Microstructure and Mechanical Properties of Nb-Ti-V-Zr Refractory Medium-Entropy Alloys

Low-density refractory medium entropy alloys (NbTiVZr, Nb(0.)5TiVZr, and NbTiV) were produced by vacuum arc melting, then heat-treated at 1,200 degrees C for 1 h, water quenched, and finally annealed at 500 degrees C for 0.5 h. Their respective microstructures, elevated-temperature (600-1,000 degrees C) mechanical properties, and thermal expansion behavior were then investigated. All the alloys are characterized by a BCC structure with a grain size of c. 85-135 mu m. The results demonstrated that NbTiVZr alloy exhibits relatively high yield strength and specific strength at 600, 800, and 1,000 degrees C. Moreover, a low coefficient of thermal expansion was also obtained for this alloy when the temperature was below 750 degrees C. This study provides guidance for the engineering application of low-density refractory medium entropy alloys at elevated temperatures.