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Microstructural characterisation of subsurface deformation and the degradation of Stellite 6 induced by self-mated sliding contact in a simulated PWR environment

Carrington, Matthew John; Daure, Jaimie; Ratia-Hanby, Vilma Liisa; Zhang, Deen; Shipway, Philip H.; Stewart, David A.; McCartney, David Graham

Microstructural characterisation of subsurface deformation and the degradation of Stellite 6 induced by self-mated sliding contact in a simulated PWR environment Thumbnail


Authors

Matthew John Carrington

Vilma Liisa Ratia-Hanby

Deen Zhang

David A. Stewart

David Graham McCartney



Abstract

© 2021 Elsevier Ltd Stellite 6 (Co-29.5%Cr-5%W-1.2%C in wt%) is traditionally used as a hardfacing material in the primary circuit of pressurised water reactors (PWRs) due to its good corrosion and wear resistance in water at up to 300 °C. In this study, pin-on-disc type sliding contact tribocorrosion testing was conducted on HIPed Stellite 6 at 20 °C and 250 °C using a bespoke tribometer to simulate a primary circuit environment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize, for the first time, the material affected by tribocorrosion. Whilst the material loss increases by 16–39 times when the test temperature is increased from 20 °C to 250 °C, the mechanisms of degradation and deformation remain largely unchanged. Furthest from the sliding contact, strain is principally accommodated by the deformation-induced transformation of the γ Co-based matrix to ε-martensite. Closer to the sliding contact, the ε-martensite phase accommodates further strain via twinning and dislocation slip. At the sliding contact the intense deformation generates a nanocrystalline structure. The tribologically affected material is resistant to plastic strain localisation; this confines wear to the nanoscale where the synergistic effects of chemical degradation and mechanical deformation permit the removal of nanoscale particulates (corrosion enhanced nanowear (tribocorrosion)). The increased wear rate at 250 °C is attributed to a temperature dependent increase in corrosion enhanced nanowear. The degradation mechanisms revealed are important for the design of future hardfacings.

Journal Article Type Article
Acceptance Date Jan 24, 2021
Online Publication Date Feb 12, 2021
Publication Date Jun 1, 2021
Deposit Date Feb 3, 2021
Publicly Available Date Feb 13, 2022
Journal Tribology International
Print ISSN 0301-679X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 158
Article Number 106899
DOI https://doi.org/10.1016/j.triboint.2021.106899
Public URL https://nottingham-repository.worktribe.com/output/5290989
Publisher URL https://www.sciencedirect.com/science/article/pii/S0301679X21000475