Investigating the thermal and localised stress induced effects on discontinuous dynamic recrystallisation behaviour of CuCrZr alloy for fusion devices

Copper-Chromium-Zirconium alloys are candidate heat sink materials for divertors in fusion devices. The heat sinks used to keep divertor temperatures under control, and will be subjected to high thermal loads, neutron irradiation and high stress levels for extended durations resulting to creep deformation. The technology readiness level of the alloys is in the developmental phase, as there is a lack of long-term experimental data of the alloy in fusion-relevant environments. This study investigates the discontinuous dynamic recrystallisation phenomena and dislocation-based creep deformation mechanisms of the CuCrZr at multiple length scales, employing characterisation techniques like optical digital image correlation, high-resolution digital image correlation and electron back scatter diffraction measurements. The work presented focuses on the changes in the grain size, the grain orientation spread, twin boundary fraction, the shape functions of the grains, fractional dimension, local misorientation changes as a function of stress gradient, forming corroborative evidence of the underlying partial dynamic recrystallisation mechanisms and dynamic precipitation. Classic features like, necklace-like structures of the newly formed fine equiaxed grains, higher grain orientation spread, lower twin boundary fraction and increased hardness and increased boundary misorientation in high-strain regions are highlighted, signalling towards the two dominant mechanisms. • Optical and high-resolution DIC capture bulk and local strain on the same specimen. • Correlated EBSD and DIC maps reveal strain localisation and grain-scale recrystallisation. Large area EBSD map captures roughly 21,400 grains to provide statistical representation of granular deformation and misorientation information along the gauge length of the sample, thus a different stress regimes too. • Large-area HR-DIC mapping captures deformation across grains sized between 50 and 200 microns. • Hardness profiling along the gauge length links strain, precipitation stability, and creep response.