Investigations on the role of chemical short-range order in the tensile deformation of FCC Co30Fe16.67Ni36.67Ti16.67 high-entropy alloys via Monte Carlo and molecular dynamics hybrid simulations

Abstract

As the research on high-entropy alloys (HEAs) is gradually deepening, it has been reported that chemical short-range order (CSRO) remarkably influences their mechanical performances. Here, the atomic models of FCC Co₃₀Fe_16.67Ni_36.67Ti_16.67 HEAs containing different levels of CSRO were constructed using the Monte Carlo (MC) atom swaps and molecular dynamics (MD) hybrid method. Tensile loads were applied to Co₃₀Fe_16.67Ni_36.67Ti_16.67 HEAs along [0 0 1], [1 1 0] and [1 1 1] crystal orientations at 1 K and 300 K to reveal from the atomic scale how CSRO influences mechanical performances and plastic deformation. The results indicate that significant CSRO appears in Fe-Ti atomic pair, and as the annealing temperature rises, the CSRO level reduces. The crystal orientation notably affects the deformation behavior of Co₃₀Fe_16.67Ni_36.67Ti_16.67 HEAs, and CSRO increase the anisotropy. In terms of plastic deformation mechanism, stretching along [0 0 1] crystal orientation is the FCC to BCC phase transition and stretching along [1 1 0] and [1 1 1] crystal orientations are Shockley dislocations nucleation and slip. CSRO can simultaneously improve the strength and ductility of Co₃₀Fe_16.67Ni_36.67Ti_16.67 HEAs. This is because CSRO increases the energy required for the FCC to BCC phase transition and the stacking fault energy, which impedes the plastic deformation during stretching. Owing to the weakened atomic thermal vibrations, low temperature hinders the FCC to BCC phase transition and dislocations nucleation, which strengthens Co₃₀Fe_16.67Ni_36.67Ti_16.67 HEAs.