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Comparison of fatigue crack propagation behaviour in two gas turbine disc alloys under creep–fatigue conditions: evaluating microstructure, environment and temperature effects

Comparison of fatigue crack propagation behaviour in two gas turbine disc alloys under creep–fatigue conditions: evaluating microstructure, environment and temperature effects
Comparison of fatigue crack propagation behaviour in two gas turbine disc alloys under creep–fatigue conditions: evaluating microstructure, environment and temperature effects
Gas turbine disc materials should possess excellent fatigue and creep performance due to the severe in service conditions experienced. In this study, a comparison of fatigue crack propagation behaviour in two turbine disc alloys, i.e. N18 and low solvus high refractory (LSHR) superalloy, has been made in terms of the propagation rate and fractography observed under equivalent testing conditions. Temperatures of 650 and 725uC are compared for a trapezoidal dwell fatigue cycle (1– 20–1–1) in both air and vacuum at an R ratio of 0?1. It is found that coarse grained LSHR superalloy has better fatigue crack propagation resistance than fine grained N18 in vacuum, which is ascribed to its better creep performance. Oxidation causes significant degradation of fatigue performance of these two alloys, especially in the LSHR superalloy at higher temperature (725uC), resulting in its inferior fatigue performance compared with N18. In the LSHR superalloy, it seems that oxidation is the principal contributor to the deterioration of fatigue resistance. This is supported by observations of transgranular fracture in vacuum and intergranular fracture in air. In contrast, creep is a greater contributor to the deterioration in fatigue performance of N18 (as indicated by the intergranular failure modes observed in vacuum). An apparent activation energy analysis is able to provide further insight into the underlying mechanisms of fatigue crack propagation under creep–oxidation– fatigue conditions in these two alloys.
0267-0836
781-787
Everitt, Stewart
feb53801-b349-4476-bc9d-a357c352ad10
Jiang, Rong
b78f0919-0168-43cd-9cda-dd922d8776bf
Gao, Nong
9c1370f7-f4a9-4109-8a3a-4089b3baec21
Starink, Marco J.
fe61a323-4e0c-49c7-91f0-4450e1ec1e51
Brooks, Jeffery
8c46dd14-3fde-4fed-be98-7491ae69ca1e
Reed, Philippa A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Everitt, Stewart
feb53801-b349-4476-bc9d-a357c352ad10
Jiang, Rong
b78f0919-0168-43cd-9cda-dd922d8776bf
Gao, Nong
9c1370f7-f4a9-4109-8a3a-4089b3baec21
Starink, Marco J.
fe61a323-4e0c-49c7-91f0-4450e1ec1e51
Brooks, Jeffery
8c46dd14-3fde-4fed-be98-7491ae69ca1e
Reed, Philippa A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17

Everitt, Stewart, Jiang, Rong, Gao, Nong, Starink, Marco J., Brooks, Jeffery and Reed, Philippa A.S. (2013) Comparison of fatigue crack propagation behaviour in two gas turbine disc alloys under creep–fatigue conditions: evaluating microstructure, environment and temperature effects. Materials Science and Technology, 29 (7), 781-787. (doi:10.1179/1743284713Y.0000000229).

Record type: Article

Abstract

Gas turbine disc materials should possess excellent fatigue and creep performance due to the severe in service conditions experienced. In this study, a comparison of fatigue crack propagation behaviour in two turbine disc alloys, i.e. N18 and low solvus high refractory (LSHR) superalloy, has been made in terms of the propagation rate and fractography observed under equivalent testing conditions. Temperatures of 650 and 725uC are compared for a trapezoidal dwell fatigue cycle (1– 20–1–1) in both air and vacuum at an R ratio of 0?1. It is found that coarse grained LSHR superalloy has better fatigue crack propagation resistance than fine grained N18 in vacuum, which is ascribed to its better creep performance. Oxidation causes significant degradation of fatigue performance of these two alloys, especially in the LSHR superalloy at higher temperature (725uC), resulting in its inferior fatigue performance compared with N18. In the LSHR superalloy, it seems that oxidation is the principal contributor to the deterioration of fatigue resistance. This is supported by observations of transgranular fracture in vacuum and intergranular fracture in air. In contrast, creep is a greater contributor to the deterioration in fatigue performance of N18 (as indicated by the intergranular failure modes observed in vacuum). An apparent activation energy analysis is able to provide further insight into the underlying mechanisms of fatigue crack propagation under creep–oxidation– fatigue conditions in these two alloys.

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More information

Published date: July 2013
Organisations: Engineering Mats & Surface Engineerg Gp

Identifiers

Local EPrints ID: 353151
URI: http://eprints.soton.ac.uk/id/eprint/353151
ISSN: 0267-0836
PURE UUID: 4a6e240d-f14d-4c3b-8553-2a56ffa78e3b
ORCID for Nong Gao: ORCID iD orcid.org/0000-0002-7430-0319
ORCID for Philippa A.S. Reed: ORCID iD orcid.org/0000-0002-2258-0347

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Date deposited: 03 Jun 2013 10:51
Last modified: 15 Mar 2024 03:10

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Contributors

Author: Stewart Everitt
Author: Rong Jiang
Author: Nong Gao ORCID iD
Author: Jeffery Brooks

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