A Finite Elements Study on Porosity Creation Mechanisms in Cold Sprayed Coatings

Porosity is a crucial property in cold sprayed coatings. If it can be beneficial for certain applications, e.g. lubricated contacts in tribology, it is generally detrimental for mechanical and anti-corrosion properties and for gas tightness of the coating. It is thus important to understand what are the process variables affecting coating porosity and quantify their effects. However, at present day, the experimental observation of cold spray coating build up and porosity creation mechanisms is far from achievable. In this study, a Coupled Eulerian Lagrangian (CEL) numerical 3D finite element analysis of single and multi-particle impacts was led to understand the mechanisms involved in the creation of porosity. All simulations were carried out on Abaqus/Explicit v6.14. Single particle impact simulations addressed the influence of mesh size, particle temperature, size and speed on particle temperature and equivalent plastic deformation after impact. Jetting phenomena appeared and their relationship to the mesh size was established. Nevertheless, the porosity creation mechanisms seemed to arise within the more complex context of multiple particle interactions at impact. For this reason, multiparticle impact simulations were carried out, based on experimental powder granulometry distributions and particle in-flight velocity measurements. Porosity in these simulations was quantified by computing the successive layered convex hulls of the particle cluster after impact. Individual particles were also tracked during the simulations, in order to understand the porosity creation mechanisms. Finally, those porosity rates were compared to those experimentally measured in 2D by SEM image analysis.