Effect of irradiation on the high strain rate indentation response of iron

We investigate the effect of self-ion irradiation on the indentation response of single crystal Fe up to indentation strain rates approaching 10⁴/s. Our investigation relies on a novel nanoindentation instrument that uses dynamic impact to achieve unprecedented indentation strain rates. Samples were irradiated with 1 MeV Fe⁺² ions up to 100 dpa. Indentation tests were conducted at strain rates from 10^–2 s⁻¹ to nearly 10⁴ s⁻¹. Based on analysis of load–displacement curves, we find that radiation enhances indentation hardness, as expected. Moreover, it also reduces strain rate sensitivity. Solids with low strain rate sensitivity are generally considered to be more prone to failure by shear banding under ballistic impact or blast loading. Thus, our findings suggest that irradiation has a deleterious influence on the high strain rate mechanical performance of some metals.