Investigation of defect clusters in ion-irradiated Ni and NiCo using diffuse X-ray scattering and electron microscopy

The nature of defect clusters in Ni and Ni50 Co50 (NiCo) irradiated at room temperature with 2-16 MeV Ni ions is studied using asymptotic diffuse X-ray scattering and transmission electron microscopy (TEM). Analysis of the scattering data provides separate size distributions for vacancy and interstitial type defect clusters, showing that both types of defect clusters have smaller sizes and higher densities in NiCo than in Ni. Diffuse scattering results show good quantitative agreement with TEM size distributions for cluster sizes greater than 2 nm in diameter, but we find that TEM under represents the number of defect clusters ≤ 2 nm, which comprise the majority of vacancy clusters in NiCo. Interstitial dislocation loops and stacking fault tetrahedra are identified by TEM. Comparison of diffuse scattering lineshapes to those calculated for dislocation loops and SFTs indicates that most of the vacancy clusters are SFTs.