Supplementary materials

FIG. S1. (a) Schematic setup for ultrasonic interferometry measurements on acoustic velocities and elasticity of NbxTiZrHf HEAs; (b) Representative compressional and shear wave echoes of Nb0.2TiZrHf HEAs. FIG. S2. SEM micrographs of the well-polished surface of the NbxTiZrHf (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) specimens together with their corresponding EDS mapping. FIG. S3. SEM images and grain size distributions of the NbxTiZrHf (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) HEAs. FIG. S4. Vickers hardness of refractory NbxTiZrHf HEAs at various loading forces. FIG. S5. (a) A schematic diagram of cracking modeling for indentation fracture toughness; (b) Representative SEM micrographs of the fracture surface from our Vickers hardness indentation measurement of the Nb0.2TiZrHf specimen. FIG. S6. Selected area TEM imaging of the propagation crack of Nb0.2TiZrHf specimen. FIG. S7. High-resolution TEM images corresponding to the bcc phase and hcp phase in Nb0.2TiZrHf HEAs.