Abstract

Ongoing developments in alternative fuels and engine cycle design are expected to modify the thermal and environmental conditions of future aircraft gas turbine engines. Some concepts involve the presence of steam in regions where tribological contacts are present. Understanding how temperature and steam affect friction, wear, and interfacial behavior is therefore necessary.
This thesis investigates the high-temperature sliding behavior of materials relevant to aircraft gas turbine applications under controlled steam exposure. Two contact configurations were studied. In the first, Inconel 718 was tested in a metal–metal contact by sliding against itself. In the second, a Cr2O3 ceramic coating deposited by suspension plasma spraying (SPS) on a steel substrate was tested against Inconel 718 to represent a coating–metal interface.
Reciprocating ball-on-flat tests were carried out under dry conditions and in the presence of superheated steam, at room temperature and at temperatures up to 450 °C. Steam was introduced directly at the contact using a dedicated experimental setup. After testing, wear tracks and counterfaces were examined using 3D optical profilometry, SEM/EDS, and Raman spectroscopy.
In the case of Inconel 718, changes in friction and wear were driven by temperature. Friction decreased as temperature increased, while wear increased. Steam had mild influence, and oxide-related features remained weak.
The behavior of the Cr2O3 coating was different. The coating itself showed high wear resistance, and most of the wear was observed on the counterface. Here, steam affected how surface layers developed and remained stable, depending on temperature.