Investigation of the effects of particle temperature and spacing on multi-particle impacts in cold spray

Abstract

Cold spray deposition is a process in which micrometer sized metal particles are shot upon a surface using a high pressure and temperature gas to form a dense coating. The high strain rates and temperatures occurring in this process significantly affect the material properties of the particles such as flow stress, elastic modulus and thermal properties. A comprehensive understanding of the thermal conditions of both particle and substrate is paramount when assessing the effectiveness of particle deposition for a given input gas condition. Momentum and heat transfer between the particle and gas must be determined through a gas-particle flow model. The heat transfer between the incoming gas and the substrate must be determined as well. In addition to thermal interactions between the gas and material, localized heating occurs during particle plastic deformation. The generated heat may or may not have time to fully dissipate into the substrate before subsequent impacts occur. Therefore, the current state of an initially deposited particle must be accounted for when impacting subsequent particles. In this work, an analytical three-dimensional finite element model utilizing material damage is introduced. A series of single particle impacts followed by two simultaneous impacts are simulated systematically by using conditions common to cold spray procedures. Both aluminum and copper are used for the particles and substrate. This model is then extended to impacting 100 successive particles to form a small coating. Computational results are compared to scanning electron micrographs of coatings created through the cold spray process. In particular, particle morphology is compared for results with similar input parameters. It is found that higher input gas temperatures result in higher particle velocities and temperatures. Furthermore, particles impact with greater kinetic energy and cause more damage to the surface. Copper particles deform more than aluminum particles due to their higher density and thus higher kinetic energy. Accounting for an elevated substrate temperature results in larger crater depth and substrate deformation. As operating temperature increases, the difference in deformation with and without allowing the initial particle to cool becomes more pronounced and simulated deformed particles show similar morphology to those seen in experimental results.