Self-toughened high entropy alloy with a body-centred cubic structure

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• High entropy alloys (HEAs) offer unique properties due to their complex compositions.
• Interstitial elements can significantly influence alloy properties, but their role in HEAs is complex.
• Developing advanced alloys with high strength and ductility remains a key challenge.

Purpose of the Study:

• To investigate the incorporation of interstitial elements (B, C, O) into a BCC FeMnCoCr-based HEA.
• To characterize the mechanical properties, particularly yield strength and ductility, of the developed interstitial HEA (iHEA).
• To elucidate the strengthening mechanisms and deformation pathways in this novel BCC-structured iHEA.

Main Methods:

• Synthesis of a body-centered cubic (BCC) FeMnCoCr-based interstitial high entropy alloy (iHEA) with boron, carbon, and oxygen.
• Mechanical testing to determine yield strength and assess ductility under load.
• Microstructural analysis to understand phase transformations (BCC, HCP, FCC) and deformation mechanisms like dislocation motion, grain boundary segregation, and twinning.

Main Results:

• The BCC-structured iHEA achieved a remarkable yield strength of 2.55 GPa with significant ductility.
• Strengthening resulted from interstitial atoms, compositional fluctuations, and fine grain size inhibiting dislocation motion.
• The alloy exhibited phase transformations (BCC to HCP to FCC) and nanolaminate formation, enhancing plasticity through strain partitioning and deformation twinning.

Conclusions:

• The newly developed BCC-structured iHEA demonstrates a unique combination of high strength and remarkable ductility.
• Interstitial elements play a crucial role in strengthening, grain boundary reinforcement, and tuning phase stability.
• Multiple deformation pathways, including phase transformation and twinning, contribute to the alloy's exceptional mechanical performance.