Abstract

Aerospace components operating in extreme environments commonly face severe degradation due to wear, corrosion, oxidation and fatigue. Conventional materials used for such components face limitations with such degradation issues and thus, there is a need to develop new alloy systems capable of operating effectively in extreme conditions. High entropy alloys (HEAs) have gained a lot of attention recently due to their outstanding mechanical properties and tribological behavior. These advance HEAs need to be deposited in the most effective way suitable for tribological applications. Thermal spraying techniques have proven to be one of the most efficient technologies for mitigating wear and corrosion damage that occurs due to harsh environmental conditions. The modularity of these techniques has made it possible to spray and/or repair intricate components in an effective manner.
The main purpose of this research is to evaluate the tribological performance of a novel AlCoCrFeMo HEA system deposited via cold spraying, flame spraying and HVOF spraying technologies and identify the most suitable thermal deposition technique. This thesis comprises of two research studies in which the first study focuses on tribological behavior of cold sprayed and flame sprayed HEA at room temperature under varying loads (5N and 10N) and the effect of polishing. The second study investigates the temperature response (room temperature and 450C) on tribological behavior of the HEA deposited via cold spraying, flame spraying and HVOF for the first time in scientific community.
In both the studies, the tribology tests were performed using ball-on-flat tribometer and the wear profiles were extracted using a laser confocal microscope. The ex-situ characterization of the coatings was done using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), image analysis, and Vickers micro-hardness testing. The HVOF sprayed HEA showed the least wear rates followed by flame sprayed HEA coating and cold sprayed HEA at both temperatures (room temperature and 450C). The research suggests that HVOF is the most suitable thermal spray deposition technique for high entropy alloy systems involving tribological applications.