Effect of lamellar microstructure on fatigue crack initiation and propagation in AlCoCrFeNi2.1 eutectic high-entropy alloy

A theoretical model is established to describe the crack initiation and propagation in AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA). By the Gibbs free energy change, the critical cycle number for crack initiation has been calculated which indicates B2 precipitates in FCC lamellae can delay crack initiation. The dislocation motion from crack tip has been analyzed. The results show that the equilibrium number of dislocations increases and the maximum tensile stress of crack tip reduces, when FCC lamellae thickness increases, thereby the cleavage is suppressed. Moreover, the critical stress for dislocation penetrating semi-coherent phase boundary (SCPB) is about 3.9 GPa, which can hinder dislocation motion and prevent crack propagation. In addition, the calculated result shows that the crack growth rate reduces by reducing the thickness of the BCC lamellae. Therefore, this work has provided a theoretical model to study fracture characteristics of AlCoCrFeNi2.1 EHEA.