Use of synthetic Fe₃O₄-rich tribofilms to investigate the effect of microconstituents, temperature and atmosphere on the friction coefficient during pin-on-disc tribotest

Abstract

This work investigates the effect of the tribotesting parameters (temperature, atmosphere, and chemical composition) on the coefficient of friction (CoF) during pin-on-disc dry sliding tribotests using artificial third bodies. The third body comprised nanometric Fe3O4-based binary to quaternary chemical compositions containing copper, graphite, and zirconia. These mixtures were manually, or ball-milled prepared, and pin-on-disc tribotests were conducted at 23 ºC and 400 ºC under air or nitrogen atmospheres. Combining PoD and artificial third body to create synthetic tribofilms might be useful to test new formulations of Cu-free friction materials. Microstructural characterisation of the tribofilms was used to study the stability of the Fe3O4, copper, and graphite nanoparticles under different testing conditions to understand their effects on the CoF. For the Fe3O4-C-ZrO2-X systems, the ball milling mixing promoted the formation of turbostratic graphite in the tribofilm, impairing its lubricating effect under air atmosphere at 23 ºC. The formation of monoclinic CuO in the tribofilm during tribotest at 400 ºC under air atmosphere and N2 promoted a lubricating effect.