Abstract: The compositional heterogeneity in high-entropy alloys (HEAs) has been reported to be an inherent entity, which significantly alters the mechanical properties of materials by tuning the variation of lattice resistance for dislocation motion. However, since the body-centered cubic (BCC) structure is not close-packed, the change of lattice resistance is less sensitive to the normal concentration wave compared to that in face-centered cubic (FCC) structured materials. In this work, we selected a refractory bcc HEAs TiZrNbTa for the matrix and added a small amount of Al to facilitate the special spinodal decomposition structure. In particular, (TiZrNbTa)_98.5Al_1.5 displayed a typical basket-weave fabric morphology of spinodal decomposition structure with a characteristic periodicity of ∼8 nm and had an optimal combination of strength and ductility (the yield strength of 1123 ± 9 MPa and ductility of ∼20.7% ± 0.6%). It was determined that by doing in situ TEM mechanical testing, the plastic deformation was dominated by the formation and operation of dislocation loops which provided both edge and screw components of dislocations. The synergetic effect of the remarkable chemical heterogeneity created by the spinodal decomposition and the spreading lattice distortion in high entropy alloys is quite effective in tuning the mobility of different types of dislocations and facilitates dislocation interactions, enabling the combination of high strength and ductility.

Key words: Bcc high-entropy alloys, Spinodal decomposition, Compositional heterogeneity, Dislocation loops, High strength, Ductility