Microstructure and bonding mechanisms in cold spray coatings

Cold spray additive manufacturing is a solid state deposition process with applications in surface coatings, manufacture of near net shape parts and component repairs. The technology can be used to spray a wide range of metallic powders onto varying substrates to produce the desired properties for application. This is a review of the progress in cold spray technology with particular interest in the bonding behaviour and deformation microstructure. Comparisons between cold spray and other thermal spray technologies such as plasma, wire arc, flame and high velocity oxyfuel spraying are discussed. The key advantage of cold spray over thermal spray is the reduced heat input and absence of melting. This drastically changes the mechanisms in which coatings are formed and bonded to the substrate, thus material properties and particle velocity have a large influence on the mechanical and microstructural properties of the coating. Fundamental understanding of the cold spray process is the key to its rapid uptake into the industry. This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.