Tribological Performance of TiO2-Nanostructured Particles as Oil-Lubricant Additives for Different Iron-Carbon Alloys

Abstract

We evaluated the tribological performance of a dispersion of titanium dioxide (TiO2) nanostructured particles in car engine base oil for three different iron-carbon alloy materials (bearing steel, carbon steel and cast iron) in a disc–disc tribometer. The lubrication, friction and wear performance of the nanostructured particles was measured by testing three different configurations: 1) pure base oil, 2) base oil with additive package and 3) nanodispersion formulation. For the bearing steel – carbon steel configuration we found that the oil additive package reduces the coefficient of friction from µ =0.12 to µ=0.03. Upon adding TiO2-nanostructured particles to this formulation a further friction reduction by a factor of 3 to a superior frictional coefficient of µ<0.01 could be measured. This effect, however, could not be verified for the other two alloy material combinations, where the frictional coefficient was not affected by the nanostructured particle addition. Since carbon steel is characterized by the lowest Brinell hardness of the three tested alloy materials and exhibited the lowest surface roughness after the test procedure, we attribute the observed friction reduction to a lubricating titanium (dioxide) overlayer that builds up on the carbon steel surface but not on bearing steel and cast iron. This is supported by element-specific energy dispersive X-Ray analysis (EDX). Further attempts to optimize and predict nanotribological formulations for industrial applications are under way.