Thermally sprayed coatings are often used to enhance the surface properties (wear resistance, corrosion resistance, etc.) of engineering components in order to extend their performance and service lifetime. Typically, the industrial components to be coated possess complex geometries and are fabricated using different materials with varied mechanical properties such as hardness, which can influence the deposited coating’s microstructure and its subsequent performance. High-velocity air fuel (HVAF) process is a relatively new thermal spray processing technique that has shown tremendous potential to deposit high performance coatings for durable industrial components. However, so far, no studies have been reported on HVAF sprayed coating formation mechanisms in relation to the spray angle, substrate properties (hardness) and coating material composition. Therefore, this work aims to plug the above knowledge gap by systematically examining the influence of spray angle, substrate properties (hardness) and coating material composition (cermet and metallic) on coating formation. For a given coating material, the effect of spray angle and substrate material on coating properties is also investigated.

In this study, one cermet (WC-Co) and one metallic (Inconel 625) feedstock were deposited onto three different substrates (Aluminum, Steel and Hastelloy) utilizing different spray angles (40º, 50º, 60º, 70º, 80º and 90º). The preliminary effort at understanding the coating evolution involved splat characteristics analysis as well as careful examination of microstructures of coatings deposited with increasing number of passes. The coating evolution was analysed utilizing SEM/EDS, image analysis (porosity, surface coverage etc.), white light interferometry and micro-indentation technique. The deposited coating’s microstructure, porosity content, hardness, and surface roughness for Inco 625 and WC-CoCr coatings were correlated to the HVAF pro-cessing conditions (spray angle, substrate hardness). Furthermore, to determine the tribological performance, coatings were subjected to dry sliding wear test and the coefficient of friction and specific wear rates were obtained.

It was shown that, substrate material affects splat formation but not the final coating properties. Spray angle, on the other hand, displayed a strong effect on coating formationand on some of the final coating properties such as micro-hardness and coating roughness.To the author’s knowledge, this study demonstrates the first approach to investigate deposition behaviour of different HVAF coating materials.