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Deformation mechanisms in iron-base hard facing alloys

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Title: Deformation mechanisms in iron-base hard facing alloys
Authors: Poole, Benjamin Oliver
Item Type: Thesis or dissertation
Abstract: A combination of crystal plasticity finite element modelling and experimental micromechanical examination has been used to investigate the deformation behaviour of iron-base hard facing alloys. This is in the context of future iron-base hard facing alloys for use in light water nuclear reactors, avoiding the radiological issues presented by cobalt-base hard facings. Transient thermal effects were examined in normally loaded, sliding surfaces with representative simulations, and found to be not significant to the initiation of galling. New experimental equipment has been developed to allow elevated temperature, small scale micromechanical testing to be performed. This new equipment was used to perform detailed deformation studies of the alloys Nitronic 60 and Tristelle 5183. These studies applied correlated high-resolution digital image correlation and high-angular resolution electron backscatter diffraction to link measurements of plastic strain with geometrically necessary dislocation (GND) density. Direct connection between the behaviour of interacting slip bands and the generation of GNDs has been made with this correlated methodology. Alloy microstructure controlled deformation with hardening achieved through different mechanisms in the two alloys, outweighing the influence of elevated temperature on deformation behaviour. A fine, carbide-containing microstructure was demonstrated to be superior in resisting plastic deformation. To complement these experimental studies, microstructures of experimentally examined specimens were explicitly reproduced within a crystal plasticity framework, allowing the extraction of crystal level properties for these alloys at 300°C. These representative material models were then used to perform a preliminary investigation into the effect of carbide decohesion under sliding contact. The studies demonstrated that the rapid decrease in galling strength which occurs in these alloys at approximately 200oC does not occur as a result of the intrinsic material property changes with temperature. Rather, it is hypothesised to be a combination of factors including local phase transformation leading to interfacial degradation. These observations of deformation behaviour can now be used to inform the design of future iron-base hard facing alloys for galling resistance.
Content Version: Open Access
Issue Date: Aug-2020
Date Awarded: Nov-2020
URI: http://hdl.handle.net/10044/1/84595
DOI: https://doi.org/10.25560/84595
Copyright Statement: Creative Commons Attribution-Non Commercial 4.0 International Licence
Supervisor: Dunne, Fionn
Dini, Daniele
Sponsor/Funder: Rolls-Royce Group plc
Engineering and Physical Sciences Research Council
Funder's Grant Number: EP/L015900/1
Department: Materials
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Materials PhD theses



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