Microstructure and mechanical properties of Nb25Mo25Ta25W25 and Ti8Nb23Mo23Ta23W23 high entropy alloys prepared by mechanical alloying and spark plasma sintering

In the present work, Nb25Mo25Ta25W25 and Ti8Nb23Mo23Ta23W23 refractory high entropy alloys (HEAs) were successfully prepared by mechanical alloying (MA) and spark plasma sintering (SPS) technologies. With the aid of ball milling, the stabilized single-phase BCC nano-crystalline structures can be obtained with the average crystallite size of about 10 nm. After the SPS process, the grain size of both alloys is less than 1 µm. The compressive yield strength, fracture strain and Vickers hardness of bulk Nb25Mo25Ta25W25 HEA are 2460 MPa, 16.8% and 7.78 GPa, respectively, which are remarkably superior to the same alloy prepared by the vacuum arc-melting (VAM) method. The addition of Ti can further promote the compressive properties in the Ti8Nb23Mo23Ta23W23 HEA, where the fracture strain and peak compressive stress surprisingly increased by 56.5% and 10.7%, respectively.