PSI - Issue 19

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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 19 (2019) 312–319

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. Keywords: Alloy 718; fatigue limit; small defects; non-propagating crack; √ area parameter model; hydrogen embrittlement Abstract Tension-compression fatigue tests were performed on t o types of Ni-based superalloy 718 with different microstructures, to which mall artificial defects of various shapes and sizes were introduced. Similar tests were also conducted on hydrog n-charged specimens with defects, with a solute hydrogen content ranging from 26.3 to 91.0 mass ppm. In the non-charged specimens in particular, the fatigue strength susceptibility to defects varied significantly according to the type of microstructural morpholog , i.e. , a smaller rain size made the alloy more vulnerable to def cts. The fatigue limit as a small-crack threshold was successfully pr dicted using the √ area param ter model. Depending on the size of defects, the fati ue limit was alculated i relation t three phases: (i) harmless-defect regime, (ii) small-crack regime and (iii) larg -crack regime. Such a classification enabled omprehensiv fatigue limit evaluation in a wide array of defects, taking into consideration (a) the defect size over a range f small cr ck an large crack and (b) the c aracteristics of the matrix represented by grain size and hardness. I addition, the effect of defects and hydrogen on fatigue strength will be comprehensively discussed, based on a series of experimental results. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. Keywords: Alloy 718; fatigue limit; small defects; non-propagating crack; √ area parameter model; hydrogen embrittlement Kevinsanny a , Saburo Okazaki b,c , Osamu Takakuwa b,d,e , Yuhei Ogawa e , Koichi Okita f , Yusuke Funakoshi f , Junichiro Yamabe e,g , Saburo Matsuoka h , Hisao Matsunaga b,d,i* a Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, Japan b Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, Japan c Kobe Materials Testing Laboratory Co., Ltd., 47-13 Niijima, Harima-cho, Kako-gun, Hyogo, Japan d Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, Japan e AIST-Kyushu University Hydrogen Materials Laboratory (HydroMate), 744 Motooka, Nishi-ku, Fukuoka, Japan f Japan Aerospace Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, Ibaraki, Japan g Department of Mechanical Engineering, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka, Japan h Professor Emeritus, Kyushu Univerisity, 744 Motooka, Nishi-ku, Fukuoka, Japan i International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, Japan Abstract Tension-compression fatigue tests were performed on two types of Ni-based superalloy 718 with different microstructures, to which small artificial defects of various shapes and sizes were introduced. Similar tests were also conducted on hydrogen-charged specimens with defects, with a solute hydrogen content ranging from 26.3 to 91.0 mass ppm. In the non-charged specimens in particular, the fatigue strength susceptibility to defects varied significantly according to the type of microstructural morphology, i.e. , a smaller grain size made the alloy more vulnerable to defects. The fatigue limit as a small-crack threshold was successfully predicted using the √ area parameter model. Depending on the size of defects, the fatigue limit was calculated in relation to three phases: (i) harmless-defect regime, (ii) small-crack regime and (iii) large-crack regime. Such a classification enabled comprehensive fatigue limit evaluation in a wide array of defects, taking into consideration (a) the defect size over a range of small crack and large crack and (b) the characteristics of the matrix represented by grain size and hardness. In addition, the effect of defects and hydrogen on fatigue strength will be comprehensively discussed, based on a series of experimental results. Kevinsanny a , Saburo Okazaki b,c , Osamu Takakuwa b,d,e , Yuhei Ogawa e , Koichi Okita f , Yusuke Fun koshi f , Junichiro Yamabe e,g , Saburo Matsuoka h , Hisao Matsunaga b,d,i* a Graduate School of Engi eering, Kyushu University, 744 Motooka, Nish -ku, Fuku ka, J pan b Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, 744 Moto ka Nishi-ku, Fukuoka, Japan c Kobe Materials Testi g Laboratory Co., Ltd., 47-13 Niij ma, Harima-cho Kako g n, Hyogo, Japan d Departme t of Mechanical Engin ering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, Jap n e AIST-Kyushu University Hydrogen M terials Laboratory (HydroMate), 744 Motooka, Nishi-ku, Fukuoka, Japan f Japan Aerosp ce Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, Ibaraki, Japan g Department of Mechanical Engineering, Fukuoka University, 8-19-1 ana ma, Jonan-ku, Fukuoka, Japan h Professor Emeritus, Kyushu Univerisity, 744 Motooka, Nishi-ku, Fukuoka, Japan i International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, Japan Fatigue Design 2019 Effect of defects and hydrogen on the fatigue limit of Ni-based superalloy 718 Fatigue Design 2019 Effect of defects and hydrogen on the fatigue limit of Ni-based superalloy 718

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. * Correspon ing author. Tel.: +81-92-802-3232; fax: +81-92-802-0001. E-mail address: matsunaga.hisao.964@m.kyushu-u.ac.jp * Corresponding author. Tel.: +81-92-802-3232; fax: +81-92-802-0001. E-mail address: matsunaga.hisao.964@m.kyushu-u.ac.jp

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.034