PLASMA SPRAYING — A Versatile Coating Technique

Abstract

Plasma spray technology, with its great number of coating-substrate combinations, satisfies the demand of new materials needed to work in severe environments. After a general introduction on thermal spraying processes, the fundamentals specific to plasma spray are described. Depending on the pressure level, the chemical composition of the environment and the type of electrical arc, the plasma spray process is divided into the following types: atmosphere (APS), vacuum (VPS), inert gas (IPS), controlled atmosphere (CAPS), under water (UPS) and inductive coupled (ICPS) plasma spray. Their operating principles and their fields of application are reported. The components of the plasma torch, particularly their shapes influence, the shape at the produced arc and its capability to accelerate particles. The composition of the plasmogenic gases, their behaviour under discharge and the effects on melting and acceleration of powder particles are briefly discussed. The deposition parameters determine the microstructure of the coating: unmelted particles, poor adherence and coherence, cracks, open and closed porosity, are intrinsic to the coating procedure. Surface pretreatments, degreasing, sand blasting, sputter-cleaning and preheating, increase coating adherence. Post-coating treatments such as thermal annealing, sealing (e.g. liquid-metal, organic compound infiltration), hot isostatic pressing and electron beam or laser surface melting are used to increase the adhesion and reduce the porosity. Coating materials and coating evaluations are also considered. A broad list of industrial applications typical of plasma spray together with a potential list of further process and material developments are outlined.KeywordsThermal SprayingPlasma SprayThermal Barrier CoatingPlasma TorchSpray DistanceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.