Microstructural Evolution of Quaternary AlCoCrNi High-Entropy Alloys during Heat Treatment

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• High-entropy alloys (HEAs) offer unique properties due to their complex compositions.
• Understanding microstructural evolution under thermal treatment is crucial for HEA applications.
• Quaternary AlCoCrNi alloys are of interest for their potential mechanical performance.

Purpose of the Study:

• To investigate the impact of prolonged heat treatment on the microstructure and mechanical properties of AlCoCrNi HEAs.
• To analyze phase transformations and nanostructural changes at different annealing durations.
• To correlate microstructural evolution with resulting mechanical behavior, particularly yield strength and compressive strain.

Main Methods:

• Quaternary AlCoCrNi high-entropy alloys were subjected to heat treatment at 873 K for 72 and 192 hours.
• Microstructural analysis was performed to observe changes in nanostructure and phase composition.
• Mechanical property testing, including yield strength and compressive strain measurements, was conducted.

Main Results:

• Heat treatment for 72 hours resulted in B2 dendrite, BCC interdendrite, and sigma phases.
• Extended annealing to 192 hours led to B2 dendrite, interdendritic sigma, and BCC phases.
• Morphological changes included dendritic regions shifting from spherical to needle-like and interdendritic regions transforming from spinodal-like to plate-like.
• Nano-scale phase transformation occurred in the dendritic regions.
• The sigma phase presence increased yield strength to approximately 1172 MPa.
• However, the sigma phase significantly reduced compressive strain to 0.62%.

Conclusions:

• Heat treatment duration critically influences the phase constitution and nanostructure of AlCoCrNi HEAs.
• The formation of the sigma phase is a key factor in enhancing yield strength.
• The presence of the sigma phase leads to a detrimental decrease in ductility, limiting overall mechanical performance.