Mobility of dislocations in FeNiCrCoCu high entropy alloys

Abstract

Dislocations in high entropy alloys (HEAs) are wavy and have natural pinning points due to the variable chemical and energetic landscape surrounding the dislocation core. This can influence the critical shear stress necessary to initiate dislocation motion and the details associated with sustained dislocation glide. The objective of this work is to determine the relationship between Schmid shear stress and dislocation velocity in single phase FCC FeNiCrCoCu HEAs using molecular dynamics simulations, with comparisons made to dislocation motion in homogeneous Ni and Cu. Simulations are performed for four different dislocation character angles: 0° (screw), 30°, 60° and 90° (edge). Several key differences are reported, compared to what is previously known about dislocation motion in homogeneous FCC metals. For example, the drag coefficient B in the phonon damping regime for HEAs has a nonlinear dependence on temperature, whereas this dependence is linear in Ni. Mobility relationships between different types of dislocations common in homogeneous FCC metals, such as the velocity of screw and 60° dislocations being lower than edge and 30° dislocations at the same shear stress, do not necessarily hold in HEAs. Dislocation waviness is measured and is found to correlate with the ability of dislocations to glide under an applied shear stress, including the temperature dependence of the drag coefficient B. These results confirm that the influence of HEA chemical complexity on dislocation motion is important and this data can be used to guide development of analytical or empirical models for dislocation mobility in HEAs.