Refractory complex concentrated alloys (RCCAs) have the potential for unmatched mechanical strength and thermal stability in extreme environments, yet poor ductility remains as a critical design challenge—especially among alloys based on V, Nb, Ta, Cr, Mo, and W, with a body-centered cubic (BCC) structure. Experimental assessments of RCCA properties are complicated by various processing hurdles including high melting points, an expansive composition space, and microstructural variation arising from process history. This study demonstrates that RCCA thin films can be grown epitaxially on MgO (100) substrates, leading to films with reduced grain boundary densities. Kinetic factors such as deposition rate and temperature influence the crystallographic orientation. The (110)BCC//(100)MgO growth direction, which is preferred at slow deposition rates, leads to columnar grains arising from two competing in-plane orientations, while the (100)BCC//(100)MgO growth direction, at higher deposition rates, leads to near-single crystal films in which grain widths span many times the film thickness. The resulting films are ideal for nanomechanical characterization aimed at screening RCCA properties or investigating deformation mechanisms as a function of composition without the influence of grain boundary effects.
Wissuchek et al. (Sun,) studied this question.