Atomistic simulations of dislocation behavior in a model FCC multicomponent concentrated solid solution alloy

In this work, molecular statics and molecular dynamics simulations of a/2<110> dislocation behavior for a model FCC Co30Fe16.67Ni36.67Ti16.67 alloy are discussed. It is shown that the single FCC phase is elastically stable in this alloy. Local stacking fault energies for the FCC alloy are determined as a function of average composition. The core structure of a/2<110> screw and edge dislocations in the FCC Co30Fe16.67Ni36.67Ti16.67 alloy is shown to be planar with significant variations in the Shockley partial splitting along the dislocation line (factor of ∼3) due to concentration fluctuations. The correlation lengths for dislocation line fluctuations in this alloy are determined and discussed. The critical stress to move both a/2<110> screw and edge dislocations at 0 K in the model FCC Co30Fe16.67Ni36.67Ti16.67 alloy is of the order of 0.0025-0.005μ, where μ is the (111) shear modulus, and is significantly higher than that of pure FCC Ni. Molecular dynamics simulation results on the critical stress to move a/2<110> screw and edge dislocations in the model FCC concentrated solid solution alloy show that it decreases with increasing temperature, similar to solid-solution strengthened FCC metals. These molecular dynamics simulation results are in reasonable agreement with experimental tensile yield strength data for an analogous FCC concentrated solid solution alloy. It is also shown that local fluctuations in the concentration of solutes has a strong effect on the effective cross-slip activation energy of screw dislocations in the random alloy.

Structure of a/2[1-10] edge dislocation core under a) applied stresses of 0.00375, 0.004375μ and 0.005μ at 5 K, b) applied stresses of 0.00375 and 0.004375μ at 150 K, and c) applied stresses of 0.0025, 0.003125 and 0.00375μ at 300 K in a FCC Co30Fe16.67Ni36.67Ti30 alloy. The core structure is shown for molecular dynamics steps of 0, 25, 50 and 100 ps. Atoms with a centrosymmetry parameter greater than 4 is shown in the plot. For clarity, core structure at timesteps of 0, 25, 50 and 100 ps are displaced by −2, −1, 0 and 1 periodic units, respectively, along the 'y' direction.340