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The mobility of vacancies in alloys may limit dislocation climb. Using acombined density functional theory and kinetic Monte Carlo approach weinvestigate vacancy diffusion in Ni-Re, Ni-W, and Ni-Ta binary alloys up to 10at.% solute concentration. We introduce an interaction model that takes intoaccount the chemical environment close to the diffusing atom to capture theeffect of solute-host and solute-solute interactions on the diffusion barriers.In contrast to an ideal solid solution it is not only the diffusion barrier ofthe solute atom that influences the vacancy mobility, but primarily the changein the host diffusion barriers due to the presence of solute atoms. This isevidenced by the fact that the observed vacancy slowdown as a function ofsolute concentration is larger in Ni-W than in Ni-Re, even though Re is aslower diffuser than W. To model diffusion in complex, non-dilute alloys anexplicit treatment of interaction energies is thus unavoidable. In the contextof Ni-based superalloys two conclusions can be drawn from our kinetic MonteCarlo simulations: the observed slowdown in vacancy mobility is not sufficientto be the sole cause for the so-called Re-effect; and assuming a directcorrelation between vacancy mobility, dislocation climb, and creep strength theexperimentally observed similar effect of W and Re in enhancing creep strengthcan be confirmed.

Kinetic Monte Carlo simulations of vacancy diffusion in non-dilute Ni-X (X=Re,W,Ta) alloys