Abstract
We examine vacancy-assisted diffusion in the 57 random, equimolar alloys that can be formed from Cu, Ag, Au, Ni, Pd, and Pt based on the well-tested embedded atom method functions of Foiles, Baskes, and Daw [Phys. Rev. B 33, 7983 (1986)]. We address the suggestion [Yeh et al., Adv. Eng. Mater. 6, 299 (2004)] that increasing the number of constituents causes diffusion to be “sluggish” in random, equimolar alloys. Using molecular dynamics (MD) simulations of random alloys with a single vacancy, combined with calculations of vacancy formation, we extract vacancy-assisted diffusivities in each alloy. After developing and applying several possible criteria for evaluating “sluggishness,” we find that only a small minority (from 1 to 8, depending on how sluggishness is defined) of the alloys exhibit sluggish diffusion whereas in the large majority of alloys diffusion is faster and in quite a few cases ought to be considered vigorous (that is, faster than in any of the constituents). We correlate diffusivity with a combination of the mean of the constituent diffusivity and a simple function of lattice mismatch. We conclude that simply increasing the number of constituents in such alloys does not systematically alter the diffusion, but that instead lattice mismatch plays a primary factor; sluggish diffusion is more likely to occur in a window of small lattice mismatch (1–3%) even in binary alloys. Quantitatively, our calculated diffusivities correlate with a combination of (1) rule of mixtures of the diffusivities of the constituents, and (2) a simple function of the lattice mismatch; this accounts for the large majority of our calculated diffusivities to within a factor of 2 (over a range of three orders of magnitude). We also find that while lattice mismatch on the order of 1–3% is necessary for sluggish diffusion, it is not sufficient.
9 More- Received 14 December 2020
- Accepted 16 February 2021
DOI:https://doi.org/10.1103/PhysRevMaterials.5.043603
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