Dynamic compression of dendritic high-entropy alloy Al0.5CoCrFeNi with various microstructures: Experiments and constitutive modeling

The mechanical properties and microstructural evolution of as-cast and heat-treated dendritic dual phase high-entropy alloy (HEA) ${\mathrm{Al}}_{0.5}\mathrm{CoCrFeNi}$ are investigated to provides valuable insights into their plastic deformation, particularly under varying strain rates and temperatures. The as-cast ${\mathrm{Al}}_{0.5}\mathrm{CoCrFeNi}$ alloy, consisting of face-centered cubic (FCC) dendritic and body-centered cubic (BCC) interdendritic phases, is compared to a heat-treated variant, which contains additional needle-shaped BCC precipitates within the dendritic domains. Uniaxial compression tests are conducted across a strain rate range of 10⁻³ to 2000 $s^{-1}$ and a temperature range of 173 to 673 K for both types of the alloys. The results show that the yield strength of the alloys increases with higher strain rates or lower temperatures. The heat-treated alloy, benefiting from the precipitate strengthening of additional needle-shaped precipitates, exhibits higher yield strength than the as-cast alloy. Dislocation slip and kink bands dominate the plastic deformation firstly. As the true strain increases, nano twins are observed. Cryogenic temperatures promote more nano twins with different variants. Additionally, different plastic deformation partitioning behaviors between the FCC and BCC phases are observed due to the microstructure differences between the two types of alloys. Furthermore, the Johnson-Cook-Cowper Symonds (JC-CS) constitutive models are developed and successfully describe the plastic flow of both types of the alloys over a wide range of strain rates and temperatures, providing a valuable tool for future research and applications.