[Paper Review] Characterisation of microstructural creep, strain rate and temperature sensitivity and computational crystal plasticity in Zircaloy-4

Yang Liu, Weifeng Wan+4 more|arXiv (Cornell University)|Sep 11, 2021

Nuclear Materials and Properties49 references4 citations

TL;DR

This study investigates crystal-level strain rate and temperature sensitivity in Zircaloy-4 using combined bending creep tests, digital image correlation, electron backscatter diffraction, and crystal plasticity modeling. It reveals that cross-slip activation near notch tips induces up to 50% higher microscale creep strain, with grain-level strain rate sensitivity highly heterogeneous and dependent on dislocation slip activity, while pyramidal <c+a> slip and dislocation pileups drive temperature-sensitive texture effects on strength and hardening.

ABSTRACT

Crystal-level strain rate sensitivity and temperature sensitivity are investigated in Zircaloy-4 using combined of bending creep test, digital image correlation, electron backscatter detection and thermo-mechanical tensile tests with crystal plasticity modelling. Crystal rate-sensitive properties are extracted from room temperature microscale creep, and temperature sensitivity from thermal polycrystalline responses. Crystal plasticity results show that large microscale creep strain is observed near notch tip increased up to 50% due to cross-slip activation. Grain-level microscale SRS is highly heterogeneous, and its crystallographic sensitivity is dependent on plastic deformation rate and underlying grain-based dislocation slip activation. Pyramidal slip and total dislocation pileups contribute to temperature-sensitive texture effect on yielding and strength hardening. A faithful reconstruction of polycrystal and accurate rate-sensitive single-crystal properties are the key to capture multi-scale SRSs.

Motivation & Objective

• To quantify crystal-level strain rate sensitivity in Zircaloy-4 at room temperature using microscale creep testing.
• To investigate temperature sensitivity of polycrystalline responses in Zircaloy-4 through thermo-mechanical tensile testing.
• To understand the role of crystallographic slip systems, particularly pyramidal <c+a> slip, in governing microstructural deformation behavior.
• To establish accurate single-crystal rate-sensitive properties for use in multi-scale crystal plasticity modeling.
• To link microstructural heterogeneity in strain rate sensitivity to underlying dislocation slip activation and grain orientation.

Proposed method

• Conducted microscale bending creep tests on notched Zircaloy-4 specimens to measure localized creep strain under controlled loading.
• Employed digital image correlation (DIC) to map full-field displacement and strain evolution during creep testing.
• Used electron backscatter diffraction (EBSD) to characterize grain orientation and microstructure for crystal plasticity model input.
• Performed thermo-mechanical tensile tests across a range of temperatures to extract temperature-dependent yield and hardening responses.
• Implemented a crystal plasticity finite element model using experimentally calibrated single-crystal rate-sensitive properties.
• Integrated microscale creep and macroscopic tensile data to validate and refine the crystal plasticity model for multi-scale strain rate sensitivity.

Experimental results

Research questions

• RQ1 How does microscale creep strain vary near stress concentrators such as notch tips in Zircaloy-4?
• RQ2 What is the role of cross-slip activation in enhancing local creep strain at the crystal level?
• RQ3 How does grain-level strain rate sensitivity vary with crystallographic orientation and dislocation slip activity?
• RQ4 To what extent do pyramidal <c+a> slip systems and dislocation pileups influence temperature-sensitive yielding and hardening?
• RQ5 Can a calibrated crystal plasticity model accurately predict multi-scale strain rate sensitivity using experimentally derived single-crystal properties?

Key findings

• Microscale creep strain near notch tips increased by up to 50% due to cross-slip activation, indicating localized strain enhancement in high-stress regions.
• Grain-level strain rate sensitivity (SRS) was highly heterogeneous, with strong dependence on plastic deformation rate and dominant dislocation slip systems.
• Pyramidal <c+a> slip and total dislocation pileups were identified as key contributors to the temperature-sensitive texture effects on yielding and strength hardening.
• Faithful reconstruction of polycrystalline microstructure and accurate single-crystal rate-sensitive properties were essential for capturing multi-scale strain rate sensitivity.
• The crystal plasticity model successfully reproduced experimental creep and tensile responses when calibrated with microscale and macroscopic data.
• Temperature sensitivity of strength was strongly influenced by crystallographic texture and dislocation dynamics, particularly in high-slip activity grains.