Ductilization of single-phase refractory high-entropy alloys via activation of edge dislocation

Refractory high entropy alloys (RHEAs) are of particular interest for their superior high-temperature strength. However, most of RHEAs are suffered from the brittleness especially at room temperature which hindered their applications. Here, we choose TiZrHfNbx (x = 0.4, 0.6, 0.8, 1) as a model alloy system in which all the alloys exhibited a single-phase BCC structure. With the increasing Nb content, the fracture strain significantly increased from 8.76 % to 33.21 % without sacrificing the overall yield strength. The dislocation interactions were systematically investigated through extensive experimental and theoretical approaches. The limited tensile ductility of TiZrHfNb_0.4 was attributed to the long straight screw dislocations confined in a few slip planes. In sharp contrast, the dislocations in TiZrHfNb alloy are rather homogeneously distributed and the superior tensile ductility of TiZrHfNb alloy is due to the activation of edge dislocations which is rare in ordinary BCC structured alloys. The atomic scale physical origin of different dislocation configuration and behaviors can be attributed to the higher misfit volume and elastic asymmetry of TiZrHfNb alloy. The outcome of this research not only reveal a new ductilization mechanism but also provide a new pathway to design ductile RHEAs through regulation the atomic scale environment.