Effect of oxidation on high temperature fatigue crack initiation and short crack growth in Inconel 718
Effect of oxidation on high temperature fatigue crack initiation and short crack growth in Inconel 718
Fatigue tests at 600°C in air were performed on U-notch specimens of wrought IN718, using l-l-l-l and 1-20-l-l trapezoidal cycles. SEM examination and acetate replication was used to study crack initiation and growth. In support of the fatigue tests, thermal exposure experiments were performed on unstressed specimens to study surface and sub-surface primary carbide oxidation. Compared to a 1 second dwell, a dwell time of 20 seconds at maximum load had a beneficial effect on fatigue lifetime. Polishing the U-notch to remove broaching marks also had a beneficial effect on fatigue life. Multi-site crack initiation along the root of the U-notch was observed in fatigue specimens. Many of the cracks initiated at bulge-like features, associated with the oxidation of sub-surface primary carbides. Crack initiation was first observed as early as 12% of the total fatigue life, with further crack initiation occurring as tests progressed. Short cracks in the U-notches grew at a constant rate, except when interactions between parallel cracks resulted in crack arrest or coalescence. Significant crack coalescence occurred towards the end of the fatigue life, producing a dominant defect which propagated rapidly to failure. Surface eruptions and localised surface deformation were observed in fatigue and unstressed thermal exposure specimens, demonstrating a considerable volume expansion when primary (Nb,Ti)C carbides oxidised. It is proposed that the misfit strains due to primary carbide oxidation were superimposed on the plastic strain field in the U-notch due to external loading. This would create local strains high enough to cause rupture of the matrix, hence initiating a fatigue crack.
0873395062
435-444
The Minerals, Metals & Materials Society
Connolley, T.
d4204c5c-a26b-4682-8d1b-2ce79e3810a3
Starink, M.J.
fe61a323-4e0c-49c7-91f0-4450e1ec1e51
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
2000
Connolley, T.
d4204c5c-a26b-4682-8d1b-2ce79e3810a3
Starink, M.J.
fe61a323-4e0c-49c7-91f0-4450e1ec1e51
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Connolley, T., Starink, M.J. and Reed, P.A.S.
(2000)
Effect of oxidation on high temperature fatigue crack initiation and short crack growth in Inconel 718.
Pollock, T.M., Kissinger, R.D., Bowman, R.R., Green, K.A., McLean, M., Olson, S. and Scbirra, J.J.
(eds.)
In Proceedings of the 9th International Symposium on Superalloys.
The Minerals, Metals & Materials Society.
.
Record type:
Conference or Workshop Item
(Paper)
Abstract
Fatigue tests at 600°C in air were performed on U-notch specimens of wrought IN718, using l-l-l-l and 1-20-l-l trapezoidal cycles. SEM examination and acetate replication was used to study crack initiation and growth. In support of the fatigue tests, thermal exposure experiments were performed on unstressed specimens to study surface and sub-surface primary carbide oxidation. Compared to a 1 second dwell, a dwell time of 20 seconds at maximum load had a beneficial effect on fatigue lifetime. Polishing the U-notch to remove broaching marks also had a beneficial effect on fatigue life. Multi-site crack initiation along the root of the U-notch was observed in fatigue specimens. Many of the cracks initiated at bulge-like features, associated with the oxidation of sub-surface primary carbides. Crack initiation was first observed as early as 12% of the total fatigue life, with further crack initiation occurring as tests progressed. Short cracks in the U-notches grew at a constant rate, except when interactions between parallel cracks resulted in crack arrest or coalescence. Significant crack coalescence occurred towards the end of the fatigue life, producing a dominant defect which propagated rapidly to failure. Surface eruptions and localised surface deformation were observed in fatigue and unstressed thermal exposure specimens, demonstrating a considerable volume expansion when primary (Nb,Ti)C carbides oxidised. It is proposed that the misfit strains due to primary carbide oxidation were superimposed on the plastic strain field in the U-notch due to external loading. This would create local strains high enough to cause rupture of the matrix, hence initiating a fatigue crack.
This record has no associated files available for download.
More information
Published date: 2000
Venue - Dates:
9th International Symposium on Superalloys (Superalloys 2000), Champion, USA, 2000-09-17 - 2000-09-21
Identifiers
Local EPrints ID: 21501
URI: http://eprints.soton.ac.uk/id/eprint/21501
ISBN: 0873395062
PURE UUID: 7c67a38e-833c-4233-826f-4b65c0898511
Catalogue record
Date deposited: 19 Feb 2007
Last modified: 31 Jan 2024 02:33
Export record
Contributors
Author:
T. Connolley
Editor:
T.M. Pollock
Editor:
R.D. Kissinger
Editor:
R.R. Bowman
Editor:
K.A. Green
Editor:
M. McLean
Editor:
S. Olson
Editor:
J.J. Scbirra
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics