Composition and Structure of fcc-Structured High-Entropy Alloys Irradiated with Helium Ions

Abstract

Bulk samples of CoCrFeNi and CoCrFeMnNi high-entropy alloys, prepared by arc melting from a powder of a purity up to 99.97% under an argon atmosphere followed by annealing (1150С, 24 and 72 h) and cold rolling (85% reduction in thickness), are irradiated with He2+ ions (energy of 40 keV, f luence of 2 × 1017 cm–2). CoCrFeNi and CoCrFeMnNi samples are substitutional solid solutions with a composition close to equiatomic and a uniform distribution of elements over the depth of the alloys. They have a coarse grain structure with a grain size of about 80 μm for CoCrFeNi and 100 μm for CoCrFeMnNi. The surface microstructure and the phase and elemental composition of high-entropy alloys are resistant to irradiation. No traces of radiation erosion or changes in the elemental and phase composition of the alloys are found. In alloys, the dislocation density increases, which leads to a decrease in the size of the coherent-scattering regions, and helium bubbles are also formed, leading to an increase in compressive macrostress. Tensile microstress prevails in irradiated CoCrFeNi alloys, while compressive stress prevails in CoCrFeMnNi alloys. High-entropy CoCrFeMnNi alloys with a more complex composition are more resistant to radiation damage.