Phase stability and the Portevin-Le Chatelier effect in Cr-Mn-Fe-Co-Ni High-Entropy Alloys
type: CreativeWork
description: High-Entropy Alloys (HEAs) are a new class of metallic materials based on the combination of multiple principal elements, often with the intention to form a concentrated solid solution. It has been suggested that these solid solution phases could offer enhanced mechanical properties, due to fluctuations in their local atomic environments. However, at present, the thermodynamic stability of the solid solution phases which form in HEAs is poorly understood. This study aims to improve our understanding of phase stability in HEAs and investigate possible differences in the mechanical behaviour of dilute and concentrated solid solutions. Firstly, a systematic series of experiments is presented, which establish the effect of Co and Fe on the phase equilibria of the widely studied CrMnFeCoNi system. Both Co and Fe were found to stabilise the A1 matrix relative to the A2 and D8b phases at elevated temperatures but did not prevent the formation of ordered phases at 500°C. Alongside literature data, the results show that stable single-phase alloys are rare in the CrMnFeCoNi system. Secondly, a systematic assessment of the AlxCrFeCoNi alloy system showed that Al promotes the formation of B2, D8b and A2 phases, and improved our understanding of phase stability in this system, which has strong potential for developing alloys with desirable mechanical properties. In each study, experimental observations were used to test the fidelity of thermodynamic predictions from the latest CALPHAD databases. Whilst the predictions generally provided a close approximation of the observed phase equilibria, inaccuracies were common, especially at lower temperatures. Phase stability investigations also served to identify thermodynamically stable alloys, suitable for the investigation of the Portevin-Le Chatelier (PLC) effect - a discontinuous yielding phenomenon widely attributed to the repeated pinning of dislocations by mobile solute atoms over certain regimes of temperature and strain-rate. U…
abstract: High-Entropy Alloys (HEAs) are a new class of metallic materials based on the combination of multiple principal elements, often with the intention to form a concentrated solid solution. It has been suggested that these solid solution phases could offer enhanced mechanical properties, due to fluctuations in their local atomic environments. However, at present, the thermodynamic stability of the solid solution phases which form in HEAs is poorly understood. This study aims to improve our understanding of phase stability in HEAs and investigate possible differences in the mechanical behaviour of dilute and concentrated solid solutions. Firstly, a systematic series of experiments is presented, which establish the effect of Co and Fe on the phase equilibria of the widely studied CrMnFeCoNi system. Both Co and Fe were found to stabilise the A1 matrix relative to the A2 and D8b phases at elevated temperatures but did not prevent the formation of ordered phases at 500°C. Alongside literature data, the results show that stable single-phase alloys are rare in the CrMnFeCoNi system. Secondly, a systematic assessment of the AlxCrFeCoNi alloy system showed that Al promotes the formation of B2, D8b and A2 phases, and improved our understanding of phase stability in this system, which has strong potential for developing alloys with desirable mechanical properties. In each study, experimental observations were used to test the fidelity of thermodynamic predictions from the latest CALPHAD databases. Whilst the predictions generally provided a close approximation of the observed phase equilibria, inaccuracies were common, especially at lower temperatures. Phase stability investigations also served to identify thermodynamically stable alloys, suitable for the investigation of the Portevin-Le Chatelier (PLC) effect - a discontinuous yielding phenomenon widely attributed to the repeated pinning of dislocations by mobile solute atoms over certain regimes of temperature and strain-rate. U…
author: Bloomfield, Maximilian
language: eng
keywords: Digital image correlation, Electron microscopy, High Entropy Alloys, Mechanical properties, Phase stability, Portevin-Le Chatelier effect, Serrated flow, Short range order, CALPHAD
license: https://creativecommons.org/licenses/by/4.0/
date published: 2022-09-01
date modified: 2026-07-22T22:24:00Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.96318