Detecting irradiation-induced strain localisation on the microstructural level by means of high-resolution digital image correlation

Materials subjected to irradiation damage often undergo local microstructural changes that can affect their expected performance. To investigate such changes, this work proposes a novel approach to detect strain localisation caused by irradiation-induced damage in nuclear materials on the microstructural level, considering a statistically relevant number of grains. This approach determines local strains using highresolution digital image correlation (HRDIC) and compares them with the underlying material microstructure. Sets of images captured before and after irradiation are compared to generate full-field displacement maps that can then be differentiated to yield high-resolution strain maps. These strain maps can subsequently be used to understand the effects of irradiation-induced dimensional change and cracking on the microscale. Here, the methodology and challenges involved in combining scanning electron microscopy (SEM) with HRDIC to generate strain maps associated with radiation-induced damage are presented. Furthermore, this work demonstrates the capabilities of this methodology by analysing three different materials subjected to proton irradiation: a zircaloy-4 (Zry-4) metal irradiated to 1 & 2 dpa, and two ceramics based on MAX phase compounds, i.e., the Nb4AlC3 ternary compound and a novel (Ta,Ti)(3) AlC2 solid solution, both irradiated to -0.1 dpa. These results demonstrated that all materials show measurable expansion, and the very high strains seen in the MAX phase ceramics can be easily attributed to their microstructure. Grain-to-grain variability was observed in Zry-4 with a macroscopic expansion along the rolling direction that increased with irradiation damage dose, the Nb4AlC3 ceramic showed significant expansion within individual grains, leading to intergranular cracking, while the less phase-pure (Ta,Ti)(3) AlC2 ceramic exhibited very high strains at phase boundaries, with limited expansion in the binary carbide phases. This ability to measure irradiation-induced dimensional changes at the microstructural scale is important for designing microstructures that are structurally resilient during irradiation. (c) 2023TheAuthors. Publishedby Elsevier B.V.

Automated summary

This work proposes a novel approach to detect strain localisation caused by irradiation-induced damage in nuclear materials on the microstructural level. High-resolution digital image correlation (HRDIC) is used to determine local strains and generate high-resolution strain maps, which can help understand the effects of irradiation-induced dimensional change and cracking. The combination of scanning electron microscopy (SEM) and HRDIC is demonstrated to measure irradiation-induced dimensional changes in three different materials and is crucial in designing microstructures that are structurally resilient during irradiation.