In-situ studies of bulk deformation structures: Static properties under load and Dynamics during deformation

TL;DR

This study introduces a novel in-situ 3D reciprocal space mapping technique using synchrotron radiation to analyze deformation structures in copper during tensile deformation, revealing subgrain formation and dislocation dynamics.

Contribution

A new synchrotron-based method for in-situ 3D mapping of individual grains during deformation in polycrystalline metals is developed and applied to study subgrain evolution.

Findings

Dislocation-free subgrains produce sharp peaks in 3D reciprocal space maps.

Strain distribution varies within and between subgrains under static load.

Subgrain formation and refinement are observed during deformation.

Abstract

(Abridged, full abstract available in the text) The main goal of the study presented in this thesis was to perform in-situ investigations on deformation structures in plastically deformed polycrystalline copper at low degrees (<5%) of tensile deformation. Copper is taken as a model system for pure fcc metals. A novel synchrotron-radiation based technique has been developed. The technique allows for in-situ 3D reciprocal space mapping of reflections from deeply-embedded individual grains in polycrystalline samples during tensile deformation. We have shown that the resulting 3D maps from copper, consists of bright sharp peaks superimposed on a cloud of enhanced intensity. It is concluded that the individual peaks arise from the individual dislocation-free regions (the subgrains) in the dislocation structure. Based on data taken under static load, the strain distribution in and between the individual subgrains is analyzed and compared to composite type models. The consequences of stress relaxation and unloading is moreover discussed. The dynamics of the dislocation structure are investigated by continuous and stepwise deformation experiments. On the basis of such data the unset of subgrain formation and the subgrain refinement process is analyzed.