The role of oxidation damage in fatigue crack initiation of an advanced Ni-based superalloy |
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| Affiliation: | 1. School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK;2. Rolls-Royce plc, Derby DE24 8BJ, UK;1. Department of Applied Physics, Chalmers University of Technology, SE-41296 Göteborg, Sweden;2. GKN Aerospace Engine Systems, SE-46181 Trollhättan, Sweden;3. Department of Materials, University of Oxford, Oxford OX1 3PH, UK;1. School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK;2. Rolls-Royce plc, Derby DE24 8BJ, UK;1. Université de Lorraine, CNRS, IJL, F-54000 Nancy, France;2. Safran Tech, Rue Des Jeunes Bois, Châteaufort, CS 80112, 78772, Magny-Les-Hameaux, France;3. Safran Aircraft Engines, Rue Henri Auguste Desbruères, 91000, Évry, France;1. School of Metallurgy and Materials, College of Engineering and Physical Science, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom;2. Rolls-Royce plc, PO Box 31, Derby DE24 8BJ, United Kingdom;1. School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, PR China;2. Beijing Institute of Aeronautical Materials, Beijing 100095, PR China |
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| Abstract: | The effects of prior oxidation on the room temperature fatigue life of coarse-grained Ni-based superalloy, RR1000, have been investigated. High cycle fatigue tests were conducted, on both machined and pre-oxidised testpieces, at room temperature at an R ratio of 0.1. The oxidation damage was produced by pre-exposures at 700 °C for either 100 or 2000 h. Pre-oxidised testpieces tended to fail with shorter fatigue lives than those obtained from the as-machined testpieces although they were also observed to outperform the as-machined test pieces at peak stress levels around 900 MPa. The chromia scale and intergranular alumina intrusions formed during pre-oxidation are prone to crack under fatigue loading leading to early crack nucleation and an associated reduction in fatigue life. This has been confirmed to be the case both below and above a peak stress level of ～900 MPa. The better fatigue performance of the pre-oxidised specimens around this stress level is attributed to plastic yielding of the weaker γ′ denuded zone, which effectively eases the stress concentration introduced by the cracking of the chromia scale and intergranular internal oxides. This γ′ denuded zone is also a product of pre-oxidation and develops as a result of the selective oxidation of Al and Ti. Over a limited stress range, its presence confers a beneficial effect of oxidation on fatigue life. |
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| Keywords: | Oxidation Fatigue crack initiation High cycle fatigue RR1000 |
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