The microstructure and He+ ion irradiation behavior of novel low-activation W-Ta-Cr-V refractory high entropy alloy for nuclear applications
Damian Kalita, I. Jóźwik, Ł. Kurpaska, Yanwen Zhang, K. Mulewska, Witold Chromiński, J.H. O’Connell, Yanling Ge, Walker L. Boldman, Philip D. Rack, Yongqiang Wang, William J. Weber, J. Jagielski
Abstract
Microstructure and nanohardness of a nearly equimolar W-Ta-Cr-V high entropy alloy (HEA), as well as its irradiation response under He+ irradiation, were investigated. The single-phase body-centered cubic nanostructured alloy with a 1 µm thick layer was fabricated on a silicon substrate using a magnetron sputtering method. The HEA film has a complex microstructure consisting of micrometric domains that exhibit internal nanostructure controlled by their crystal orientation. The measured nanohardness of the W-Ta-Cr-V alloy is 13±2 GPa, which significantly exceeds the hardness of nanocrystalline tungsten as a result of the high solid-solution strengthening effect. In order to evaluate the irradiation resistance of the HEA film, the material was irradiated with 200 keV He+ ions at room temperature, with two different ion fluences: 1×1016 and 5×1016 ions/cm2. Using transmission electron microscopy, a high density of extremely fine He bubbles is observed that were uniformly distributed in the matrix. The increase of He+ ion fluence increased the density of bubbles, whereas their size remained at a similar level, which indicates that the damage proceeds by the nucleation of additional He bubbles, not by their growth.