Investigation of mechanical behavior, constitutive modeling, and fracture criteria for as-cast Al0.3CoCrFeNi high entropy alloy

Abstract

High entropy alloys (HEAs) have garnered significant attention in recent years, primarily focusing on alloying design and thermal processing. The objective of this study was to investigate the mechanical response of Al0.3CoCrFeNi, a representative HEA, under various stress states, temperatures, and strain rates, aiming to establish its constitutive equation and fracture criteria. Employing a hybrid FEM/EX approach, the constitutive behaviour of the alloy was characterized using the modified Johnson-Cook (MJC) model, while the fracture properties were assessed using the Hosford-Coulomb (HC) equation. Experimental findings highlighted the remarkable tensile strength (578.1 MPa) and ductility (69%) of the as-cast Al0.3CoCrFeNi at room temperature. However, at elevated temperatures ranging from 400 °C to 650 °C, a reduction in ductility was observed, accompanied by serration behaviour. Notably, precipitation hardening was detected at 800 °C, indicative of strengthening through precipitate formation. Additionally, Al0.3CoCrFeNi exhibited significant strain rate sensitivity and a positive strain rate effect, emphasizing its dynamic response under different loading conditions. The accuracy of the constitutive model and fracture criteria was validated through the examination of deformation and fracture modes in Taylor impact tests. The MJC model demonstrated predictions within a 10% deviation from experimental data, while the HC fracture criterion, accounting for stress triaxiality and Lode parameters, effectively predicted shear fracture in the projectiles. Crack formation in the projectiles resulted from a combination of tension and shear, followed by propagation at a 45° angle under combined compression and shear loading. This comprehensive study enhances understanding of the mechanical properties of Al0.3CoCrFeNi, providing valuable insights for its application in engineering, particularly in impact protection.