Materials and wear modelling of a cobalt-chromium alloy in self-mated reciprocated sliding

Abstract

Many sliding applications depend upon cobalt-based hard-facing materials, due to their excellent friction and wear properties, where it is not possible to lubricate the mating surfaces. However, wear produced in such systems present a significant health risk and so there is motivation to understand cobalt-based wear to aid the development of cobalt-free alternatives. The focus of this work is to build a mechanistic model of sliding wear for a given cobalt-based hard-facing alloy. The chosen numerical approach was informed by a series of delineating simple reciprocated sliding wear tests, in accordance with Rolls-Royce research aims, as a stepping stone to more complex environments. Wear testing of a cobalt-based hard-facing alloy, Stellite 6TM, was performed under selfmated reciprocating dry room-temperature conditions. The wear-rate as a function of load was not constant, suggesting a different model of wear than typical linear models of wear. Probing the debrWis morphology, surface topography, and subsurface behaviour of the alloy revealed plate-like particle formation and separation via subsurface material rupture. Unique to this thesis, the sliding wear behaviour for the load range of 400 N to 1000 N was interpreted as belonging to a ratcheting-type wear mechanism. A multiscale model of sliding wear was developed as part of this project. This model incorporates a modified microscale ratcheting wear subroutine into a standard finite element model of sliding wear via statistical homogenisation. This approach is a novel extension to the typical numerical models of sliding wear, and allows the user to see how macroscopic wear is affected as the result of material properties, evolution of surface roughness, or microscale imperfections. The model predicts the correct scale of wear, close to a wear-rate of 1×10−14 m3/Nm. Presently this model only accounts for the purely mechanical aspect of wear, but may be adapted for use in synergetic tribocorrosion models to better understand how Stellite 6TM behaves in a nuclear environment.

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Identifiers

ORCID for Paul Sebastian George Cross: orcid.org/0000-0001-7768-5659

ORCID for Robert Wood: orcid.org/0000-0003-0681-9239

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