Abstract: The adiabatic shear band is a crucial precursor of catastrophic failure for materials subjected to dynamic loading, deeply influenced by the microstructural characteristics. In this work, an optimized specimen type was first developed to make the stress state in the shear region closer to pure shear during the entire deformation. To elucidate the effect of nanoprecipitates on the formation of adiabatic shear band, dynamic shear behaviors of two L1₂ nanoprecipitate-strengthened high-entropy alloys at different temperatures (77, 293, and 873 K) were tested using a split Hopkinson pressure bar and the optimized specimen type, and the corresponding microstructure evolutions were characterized with the aid of interrupt experiments. The nanoprecipitates dispersed in a face-centered cubic matrix exhibit a significant and intriguing effect on the dynamic shear behavior of the high-entropy alloys. The subtle combination of relatively large size and advisable volume fraction of L1₂ nanoprecipitates promotes multiple strain hardening mechanisms and resists thermal softening, leading to the exceptional resistance to adiabatic shear band. Immediately after the instantaneous redissolution of L1₂ nanoprecipitates in the shear region due to the synergetic effect of high-density dislocations, adiabatic temperature rise, and high shear stress, the adiabatic shear bands induced by dynamic recrystallization form. Finally, a deformation mechanism map for the two L1₂ nanoprecipitate-strengthened high-entropy alloys is proposed at different temperatures. The systematic study looks forward to opening a potentially new avenue for the design of nanoprecipitate-strengthened high-entropy alloys with superior adiabatic shear resistance over a wide range of temperatures.

Key words: High-entropy alloys, Dynamic shear behavior, Microstructure evolution, Adiabatic shear band, L1₂ nanoprecipitates