4.7 Article

Phase equilibria, mechanical properties and design of quaternary refractory high entropy alloys

Journal

MATERIALS & DESIGN
Volume 155, Issue -, Pages 244-256

Publisher

ELSEVIER SCI LTD
DOI: 10.1016/j.matdes.2018.06.003

Keywords

Refractory high entropy alloys; Phase equilibria; CALPHAD; Materials characterization; Mechanical properties; Solid solution strengthening

Funding

  1. CNPq, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico - Brasil [233746/2014-5]
  2. Center for Advanced Non-Ferrous Structural Alloys (CANFSA)
  3. National Science Foundation Industry/University Cooperative Research Center (I/UCRC) at the Colorado School of Mines (CSM) in Golden, CO, USA [1624836]
  4. Office of Naval Research [12488790]
  5. DOE Office of Science [DE-AC02-06CH11357]

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Refractory high entropy alloys (RHEAs) are candidates for replacing conventional refractory alloys. In this work, twelve new RHEAs were selected and produced. The phases present in the as-cast and heat-treated conditions were characterized and compared with CALPHAD simulations and empirical parameters. Here we propose a new interpretation for the two widely used delta and Omega empirical parameters. In this work, they are shown to be inaccurate when applied to a large group of RHEAs, but can be a powerful alloy design tool if applied on specific subsystems of alloys. Experimentally, chromium-containing alloys are shown to form Laves phases, especially when the lattice distortion (delta) is high, while aluminum-containing alloys are shown to form the A15 phase upon heat-treatment, due to their highly negative enthalpy of mixing (Delta H-mix). In addition to microstructural characterization, mechanical properties of these alloys via hardness testing were assessed. A poor correlation was observed between the hardness and the atomic size and elastic modulus mismatch in these single-phase BCC RHEAs, suggesting that core structure of the screw dislocations is a crucial parameter in understanding the strength of these alloys. (C) 2018 Elsevier Ltd. All rights reserved.

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