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

Abstract

The nature of defect clusters in Ni and Ni 50 Co 50 (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 underrepresents 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.

Differences in the accumulation of ion-beam damage in Ni and NiFe explained by atomistic simulations

“…At 1 dpa, similar integrated damage levels are observed in Ni and NiFe. The RBS measurements concord with recent diffuse X-ray scattering in NiCo irradiated at 1 dpa [7]. At higher doses, RBS suggests that the integrated damage level continues to steadily grow in NiFe, while it saturates and even declines in Ni [6].…”

Historical Perspective on Diffraction Line-Profile Analyses for Crystals Containing Defect Clusters

“…Disagreement between X-ray and TEM size distribution determinations were observed in the smallsize ranges in a number of cases [30,31,33] and attributed in each case to limitations in the resolution of TEM imaging. As illustrated in a more recent comparison [34] between X-ray and electron microscopy size distributions in Figure 6, electron microscopy resolution today is capable of imaging loops significantly smaller than 20-Å radii when weak-beam dark-field (WBDF) imaging is used, and of course much smaller sizes using high-resolution lattice imaging. However, as indicated in the Figure 6 comparison between WBDF and bright-field (BF) defect cluster densities in ion-irradiated Ni, bright-field densities start to fall below WBDF at ~20-Å radius, and, by ~10-Å radius, BF densities are a factor of ten less than WBDF densities.…”

“…This is as would be expected for loop glide and aggregation and not for interstitial loop shrinkage, since interstitials would require energies of~5 eV or a temperature of 700 K to be emitted from loops. In more recent X-ray diffraction line-profile investigations, Olsen et al [34] compared dislocation loop damage in Ni and NiCo produced by Ni-ion irradiation in terms of vacancy and interstitial loop size distributions, and the distribution of point defects in clusters as a function of loop sizes. This work was part of a study directed toward understanding the impact of alloying in Ni-based concentrated solid solutions.…”

Atomic-level heterogeneity and defect dynamics in concentrated solid-solution alloys

“…Ab initio theory, time-dependent density functional theory (TD-DFT), AIMD, and classical MD simulations have revealed how alloy complexity can alter energy dissipation (the first distinctive property described in Section 3A) in the electronic and atomic subsystems [48][49][50][51], thereby offering the possibility of enhanced defect recombination or self-healing radiation resistance. Increasing experimental activities are evident in recent literatures [2,[12][13][14]23], including the successful growth of large single crystals, the integrated experiments and modeling predictions [2,12,13,[52][53][54][55][56][57], and the collaborative execution of well-defined irradiation experiments and microstructural characterization to evaluate compositional effects on radiation response [12][13][14]17,23,[55][56][57][58][59].…”