Influence of particle size of feedstock powder on the properties of cold-sprayed Cu coatings

In the cold spray process, particle size characteristics are very important since they directly affect the particle velocity for a given spray temperature and pressure, as well as the critical velocity (i.e., the velocity at which there is a positive deposition efficiency) of the feedstock. In the present study, powders of different sizes (“fine”, “medium” and “coarse”) are cold sprayed on Al substrates under the same temperatures and pressures, and their particle velocities are measured during spraying and compared to predictions by numerical simulation. The mechanical properties of the coatings (as-sprayed and heat-treated) are evaluated by the Shear Punch Test (SPT) and electrical resistivity using the four-point probe method. The coating cross-sections and fracture surfaces are also microstructurally characterized. It was found that decreasing the size of the feedstock powder results in increased particle velocities, and these coatings have a better response to heat treatment, which leads to superior mechanical and electrical properties. To determine the contributions of velocity and critical velocity to the annealing response, the powders were sprayed under different conditions to attain the same velocity, and then heat treated and evaluated as before. The results are reported in this work.