Analysis of Radiation Damage in Light Water Reactors: Comparison of Cluster Analysis Methods for the Analysis of Atom Probe Data.

Irradiation of reactor pressure vessel (RPV) steels causes the formation of nanoscale microstructural features (termed radiation damage), which affect the mechanical properties of the vessel. A key tool for characterizing these nanoscale features is atom probe tomography (APT), due to its high spatial resolution and the ability to identify different chemical species in three dimensions. Microstructural observations using APT can underpin development of a mechanistic understanding of defect formation. However, with atom probe analyses there are currently multiple methods for analyzing the data. This can result in inconsistencies between results obtained from different researchers and unnecessary scatter when combining data from multiple sources. This makes interpretation of results more complex and calibration of radiation damage models challenging. In this work simulations of a range of different microstructures are used to directly compare different cluster analysis algorithms and identify their strengths and weaknesses.

Data on Cu- and Ni-Si-Mn-rich solute clustering in a neutron irradiated austenitic stainless steel.

The data presented in this article is supplementary to the research article "Phase instabilities in austenitic steels during particle bombardment at high and low dose rates" (Levine et al.) [5]. Needle-shaped samples were prepared with focused ion beam milling from a 304L stainless steel that was irradiated with fast neutrons (E > 0.1 MeV) in the BOR-60 reactor at 318 °C to 47.5 dpa. Atom probe tomography (APT) experiments in voltage mode were then conducted on a Cameca LEAP 5000X HR. Atom position, range, and mass spectrum files after reconstruction with Cameca's IVAS software are included. Cu- and Ni-Si-Mn-rich solute nanoclusters were identified and analyzed using the Open Source Characterization of APT Reconstructions (OSCAR) program. Python code for OSCAR [4], information on the program's underlying algorithm, and sample output files are provided. A proximity histogram of a Ni-Si-Mn-rich cluster and a 1D density/solute concentration profile of a Cu-rich cluster are given to demonstrate OSCAR's analytical functionalities. The provided APT dataset is valuable for benchmarking phase instabilities in neutron-irradiated austenitic stainless steels that occur at high doses. The OSCAR program can be reused to process other APT data sets where solute nanoclustering is of interest.

Phase transformation and segregation to lattice defects in Ni-base superalloys.

Nanostructural features of nickel-base superalloys as revealed by atom probe field ion microscopy (APFIM) and atom probe tomography (APT) are reviewed. The more salient information provided by these techniques is discussed through an almost exhaustive analysis of literature over the last 30 years. Atom probe techniques are shown to be able to measure the composition of tiny gamma' precipitates, a few nanometers in size, and to reveal chemical order within these precipitates. Phase separation kinetics in model NiCrAl alloys was investigated with both 3DAP and Monte-Carlo simulation. Results are shown to be in good agreement. Plane by plane analysis of {001} planes of Ni(3)Al-type gamma' phase makes it possible to estimate the degree of order as well as the preferential sites of various addition elements (Ti, Cr, Co, W, Ta, Re, Ru, etc.) included in superalloys. Clustering effects of Re in the gamma solid solution were also exhibited. Due to its ultrahigh depth resolution, the microchemistry of interfaces and grain boundaries can be characterized on an atomic scale. Grain boundaries in Astroloy or N18 superalloys were found to be enriched in B, Mo, and Cr and Al depleted.