unprecedented computational performance via high accuracy SPH version and massive MPI parallelization, and explaining the mechanisms governing the formation of pores. Three distinct types of pores with varying sizes are characterized, which are attributed to the spatial distribution intensity of powders, differences in powder size, and the phenomena of slipping and rebounding. Through control of feed rate, nozzle speed, feedstock quality, and distribution intensity, the porosity of the deposited track could be significantly reduced.