A Laser Shock Approach to Cold Spray

Abstract

Cold spray utilizes supersonic jets of compressed gas to accelerate powder particles at high velocities. A coating is formed on a substrate by the impact and deformation of particles. Laser Shock consists in illuminating a sample with a pulsed laser to generate a high pressure shock. Cold spray and laser shock are extremely dynamic processes (time scales of about 10-100 ns). In this paper, applications of laser shock for the study of cold spray are presented. A powder particle of a given size and morphology can be laser shock accelerated at cold spray velocities, finally hitting a substrate in a controlled experimental simulation of the process. Results allow also the characterization of powder materials, through the comparison of deformed particles with numerical impact simulations and the fitting of a plasticity model. Two main advantages compared to the split-Hopkinson pressure bar emerge: deformation rates are closer to cold spray conditions and powders are directly tested, rather than macroscopic cylinders. Laser shock can also be used to measure adhesion and internal cohesion of cold-sprayed coatings (LAser Shock Adhesion Test, LASAT). Cold LAser Shock Spray (CLASS), consisting in laser shocking a coating to re-spray it, can be used to characterize property gradient within a coating or as a new spraying process. Laser shock techniques can prove beneficial for the knowledge of powder materials, which is key for advances in cold spray and other powder based processes. Moreover, the combination of the two techniques could lead to hybrid processes.