Structure, mechanical properties, and oxidation behaviour of refractory NbTiZrM (M = Ta, Mo, V) complex concentrated alloys

Abstract

In this study, we systematically explored the effect of Ta, Mo, and V on the structure, mechanical properties, and oxidation behaviour of a single-phase body-centred cubic (bcc) NbTiZr alloy. Alloying with Ta or Mo in concentrations of 10, 25, or 40 at% retained the single-phase bcc structure, yet led to elemental segregations, with the formation of Ta/Mo-rich dendrites. Among the V-containing alloys, the (NbTiZr)₉₀V₁₀ and (NbTiZr)₇₅V₂₅ alloys possessed the single-phase bcc structure, while, in the (NbTiZr)₆₀V₄₀ alloy, two extra bcc phases, namely Zr- and V-rich ones, were formed. These phases adopted a “cube-on-cube” orientation relationship with the Nb-rich bcc matrix. Сompression tests showed that the additions of Ta and Mo increased the yield strength at 22–1000 °C linearly. The strengthening effect of Mo at 22–800 °C was two-to-three times higher than that of Ta, yet it became comparable at 1000 °C. Alloying with V also increased the yield strength at 22 °C linearly, while it degraded the strength at higher temperatures. Oxidation tests at 1000 °C revealed that the effect of alloying elements was dependent on the oxidation time. At a short period (1 h), the maximum content of Ta could eliminate the oxide scale spallation. For longer durations, however, all the elements added had an inferior effect accompanied by the oxide scale spallation, with the shortest time to complete disintegration demonstrated by the V-containing alloys. The correlations between the chemical composition, structure, and properties of the alloys were thoroughly examined through a comparison of experimental and computational data.