Twinning in [001]-oriented single crystals of CoCrFeMnNi high-entropy alloy at tensile deformation

This paper presents research about the tensile deformation behaviour and deformation mechanisms (slip and twinning) in single crystals of the equiatomic Co20Cr20Fe20Mn20Ni20 (at%) high-entropy alloy (HEA) oriented along the [001] direction in the temperature range T = 77-573 K. Classical studies on single crystals of pure metals and their substitution alloys with the face-centered cubic (FCC) structure, with a low stacking fault energy, have shown that deformation twinning in single crystals oriented along the [001] direction does not develop at tensile deformation. In the present paper, extrinsic stacking faults and deformation twinning in the [001]-oriented single crystals of the equiatomic Co20Cr20Fe20Mn20Ni20 HEA were detected under tensile loading at the temperature of liquid nitrogen after a strain of 5%. The critical resolved shear stress for twinning was determined as tau(tw)(cr) = 210 +/- 10 MPa. Deformation twinning in the [001]-oriented single crystals leads to an increase in the strain hardening coefficient in comparison with the slip deformation in these crystals at T > 77 K.