A multiscale finite element model of sliding wear for cobalt-chromium undergoing ratcheting wear

Abstract

Cobalt-chromium alloys are used in reciprocated sliding wear applications where the mated surfaces cannot be lubricated, due to their excellent frictional properties and ability to resist seizure. However, various health risks due to cobalt wear particle generation motivate the replacement of cobalt-based systems. It is suggested that a numerical model of reciprocated dry sliding wear for cobalt-chromium alloys would aid in the development of cobalt-free alternatives to remove any health risks. Therefore, this work focuses on building a mechanistic, i.e. determined purely through physical terms, numerical degredation model of dry reciprocated sliding wear for a specific cobalt-chromium alloy, informed by the experimental literature, to gain an understanding of cobalt wear-rates in response to the tribological loading conditions. A multi-scale method is employed, where the wear is determined by a microscale model of wear, which simulates wear after the material is brought up to a critical strain to failure and material rupture occurs, and the microscale wear-rates are homogenised to the macroscale by use of a statistic model of rough contact. This improves over previous methods by allowing one to observe how material wear-rates are controlled by changes in the elasto-plastic material parameters and geometry of an engineering component. The current numerical model predicts the correct scale of wear, in the range of 1×10−14 m3/Nm or 1×10−5 mm3/Nm, typical for the chosen alloy under dry sliding conditions and is validated against experimental data. The model allows for further development, such as the incorporation of frictional heating, microscale heterogeneity, or the evolution of surface roughness parameters during wear.