Thermal and cold spraying technology in manufacturing

Abstract

Thermal spray refers to a group of coating techniques whereby droplets of molten or partially molten materials are sprayed onto a solid substrate to develop the coating. Based on the applied heat source and the process characteristics, a large number of thermal spray techniques are commercially available, enabling a wide range of materials to be coated. In thermal spray, the basic bonding mechanism is mechanical interlocking, and the bonding between splats can be improved by increasing temperature or particle velocities during particle impact. However, for coating of metallic materials or composites, high processing temperatures can increase the amount of oxides embedded in the coating and, therefore, reducing their performance for structural application. Cold spray is another solid-state spraying process in which the coating materials are not melted in the spray gun; instead, the kinetic energy of fast-traveling solid particles is converted into heat, and there is interfacial deformation upon impact with the substrate, producing a combination of mechanical interlocking and metallurgical bonding. In the present contribution, a detailed overview of the thermal spray and cold spray techniques on coating of materials is presented. Finally, the future scope of the application of thermal spray and cold spray techniques is presented.