TY - JOUR
T1 - Fatigue deformation in a polycrystalline nickel base superalloy at intermediate and high temperature
T2 - Competing failure modes
AU - Stinville, Jean Charles
AU - Martin, Etienne
AU - Karadge, Mallikarjun
AU - Ismonov, Shak
AU - Soare, Monica
AU - Hanlon, Tim
AU - Sundaram, Sairam
AU - Echlin, McLean P.
AU - Callahan, Patrick G.
AU - Lenthe, William C.
AU - Miller, V. M.
AU - Miao, Jiashi
AU - Wessman, Andrew E.
AU - Finlay, Rebecca
AU - Loghin, Adrian
AU - Marte, Judson
AU - Pollock, Tresa M.
N1 - Publisher Copyright:
© 2018 Acta Materialia Inc.
PY - 2018/6/15
Y1 - 2018/6/15
N2 - The microstructural configurations that favor early strain localization and fatigue crack initiation at intermediate and high temperature (400 °C–650 °C) have been investigated using novel experimental techniques, including high resolution digital image correlation and transmission scanning electron microscopy. Cyclic fatigue experiments in the high and low cycle fatigue regimes have been performed on a René 88DT polycrystalline nickel-base superalloy at temperatures up to 650 °C and compared to previous fatigue results obtained from tests in the very high cycle fatigue regime. Competing failure modes are observed along with an inversion in the temperature fatigue life dependence of fatigue strength from the low to high cycle fatigue regime. Oxidation-assisted processes are dominant at high applied stresses while cyclic plastic localization and accumulation govern fracture at low applied stresses. In addition, a second competing mode exists in the high and very high cycle fatigue regime from non-metallic inclusions as compared to internal intrinsic initiation sites. The grain-scale features that exhibit strain localization and crack initiation were investigated in detail. Transmission electron microscopy (TEM), transmission scanning electron microscopy (TSEM) and electron channeling contrast imaging have been conducted on samples removed from targeted regions with microstructural configurations that favor crack initiation to characterize the associated dislocation sub-structure and its evolution with temperature. Plasticity is observed to be less localized during cyclic loading at high temperature compared to room temperature. The microstructural features that drive initiation across the temperature range investigated are: twin-parent grains pairs that are at the upper end of the size distribution, are oriented for near maximum elastic modulus mismatch, and have high stresses along planes parallel to the twin boundaries.
AB - The microstructural configurations that favor early strain localization and fatigue crack initiation at intermediate and high temperature (400 °C–650 °C) have been investigated using novel experimental techniques, including high resolution digital image correlation and transmission scanning electron microscopy. Cyclic fatigue experiments in the high and low cycle fatigue regimes have been performed on a René 88DT polycrystalline nickel-base superalloy at temperatures up to 650 °C and compared to previous fatigue results obtained from tests in the very high cycle fatigue regime. Competing failure modes are observed along with an inversion in the temperature fatigue life dependence of fatigue strength from the low to high cycle fatigue regime. Oxidation-assisted processes are dominant at high applied stresses while cyclic plastic localization and accumulation govern fracture at low applied stresses. In addition, a second competing mode exists in the high and very high cycle fatigue regime from non-metallic inclusions as compared to internal intrinsic initiation sites. The grain-scale features that exhibit strain localization and crack initiation were investigated in detail. Transmission electron microscopy (TEM), transmission scanning electron microscopy (TSEM) and electron channeling contrast imaging have been conducted on samples removed from targeted regions with microstructural configurations that favor crack initiation to characterize the associated dislocation sub-structure and its evolution with temperature. Plasticity is observed to be less localized during cyclic loading at high temperature compared to room temperature. The microstructural features that drive initiation across the temperature range investigated are: twin-parent grains pairs that are at the upper end of the size distribution, are oriented for near maximum elastic modulus mismatch, and have high stresses along planes parallel to the twin boundaries.
KW - Coherent twin boundary
KW - Elastic anisotropy
KW - Fatigue crack initiation at intermediate and high temperature
KW - High resolution digital image correlation
KW - Microstructural effect
KW - Polycrystalline microstructure
KW - René 88DT polycrystalline superalloy
KW - Strain localization
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U2 - 10.1016/j.actamat.2018.03.035
DO - 10.1016/j.actamat.2018.03.035
M3 - Article
AN - SCOPUS:85045461746
SN - 1359-6454
VL - 152
SP - 16
EP - 33
JO - Acta Materialia
JF - Acta Materialia
ER -