Simulations and Modelling of the High Temperature Yield Behavior of Compositionally Complex Concentrated BCC Alloys

Atomistic simulations, using Johnson-Zhou and/or Snap potentials, of the core structure and mobility of ½[111] screw, edge and mixed dislocations in complex concentrated BCC alloys are presented. The core structure and its variations obtained for screw dislocations in NbTiZr using atomistic simulations are compared with first-principles calculation results and good agreement is found. Molecular Dynamics results show that a moving screw dislocation leaves behind interstitial and vacancy dipoles in these alloys. Average solute-dislocation core interaction energies are used to determine the critical stress for the motion of screw dislocations as a function of temperature using Rao- Suzuki model of kink migration / kink-kink collisions controlled mobility, developed for concentrated BCC random alloys. In addition, diffusional effects at very high temperatures on the predicted yield behavior are modelled. Simple expressions for yield stress based on the Rao-Suzuki model is presented. Edge dislocation mobilities in these alloys are modelled using the Maresca-Curtin model. The model results on yield behavior are shown to be in good agreement with experimental data in selected BCC complex concentrated alloys.