Unravelling Microstructure Selection in an Additively Manufactured Eutectic High-Entropy Alloy

Area of Science:

• Materials Science
• Metallurgy
• Additive Manufacturing

Background:

• High-entropy alloys (HEAs) exhibit excellent mechanical properties for structural applications.
• Additive manufacturing (AM) creates unique nonequilibrium microstructures due to rapid solidification.
• Understanding the interplay between AM processing, HEA microstructure, and properties is crucial.

Purpose of the Study:

• Investigate the influence of solidification rate on microstructure evolution and phase transformation in laser additively manufactured AlCrFe2Ni2 HEAs.
• Explore how varying laser scan speed affects solidification modes and resulting material properties.
• Provide a multiscale understanding of solidification mechanisms in HEAs under nonequilibrium conditions.

Main Methods:

• Laser additive manufacturing of AlCrFe2Ni2 HEAs at varying scan speeds.
• Microstructural characterization to identify solidification modes (coupled eutectic, anomalous eutectic, single-phase).
• Thermodynamic modeling and molecular dynamics simulations to elucidate atomic diffusion and interface stability.

Main Results:

• Increasing solidification rate (via laser scan speed) transitions solidification from coupled eutectic to anomalous eutectic, and then to single-phase.
• Distinct microstructures and a wide range of mechanical properties are achieved with these transitions.
• Low cooling rates favor diffusion and coupled eutectic growth, while rapid cooling suppresses diffusion, promoting anomalous or single-phase solidification.

Conclusions:

• Kinetic effects during rapid solidification in AM can override thermodynamic predictions for HEAs.
• Additive manufacturing offers a powerful route to design HEAs with tailored microstructures and properties.
• The study provides fundamental insights into solidification mechanisms in HEAs produced by AM.