Tensile behavior of hexagonal rare-earth-based low, medium, and high entropy alloys: Strengthening effect of configurational entropy

In the equiatomic hexagonal close packed high entropy alloy Ho-Dy-Y-Gd-Tb, there is a discrepancy, called the Gibbs paradox, between the extraordinary similarity of the constituent rare earth elements and its calculated configurational entropy. Equiatomic alloys made from one to five rare earth elements, with varying configura-tional entropy, are investigated for this work to evaluate this paradox in the context of tensile behavior. Assuming comparable microstructures and minimized solid solution strengthening due to the similarity of the constituent elements, a possible strengthening effect of the high configurational entropy is assessed. The alloys are successfully prepared via arc melting with comparable grain sizes and near equiatomic compositions. X-Ray diffraction, and elemental mappings with energy-dispersive X-Ray spectroscopy indicate single-phase micro-structures in all alloys except for Ho-Y and Ho-Y-Gd. Tensile tests at room temperature show that the tensile strength of the single-phase alloys lies in the range of the pure elements, which confirms the hypothesis of minimized solid solution strengthening. Those alloys containing additional phases as well as the high entropy alloy show pronounced brittle behavior. No direct correlation between tensile behavior at room temperature and configurational entropy is observed. We state that this alloy system is a suitable candidate for evaluating the Gibbs paradox and disproving an entropy effect on the tensile behavior of this alloy system. This work con-tributes to understanding mechanical properties and the influence of configurational entropy on the hexagonal close packed high entropy alloy Ho-Dy-Y-Gd-Tb.

Automated summary

In the equiatomic hexagonal close packed high entropy alloy Ho-Dy-Y-Gd-Tb, a discrepancy known as the Gibbs paradox exists between the similarity of the rare earth elements and the calculated configurational entropy. This study investigates equiatomic alloys made from one to five rare earth elements to evaluate this paradox in terms of tensile behavior. The results show that there is no direct correlation between tensile behavior and configurational entropy in this alloy system.