Martensitic Transformation in Fe_{x}Mn_{80-x}Co_{10}Cr_{10} High-Entropy Alloy

Area of Science:

• Materials Science
• Computational Materials Science
• Alloy Design

Background:

• High-entropy alloys (HEAs) and medium-entropy alloys (MEAs) offer tunable structure-property relationships through alloying and chemical disorder.
• Understanding phase stability and transformations is crucial for designing advanced HEAs and MEAs.

Purpose of the Study:

• To computationally tune the free energies between face-centered-cubic (FCC) and hexagonal-close-packed (HCP) phases in Fe-Mn-Co-Cr systems.
• To investigate the correlation between martensitic transformation, chemical short-range order, and phase energy differences in Fe-Mn-based alloys.
• To provide a design guide for controlling electronic-level physics in HEAs.

Main Methods:

• Density-functional theory (DFT) combined with the coherent-potential approximation (CPA) for averaging chemical configurations.
• Thermodynamic calculations to determine free energies and stacking-fault energies.
• Experimental validation using transmission electron microscopy (TEM), selective-area diffraction (SAD), and electron-backscattered diffraction (EBSD) on single crystals.

Main Results:

• Calculations accurately predicted the FCC and HCP energy difference and stacking-fault energies in Fe_{x}Mn_{80-x}Co_{10}Cr_{10} systems.
• A direct correlation was established between martensitic transformation, chemical short-range order, and the calculated energy differences.
• Experimental results quantitatively agreed with theoretical predictions, confirming the two-phase region at x=40 at.%.

Conclusions:

• The study provides a fundamental understanding of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) in HEAs.
• The findings offer a computational design strategy for controlling phase stability and properties at the electronic level.
• This work facilitates the rational design of novel HEAs with desired mechanical properties.