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, fluence 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 compositions of high-entropy alloys are resistant to irradiation. No traces of radiation erosion or changes in the elemental and phase compositions 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.