Characterising Ion-Irradiated FeCr: Hardness, Thermal Diffusivity and Lattice Strain

TL;DR

This study systematically investigates how ion irradiation affects the hardness, thermal diffusivity, and lattice strain in FeCr alloys, revealing that Cr content influences defect retention and material properties.

Contribution

It provides new insights into the effects of Cr on irradiation-induced defects, thermal transport, and lattice strain in FeCr alloys using multiple characterization techniques.

Findings

Cr increases retention of irradiation defects

Thermal diffusivity decreases mainly with Cr content

Lattice strain indicates higher defect density than TEM suggests

Abstract

Ion-irradiated FeCr alloys are useful for understanding and predicting neutron-damage in the structural steels of future nuclear reactors. Previous studies have largely focused on the structure of irradiation-induced defects, probed by transmission electron microscopy (TEM), as well as changes in mechanical properties. Across these studies, a wide range of irradiation conditions has been employed on samples with different processing histories, which complicates the analysis of the relationship between defect structures and material properties. Furthermore, key properties, such as irradiation-induced changes in thermal transport and lattice strain, are little explored. Here we present a systematic study of Fe3Cr, Fe5Cr and Fe10Cr binary alloys implanted with 20 MeV Fe$^{3+}$ ions to nominal doses of 0.01 dpa and 0.1 dpa at room temperature. Nanoindentation, transient grating spectroscopy (TGS) and X-ray micro-beam Laue diffraction were used to study the changes in hardness, thermal diffusivity and strain in the material as a function of damage and Cr content. Our results suggest that Cr leads to an increased retention of irradiation-induced defects, causing substantial changes in hardness and lattice strain. However, thermal diffusivity varies little with increasing damage and instead degrades significantly with increasing Cr content in the material. We find significant lattice strains even in samples exposed to a nominal displacement damage of 0.01 dpa. The defect density predicted from the lattice strain measurements is significantly higher than that observed in previous TEM studies, suggesting that TEM may not fully capture the irradiation-induced defect population.