arXiv subjects

Chris Hardie

Publications and source records attributed to Chris Hardie.

4 recordsLinked to original sources

arXiv2026

Decoupling Strain-Rate Sensitivity and Deformation Length Scale Effects in Neutron-Irradiated Tungsten: A Coupled Nano-Indentation, HR-EBSD and Crystal Plasticity Study

Plastic deformation during strain-rate-controlled spherical nanoindentation is governed by the coupled evolution of constitutive strain-rate sensitivity and deformation length scale, making the intrinsic influence of strain rate difficult to isolate experimentally. This coupling is investigated in unirradiated and neutron-irradiated single-crystal tungsten using spherical nanoindentation, atomic force microscopy, high-resolution electron backscatter diffraction (HR-EBSD), and crystal plasticity finite element (CPFE) modeling. Nanoindentation experiments were performed at strain rates from 3.2e-5 to 3.2e-3 per second. AFM and HR-EBSD quantified surface pile-up, residual lattice strain, and geometrically necessary dislocation (GND) distributions. A strain-gradient CPFE framework incorporating thermally activated slip, GND hardening, irradiation-induced obstacle hardening, and strain-dependent softening was calibrated using a single experimental condition and validated across all remaining strain rates without further parameter adjustment. The validated model was then used to independently vary strain rate and indentation depth. Simulations show that strain rate primarily controls the stress required for thermally activated plastic flow, whereas indentation depth governs plastic-zone evolution, pile-up, and GND accumulation. Irradiation increases obstacle strength and promotes deformation localization while remaining consistent with a common thermally activated mechanism. The framework also predicts the compression response of a polycrystalline cube, demonstrating transferability across loading conditions and length scales, providing a robust basis for constitutive modeling of irradiation-hardened materials under transient loading.

cond-mat.mtrl-sci↗

arXiv2026

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

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.

cond-mat.mtrl-sci↗

arXiv2026

Precipitation induced recrystallisation (PIX) in a Ti-Fe-Mo bcc-superalloy driven by lattice misfit

Beta-Ti bcc-superalloys, comprising an A2 beta-Ti matrix reinforced by ordered intermetallic B2 beta-prime-TiFe precipitates, exhibit an unusual recrystallisation that occurs with no externally applied strain (i.e. no thermomechanical processing). Thermal ageing at 750 degrees Celsius for 72 h results in refinement of the grain size from 364 um to 30 um. This grain refinement is driven by discontinuous precipitation of beta-prime-TiFe lamellae with the beta-Ti matrix from grain/phase boundaries, which is associated with significant misorientation and increased dislocation density, attributed as precipitation induced recrystallisation (PIX).

cond-mat.mtrl-sci↗

arXiv2024

Quench Risk Increase With Irradiation Damage

Superconducting material enables fusion reactor magnet concepts to operate with current densities that would melt materials with non-zero resistance. The application of superconducting material is considered essential for net-positive power machines. Catastrophic damage can occur when superconductivity is lost and the current generates heat. This scenario is called a quench. Stabilizer material carries the magnet current (typically copper) during a quench and is the focus of this work. Irradiation-induced defects store energy in the Cu crystalline lattice. The release of stored energy in the magnet materials, combined with the associated magnet material property changes, can cause extreme off-normal events in superconducting magnets that worsen with fluence at an increasing rate. Stored energy can be released causing local heating and increasing the risk of a quench. For example, following irradiation at 4.6K and an estimated fluence of 0.45*10^18 n/cm^2, an energy release of 0.023 J/g was measured from Cu when increased in temperature from 10K to 18K, which would have been enough energy to create the same temperature increase spontaneously. Extrapolations of experimental data are used to estimate when spontaneous heating can occur due to the release of energy stored in irradiation-induced defects. Critical fluence values are estimated between 1.74*10^18 n/cm^2 and 2.85*10^19 n/cm^2 for neutron irradiation of Cu at a temperature of 20K. High-temperature ramp rate in-situ cryogenic calorimetry experiments of magnet materials following irradiation would provide more clarity to designers of fusion magnet systems. Due to the increased quench risk with superconducting magnet dose, magnetic confinement reactor designers should consider the frequency of maintenance temperature cycles to maintain an appropriate level of risk during operation.

physics.plasm-ph↗