LOW CYCLE FATIGUE BEHAVIOUR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C

1 ŠULÁK Ivo
Co-authors:
1 OBRTLÍK Karel 2 HRBÁČEK Karel
Institutions:
1 Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62 Brno, Czech Republic, sulak@ipm.cz
2 PBS Velká Bíteš a.s, Vlkovská 279, 595 12 Velká Bíteš, Czech Republic
Conference:
26th International Conference on Metallurgy and Materials, Hotel Voronez I, Brno, Czech Republic, EU, May 24th - 26th 2017
Proceedings:
Proceedings 26th International Conference on Metallurgy and Materials
Pages:
1580-1586
ISBN:
978-80-87294-79-6
ISSN:
2694-9296
Published:
9th January 2018
Proceedings of the conference were published in Web of Science and Scopus.
Metrics:
15 views / 5 downloads
Abstract

The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at elevated temperatures in hostile environments. The microstructure consists mainly of the face centred cubic γ matrix and ordered γ´ strengthening precipitates (L12 crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambient air. Cyclic stress-strain curves and fatigue life curves in the representation of plastic strain amplitude vs. stress amplitude and stress amplitude vs. the number of cycles to failure, respective, were plotted and compared with data obtained on Inconel 713LC. Special attention is paid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation. Observations in transmission electron microscope (TEM) confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long.

Keywords: Nickel-based superalloy, cyclic stress-strain curve, fatigue life, fatigue crack initiation, focus ion beam
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