On the Effect of Environmental Exposure on Dwell Fatigue Performance of a Fine-Grained Nickel-Based Superalloy
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On the Effect of Environmental Exposure on Dwell Fatigue Performance of a Fine-Grained Nickel-Based Superalloy S. PEDRAZZINI, D.J. CHILD, T. AARHOLT, C. BALL, M. DOWD, A. GIRLING, H. COCKINGS, K. PERKINS, M.C. HARDY, H.J. STONE, and P.A.J. BAGOT The influence of sulfur contamination on the corrosion-fatigue behavior of a polycrystalline superalloy used in aero-engines is considered. Samples tested under a variety of environmental conditions (including exposures to air, SOx gas, and salt) are characterized through a suite of high-resolution characterization methods, including transmission electron microscopy (TEM), secondary ion mass spectroscopy (nanoSIMS), and atom probe tomography (APT). The primary effect of sulfur contamination is to accelerate the crack growth rate by altering the failure mechanism. The SIMS and TEM analyses indicate Cr-Ti sulfide particle formation at grain boundaries ahead of and around oxidized cracks. The APT analysis suggests that these particles then oxidize as the crack propagates and are enveloped in chromia. The chromia is surrounded by a continuous layer of alumina within the cracks. All of the sulfur detected was confined within the particles, with no elemental segregation found at grain boundaries. https://doi.org/10.1007/s11661-018-4752-7 The Author(s) 2018
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INTRODUCTION
SULFUR, as an impurity, typically has a significant, detrimental effect on the mechanical properties of nickel-based superalloys, particularly corrosion fatigue.[1–3] Corrosion mechanisms are complex and vary with alloy composition, temperature, and loading regimes. They are broadly categorized into two main regimes: type I and type II.[4] Type I hot corrosion occurs at elevated temperatures (generally > 800 C) and is a result of molten salt deposits, while type II describes the attack of lower melting temperature eutectic salt mixtures that can exist in a stable liquid form around 600 C to 750 C.[5] The increase in operating temperatures of aero-engine components, S. PEDRAZZINI and H.J. STONE are with the Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK. Contact e-mail: [email protected] D.J. CHILD is with the Department of Materials, Loughborough University, Loughborough LE11 3TU, UK. T. AARHOLT is with the Department of Physics, University of Oslo, Postboks 1048, Blindern, 0316 Oslo, Norway. C. BALL and M. DOWD are with the Institute for Structural Materials, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, UK. A. GIRLING, H. COCKINGS and K. PERKINS are with the College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, UK. M.C. HARDY is with Rolls-Royce plc, PO box 31, Derby DE24 8BJ, UK. P.A.J. BAGOT is with the Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK. Manuscript submitted April 5, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
such as turbine discs, leads to conditions in which type II hot corrosion may be active. It is, therefore, essential to gain a deeper
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