AlCoCrFeNi_2.1 eutectic high entropy alloy: defect analysis, microstructural stability and ion irradiation resilience

The AlCoCrFeNi_2.1 eutectic high entropy alloy (EHEA) features a dual-phase lamellar microstructure composed of ordered L1₂ and B2 phases, offering a unique combination of strength, ductility, and thermal stability. This study investigates the microstructural evolution, phase stability, and irradiation resilience of AlCoCrFeNi_x alloys with x = 1.9, 2.1, and 2.6. Advanced electron microscopy techniques revealed composition-dependent microstructure and confirmed the eutectic nature of the x = 2.1 alloy. Thermomechanical processing via cold rolling and annealing preserved phase ordering and enhanced mechanical properties. Irradiation of transmission electron microscopy (TEM) samples with Ne ions at doses up to 1.5 dpa enabled precise microstructure and defect analysis by comparing pre- and post-irradiation states of the same samples. The L1₂ phase exhibited dose-dependent disordering (assessed via evaluation of the fraction of 〈110〉-type dislocations), while the B2 phase retained its ordered structure, showing localized disorder and anti-phase boundaries. As a function of dose, a significant decrease in the network dislocation density (excluding dislocation loops) was observed in L1₂. On the other hand, this phase exhibited dose-dependent increase in both the density and size of dislocation loops. The B2 phase exhibited a similar effect, although the change was more moderate compared to L1₂. Semi-coherent L1₂/B2 boundaries, initially rich in dislocations, retained the Kurdjumov–Sachs orientation relationship post-irradiation, although dislocations vanished and stacking faults occasionally formed. These findings elucidate phase-specific radiation damage mechanisms and confirm the superior irradiation tolerance and structural integrity of AlCoCrFeNi_2.1, highlighting its potential for nuclear structural applications.