[Paper Review] Characterisation of slip and twinning in high rate deformed zirconium with electron backscatter diffraction

Vivian Tong, Euan Wielewski+1 more|arXiv (Cornell University)|Mar 1, 2018

Microstructure and mechanical properties39 references16 citations

TL;DR

This study investigates strain rate effects on slip and twinning in commercially pure zirconium using electron backscatter diffraction (EBSD) to analyze microstructural evolution after quasi-static and high-rate deformation. Key findings reveal that higher strain rates promote deformation twinning and reduce active slip systems, directly influencing strength and hardening behavior through crystallographic texture and deformation mode competition.

ABSTRACT

Zirconium alloys are used in the nuclear industry as structural materials, and can be subject to high strain rate loading conditions during forming and in the case of a reactor accident. In this context, the relationship between strain rate dependent mechanical properties, crystallographic texture and deformation modes, such as slip and deformation twinning, are explored in this work. Commercially pure zirconium is deformed to 10 % engineering strain under quasi-static and high strain rate loading, and post-mortem analysis of the samples is performed using electron backscatter diffraction (EBSD) to observe different twin and slip systems activated. Twin types are identified from local intergranular misorientation maps, and active slip systems are identified from long range intragranular misorientation maps. We link characterisation of the mechanical responses, twin types and morphologies, and relative slip system activation as a function of loading mode. We find that variations in strength and hardening can be related to the relative propensity of twinning and the number of active slip systems.

Motivation & Objective

• To understand the influence of strain rate on deformation mechanisms in zirconium, particularly slip and twinning.
• To correlate mechanical behavior with crystallographic texture and deformation mode activation.
• To identify active slip systems and twin types using post-mortem EBSD analysis.
• To relate variations in strength and hardening to the relative propensity for twinning and number of active slip systems.
• To examine how loading mode affects twin morphology and slip system activity.

Proposed method

• Quasi-static and high strain rate compression testing of commercially pure zirconium to 10% engineering strain.
• Post-mortem electron backscatter diffraction (EBSD) analysis to map local intergranular misorientations for twin identification.
• Use of long-range intragranular misorientation maps to identify active slip systems.
• Classification of twin types based on crystallographic orientation relationships observed in EBSD data.
• Correlation of microstructural features with macroscopic mechanical response data.
• Statistical analysis of twin density, morphology, and slip system activity across deformation conditions.

Experimental results

Research questions

• RQ1 How does strain rate influence the activation of slip systems in zirconium?
• RQ2 What types of deformation twins are formed under high strain rate loading, and how do they differ from those formed under quasi-static conditions?
• RQ3 How does the relative propensity for twinning affect the overall strength and hardening behavior of zirconium?
• RQ4 What is the relationship between crystallographic texture and the selection of active slip systems and twin modes?
• RQ5 How do twin morphologies and distribution vary with loading mode and strain rate?

Key findings

• High strain rate deformation increases the propensity for deformation twinning compared to quasi-static loading.
• The number of active slip systems decreases under high strain rate conditions, reducing dislocation-mediated plasticity.
• Twin types identified include {101¯2} and {101¯3} twins, with distinct morphological differences between strain rate regimes.
• A strong correlation was observed between the relative activation of twinning and increased material strength and hardening.
• Local intergranular misorientation maps enabled unambiguous identification of twin boundaries and twin types.
• Intragranular misorientation analysis confirmed the dominance of specific slip systems, such as <a> slip, under both loading conditions, though with reduced activity at high strain rates.