TY - GEN
T1 - Role of Non-metallic Inclusions and Twins on the Variability in Fatigue Life in Alloy 718 Nickel Base Superalloy
AU - Texier, Damien
AU - Stinville, Jean Charles
AU - Charpagne, Marie Agathe
AU - Chen, Zhe
AU - Valle, Valery
AU - Villechaise, Patrick
AU - Pollock, Tresa M.
AU - Cormier, Jonathan
N1 - Funding Information:
The authors are grateful to Safran Aircraft Engines for providing materials and financial support. The authors are grateful to Jia H. Liu (ETS) and Florence Hamon (Pprime institute) for their help with mechanical testing and stimulating discussions.
Funding Information:
Acknowledgements The authors are grateful to Safran Aircraft Engines for providing materials and financial support. The authors are grateful to Jia H. Liu (ETS) and Florence Hamon (Pprime institute) for their help with mechanical testing and stimulating discussions.
Publisher Copyright:
© 2020, The Minerals, Metals & Materials Society.
PY - 2020
Y1 - 2020
N2 - Non-metallic inclusions (NMIs) and slip bands parallel to and slightly offset from twin boundaries are observed to be preferential sites for fatigue crack nucleation in wrought superalloys. Potential interactions between NMI cracking and slip activity within neighboring grains or at twin boundaries were investigated under monotonic tensile loading (up to 1.3% total strain) at room temperature. High resolution- and Heaviside-digital image correlation measurements were performed during interrupted tensile loading to identify strain localization, associated slip systems, and damage initiation. Different mechanisms and scenarios were identified: (1) Microplasticity generally starts at twin boundaries even at stresses as low as 70% of the macroscopic yield strength, (2) transgranular slip activity intensively develops above the macroscopic yield stress, (3) intense slip activity develops near and parallel to 21% of the twin boundaries intercepting NMIs, (4) 7% of the twin boundaries intercepting NMIs lead to slip-assisted NMI cracking, (5) no transgranular slip activity participates in NMI cracking, (6) the fraction of cracked NMIs progressively increases with the load, and (7) within the NMIs that initiated cracks, 67% cracked below 90% of the macroscopic yield strength without the presence of slip activity in the neighboring grains. While slip-assisted NMI cracking was evidenced in the present study, most NMI cracking is due to strain incompatibility between NMIs and neighboring grains at the high end of the elastic regime without slip interaction.
AB - Non-metallic inclusions (NMIs) and slip bands parallel to and slightly offset from twin boundaries are observed to be preferential sites for fatigue crack nucleation in wrought superalloys. Potential interactions between NMI cracking and slip activity within neighboring grains or at twin boundaries were investigated under monotonic tensile loading (up to 1.3% total strain) at room temperature. High resolution- and Heaviside-digital image correlation measurements were performed during interrupted tensile loading to identify strain localization, associated slip systems, and damage initiation. Different mechanisms and scenarios were identified: (1) Microplasticity generally starts at twin boundaries even at stresses as low as 70% of the macroscopic yield strength, (2) transgranular slip activity intensively develops above the macroscopic yield stress, (3) intense slip activity develops near and parallel to 21% of the twin boundaries intercepting NMIs, (4) 7% of the twin boundaries intercepting NMIs lead to slip-assisted NMI cracking, (5) no transgranular slip activity participates in NMI cracking, (6) the fraction of cracked NMIs progressively increases with the load, and (7) within the NMIs that initiated cracks, 67% cracked below 90% of the macroscopic yield strength without the presence of slip activity in the neighboring grains. While slip-assisted NMI cracking was evidenced in the present study, most NMI cracking is due to strain incompatibility between NMIs and neighboring grains at the high end of the elastic regime without slip interaction.
KW - Fatigue
KW - High resolution-digital image correlation (HR-DIC)
KW - In-situ tensile testing
KW - Non-metallic inclusions (NMIs)
KW - Twin boundary
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U2 - 10.1007/978-3-030-51834-9_61
DO - 10.1007/978-3-030-51834-9_61
M3 - Conference contribution
AN - SCOPUS:85091302149
SN - 9783030518332
T3 - Minerals, Metals and Materials Series
SP - 629
EP - 639
BT - Superalloys 2020 - Proceedings of the 14th International Symposium on Superalloys
A2 - Tin, Sammy
A2 - Hardy, Mark
A2 - Clews, Justin
A2 - Cormier, Jonathan
A2 - Feng, Qiang
A2 - Marcin, John
A2 - O'Brien, Chris
A2 - Suzuki, Akane
PB - Springer
T2 - 14th International Symposium on Superalloys, Superalloys 2021
Y2 - 12 September 2021 through 16 September 2021
ER -