Divergent interfacial behaviors of homo-/hetero-phase boundaries in a dual-phase eutectic high-entropy alloy

The interfacial structures and behaviors are critical in determining the material properties. Our study aims to investigate such unique interfacial structures and behaviors in multiphase systems involving complex compositions. Herein, we report the divergent interfacial behaviors of the L1(2)-L1(2), B2-B2, and L1(2)-B2 boundaries prepared via the bonding of AlCoCrFeNi2.1 eutectic high-entropy alloys (HEAs). Specifically, interfacial dynamic recrystallization (DRX) occurs in the L1(2)-L1(2) boundary owing to the thermostrain-induced grain boundary evolution. In contrast, the bonding of the B2-B2 boundary may be realized by interface diffusion, and no evident DRX occurs owing to the small interfacial shear strain. The DRX grains only developed on the L1(2) side in the L1(2)-B2 boundary because of the difference in the intrinsic structural traits between L1(2) and B2. The diffusion of elements contributed to the bonding of this dissimilar boundary. Moreover, a strain-induced B2(II) precipitation phenomenon surrounding the bonding interface was revealed because of the high defect-precipitation sensitivity of HEAs. The B2(II) particle precipitation depleted the Al and Ni within the matrix, leading to L1(2) disordering. The Zener pinning effect exerted by B2(II) precipitates was quantitatively evaluated by calculating the corresponding limited grain radius R-L = 1.8 mu m. This pinning effect of B2(II) precipitates and the sluggish diffusion effect may induce temperature-dependent DRX behaviors of the L1(2)-L1(2) boundary. This study reveals the understanding of the unique interfacial behaviors of multiphase HEAs and provides new insights into the effects of multiple phases, complex composition, and interfacial precipitation on interfacial evolution.