MATEC Web of Conferences
Volume 14, 2014EUROSUPERALLOYS 2014 – 2nd European Symposium on Superalloys and their Applications
|Number of page(s)||6|
|Section||Session 3: Deformation and Damage Mechanisms II: Fatigue, Oxidation and Crack Propagation|
|Published online||29 August 2014|
Mechanisms of dwell fatigue crack growth in an advanced nickel disc alloy RR1000
1 School of Metallurgy and Materials, College of Engineering and Physical Science, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
2 Rolls-Royce plc, PO Box 31, Derby DE24 8BJ, UK
3 Manchester X-ray Imaging Facility, School of Materials, University of Manchester, Manchester M13 9PL, UK
a Corresponding author: SXY182@bham.ac.uk
RR1000 is one of an advanced class of nickel-based superalloys developed for disc applications. Under one hour dwell fatigue loading, complex crack growth behaviour has been observed especially in a coarse grained version of this alloy. At a temperature of 700 ∘C in air an increase of nearly two orders of magnitude in crack growth rates compared to baseline fatigue crack growth rates may be seen. However for certain microstructural conditions, cracks can also demonstrate retardation following initial acceleration. When using a direct current potential difference (d.c.p.d) technique for monitoring crack growth, a damage zone of a few hundred microns is often measured ahead of a fast growing crack. Advanced characterisation techniques including SEM, ECCI and X-ray tomography have been adopted in the current study to understand the observed damage zone and retardation phenomenon. It is found that damage zones measured by d.c.p.d reflect brittle and non-uniform advance of the crack resulting from continuous dynamic or quasi-dynamic fracture of an oxide intrusion ahead of the crack tip during the dwell period. In contrast, cracking of the oxide intrusion is less frequent or even prevented during dwell periods associated with a retarded and slow growing crack. Crack tip stress relaxation plays an important role in dictating whether or not dynamic cracking of the oxide intrusion can be avoided.
© Owned by the authors, published by EDP Sciences, 2014
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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