Anomalous, pre-yield grain-boundary sliding in copper revealed with in-situ high-resolution strain mapping

TL;DR

This study reveals that grain boundary sliding in copper occurs extensively before yield at room temperature, detected through in-situ high-resolution strain mapping, challenging traditional understanding of deformation mechanisms.

Contribution

It demonstrates the occurrence of pre-yield grain boundary sliding in copper at room temperature using in-situ high-resolution strain mapping techniques.

Findings

Grain boundary sliding occurs prior to macroscopic yield.

Extreme strain and rotation are observed at grain boundaries before slip.

Multiple modes of grain boundary sliding are identified.

Abstract

Grain boundary sliding is typically associated with high temperature deformation in engineering alloys. Here, we examine grain boundary sliding at room temperature in oxygen-free high-conductivity copper under quasi-static tensile testing. By using high-resolution digital image correlation (HRDIC) conducted in-situ within a scanning electron microscope to produce time-series strain maps, we unexpectedly observe that grain boundary sliding occurs extensively prior to macroscopic yield, and before the onset of significant crystallographic slip. Extreme values in strain and in-plane rotation are found to be associated with grain boundaries immediately prior to yield and during the initial stages of plastic deformation, which are higher than those associated with crystallographic slip. By combining laser scanning confocal microscopy height mapping with the strain maps and orientation maps from electron backscatter diffraction, grain boundary sliding character is determined, finding evidence of pure in-plane, pure out-of-plane and mixed-mode sliding.