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

Abstract

In this study bulk samples of high-entropy alloys CoCrFeNi and CoCrFeMnNi, fabricated by arc melting (of pure metal powders up to 99.97%, argon atmosphere) followed by annealing (1150°C, 24 and 72 h) and cold rolling (85% decrease in thickness) were irradiated with He2+ ions (40 keV, fluence 2 × 1017 cm–2). Samples of CoCrFeNi and CoCrFeMnNi are substitutional solid solutions with a close to equiatomic composition 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 alloys. It was revealed that the surface microstructure, phase and elemental composition of high-entropy alloys are resistant to irradiation. No traces of radiation erosion and changes in the elemental and phase composition of the alloys were found. In alloys, the dislocation density increases, which leads to a decrease in the size of coherent scattering regions, and helium bubbles are also formed, leading to an increase in compressive macrostresses. It was found that tensile microstresses prevail in irradiated CoCrFeNi alloys, while compressive stresses prevail in CoCrFeMnNi alloys. It has been found that high-entropy CoCrFeMnNi alloys with a more complex composition are more resistant to radiation damage.