In cold spray, particles undergo large plastic deformation upon impact in a rapid dynamic regime (up to 109 s-1) at solid state. The simulation of this impact is key to understanding the cold spray process. In this study, an approach based on laser shock and micro-compression testing was developed to characterize the mechanical behavior of powders and fit parameters of the Johnson-Cook material behavior model. In situ micro-compression particle testing was performed in a SEM equipped with a microindentation stage. From subsequent FEM simulations of the test, static coefficients of the Johnson-Cook model were identified. A laser shock powder launcher (LASHPOL) was also developed to accelerate single particles and measure their corresponding velocity using high-speed imaging. In addition, image analysis of the particles before and after impact, together with FEM simulation, were used to determine strain rate hardening coefficients for the Johnson-Cook model.

Cold spray is a process belonging to the thermal spray family, characterized by relatively low temperatures and high particle velocities. Upon impact, particles undergo large plastic deformation at solid state in dynamic regime up to 109 s-1. The knowledge of powder behaviour in such conditions is essential to catch key phenomena in cold spray and a necessary step for a correct process modelling. However, little is known on mechanical behaviour of feed-stock powders when submitted to cold spray conditions. In this study, an approach focused on single particles combining laser shock induced impact, namely LASHPOL (LAser SHock POwder Launcher), and quasi-static compression was therefore developed. This method was applied in this study on spherical Aluminium powders but can work with any other powder material. The mechanical behaviour of powders was characterized and used to fit the parameters of Johnson-Cook constitutive model, by means of finite element inverse method. The combination of static and dynamic tests resulted in an original characterization of powder, which revealed having a different mechanical behaviour than the corresponding bulk material.