Temperature and strain rate effects in cold spray investigated by smoothed particle hydrodynamics

Cold spray is a manufacturing process that has proved to be a valuable technique for producing high strength metallic coatings. It has been extensively studied in recent years, both experimentally and computationally. Among the various modelling investigations in the literature, a large number have considered the problem of a single particle impacting a substrate by means of a continuum technique, most commonly the finite element method. These models that have been used previously are generally based on two inadequate assumptions, namely 1) both particle and substrate are assumed to initially be at room temperature, and 2) the experimentally observed increase in strain rate sensitivity of the flow stress at high strain rates is ignored. To investigate the combined effect of temperature and strain rates, a three-dimensional model of a single particle impact with a metallic substrate has been developed using smoothed particle hydrodynamics. This meshless method is ideally suited to the simulation of cold spray as very large material deformations can be readily accommodated, whereas this is often a significant difficulty in mesh based techniques. A Cu-on-Cu impact was considered and quantitative comparisons with experimental cross-sections were conducted. It was found that predictions within 5% of the experimental data could be achieved only when both the softening effect due to the initial thermal field and the hardening effect due to the very high strain rates were included in the model. In contrast ignoring these effects led to results that had as much as 50% variation compared to experiments. The model described in this paper is a robust tool that will enable quantitative predictions of cold spray impacts and help further optimise the process.