Zinc dialkyl dithiophosphate antiwear tribofilm and its effect on the topography evolution of surfaces: A numerical and experimental study

Abstract

A modelling framework has recently been developed which considers tribochemistry in deterministic contact mechanics simulations in boundary lubrication. One of the capabilities of the model is predicting the evolution of surface roughness with respect to the effect of tribochemistry. The surface roughness affects the behaviour of tribologically loaded contacts and is therefore of great importance for designers of machine elements in order to predict various surface damage modes (e.g. micropitting or scuffing) and to design more efficient tribosystems. The contact model considers plastic deformation of the surfaces and employs a modified localized version of Archard’s wear equation at the asperity scale that accounts for the thickness of the tribofilm. The evolution of surface topography was calculated based on the model for a rolling/sliding contact and the predictions were validated against experimental results. The experiments were carried out using a Micropitting Rig (MPR) and the topography measurements were conducted using White Light Interferometry. Numerically, it is shown that growth of the ZDDP tribofilm on the contacting asperities affects the topography evolution of the surfaces. Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) have been employed to confirm experimentally the presence of the tribofilm and its chemistry. The effects of the contact load and surface hardnesses on the evolution of surface topography have also been examined in the present work.