The evolution mechanism of tribo-oxide layer during high temperature dry sliding wear for nickel-based superalloy

A tribo-oxide layer is generally formed on the contact surfaces during the high temperature friction and wear process, which significantly influences the tribological properties of the materials. In this work, the evolution mechanism of the tribo-oxide layer for nickel-based superalloy was studied. High temperature sliding wear tests were performed at the different sliding time from 1 min to 60 min for nickel-based superalloy (Ni–16Cr–13Co–4Mo) against a Si3N4 ball at 800 °C under ambient environment. Morphology and chemical composition of the worn surface and wear debris were investigated using a Scanning electron microscope (SEM), X-Ray diffraction (XRD) and Raman spectroscope. The cross-sectional microstructure and element distribution of the worn surface and unworn surface were characterized by EDS mapping attached to the SEM. Results show that the evolution of the tribo-oxide layer can be divided into three stages. The first stage was characterized by the formation of a mixed oxide layer due to the preferential oxidation of Cr, Al and Ti in the preheating and temperature holding process. In the second stage, a dense tribo-oxide layer was formed by compacting and sintering the wear debris retained on the worn surface. Meanwhile, the inner oxidation of Cr and the dissolution and oxidation of the γ′ phase in the alloy occurred. In the third stage, the oxide layer with a layered structure formed with an outmost layer composed of mixed oxides with a spinel structure and an inner oxide layer played a barrier role to prevent further oxidation of the substrate. It is speculated that the change in the structure of spinel oxides at high temperature from order to disorder led to the decrease in shear stress, eventually resulted in the reduction of friction coefficient and the low wear rate.