Effect of short-range order on lattice distortion, stacking fault energy, and mechanical performance of Co-Fe-Ni-Ti high-entropy alloy at finite temperature

The characterization of short-range order (SRO) and its influence on performance are a widely debated topics in high-entropy alloys (HEAs). In this work, taking the Co-Fe-Ni-Ti alloy without complicated magnetism as a benchmark of $3d$ HEAs, we investigate the effect of SRO on local lattice distortion (LLD), general stacking fault energy (GSFE), tensile and shear strength of FCC ${\mathrm{Co}}_{30}{\mathrm{Fe}}_{16.66}{\mathrm{Ni}}_{36.67}{\mathrm{Ti}}_{16.67}$ via the combination of Monte Carlo (MC) and molecular dynamics (MD). This alloy shows the typical SRO of Ti-$X$ $(X=\mathrm{Fe},\mathrm{Co})$ atomic pairs, while the segregation of Ti-Ti atomic pairs. The SRO has a minor inhibition on LLD. Considering the thermal vibration induced atomic displacement, the degree of LLD increases nonlinearly with increasing temperature. Both the severe LLD and SRO are helpful to tune the GSFE at finite temperature. The SRO enhances the degree of deformation twinning and delays the appearance of the HCP phase but increases the number of HCP-type atoms as the energy buffers. For the polycrystalline systems, SRO promotes the precipitation of BCC phase at grain boundaries and the number of HCP-type atoms in the grain and activates the deformation of slip surfaces. Therefore SRO could play a key role for the outstanding strength and plasticity of Co-Fe-Ni-Ti HEAs.