Macro deformation twins in single-crystal aluminum

TL;DR

This paper demonstrates for the first time that macro deformation twins can form in single-crystal aluminum under ultrahigh strain rates and large shear strains, challenging previous beliefs about twinning in pure aluminum.

Contribution

It provides the first experimental evidence of macro deformation twins in single-crystal aluminum at high strain rates and large strains, revealing the role of dislocation and twinning rate dependence.

Findings

Macro deformation twins observed in single-crystal aluminum.

Twinning occurs under ultrahigh strain rates (~10^6 s^-1).

Twinning linked to dislocation and twinning rate dependence.

Abstract

Deformation twinning in pure aluminum has been considered to be a unique property of nanostructured aluminum. A lingering mystery is whether deformation twinning occurs in coarse-grained or single-crystal aluminum, at scales beyond nanotwins. Here, we present the first experimental demonstration of macro deformation twins in single-crystal aluminum formed under ultrahigh strain-rate ($\sim$10$^6$ s$^{-1}$), large shear strain (200$\%$) via dynamic equal channel angular pressing. Deformation twinning is rooted in the rate dependences of dislocation motion and twinning, which are coupled, complementary processes during severe plastic deformation under ultrahigh strain rates.