A STUDY OF THE STRUCTURE AND MECHANICAL PROPERTIES OF NB-MO-CO-X (X = HF, ZR, TI) REFRACTORY HIGH-ENTROPY ALLOYS

Abstract

Refractory high-entropy alloys (HEAs) are a new class of metallic materials based on group 4-6 elements of the periodic table with possible additions of Al, Si, Re, C, or B. Some single-phase refractory HEAs can maintain high strength up to 1600°C, while multiphase compositions have more attractive specific properties at temperatures up to 1200°C. Here we examine the structure and mechanical properties of refractory HEAs Nb30Mo30Co20Hf20, Nb30Mo30Co20Zr20, and Nb30Mo30Co20Ti20 (at %). The alloys consisted of an intermetallic B2 matrix and particles of a disordered bcc phase, as well as a minor volume fraction of additional bcc (Nb30Mo30Co20Hf20 and Nb30Mo30Co20Zr20) or fcc (Nb30Mo30Co20Ti20) phases. When tested for uniaxial compression, Nb30Mo30Co20Ti20 alloy showed higher yield strength in the temperature range of 22-1000°C than Nb30Mo30Co20Hf20 and Nb30Mo30Co20Zr20 alloys. Nb30Mo30Co20Zr20 alloy did not fail at temperatures of 22-800°C to a given 50% strain, while Nb30Mo30Co20Ti20 alloy turned out to be brittle. All alloys demonstrated high strain hardening in the temperature range of 22-800°C, and they can compete in terms of specific strength with commercial nickel and cobalt superalloys.