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Cyclic fatigue testing of a ni-based alloy in a corrosive environment / Hollie Cockings

Materials Science and Technology Conference and Exhibition 2015, MS and T 2015, Volume: 1, Pages: 1209 - 1223

Swansea University Author: Hollie Cockings

Abstract

Operation of gas turbines at higher temperatures can improve fuel efficiency and reduce carbon emissions, but may also lead to increased corrosion of turbine materials. A program was designed to improve the understanding of corrosion-fatigue behaviour of two grain size variants of a nickel-based sup...

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Published in: Materials Science and Technology Conference and Exhibition 2015, MS and T 2015
ISBN: 978-151081393-9 978-151081393-9
Published: USA
Online Access: https://www.scopus.com/record/display.uri?eid=2-s2.0-84961171424&origin=inward&txGid=73013c1350c0c7eb4f103324a951e608
URI: https://cronfa.swan.ac.uk/Record/cronfa52615
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Abstract: Operation of gas turbines at higher temperatures can improve fuel efficiency and reduce carbon emissions, but may also lead to increased corrosion of turbine materials. A program was designed to improve the understanding of corrosion-fatigue behaviour of two grain size variants of a nickel-based superalloy under cyclic loading at high temperatures in both air and corrosive environments. Test facilities were developed by Swansea University and Amec Foster Wheeler, to conduct fatigue and crack growth tests in corrosive environments. A salt deposition technique was implemented to replicate corrosion morphologies observed in service. It was concluded that fatigue life behaviour was dominated by initiation behaviour as baseline (1-1-1-1) crack growth rates from specimens tested in a corrosive environment showed little difference to specimens tested in air. Fatigue crack initiation appears to be related to a critical feature depth which can be achieved by corrosion pit growth in the appropriate environment. It was found that a large variation in fatigue life can be produced by influencing the initiation behaviour. For pre-corroded and fatigue-tested notched specimens, it was shown that wider notch geometries were more susceptible to attack and failure occurred preferentially at these features rather than adjacent, narrower notches with nominally similar stress concentration factors. Similarly on plain specimens, shorter lives were observed by increasing the initial salt loading level such that pit growth rates were increased. Such conditions presumably encouraged the earlier fulfilment of the apparent critical pit depth required for crack initiation and subsequent failure. © Copyright 2015 MS& T15®.
Keywords: superalloys; fatigue crack propagation; nickel-based superalloy
Start Page: 1209
End Page: 1223