High-temperature superlubricity behaviors of γ-Fe2O3@SiO2 nanocomposite coatings

Abstract

Abstract In the present chapter, γ-Fe2O3@SiO2 and Ag-doping γ-Fe2O3@SiO2 nanocomposites were prepared by the sol-gel method and nanocomposite coatings were deposited on the steel substrate. The microstructures and surface topographies of nanocomposite coatings were investigated by X-ray diffraction (XRD) analysis, Raman spectroscopy, scanning electron microscopy (SEM), as well as transmission electron microscopy (TEM), respectively. Experimental results indicated the existence of typical core-shell microstructures in γ-Fe2O3@SiO2 nanocomposite coatings. The tribological performances of nanocomposite coatings were investigated by a high-temperature tribometer from room temperature (RT) to 600°C. The coefficient of friction (CoF) was found to decrease with increasing the temperatures. It has been shown that nanocomposite coatings exhibit low and stable friction (CoFs in the range of 0.25–0.06) from RT to 600°C especially leading to high-temperature superlubricity. Ag is helpful to improve the tribological properties of nanocomposite coatings in a wide range of temperature conditions. XRD patterns, Raman spectra, and SEM micrographs have revealed that antifriction behaviors at the high temperature are ascribed to the transformation between α-Fe2O3 and γ-Fe2O3 above 500°C during the sliding step. γ-Fe2O3 is lucrative to form low shear interfaces in order to achieve high-temperature superlubricity. The core-shell structures of nanocomposite coatings inhibit the transformation of γ-Fe2O3 soft phase into α-Fe2O3, which is beneficial to form low shear interfaces and yield super low friction at high temperatures.