PSI - Issue 14

ScienceDirect Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2018) 000–000 Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2018) 000–000

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Procedia Structural Integrity 14 (2019) 790–797

2nd International Conference on Structural Integrity and Exhibition 2018 In-situ Study of the Effect of Hydrogen on Fatigue Crack Initiation in Polycrystalline Nickel Aman Arora, Rakesh Kumar, Dhiraj K. Mahajan * Ropar Mechanics of Materials Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab, India, 140001. Abstract Correlating hydrogen embrittlement phenomenon with the metallic microstructural features holds the key for developing metals resistant to hydrogen-based failures. In case of fatigue failure of hydrogen charged metals, in addition to the hydrogen-based failure mechanisms associated with monotonic loading such as HELP, HEDE etc., microstructural features such as grain size, type of grain boundary (special/random), fraction of special grain boundaries; their network and triple junctions can play a complex role. The probable sites for fatigue crack initiation in such metals can be identified as the sites of highest hydrogen concentration or accumulated plastic strain. To this end, we have developed an experimental framework based on in-situ fatigue crack initiation and propagation studies under scanning electron microscope (SEM) to identify the weakest link in the metallic microstructure leading to failure. In-situ fatigue experiments are performed on carefully designed polycrystalline nickel (99.95% pure) specimens (miniaturised, shallow-notched & electro-polished) using a 10 kN fatigue stage inside the SEM. Electron Back Scattering Diffraction (EBSD) map of the notched region surface helps identify the distribution of special/random grain boundaries, triple junctions and grain orientation. The specimen surface in the shallow notched region for both the hydrogen charged and un-charged specimens are then carefully studied to correlate the microstructural feature associated with fatigue crack initiation sites. Such correlation of the fatigue crack initiation site and microstructural feature is further corroborated with the knowledge of hydrogen trapping and grain’s elastic anisotropicity to be either the site of high hydrogen concentration, accumulated plastic slip or both. © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of Peer-review under responsibility of the SICE 2018 organizers. 2nd International Conference on Structural Integrity and Exhibition 2018 In-situ Study of the Effect of Hydrogen on Fatigue Crack Initiation in Polycrystalline Nickel Aman Arora, Rakesh Kumar, Dhiraj K. Mahajan * Ropar Mechanics of Materials Laboratory, Department of Mechan cal Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab, India, 140001. Abstract Correla ing hydrogen embrittlem nt phenomenon with the metallic microstructural features holds the key for developing metals resist t to hydr gen-based failures. In case of fatigue failure of hydrogen charged me als, in ddition to the hydrogen-bas d ailure mechanism associ te with mon tonic load ng such as HELP, HEDE etc., microstructural features uch as grain size, type of grain boundary (special/r ndom), fraction of special grain boundaries; their etwork and tripl junct ons can play a compl x ole. The probable sites for fa igue crack initiation in such metals can b id ified as the site of highes hydrogen oncentration or accumulated plastic strain. To th s end, we have developed an experimental framework based on in-situ fatigue crack initiation a d propagation studies under scanning electron microscope (SEM) to identify the weakest link i the m tallic microstructure leadi g to failure. In-situ fatigue experim nts are performed on c refully des n d polycry talline nickel (99.95% pure) specime s (mini turised, shallow-notched & el ctro-p lished) using a 10 kN fatigue stage inside the SEM. Electron Back Scattering Diffraction (EBSD) map of the notch d region surface elps identify he istributi n of special/random gr in bou aries, t iple jun tions and grai orientation. Th specimen surfac in the hallow notched region for both t e hydrogen harged and un-charged specimens are then car fully studied to correlate the microstructur l f ature associated with fatigue crack initiation sites. Such correlatio of the fatigue r ck initiation site and microstructural feature is further orrob rated with th knowledge of hydrogen trapping and grain’s elastic anisotropicity to be either the site of high hydrogen concentration, accumulated plastic slip or both. © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by- c-nd/4.0/) Selection and peer-review under responsibility of Peer-review under responsibility of the SICE 2018 organizers. © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of Peer-review under responsibility of the SICE 2018 organizers.

Keywords: In-Situ fatigue testing; SEM; EBSD; polycrystalline nickel; hydrogen charging Keywords: In-Situ fatigue testing; SEM; EBSD; polycrystalline nickel; hydrogen charging

*Corresponding author. Tel.: +91-1881-242244; E-mail address: dhiraj.mahajan@iitrpr.ac.in *Corresponding author. Tel.: +91-1881-242244; E-mail address: dhiraj.mahajan@iitrpr.ac.in

2452-3216 © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of Peer-review under responsibility of the SICE 2018 organizers. 2452-3216 © 2018 The Authors. Published by Elsevi r B.V. This is a open access article und r the CC BY-NC-ND lic nse (https://creat vecommons.org/licenses/by- c-nd/4.0/) Selection and peer-review under responsibility of Peer-review under responsibility of the SICE 2018 organizers.

2452-3216  2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of Peer-review under responsibility of the SICE 2018 organizers. 10.1016/j.prostr.2019.07.057