n this study, the critical, maximum and optimum velocity of a single cold sprayed (CS) particle is estimated using the smoothed particle hydrodynamics (SPH) method by evaluating the impact shape coefficient of restitution, as well as the rebound and deposit energy ratio. The contact surfaces of the particle and the substrate are modelled as intersurface forces using the DugdaleBarenblatt cohesive zone model. The application of SPH allows the simulation of the CS process without the use of mesh, thereby avoiding the disadvantages of the traditional numerical method in handling large deformations and tracing moving interfaces. The impact of CS particles is simulated using various powder and substrate materials. The influence of the materials on the optimum velocity and the coating quality is discussed. The reliability of the model is verified with CS experiments.
The surface of most metals is covered with thin native oxide films. It has generally been believed that to achieve bonding, the oxide covering the surface of metallic particles or metal substrates must be broken and removed by adiabatic shear instability (ASI), whether induced at the particle–substrate interface or at the particle–particle interface. The aim of the present research is to investigate the correlation between the remaining oxide amorphous layer and substrate-deformation with the adhesion strength of cold-sprayed TiO2 coatings towards the bonding mechanism involved. Relevant experiments were executed using stainless steel (SUS 304), subjected to various annealing temperatures and cold-sprayed with TiO2 powder. The results indicate an increasing trend of coating adhesion strength with increasing annealed substrate temperature. The influence of substrate plastic deformation and atomic intermixing at the remaining amorphous oxide layer is discussed as the factors contributing to the increasing adhesion strength of cold-sprayed TiO2 coatings.
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