Zacharis, E., Utton, C. and Tsakiropoulos, P. orcid.org/0000-0001-7548-3287 (2022) A study of the effects of Hf and Sn on the microstructure, hardness and oxidation of Nb-18Si silicide-based alloys-RM(Nb)ICs with Ti addition and comparison with refractory complex concentrated alloys (RCCAs). Materials, 15 (13). 4596. ISSN 1996-1944
Abstract
In this paper, we present a systematic study of the as-cast and heat-treated microstructures of three refractory metal intermetallic composites based on Nb (i.e., RM(Nb)ICs), namely the alloys EZ2, EZ5, and EZ6, and one RM(Nb)IC/RCCA (refractory complex concentrated alloy), namely the alloy EZ8. We also examine the hardness and phases of these alloys. The nominal compositions (at.%) of the alloys were Nb-24Ti-18Si-5Hf-5Sn (EZ2), Nb-24Ti-18Si-5Al-5Hf-5Sn (EZ5), Nb-24Ti-18Si-5Cr-5Hf-5Sn (EZ6), and Nb-24Ti-18Si-5Al-5Cr-5Hf-5Sn (EZ8). All four alloys had density less than 7.3 g/cm3. The Nbss was stable in EZ2 and EZ6 and the C14-NbCr2 Laves phase in EZ6 and EZ8. In all four alloys, the A15-Nb3X (X = Al,Si,Sn) and the tetragonal and hexagonal Nb5Si3 were stable. Eutectics of Nbss + Nb5Si3 and Nbss + C14-NbCr2 formed in the cast alloys without and with Cr addition, respectively. In all four alloys, Nb3Si was not formed. In the heat-treated alloys EZ5 and EZ8, A15-Nb3X precipitated in the Nb5Si3 grains. The chemical compositions of Nbss + C14-NbCr2 eutectics and some Nb5Si3 silicides and lamellar microstructures corresponded to high-entropy or complex concentrated phases (compositionally complex phases). Microstructures and properties were considered from the perspective of the alloy design methodology NICE. The vol.% Nbss increased with increasing ΔχNbss. The hardness of the alloys respectively increased and decreased with increasing vol.% of A15-Nb3X and Nbss. The hardness of the A15-Nb3X increased with its parameter Δχ, and the hardness of the Nbss increased with its parameters δ and Δχ. The room-temperature-specific strength of the alloys was in the range 271.7 to 416.5 MPa cm3g−1. The effect of the synergy of Hf and Sn, or Hf and B, or Hf and Ge on the macrosegregation of solutes, microstructures, and properties of RM(Nb)ICs/RCCAs from this study and others is compared. Phase transformations involving compositionally complex phases are discussed.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). |
Keywords: | refractory metal intermetallic composites; Nb silicide-based alloys; complex concentrated alloys; alloy design; high-entropy phases; complex concentrated phases; compositionally complex phases |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Materials Science and Engineering (Sheffield) |
Funding Information: | Funder Grant number ENGINEERING AND PHYSICAL SCIENCE RESEARCH COUNCIL EP/H500405/1 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 18 Aug 2022 15:57 |
Last Modified: | 20 Aug 2022 03:58 |
Status: | Published |
Publisher: | MDPI AG |
Refereed: | Yes |
Identification Number: | 10.3390/ma15134596 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:190000 |