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Metals 2017, 7(3), 71; doi:10.3390/met7030071

The Effect of Nb/Ti Ratio on Hardness in High-Strength Ni-Based Superalloys

Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan
Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Yokohama 226-8502, Japan
Department of Engineering Science, University of Oxford, Parks Road, Oxford OX5 1PF, UK
Department of Materials, University of Oxford, Parks Road, Oxford OX5 1PF, UK
Author to whom correspondence should be addressed.
Academic Editor: Jonathan Cormier
Received: 12 January 2017 / Accepted: 20 February 2017 / Published: 23 February 2017
(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)
View Full-Text   |   Download PDF [4733 KB, uploaded 24 February 2017]   |  


The age-hardening behaviour and microstructure development of high strength Ni-based superalloys ABD-D2, D4, and D6 with varying Nb/Ti ratios have been studied. The studied alloys have large volume fractions and multimodal size distributions of the γ′ precipitates, making them sensitive to cooling conditions following solution heat treatment. Differential scanning calorimetry was conducted with a thermal cycle that replicated a processing heat treatment. The hardness of these alloys was subsequently evaluated by nanoindentation. The Nb/Ti ratio was not observed to influence the size and distribution of primary and secondary γ′ precipitates; however, the difference in those of tertiary γ′ and precipitate morphology were observed. The nanoindentation hardness for all alloys reduces once they have been solution-heat-treated. The alloys exhibited specific peak hardness. The alloy with the greatest Nb content was found to have the best increase in hardness among the alloys studied due to its large tertiary γ′ precipitate. View Full-Text
Keywords: superalloy; nanoindentation; age-hardening; Nb/Ti ratio superalloy; nanoindentation; age-hardening; Nb/Ti ratio

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Hisazawa, H.; Terada, Y.; Adziman, F.; Crudden, D.J.; Collins, D.M.; Armstrong, D.E.; Reed, R.C. The Effect of Nb/Ti Ratio on Hardness in High-Strength Ni-Based Superalloys. Metals 2017, 7, 71.

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