RADIATE - Łukasz Kurpaska
Title:
Effects of high temperature ion irradiation on hardening and defects nucleation mechanisms in ferritic/martensitic and ferritic steels as well as model High Entropy Alloy.
Abstract:
Due to their promising mechanical properties, ferritic/martensitic (F/M) and ferritic (F) steels and high entropy alloys are considered advanced materials for applications in extreme operating environments, e.g., core components for fusion and fission reactors. The main advantages of these F/M steels over traditional ones are their high thermal conductivity and high resistance to radiation-induced swelling. High Entropy Alloys also seem to have excellent radiation resistance due to random nature of alloying elements which may trigger recovery damage via efficient dynamic annealing (especially in the early stages of the radiation build-up). However, described mechanism of energy dissipation remains unclear – especially at high temperatures. To better understand and explain the hardening and plasticity mechanisms of these materials related to radiation damage build-up, one needs to correlate mechanical properties with the material's microstructure.
Since the microstructure of m/f steels is complex, the only way to decouple the impact of each variable (and their interaction) is to progress with structural complexity. We propose to perform ion irradiation on eight different specimens: high-purity Fe, Fe-9%Cr, Fe-9%Cr-NiSiP, Co25Cr25Fe25Ni25, commercial Eurofer 97 and three ferritic steels: Fe-12Cr-0.3W-0.3Ti (working as a base) with addition of: 0.3Y2O3 or 0.3Al2O3 or 0.3ZrO2 at 300 oC. The proposed irradiation campaign fits nicely into the recently funded by European Commission INNUMAT project research agenda, and obtained results will be reported as a contribution to the activity of the experimental group in this project.
The microstructural changes during irradiation of F/M steels at temperatures of 300-350oC include the formation of (i) dislocation loops, probably decorated by solutes, in particular, Cr; (ii) thermodynamically stable Cr-rich a' precipitates, if the Cr content is high enough; (iii) Cr-rich radiation-induced clusters also containing solutes such as Si, Ni, P and Mn; and (iv) Si and P segregation and Cr depletion/enrichment at dislocations and grain boundaries. Moreover, vacancy clusters and voids also form (if the dose is high enough). Another key element in F/M steels is the influence of carbon concentrations on their plasticity mechanisms that are introduced to the material during irradiation. C can influence the microstructure evolution due to the migration of defects produced during ion irradiation, particularly forming complexes with vacancies that pin and migrate dislocation loops. As described above, the portfolio of phenomena occurring in M/F steels during irradiation is very complex. By conducting systematic irradiation on specimens with different microstructures, we aim to isolate and describe interactions between alloying elements and impurities present in F/M steels during irradiation. This will allow us to better understand the mechanical properties of these steels.
