Ab initio study of strain-driven vacancy clustering in aluminum

TL;DR

This study investigates how hydrostatic strain affects vacancy clustering in FCC aluminum using first-principles Kohn-Sham DFT. It defines vacancy energetics via binding enthalpy and formation energy and analyzes a set of vacancy configurations (monovacancy, divacancies, trivacancies, quadvacancies, and a heptavacancy) under unstrained, and compressive strains. The results show that compressive strains promote clustering, especially on the (111) plane, with specific clusters like the A trivacancy, A1 quadvacancy, and the heptavacancy transforming toward collapse into prismatic dislocation loops at modest strains, aligning with experimental observations and highlighting strain as a key driver of defect evolution. The findings refine understanding beyond orbital-free DFT and point to future work on kinetics and temperature effects to map clustering pathways and loop nucleation in aluminum.

Abstract

We present a first principles investigation of strain-driven vacancy clustering in aluminum. Specifically, we perform Kohn-Sham density functional theory calculations to study the influence of hydrostatic strains on clustering in tri-, quad-, and heptavacancies. We find that compressive strains are a key driving force for vacancy aggregation, particularly for collapse of clusters on the (111) plane, consistent with prior experimental observations of vacancy clusters on this plane. Notably, we find that the heptavacancy on the (111) plane collapses to form a prismatic dislocation loop for hydrostatic compressive strains exceeding 5\%, highlighting the critical role of such strains in prismatic dislocation loop nucleation in aluminum.

Figures (5)

• Figure 1: Equation of state for bulk aluminum, with the shaded area indicating the range of pressures studied.
• Figure 2: Binding energy for the various vacancy configurations in the unstrained, 5% compressive, and 10% compressive strain cases. The labels along the x-axis denote the vacancy clusters that are used as reference. For instance, {Mono,NN} indicates that the binding energy is computed with respect to a combination of a monovacancy and an NN divacancy in the case of a trivacancy, whereas for a quadvacancy, it refers to a combination of two monovacancies and an NN divacancy.
• Figure 3: Contours of electron density on the $(111)$ plane and displacement of atoms for the collapsed (a) A trivacancy and (b) A1 quadvacancy clusters at 10% compressive strain. White spheres indicate vacancy locations, blue spheres represent initial atomic positions, red spheres highlight atoms with the largest displacements, and arrows show the direction and magnitude of atomic movement.
• Figure 4: Contours of electron density on the $(111)$ plane and displacement of atoms for the collapsed heptavacancy cluster, i.e., prismatic dislocation loop, at 10% compressive strain. White spheres indicate vacancy locations, blue spheres represent initial atomic positions, red spheres highlight atoms with the largest displacements, and arrows show the direction and magnitude of atomic movement.
• Figure 5: Formation energy for the various vacancy configurations in the unstrained, 5% compressive, and 10% compressive strain cases. See text for the exact strain values.