Effect of particle size distribution width on repeatability of coating characteristics in atmospheric plasma spraying

Abstract

Atmospheric plasma spraying (APS) is a widely used thermal spraying process for producing coatings for various applications. The characteristics of the produced coatings is influenced by multiple tens of process parameters and their complex interactions. Even when the same process parameters are used, there is a considerable variability in the characteristics of the produced coatings. The poor repeatability of the coating characteristics can be attributed to process instabilities as well as to relatively large measurement uncertainties of the coating characterization methods. In this study, it was investigated how the particle size distribution (PSD) width affects the repeatability of the coating characteristics between multiple spray runs. It focused on four coating parameters: thickness, porosity, microhardness and deposition efficiency (DE). First, the measurement uncertainties of these parameters were evaluated. Then, the effect of the PSD width on the repeatability of the four coating characteristics was examined by comparing two sets of produced coatings. One set was sprayed using a powder with a wide PSD; while for the other, the powder was sieved to narrower PSD but with the same mean size. All other process parameters were the same for both sets of coatings. The results show that a narrow PSD improves both the coating characteristics while also improving the coating repeatability.