Proton irradiation induced chemical ordering in an Al0.3CoFeNi high entropy alloy

Abstract

The radiation resistance of single-phase high entropy alloys has been reported to be superior to conventional alloys, due to their high lattice distortion and sluggish diffusion kinetics. The current study combines the beneficial effects of a concentrated multi-component solid solution and chemical ordering on the parent lattice of a candidate alloy, Al_0.3CoFeNi, to enhance proton radiation resistance. The strong ordering tendency in this alloy results in the formation of Ni-Al-rich short-range ordered (SRO) domains when it is annealed in a single FCC phase field and water quenched. The irradiation of these microstructures with high-fluence MeV-energetic protons aids the transformation of the prior metastable single FCC solid-solution with SRO domains toward a more stable condition with L1₂ long-range ordered (LRO) domains embedded within the FCC solid solution matrix. Potentially, the creation of radiation-induced vacancy cascades within the FCC solid-solution enhances local diffusivity aiding the transition from SRO domains to LRO L1₂ domains. Therefore, this can be considered as a recovery mechanism, since the radiation-induced damage is not allowed to accumulate and is minimized via nanometer-scale precipitation of the ordered intermetallic phase. Additionally, preferential Co segregation to defect clusters or dislocation loops was also observed. In comparison, purely thermal activation via annealing at 500 °C for 30 min induces a similar transformation from SRO to LRO in this alloy, driving the system closer to equilibrium.