Numerical Modelling of Cold Spray: Predicting Porosity and Residual Stress

Cold spray is an innovative coating technology for depositing materials in the solid state. In the cold spray (CS) process, deposits are produced by projecting powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate; it is this feature which makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites.

During processing, the particles undergo severe plastic deformation creating a mechanical bond with the substrate. The integrity and performance of the CS coating depends on many factors including powder characteristics, geometric parameters, and processing parameters. While cold spray technology has matured during the last decade, the complex effects of deposition parameters on porosity, residual stress and microstructure is unclear. Having a reliable simulation capability to assist with this understanding and optimisation of CS processing can add value by reducing the overall cost and timescale.

However, simulation of cold spray is challenging due to the highly non-linear and dynamic features of the process. In particular, an accurate model must account for excessive deformation of material particles, non-linear mechanical contact between particle-particle and particle-substrate interfaces, heat exchange between material regions, non-linear elastic-plastic (and rate- and temperature-dependent) responses, and heat generation due to plasticity. Nevertheless, an accurate and efficient numerical model has the potential to enable a better fundamental understanding of process parameters and powder particle size distribution on residual stress, porosity and mechanical performance.

In this presentation, a novel modelling technique (called Coupled Eulerian Lagrangian) is used to simulate the cold spray process. Validation of the model is provided through several examples of experimental measurements that demonstrate the accuracy of the technique and its ability to provide an improved fundamental understanding of the process.