Abstract
Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co–Cr–Fe–Mn–Ni system was implemented to find ‘islands’ of single phase FCC structure within the compositional space in order to reduce the cost of this well-studied alloy system. The screening identified a region centred around Co10Cr12Fe43Mn18Ni17, reducing the material cost compared to the equiatomic alloy by ∼40%. The alloy was experimentally investigated at room and elevated temperatures, including in-situ tensile testing. The alloy was found to possess slightly lower strength compared to the equiatomic alloy at room temperature, however, exhibited excellent thermal strength up to 873K. Deformation twinning was observed after tensile testing at room temperature, primarily attributed to the reduced stacking fault energy (SFE), which was proven by a thermodynamic model for calculating the SFE. The softening behaviour at room temperature can be explained through solid solution hardening (SSH), whereby a modified approach to Labusch's model was used to calculate the SSH in reported alloys in this study within the Co–Cr–Fe–Mn–Ni system. The modified models for SFE and SSH are proposed to be implemented into high-throughput screening algorithms for accelerated alloy design towards specific mechanical properties.
Highlights
Similar to most alloys within the Cantor alloy system [43], it is worth noting that the single-phase region is metastable at lower temperatures, with ThermoCalc predicting the formation of a BCC phase
This research designed an alloy within the CoCrFeMnNi system based on high-throughput screening of CALPHAD predictions
The alloy that was designed, produced and studied, Co10Cr12Fe43Mn18Ni17, had the goal of applying constraints to the expensive elements, Co and Ni, in order to address the barrier of high cost, which limit the industrialisation of High Entropy Alloys (HEAs) and Compositionally Complex Alloys (CCAs)
Summary
The term High Entropy Alloys (HEAs) was first coined by Yeh et al [1] in 2004 when multi-principal elements were proposed, mostly limited to equi-molar proportion of elements in the composition [1,2]. Complex Alloys (CCAs) was proposed to broaden the definition to non-equiatomic or multi-phase alloys [3]. Due to the inherent design approach of multi-principal elements, HEAs/CCAs often result in the use of high quantities of expensive elements such as Co and Ni, drastically increasing the cost of the alloy. It is critical to find compositional regions that reduce the quantity of these critical and expensive elements, while maintaining the mechanical properties already reported for cur rent HEAs. An additional benefit of minimising the use of Co is the sustainability issue of Co being a critical raw material [14]
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