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# The oxidation damage of Ni-based superalloy, RR1000, with different surface modifications and the role of oxidation in fatigue crack initiation

Cruchley, Sam (2015)
Ph.D. thesis, University of Birmingham.

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## Abstract

The oxidation behaviour of RR1000 with different surface modifications has been well studied using detailed metallographic and mass gain measurements. The oxide comprises of an external chromia scale with isolated grains of TiO$$_2$$ on the outer surface. Sub-surface internal alumina is present, beneath which the presence of TiN occurs (at higher temperatures >800$$^o$$C), all contained within a ɣ' denuded zone. The chromia external scale growth rate is significantly greater than pure chromia on chromium and the enhancement is attributed to the increased ionic transport caused by doping of the chromia layer with Ti. This effect is still seen regardless of surface condition prior to oxidation.

Oxides, especially internal intergranular oxides have been shown to crack under room temperature fatigue conditions, causing a significant fatigue life deficit at a maximum applied stress of 800 MPa and 1000 MPa. At 825 MPa, it is suggested that plastic yielding of the ɣ' denuded zone initiated leading to a substantial increase in fatigue life, through either blunting the crack by deforming to accommodate the stress concentration at the crack tip or by preventing cracking of the oxides.

Type of Work: Ph.D. thesis. Evans, Hugh and Bowen, Paul Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Metallurgy and Materials Embargo until: 31/12/2018. Publications arising from research: S. Cruchley, M.P. Taylor, H.E. Evans, P. Bowen, M.C. Hardy, and S. Stekovic, Microstructural Characterisation of High Temperature Oxidation of Nickel Base Superalloy RR1000 and the Effect of Shot-Peening, in Superalloys 2012: 12th International Symposium on Superalloys, 2012, TMS: Seven Springs, PA. p. 751-758. http://dx.doi.10.1002/9781118516430.ch83. S. Cruchley, M.P. Taylor, H.E. Evans, P. Bowen, M.C. Hardy, and S. Stekovic, Chromia layer growth on a Ni-based superalloy: Sub-parabolic kinetics and the role of titanium, Corrosion Science, 2013. 75: p. 58-66. http://dx.doi.10.1016/j.corsci.2013.05.016. S. Cruchley, M.P. Taylor, H.E. Evans, P. Bowen, J. Sumner, J.R. Nicholls, N.J. Simms, R.J. Chater, B. A. Shollock, B. Foss, M. C. Hardy and S. Stekovic, A Cautionary Note on the use of Focused Ion Beam (FIB) Sectioning as a Technique for Characterising Oxidation Damage in Ni-based Superalloys, Materials at High Temperatures, 2014. 31(1): p. 27-33. http://dx.doi.org/10.1179/0960340913Z.0000000004 S. Cruchley, M.P. Taylor, H.E. Evans, M.C. Hardy and D.J. Child, Characterisation of the sub-surface oxidation damage in Ni-based superalloy, RR1000, Materials Science and Technology, 2014. 30(15): p. 1884-1889. http://dx.doi.org/10.1179/1743284714Y.0000000541 S. Cruchley, M.P. Taylor, H.Y. Li, H.E. Evans, P. Bowen, M.C. Hardy and D.J. Child, Effect of prior oxidation on high cycle fatigue performance of RR1000 and the role of oxidation in fatigue crack initiation, Materials at High Temperature, 32(1-2): p. 68-73. http://dx.doi.org/10.1179/0960340914Z.00000000064. QD ChemistryTN Mining engineering. Metallurgy University of Birmingham 5894
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