Effect of B2 ordering on the tensile mechanical properties of refractory AlxNb40Ti40V20−x medium-entropy alloys

Most of refractory high/medium-entropy alloys show promising compressive mechanical properties at elevated temperatures. However, scarce tensile testing data hinder the estimation of the applicability of these alloys for potential high-temperature service. It is also unclear how an ordered structure, which improves high-temperature compressive strength, will affect the tensile performance. This work demonstrated that the effect of B2 ordering on the tensile mechanical properties of new refractory AlxNb40Ti40V20−x (x = 0; 15; 20 at%) medium-entropy alloys was manifold, and it depended on the chemical composition. In an Al15Nb40Ti40V5 alloy having a weak degree of B2 ordering, large uniform room-temperature elongation and moderate high-temperature strength, comparable with a bcc Nb40Ti40V20 alloy, were found. An Al20Nb40Ti40 alloy with the high degree of B2 ordering was brittle at room-temperature and sensitive to testing environment at elevated temperatures. Meantime, it softened notably slower up to 0.4 Tm, albeit losing strength at> 0.4 Tm faster than the bcc Nb40Ti40V20 or weakly B2-ordered Al15Nb40Ti40V5 alloys. Factors responsible for the resulted mechanical properties were thoroughly discussed.