Abstract
Molecular dynamics (MD) simulations are applied to study solute drag by curvature-driven grain boundaries (GBs) in Cu–Ag solid solution. Although lattice diffusion is frozen on the MD timescale, the GB significantly accelerates the solute diffusion and alters the state of short-range order in lattice regions swept by its motion. The accelerated diffusion produces a nonuniform redistribution of the solute atoms in the form of GB clusters enhancing the solute drag by the Zener pinning mechanism. This finding points to an important role of lateral GB diffusion in the solute drag effect. A 1.5 at.%Ag alloying reduces the GB free energy by 10–20% while reducing the GB mobility coefficients by more than an order of magnitude. Given the greater impact of alloying on the GB mobility than on the capillary driving force, kinetic stabilization of nanomaterials against grain growth is likely to be more effective than thermodynamic stabilization aiming to reduce the GB free energy.
Highlights
Metallic materials with grain sizes on the order of nanometers have attracted significant technological interest due to many superior properties that they often demonstrate over the traditional coarse-grained materials [1]
The beneficial properties of nanocrystalline materials originate from the large specific area of the grain boundaries (GBs), phase boundaries, and other internal interfaces [2,3]
We have studied the solute drag on GBs in Cu–Ag solid solutions by Molecular dynamics (MD) simulations
Summary
Metallic materials with grain sizes on the order of nanometers have attracted significant technological interest due to many superior properties that they often demonstrate over the traditional coarse-grained materials [1]. The high mechanical strength of nanocrystalline materials is largely due to the restraining effect imposed by the GBs on the dislocation glide. The most common strengthening mechanism in polycrystalline materials is the formation of dislocation pileups stopped at the GBs [4]. This mechanism, known as the Hall–Petch effect [4], operates at grain sizes down to about nm. At even smaller grain sizes, the mechanical strength plateaus and reverses as the dislocation sources inside the grains cease to operate and the dislocation pileups can no longer form. Chemical effects, such GB segregation and GB chemical reactions, strongly impact the sliding resistance of GBs and their mobility in alloy systems
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