High-temperature lubrication mechanisms of laser cladding austenitic stainless steel coatings: XPS and DFT calculations

Abstract

Austenitic stainless steels are widely utilized in engine components due to their stable crystal structure, excellent heat resistance, and relatively low cost. This study investigates the high-temperature dry sliding friction and wear behavior of laser-clad austenitic stainless steel coatings over a temperature range from room temperature to 800 °C, and further explores the wear mechanisms through X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. As the temperature increases, a series of metal oxides such as Fe₃O₄, Fe₂O₃, FeO, Cr₂O₃, CrO₃, and NiO will be produced by friction chemical reaction during the friction process. The thickness of the oxide layer will be increased with the increase in temperature. However, when the temperature is higher than 600 °C, the internal stress condition of the oxide layer deteriorates. Peeling and fracture will occur, which will increase the wear rate of the coating slightly. The wear rate rises gradually from 1.09 mm³/(N·m) at 600 °C to 1.82 mm³/(N·m) at 800 °C. DFT calculations show that the binding energies of Fe-O bond in FeO (−6.83 eV) and Ni-O in NiO (−5.89 eV) are much lower than those of Fe-O and Cr-O bonds in Fe₃O₄, Fe₂O₃ Cr₂O₃ and CrO₃. It indicates that the Fe-O and Ni-O bonds of the former are more prone to fracture during the wear process, which leads to the excellent lubrication properties of FeO and NiO, which can explain the excellent tribological properties of the coatings at high temperatures and help to reveal the high-temperature lubrication mechanism of austenitic stainless steels.