Comparison of dislocation density, twin fault probability, and stacking fault energy between CrCoNi and CrCoNiFe medium entropy alloys deformed at 293 and 140K

To elucidate deformation behavior behind the exceptional mechanical properties of CrCoNi based medium entropy alloys, the deformation related microstructural parameters were determined by using in situ neutron diffraction and peaks profile analysis methods. Superior tensile strength and elongation of the CrCoNi alloy is relevant to higher twin fault probability (P_tw, up to 3.8%) and dislocation density (ρ, up to 9.7 x 10¹⁵ m⁻²) compared to those (1.3% and 3.4 x 10¹⁵ m⁻², respectively) of the CrCoNiFe at 293K. Meanwhile, at 140K, the P_tw of the CrCoNiFe significantly increased up to 4.4% with the stable ρ of ~5.0 x 10¹⁵ m⁻² and its mechanical properties overwhelm those of the CrCoNi at 273K. Such twinning dominant deformation mechanism at low temperature is also assured by lower stacking fault energy (SFE) of the CrCoNiFe (7.4 mJ/m²) at 140K compared to those of the CrCoNi (16.1 mJ/m²) and CrCoNiFe (32.1 mJ/m²) alloys at 293K.