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Advances in Materials Science and Engineering
Volume 2017, Article ID 4145369, 9 pages
https://doi.org/10.1155/2017/4145369
Research Article

Looking for New Polycrystalline MC-Reinforced Cobalt-Based Superalloys Candidate to Applications at 1200°C

Institut Jean Lamour (CNRS UMR 7198), Faculty of Sciences and Technologies, University of Lorraine, BP 70239, 54506 Vandoeuvre-lès-Nancy, France

Correspondence should be addressed to Patrice Berthod; rf.eniarrol-vinu@dohtreb.ecirtap

Received 7 December 2016; Revised 17 February 2017; Accepted 22 February 2017; Published 9 March 2017

Academic Editor: Santiago Garcia-Granda

Copyright © 2017 Patrice Berthod. 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.

Abstract

For applications for which temperatures higher than 1150°C can be encountered the currently best superalloys, the single crystals, cannot be used under stress because of the disappearance of their reinforcing precipitates at such temperatures which are higher than their solvus. Cobalt-based alloys strengthened by refractory and highly stable carbides may represent an alternative solution. In this work the interest was focused on MC carbides of several types. Alloys were elaborated with atomically equivalent quantities in M element (among Ti, Ta, Nb, Hf, or Zr) and in C. Script-like eutectic TiC, TaC, NbC, HfC, and ZrC carbides were successfully obtained in the interdendritic spaces. Unfortunately, only one type, HfC, demonstrated high morphological stability during about 50 hours at 1200°C. The concerned alloy, of the Co-25Cr-0.5C-7.4Hf type (in wt.%), was further characterized in flexural creep resistance and air-oxidation resistance at the same temperature. The creep behaviour was very good, notably by comparison with a more classical Co-25Cr-0.5C-7.5Ta alloy, proving that the interest of HfC is higher than the TaC one. In contrast the oxidation by air was faster and its behaviour not really chromia-forming. Significant improvements of this chemical resistance are expected before taking benefit from the mechanical superiority of this alloy.