Small-scale mechanical behavior of a eutectic high entropy alloy

Area of Science:

• Materials Science
• Metallurgy
• Mechanical Engineering

Background:

• Eutectic high entropy alloys (EHEAs) offer a novel approach to overcome the strength-ductility trade-off in conventional alloys.
• These alloys feature a lamellar arrangement of solid-solution phases, but their dynamic strengthening mechanisms and phase-boundary interactions under load are not fully understood.

Purpose of the Study:

• To investigate the small-scale mechanical behavior of the AlCoCrFeNi2.1 EHEA, focusing on individual phase contributions.
• To elucidate the micro-mechanisms governing deformation and fracture in L12 and B2 phases within the EHEA.

Main Methods:

• Small-scale mechanical testing, including nano-indentation and micro-pillar compression, was performed on the AlCoCrFeNi2.1 EHEA.
• Phase-specific properties such as hardness, strength, strain rate sensitivity, and friction coefficient were evaluated.
• Microstructural analysis was conducted to observe deformation mechanisms and interface integrity.

Main Results:

• The AlCoCrFeNi2.1 EHEA exhibited high tensile (1165 MPa, ~18% ductility) and compressive (1863 MPa, ~34% strain) strengths.
• Dual mode fracture was observed: ductile failure in the L12 phase and brittle failure in the B2 phase.
• The B2 phase demonstrated higher hardness, strength, and strain rate sensitivity compared to the L12 phase, with distinct deformation mechanisms (barreling vs. slip steps).

Conclusions:

• The study clarifies the distinct mechanical roles of L12 and B2 phases in the AlCoCrFeNi2.1 EHEA.
• Understanding these phase-specific behaviors is crucial for designing advanced concentrated alloys with enhanced fracture toughness.
• The findings provide a foundation for tailoring EHEAs for structural applications requiring a combination of high strength and ductility.