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Refractory high entropy alloys represent a new class of metallic alloys attractive for high-temperature applications. However, most of the developed alloys have either low ductility at room temperature or high density. In this work, we report structure and mechanical properties of a novel non-equiatomic Ti 1.89 CrNbV 0.56 alloy produced by vacuum arc melting. The density of the alloy was 6.17 g/cm 3 . In the as-cast condition, the alloy had a single-phase bcc structure enabling room temperature deformation in compression to ε > 50% or cold-rolling to a thickness strain of 80%. Rolling resulted in the formation of a dislocation substructure and development of kink and shear bands. Meanwhile, microhardness measurements have revealed only a moderate increase from 396 HV in the as-cast condition to 454-469 HV after 40-80% rolling. After 80% cold rolling the alloy had yield strength of 1020 MPa, ultimate tensile strength of 1535 MPa, and elongation to fracture of 3.5%. The cold rolled alloy was annealed at 800, 1000 or 1200°C for 1-100 h. Microstructural response to the annealing strongly depended on temperature. Annealing at 800°C mostly resulted in Cr-rich fcc (C15) Laves phase particles precipitation. Annealing at 1000°C led to the bcc matrix recrystallization along with the precipitation of the Laves phase particles, thereby producing a fine duplex microstructure. Finally, annealing at 1200°C resulted in a coarse-grained recrystallized single-phase bcc microstructure. Microhardness of the alloy lowered with an increase in the annealing temperature while the annealing time had a small effect on hardness.

Four refractory high entropy alloys with different chemical compositions, which can be calculated as Ti (50-1.5625x) Nb (30-0.9375x) Cr 10 V 10 Ni 1.5x Al x (x ¼ 0, 5, 7, 10), were prepared by arc melting to determine the effect of Ni and Al on the phase composition, structure and mechanical properties. Each alloy was studied in both the as-cast and annealed at 1000 � C for 24 h conditions; compression tests at room temperature or at 800 � C was used to examine mechanical behavior of the alloys and the effect of deformation on microstructure. The replacement of Ti and Nb with Al and Ni resulted in the formation of the Ti, Ni-rich σ-phase and Ti 2 Ni phases in the bcc matrix in contrast to the ThermoCalc predictions which suggests the formation of the bcc solid solution, B2, and Laves phases. The Ti, Ni-rich σ-phase can't also be expected from the analysis of the corresponding binary and ternary phase diagrams. Annealing did not result in noticeable changes in the microstructure. The formation of the σ and Ti 2 Ni phases resulted in a considerable increase in strength (from 745 to 1600 MPa) and decrease in ductility (from a thickness reduction �50% to fracture in the elastic region) at room temperature. An increase in the testing temperature to 800 � C resulted in softening to and a substantial increase in ductility of all the alloys. Complex relationships between the fraction of the second phases and mechanical properties were discussed.

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Oxidation behavior of a refractory AlNbTiVZr0.25 high-entropy alloy at 600–900 °C was investigated. At 600–700 °C, two-stage oxidation kinetics was found: Nearly parabolic oxidation (n = 0.46–0.48) at the first stage, transitioned to breakaway oxidation (n = 0.75–0.72) at the second stage. At 800 °C, the oxidation kinetics was nearly linear (n = 0.92) throughout the entire duration of testing. At 900 °C, the specimen disintegrated after 50 h of testing. The specific mass gains were estimated to be 7.2, 38.1, and 107.5, and 225.5 mg/cm2 at 600, 700, and 800 °C for 100 h, and 900 °C for 50 h, respectively. Phase compositions and morphology of the oxide scales were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was shown that the surface layer at 600 °C consisted of the V2O5, VO2, TiO2, Nb2O5, and TiNb2O7 oxides. Meanwhile, the scale at 900 °C comprised of complex TiNb2O7, AlNbO4, and Nb2Zr6O17 oxides. The oxidation mechanisms operating at different temperatures were discussed and a comparison of oxidation characteristics with the other alloys was conducted.