Influence of Temperature on the Tribological Behaviour of Inconel 718, Haynes 25 and Silicon Carbide under Fretting Conditions for the Purpose of Long-Lasting Gas Turbine Engines

In an effort to reduce greenhouse gas (GHG) emissions in the aerospace industry, gas turbine engines will be required to significantly reduce their CO₂ emissions. To achieve this goal, the conditions in which materials are expected to operate will become harsher due to increase in temperature, pressure, and velocities. As a result, high-performance materials, with good mechanical and tribological properties, are needed to prevent the premature degradation and damage of critical engine components and improve the performance of the engines. Considering that there are many moving and contacting mechanical assemblies within the engines (bearings, seals, gears, etc.), having a good understanding of how different materials behave together is fundamental to ensure acceptable tribological performance. Therefore, the objective of this study is to fully capture the tribological behaviour under demanding environments of commonly used nickel-based and cobalt-based superalloys. Three different materials have been selected: Inconel 718, a high-strength nickel-based superalloy; Haynes 25, a cobalt-based alloy; and silicon carbide, which is a highly corrosion-resistant ceramic. Similarly, Inconel 718 and silicon carbide were selected as counterfaces to provide both a superalloy and a ceramic material. The tribological tests were performed using a ball-on-disk tribometer where the samples were subjected to high temperatures (450 & 800 degrees Celsius) and high vibration to more accurately simulate the operating environment the material would have to experience in the engine. The characterization of the worn surfaces was performed using confocal laser scanning microscopy (CLSM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Overall, this study will establish the wear and friction performance of commonly used materials in the hot section of the gas turbine engines and emphasis will be made on their interfacial behavior for tribological applications.