PNNL

Abstract

Extreme shear deformation is used for several material processing methods and is unavoidable in many engineering applications in which two surfaces are in relative motion against each other while in physical contact, such as in ball bearings. The mechanistic understanding of the microstructural evolution of multi-phase metallic alloys under extreme shear deformation is still in its infancy. Here, we highlight the influence of shear deformation on the microstructural hierarchy and mechanical properties of a binary as-cast Al-4 at. % Si alloy with a ductile Al matrix and brittle Si precipitates. Transmission electron microscopy, atom probe tomography, and finite element modeling were used to analyze microstructural evolution. Shear-deformation-induced grain refinement, multiscale fragmentation of the eutectic Si-lamellae, and metastable solute saturated phases with distinctive defect structures led to a two-fold increase in the flow stresses determined by micropillar compression testing. These results highlight that shear deformation during solid-phase processing can achieve non-equilibrium microstructures with enhanced mechanical properties in Al–Si alloys. The experimental insights obtained here are especially crucial for developing atomic-scale to mesoscale predictive models for microstructural evolution of metallic alloys under extreme shear deformation.