Abstract

Nickel-based superalloys (i.e., 718) are widely used in the aerospace industry because of their exceptional mechanical and chemical stability at high temperatures. With recent advances in sustainable aviation, there is growing interest in investigating their compatibility with hydrogen combustion and water vapor in gas turbine engines. In this study, the tribological behavior of Inconel 718 was investigated under dry and water vapor conditions at various temperatures. In addition, the friction and wear behavior of hydrogen exposed Inconel 718 was studied at room temperature (RT ~25°C). Reciprocating ball on flat type tribometer was used to perform friction tests on Inconel 718 against aluminum oxide and Inconel 718 counter surfaces in the absence or presence of water vapor at room and elevated temperatures. However, only the Inconel 718 counterball was used for the dry sliding test for hydrogen-exposed samples. The results showed that water vapor caused a reduction in friction and wear at room and elevated temperatures of 450oC against the aluminum oxide counterball when compared to tests conducted under dry conditions. The low friction and wear in water vapor was attributed to the formation of an aluminum trihydroxide (bayerite—Al(OH)3) tribofilm. On the other hand, Inconel 718 against Inconel 718 showed higher wear in the presence of water vapor at RT compared to that in dry conditions. Conversely, water vapor decreased wear at HT compared to HT dry (where RT is ~25°% and HT is 450°C). Higher wear was attributed to the lack of sufficient lubricious oxide film formation on the wear tracks for Inconel 718 against Inconel 718 at HT. On the other hand, similar tribological behavior (i.e. friction and wear) was observed for the hydrogen-exposed and unexposed Inconel 718 at room temperature ambient conditions.