Operative slip system and dislocation behavior in a brittle refractory high-entropy alloy with the B2 ordered structure

The plastic deformation behavior of a B2-ordered TiCrMo-15Al refractory high-entropy alloy (RHEA) has been investigated as a function of crystal orientation and specimen size by micropillar compression at room temperature, in an attempt to understand the origin for the brittle behavior of the B2 compound based on the identified operative slip systems and dislocation structures. Plastic flow is observed even at room temperature for all orientations investigated with the slip direction always being along <1 1 1>. While the slip plane is {1 1 0} in a wide orientation range, it is {1 1 2} in the narrow orientation range close to the twinning and anti-twinning shear directions. The dislocation structure is characterized by the preference of <1 1 1> screw dislocations, strongly indicating that the deformation is controlled by the Peierls mechanism. The < 1 1 1> dislocation is found to widely dissociate into two-coupled collinear 1/2<1 1 1> partial dislocations. The anti-phase boundary (APB) energy is estimated to be 44 mJ/m 2 , which is quite low and is considered to be the origin for the preference not only of the <1 1 1> slip direction but also of the {1 1 0} slip plane. The room-temperature brittleness is thus concluded not to be caused by the lack of the sufficient number of independent slip systems (von Mises criterion). • Operative slip systems in brittle B2-ordered 85(TiCrMo)-15Al RHEA were identified. • Slip occurs at room temperature along <111> with {110} as the preferred slip plane. • <111> dislocations dissociate into two-coupled 1/2<111> colinear partials with a low γ APB of 44 mJ/m 2 . • Dislocations aligning along screw direction indicates the Peierls mechanism’s control. • Room-temperature brittleness is not due to the lack of independent slip systems.