PSI - Issue 23

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Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000 – 000 Structural Integrity Procedia 00 (2019) 000 – 000

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Procedia Structural Integrity 23 (2019) 161–166

© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the ICMSMF organizers © 201 9 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. In the present work, the mechanisms of fatigue crack initi tion and early crack pr pagation of a γ  strengthened nickel-bas d uperalloy have been i vestigated. Low cycle fatigu tests have been performed on polycr st llin superalloy MAR-M247 under ymmetrical strain ontrolled lo di g t mbient temperature in air. The nature of early fatigue damag , crack i itiation and subs quent fatigue crack propagation was assessed for applied total strain range of 1%. Test was interrupted at given numbers of cycles correspondi g to 1%, 2%, 5%, 10%, 20%, 40%, and 80% of fatigue life. The evolution of pronounced surface relief, also known as persistent slip markings (PSMs) was observed using a omic force microscopy (AFM) and hi h res lution scanning lectron microscopy (SEM-FEG). The kineti s of extrusion growth was quantit tively measured. The regions of fast and slow extru ion growth were identified. Sharp surface PSMs ari e in areas where lamellae of local zed cyclic slip – persistent slip band (PSBs) – intersect the original flat surface. Thin PSMs cut both γ matrix and γ  pre ipitates. PSMs consist of xtrus ons accompani d by parallel intrusion . Fatigue cracks wer initiated t i dividual PSMs. Focus d ion beam (FIB) revealed fa igue cr ck nucleation from sharp intrusion and its ubsequent propagation parallel t one of the active {111} 〈 110 〉 slip systems. Transmission electron microscopy (TEM) observation showed plastic strain localization into dislocation rich slabs running parallel to {111} slip planes. © 201 9 The Authors. Published by Elsevier B.V. This is an ope acces article under CC BY-NC-ND lic nse (http://creativecommon org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. 9th International Conference on Materials Structure and Micromechanics of Fracture Mechanisms of fatigue crack initiation and early propagation in cyclically strained nickel superalloy Ivo Šulák a * , Jiří Man a , Karel Obrtlík a a Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno, Czech Republic In the present work, the mechanisms of fatigue crack initiation and early crack propagation of a γ  strengthened nickel-based superalloy have been investigated. Low cycle fatigue tests have been performed on polycrystalline superalloy MAR-M247 under symmetrical strain controlled loading at ambient temperature in air. The nature of early fatigue damage, crack initiation and subsequent fatigue crack propagation was assessed for applied total strain range of 1%. Test was interrupted at given numbers of cycles corresponding to 1%, 2%, 5%, 10%, 20%, 40%, and 80% of fatigue life. The evolution of pronounced surface relief, also known as persistent slip markings (PSMs) was observed using atomic force microscopy (AFM) and high resolution scanning electron microscopy (SEM-FEG). The kinetics of extrusion growth was quantitatively measured. The regions of fast and slow extrusion growth were identified. Sharp surface PSMs arise in areas where lamellae of localized cyclic slip – persistent slip bands (PSBs) – intersect the original flat surface. Thin PSMs cut both γ matrix and γ  precipitates. PSMs consist of extrusions accompanied by parallel intrusions. Fatigue cracks were initiated at individual PSMs. Focused ion beam (FIB) revealed fatigue crack nucleation from sharp intrusion and its subsequent propagation parallel to one of the active {111} 〈 110 〉 slip systems. Transmission electron microscopy (TEM) observation showed plastic strain localization into dislocation rich slabs running parallel to {111} slip planes. 9th International Conference on Materials Structure and Micromechanics of Fracture Mechanisms of fatigue crack initiation and early propagation in cyclically strained nickel superalloy Ivo Šulák a * , Jiří Man a , Karel Obrtlík a a Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno, Czech Republic Abstract Abstract

Keywords: AFM, FIB, Surface relief, Low cycle fatigue, Dislocation structure, MAR-M247 superalloy Keywords: AFM, FIB, Surface relief, Low cycle fatigue, Dislocation structure, MAR-M247 superalloy

* Corresponding author. Tel.: +420-541-212-345; E-mail address: sulak@ipm.cz * Correspon ing author. Tel.: +420-541-212-345; E-mail address: sulak@ipm.cz

2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an ope acces article under CC BY-NC-ND lic nse (http://creativecommon org/licenses/by-nc-nd/4.0/)

Peer-review under responsibility of the scientific committee of the IC MSMF organizers.

2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the ICMSMF organizers 10.1016/j.prostr.2020.01.080