Tribo-behaviours of textured point contacts lubricated with low and high consistency lithium greases under reciprocating motion

Abstract

Tribo-behaviours of grease-lubricated textured point contacts were experimentally explored at heavy loads (characterized in term of Hertzian pressure, P H = 1.5–3.0 GPa) and relatively low sliding speeds (0.2 and 0.4 m s−1) under the linear reciprocating motion employing lithium-based low and high consistency greases. Two contacts (grounded plate versus lapped ball & grounded textured plate versus lapped ball) were employed for the comparative investigations of friction coefficient, specific wear rate, and contact potential. Effects of grease consistency on the greases’ rheological behaviours have also been found at two temperatures 25 °C and 80 °C using controlled stress rheometer. Overall, textured concentrated contacts yielded a low coefficient of friction (reduction up to 24.6%), reduced specific wear rate of the ball (decrease up to 89.5%) and better development of contact potential in comparison to conventional contacts. The transmission electron microscopy (TEM) of used greases collected from textured contacts revealed less degradation in soap fibres. Moreover, the x-ray photoelectron spectroscopy (XPS) revealed the formation of ferric oxide (Fe2O3) and ferrous-ferric oxide (Fe3O4) protective chemical films on the worn surfaces of balls of the conventional and textured contacts.