Mechanical properties of Nb_(25)Mo_(25)Ta_(25)W_(25) and V_(20)Nb_(20)Mo_(20)Ta_(20)W_(20) refractory high entropy alloys

摘要

Two refractory high entropy alloys with compositions near Nb_(25)Mo_(25)Ta_(25)W_(25) and V_(20)Nb_(20)Mo_(20)Ta_(20)W_(20), were produced by vacuum arc-melting. Despite containing many constituents, both alloys had a single-phase body-centered cubic (BCC) structure that remained not only stable after exposure to 1400 °C, but also disordered, as confirmed by the absence of superlattice reflections in neutron diffraction data. Compressive flow properties and microstructure development of these alloys were determined from room temperature up to 1600 °C. Limited compressive plasticity and quasi-cleavage fracture at room temperature suggest that the ductile-to-brittle transition for these alloys occurs above room temperature. At 600 °C and above, both alloys showed extensive compressive plastic strain. The yield stress of both alloys dropped by 30-40% between room temperature and 600 °C, but was relatively insensitive to temperature above 600 °C, comparing favorably with conventional superalloys.