Refractory high-entropy alloys (RHEAs) are promising candidates for advanced structural applications, yet the intrinsic deformation behavior of the hexagonal close-packed (HCP) phase in RHEAs remains insufficiently understood. Here, we report an as-cast α'-dominated TiZrHf0.7Ta0.3 RHEA with pronounced strain-hardening capacity at room temperature. The alloy consists mainly of interwoven α' laths with a minor retained β phase. Under room-temperature tension, the primary load-bearing α' laths accommodate plastic deformation through lath reorientation, multiple slip modes, and locally activated hierarchical twinning. These complementary mechanisms promote local deformation compatibility and contribute to strain hardening. Consequently, the alloy achieves a yield strength of 304 MPa, an ultimate tensile strength of 817 MPa, and a fracture strain of 16.7%, corresponding to a substantial post-yield strength increment. This study elucidates the deformation mechanisms underlying the pronounced strain-hardening behavior of the HCP-dominated RHEA and provides guidance for the phase and microstructure design of high-performance RHEAs.
