Abstract

Thermal spray coating methods such as Atmospheric Plasma Spray (APS), High-Velocity Oxygen Fuel (HVOF), and newly developed High-Velocity Air Fuel (HVAF) offer one of the best technique to effectively protect new parts from high temperature, wear, corrosion, and residual stresses as well as produce hard and dense coatings which in turn helps in the improvement of the lifespan of the material. These techniques provide coatings that enable the enhancement and prolongment of component life and the reduction of component cost due to the improvement in the functionality of a low-cost material. There is also an opportunity to revamp worn parts to their original dimensions, without the need to replace the entire component. However, traditional thermal spray techniques tend to produce coatings with high oxide content and porosity resulting in undesirable coating properties. On the other hand, Cold Spray (CS), a more recent coating technique, can produce highly dense coatings with strong bonding through the plastic deformation of powder feedstock, thus avoiding most of the aforementioned issues.

The main purpose of this research is to study the tribological properties of copper-based coatings deposited by APS, HVAF and Cold spray (i.e. from high temperature to low temperature deposition methods) to determine their suitability for extreme environments. This thesis is comprised of two research studies, The first study emphasizes on development of APS-CuNi coatings on different substrate materials to investigate the influence of the substrate materials as well as the tribological performance of the coatings at various temperatures (room and elevated temperature). The second study focuses on the evaluation of copper coatings by low temperature deposition systems (HVAF and CS) to understand their microstructural, mechanical and tribological behavior (room and elevated temperature).

The microstructural evaluation of coatings produced by both studies was analysed using the scanning electron microscope (SEM). Also, the Vickers microhardness tester was used to measure the coatings hardness in both studies. Furthermore, the tribological performance of coatings developed in both studies was conducted with a reciprocating tribometer using a ball-on-flat configuration and wear profiles were measured using confocal laser microscopy. Ex-situ characterization of the worn coatings was performed using a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. In the first study, APS coatings showed lower wear rates at room temperature in comparison to high temperature sliding. With regards to the second study, cold sprayed copper coatings showed a better wear resistance compared to the HVAF copper coatings.