P03 The Micro- and Nanofocus X-ray Scattering Beamline, PETRA III, DESY PHOTON SCIENCE - Sri Tapasvi Nori

Title: Nanofocus WAXS and XRF Characterization of Chemical Segregation in Oxide Dispersion Strengthened – Concentrated Solid Solution Alloys

Abstract: The structural elements of the Generation IV nuclear reactors experience high temperatures (>500℃), radiation damage (>50 dpa), stress, and corrosion. For such applications, concentrated solid solution alloys (CSAs) have been developed for a decade. They are expected to possess superior mechanical properties and radiation resistance. Recently, novel oxide dispersion strengthened-CSAs were designed to enhance compressive and tensile, yield strengths and reduce irradiation hardening and void swelling further. The ODS-CSAs are enclosed with nanostructures such as oxide nanoprecipitates (Y2Ti2O7 type) and fine grains, which act as defect sinks and dislocation pinning sites for strengthening. Furthermore, Cr-containing ODS-CSAs possess additional defect sinks such as metal carbides of type Cr7C3. Hence, the state-of-the-art ODS-CSAs possess the best potential for irradiation damage applications. However, there is a lack of understanding of the irradiation effects in these material systems due to the limited literature. Therefore, it becomes imperative to comprehensively study the irradiation response of the novel ODS-CSAs to develop structural materials for advanced nuclear reactor concepts. There exists a huge knowledge gap regarding the irradiation effect studies in ODS-CSAs in the existing literature. Hence, the scope of the current work is to conduct a first-of-a-kind characterization of some of the ODS-CSAs to analyze the nanostructures, their interaction with irradiation-induced defects, irradiation-induced chemical segregation, and their impact on the mechanical properties following high-temperature irradiation (operating conditions of Gen. IV reactors). The aim of the proposed experiments at the P03 beamline at PETRA III, DESY, is to understand certain aspects of the overall scope such as the characterization of the nanostructures with a focus on chemical segregation and corresponding mechanical behavior. To achieve this, combined XRF and WAXS experiments will be conducted to obtain chemical and strain maps in the irradiated regions of selected ODS-CSAs along with quantification of the nanoprecipitates and segregated regions. Additionally, the effect of composition and irradiation temperature on the chemical and mechanical behavior will be assessed by examining various ODS-CSAs such as ODS-NiCoFe, ODS-NiCoFeCr, and ODS-NiCoCr. The compositional effect of Cr addition into ODS-NiCoFe will result in grain boundary segregation of ODS-NiCoFeCr, following irradiation at 580℃. It is caused by the vacancy-driven inverse Kirkendall effect, which signifies the movement of vacancy defects away from the grain boundaries and atomic diffusion towards the boundaries. Therefore, it can be hypothesized that the regions near the grain boundaries are rich in irradiation-induced interstitial-type dislocation loops. This phenomenon would result in higher plastic strains locally near the boundaries, which could be detected by strain mapping from WAXS data, while XRF data could reveal chemical segregation. Such a result is highly impactful as the aforementioned phenomenon could lead to the accumulation of vacancies to form voids away from the boundaries, which eventually could result in the most detrimental irradiation effect, void swelling. Such a correlative study of chemical segregation and mechanical behavior has never been studied. Alternatively, irradiation is expected to enhance chemical short-range ordering in CSAs such as NiCoCr; while the presence of precipitates such as oxides and carbides could reduce this effect, as Cr is consumed by the precipitates. However, precipitates could show such effects. The occurrence of short-range ordering is beneficial as it traps irradiation defects. Hence, a combined experiment of XRF and WAXS will reveal such effects and thus, assess the irradiation damage resistance of the alloys. In addition, each type of ODS-CSA should contain a different distribution of nanoprecipitates, which will impact the irradiation damage resistance accordingly.



This project has received funding from the European Union Horizon 2020 research and innovation
programme under grant agreement No 857470 and from European Regional Development Fund
via Foundation for Polish Science International Research Agenda PLUS programme grant
No MAB PLUS/2018/8.
Poland
The project is co-financed from the state budget within the framework of the undertaking of the Minister of Science and Higher Education "Support for the activities of Centers of Excellence established under Horizon 2020".

Grant: 5 143 237,70 EUR
Total value: 29 971 365,00 EUR
Date of signing the funding agreement: December 2023

The purpose of the undertaking is to support entities of the higher education and science system that have received funding from the European Union budget in the competition H2020-WIDESPREAD-2018-2020/WIDESPREAD-01-2018-2019: Teaming Phase 2. in the preparation, implementation and updating of activities, maintenance of material resources necessary for carrying out activities, acquisition and modernization of scientific and research apparatus, maintenance and development of personnel potential necessary for the implementation of activities, and dissemination of the results of scientific activities.