Moore, I.J., Taylor, J.I., Tracy, M.W. et al. (2 more authors) (2017) Grain coarsening behaviour of solution annealed Alloy 625 between 600–800°C. Materials Science and Engineering: A, 682. pp. 402-409. ISSN 0921-5093
Abstract
As with all alloys, the grain structure of the nickel-base superalloy 625 has a significant impact on its mechanical properties. Predictability of the grain structure evolution in this material is particularly pertinent because it is prone to inter-metallic precipitate formation both during manufacture and long term or high temperature service. To this end, analysis has been performed on the grain structure of Alloy 625 aged isothermally at temperatures between 600 and 800 °C for times up to 3000 h. Fits made according to the classical Arrhenius equation describing normal grain growth yield an average value for the activation energy of a somewhat inhomogeneous grain structure above 700 °C of 108.3±6.6 kJ mol−1 and 46.6±12.2 kJ mol−1 below 650 °C. Linear extrapolation between 650 and 700 °C produces a significantly higher value of 527.7±23.1 kJ mol−1. This result is ultimately a consequence of a high driving force, solute-impeded grain boundary migration process operating within the alloy. Comparison of the high and low temperature values with the activation energy for volume self-diffusion and grain boundary diffusion identifies the latter as the principle governing mechanism for grain growth in both instances. A decrease in the value of the time exponent (n) at higher temperatures despite a reduction in solute drag is attributable to the Zener pinning imposed by grain boundary M6C and M23C6 particles identified from Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDXS) analysis. Vickers hardness results show the dominance of intermetallic intragranular precipitates in the governance of the mechanical properties of the material with grain coarsening being accompanied by a significant increase in hardness. Furthermore, the lack of any correlation with grain growth behaviour indicates these phases have no significant effect on the grain evolution of the material.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Copyright, Publisher and Additional Information: | © 2016 Elsevier B.V. This is an author produced version of a paper subsequently published in Materials Science and Engineering: A. Uploaded in accordance with the publisher's self-archiving policy. Article available under the terms of the CC-BY-NC-ND licence (https://creativecommons.org/licenses/by-nc-nd/4.0/) |
Keywords: | Grain coarsening; Alloy 625; Vickers hardness; Activation energy; Precipitation; Solute drag |
Dates: |
|
Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Materials Science and Engineering (Sheffield) |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 10 Feb 2017 11:29 |
Last Modified: | 20 Nov 2017 01:38 |
Published Version: | https://doi.org/10.1016/j.msea.2016.11.060 |
Status: | Published |
Publisher: | Elsevier |
Refereed: | Yes |
Identification Number: | 10.1016/j.msea.2016.11.060 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:111917 |
Download
Filename: Grain coarsening behaviour of solution annealed Alloy 625 between 600-800C.pdf
Licence: CC-BY-NC-ND 4.0