Abstract: Both in-situ synchrotron radiation X-ray diffraction and ex-situ transmission electron microscopy were employed to investigate the pressure-induced structural evolution in the dual-phase Gd₂₅Tb₂₅Dy₂₅Ho₂₅ high-entropy alloy. During compression with a maximum pressure of 52.15 GPa, the matrix of the Gd₂₅Tb₂₅Dy₂₅Ho₂₅ high-entropy alloy undergoes a sequence of phase transitions: hcp → Sm-type → dhcp → dfcc, while its secondary phase with an fcc structure remains unchanged. The secondary phase exhibits higher incompressibility compared to the matrix, as indicated by its bulk modulus being higher than that of the matrix. The high pressure applied in this study induces large deformation in the studied alloy through dislocation movement and significant dislocation multiplication. The increased mismatch in lattice parameters between the matrix and the secondary phase, induced by increasing pressure, leads to the energy-fluctuating distorted lattices at the boundary between the two phases. This, combined with the intrinsic distorted lattices and the low-energy dislocations, hinders dislocation movement, resulting in the creation of dislocation cells. This leads to the creation of subgrains, significantly reducing the grain size of the matrix. This study not only deepens the understanding of the structural evolution of high-entropy alloys under high-pressure conditions but also provides theoretical support for investigating their multicaloric properties.

Key words: High pressure, High-entropy alloy, Phase transition, Structural evolution, Diamond anvil cell