Influence of Iron Addition on Fracture Mechanism and Toughness in the AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

The AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) is a duplex casting alloy with high strength and moderate ductility, making it attractive for as-cast applications. However, utilization of this material would require improved fracture toughness. We have therefore attempted to improve the as-cast ductility and fracture toughness of the AlCoCrFeNi2.1 EHEA by increasing the iron content by 2 atomic percent, thereby forming a novel AlCoCrFe1.15Ni2.1 alloy (Fe-EHEA). Scanning transmission electron microscopy coupled with in situ micro-digital image correlation was used to characterize the phase composition and the distribution of strain at the micro-scale, including strain gradients across interphase boundaries. We have also developed a novel DIC-based approach to measure fracture toughness, enabling a determination of defect sensitivity in this alloy. Micro-crack nucleation and strain localization were found to be controlling fracture mechanisms. The addition of Fe to this EHEA improves the fracture toughness and elongation to fracture, while maintaining tensile strength, when compared to the base EHEA composition. FCC volume fraction impacts both yield strength and crack growth resistance, leading to an improvement of as-cast mechanical properties.