Analyzing the Effects of Particle Diameter in Cold Spraying of Thermoplastic Polymers

Cold spray deposition is a process in which bonding between solid microscale particles and a substrate occurs due to high energy impact. In this process, adhesion forms between the impacted particle and the substrate within a certain multi-parameter (material, temperature, particle size, etc.)-dependent impact velocity range. The present work analyzes the effects of particle diameter (for a range of 10-60 µm) on the adhesion of thermoplastic PEEK particles on PEEK substrates using a combined numerical-analytical approach. Our findings indicate that a maximum critical velocity (i.e., impact velocity required for a successful bond formation) of ~360 m/s is required for cold spraying of 10 µm PEEK particles at room temperature. The critical velocity decreases at higher temperatures and for particle diameters in the range of 10 to 40 µm. The predicted critical velocity is shown to increase again for particles with 60 µm diameter. For PEEK particles with diameters from 10 to 60 µm, the critical velocity window is determined to be in the range of 277-360 m/s. The velocity window decreases to 208-270 m/s if the spray temperature is increased to 150°C, i.e., slightly above the nominal glass transition temperature of PEEK.