PSI - Issue 23

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ScienceDirect Science irect

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

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ScienceDirect

Procedia Structural Integrity 23 (2019) 251–256

© 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 Abstract N ickel alloys with operating temperatures up to 650 °C are used for the manufacture of turbine disks in modern gas turbine engines. During an operation or testing the high centrifugal forces, which appear in the discs, could initiate fatigue cracks formation. If the cracks start from internal defects, there is no air access and their growth occurs in a vacuum conditions. The failure mechanism will correspond to the low-cycle fatigue. Various electron microscopy methods were used in the study of billets formed from the powder nickel alloys. The fractographic analysis demonstrated that in vacuum conditions a rugged rough surfaces of the crack consisted of spherical particles with the sizes in the range between 50 and 150 µm is formed at the beginning. When a crack reaches a billet surface, the crack surface relief changes to a quasi-faceted one, and that corresponds to the first stage of fatigue fracture development. It was found that nano-grains with the size of 100 – 200 nm are formed in front of the crack tip. The crack surfaces are covered with amorphous layers with a thickness of about 20 nm. The destruction occurs mainly along the boundaries of nanocrystals layer. A model is proposed to explain the appearance of such microstructure and the key factor is the air access to a crack and hence the oxidation of the crack surfaces. 1 9 The Authors. Published by Elsevier B.V. is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) r-review under responsibility of the scientific committe of the IC MSMF organizers. Keywords: Scanning electron microscope; low-cycle fatigue; transmission electron microscope; powder nickel-base superalloy; EP741NP; fatigue crack growth mechanism; structural analysis; fatigue crack in vacuum; low-cycle fatigue 9th International Conference on Materials Structure and Micromechanics of Fracture The investigation of the of fatigue crack gro th echanis in po der etallurgy i-based superalloy .A. Artamonov a *, I.N. Trunkin b , A.V. Ovcharov b , A.L. Vasiliev b,c, a A. Lyulka Design Bureau PJSC «UEC - Ufa Engine Industrial Association» Subsidiary, Kasatkina st., 13, Moscow 129301, Russia b National Research Centre “Kurchatov Institute”, Akademica Kurchatova Sq., Moscow, 1123182, Russia, c Shubnikov Institute of Crystallography of Federal Scientific Research Centre “Crystallography and Photonics” of Russian Academy of Scie nces, Leninskiy prospect, 59, 119333, Moscow, Russia Abstract N ickel alloys with operating temperatures up to 650 °C are used for the manufacture of turbine disks in modern gas turbine engines. During an operation or testing the high centrifugal forces, which appear in the discs, could initiate fatigue cracks formation. If the cracks start from internal defects, there is no air access and their growth occurs in a vacuum conditions. The failure mechanism will correspond to the low-cycle fatigue. Various electron microscopy methods were used in the study of billets formed from the powder nickel alloys. The fractographic analysis demonstrated that in vacuum conditions a rugged rough surfaces of the crack consisted of spherical particles with the sizes in the range between 50 and 150 µm is formed at the beginning. When a crack reaches a billet surface, the crack surface relief changes to a quasi-faceted one, and that corresponds to the first stage of fatigue fracture development. It was found that nano-grains with the size of 100 – 200 nm are formed in front of the crack tip. The crack surfaces are covered with amorphous layers with a thickness of about 20 nm. The destruction occurs mainly along the boundaries of nanocrystals layer. A model is proposed to explain the appearance of such microstructure and the key factor is the air access to a crack and hence the oxidation of the crack surfaces. © 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. Keywords: Scanning electron microscope; low-cycle fatigue; transmission electron microscope; powder nickel-base superalloy; EP741NP; fatigue crack growth mechanism; structural analysis; fatigue crack in vacuum; low-cycle fatigue 9th International Conference on Materials Structure and Micromechanics of Fracture The investigation of the of fatigue crack growth mechanism in powder metallurgy Ni-based superalloy M.A. Artamonov a *, I.N. Trunkin b , A.V. Ovcharov b , A.L. Vasiliev b,c, a A. Lyulka Design Bureau PJSC «UEC - Ufa Engine Industrial Association» Subsidiary, Kasatkina st., 13, Moscow 129301, Russia b National Research Centre “Kurchatov Institute”, Akademica Kurchatova Sq., Moscow, 1123182, Russia, c Shubnikov Institute of Crystallography of Federal Scientific Research Centre “Crystallography and Photonics” of Russian Academy of Scie nces, Leninskiy prospect, 59, 119333, Moscow, Russia

* Corresponding author. Tel.: +7-499-755-08-44; fax: +7-495-683-09-97. E-mail address: maksim.artamonov@lmz.umpo.ru * Corresponding author. Tel.: +7-499-755-08-44; fax: +7-495-683-09-97. E-mail address: maksim.artamonov@lmz.umpo.ru

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 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 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.2020.01.095