Structural damage and phase stability of Al_0.3CoCrFeNi high entropy alloy under high temperature ion irradiation

An initially single phase high entropy alloy (HEA) Al0.3CoCrFeNi was irradiated by 3 MeV Au ions to a fluence of 6 x 10(15) cm(2) (similar to 31 dpa at damage peak) at four different temperatures ranging from 250 degrees C to 650 degrees C. Transmission electron microscopy (TEM) and Atom probe tomography (APT) were employed to study the evolution of structural damage and phase stability with irradiation temperature. Al0.3CoCrFeNi exhibited a similar evolution of irradiation-induced defects with temperature as compared with conventional FCC alloys. At 250 degrees C and 350 degrees C, most of the visible irradiation-induced defects were faulted 1/3(111) dislocation loops. As the irradiation temperature increased to 500 degrees C, perfect 1/2(110) dislocation loops were observed along with the faulted loops. At the highest irradiation temperature 650 degrees C, only dislocation lines and networks could be observed. Regarding phase stability, the 3 MeV Au irradiation was observed to suppress the precipitation of (Ni, Al)-enriched nano clusters and the L12 ordered structure at irradiation temperatures 250 degrees C to 500 degrees C whereas precipitation of the B2 ordered structure was accelerated at 650 degrees C. This resulted in qualitatively opposite precipitation behavior between the ion irradiated damage region and unirradiated region at 500 degrees C and 650 degrees C. The opposite phase stability of the ion-irradiated damage region and unirradiated region at different temperatures is attributed to the competing effects of ballistic dissolution vs irradiation enhanced diffusion on precipitation. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.