Comparison of low cycle (notch) fatigue behaviour at temperature in single crystal turbine blade materials
Comparison of low cycle (notch) fatigue behaviour at temperature in single crystal turbine blade materials
The scatter in notch fatigue lifetimes of CMSX4 at 650ºC and 725ºC in air and vacuum and with Rene N5 in air at 650ºC is compared under the same (plastic) notch strain range levels. Rene N5 shows shorter lifetimes under equivalent conditions and always exhibits multiple initiation sites. The role of interdendritic porosity in initiating fatigue in both alloys is identified, and the number of initiation sites is found to directly affect fatigue life. In air in CMSX4 and Rene N5, subsurface pores initiate fatigue, and this is believed to be due to the repeated in-filling of surface pores by oxidation product, reducing their associated stress concentration and effectively deactivating them as a fatigue initiation site. Tests in vacuum support this hypothesis as cracks do initiate at surface porosity under vacuum conditions. An attempt to evaluate initiating porosity distributions, has indicated a correlation between total area of initiating porosity and fatigue lifetime, which to some extent may allow for crack coalescence behaviour. A deterministic fracture mechanics based model has been proposed to allow for the effect of pore shape, size and position in determining subsequent fatigue life (and hence scatter). The predictions of the model have been assessed using full factorial design of experiments, assessing the effects of variability in pore shape, size and distance below the notch root, as well as the materials parameters (crack growth laws and Kmax) used in the lifing calculation. The model successfully explains some, but not all of the observed scatter in lifetimes.
notch fatigue, cmsx4, porosity, fatigue initiation, lifing model, scatter
527-533
Minerals, Metals and Materials Society
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Miller, M.D.
0a80ae6f-550d-4bb4-9b64-a335270b8ae9
September 2008
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Miller, M.D.
0a80ae6f-550d-4bb4-9b64-a335270b8ae9
Reed, P.A.S. and Miller, M.D.
(2008)
Comparison of low cycle (notch) fatigue behaviour at temperature in single crystal turbine blade materials.
Reed, Roger, Green, Kenneth, Caron, Pierre, Gabb, Timothy P. and Fahrmann, Michael G.
(eds.)
In Superalloys 2008: Proceedings of the Eleventh International Symposium on Superalloys.
Minerals, Metals and Materials Society.
.
Record type:
Conference or Workshop Item
(Paper)
Abstract
The scatter in notch fatigue lifetimes of CMSX4 at 650ºC and 725ºC in air and vacuum and with Rene N5 in air at 650ºC is compared under the same (plastic) notch strain range levels. Rene N5 shows shorter lifetimes under equivalent conditions and always exhibits multiple initiation sites. The role of interdendritic porosity in initiating fatigue in both alloys is identified, and the number of initiation sites is found to directly affect fatigue life. In air in CMSX4 and Rene N5, subsurface pores initiate fatigue, and this is believed to be due to the repeated in-filling of surface pores by oxidation product, reducing their associated stress concentration and effectively deactivating them as a fatigue initiation site. Tests in vacuum support this hypothesis as cracks do initiate at surface porosity under vacuum conditions. An attempt to evaluate initiating porosity distributions, has indicated a correlation between total area of initiating porosity and fatigue lifetime, which to some extent may allow for crack coalescence behaviour. A deterministic fracture mechanics based model has been proposed to allow for the effect of pore shape, size and position in determining subsequent fatigue life (and hence scatter). The predictions of the model have been assessed using full factorial design of experiments, assessing the effects of variability in pore shape, size and distance below the notch root, as well as the materials parameters (crack growth laws and Kmax) used in the lifing calculation. The model successfully explains some, but not all of the observed scatter in lifetimes.
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More information
Published date: September 2008
Venue - Dates:
Superalloys 2008: 11th International Symposium on Superalloys, Seven Springs, USA, 2008-09-14 - 2008-09-18
Keywords:
notch fatigue, cmsx4, porosity, fatigue initiation, lifing model, scatter
Organisations:
Engineering Mats & Surface Engineerg Gp
Identifiers
Local EPrints ID: 65077
URI: http://eprints.soton.ac.uk/id/eprint/65077
PURE UUID: dca6957c-1c0e-4c51-9fbb-00b68032f1b8
Catalogue record
Date deposited: 29 Jan 2009
Last modified: 12 Aug 2022 01:33
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Contributors
Author:
M.D. Miller
Editor:
Roger Reed
Editor:
Kenneth Green
Editor:
Pierre Caron
Editor:
Timothy P. Gabb
Editor:
Michael G. Fahrmann
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