Nanoindentation and TEM to Study the Cavity Fate after Post-Irradiation Annealing of He Implanted EUROFER97 and EU-ODS EUROFER

Abstract

The effect of post-helium irradiation annealing on bubbles and nanoindentation hardness of two reduced activation ferritic martensitic steels for nuclear fusion applications (EUROFER97 and EU-ODS EUROFER) has been studied. Helium-irradiated EUROFER97 and EU-ODS EUROFER were annealed at 450 °C for 100 h in an argon atmosphere. The samples were tested by nanoindentation and studied by transmission electron microscopy extracting some focused ion beam lamellae containing the whole implanted zone (≈50 µm). A substantial increment in nanoindentation hardness was measured in the area with higher helium content, which was larger in the case of EUROFER97 than in EU-ODS EUROFER. In terms of microstructure defects, while EU-ODS EUROFER showed larger helium bubbles, EUROFER97 experienced the formation of a great population density of them, which means that the mechanism that condition the evolution of cavities for these two materials are different and completely dependent on the microstructure.

Radiation-Induced Helium Bubbles in Metals

“…Ono et al [62] observed bubble migration and coalescence in He-irradiated Fe under 750 °C annealing treatment, while bubbles in Fe-9Cr show much lower mobility. In addition, Roldán et al [63] conducted post-irradiation annealing experiments on He-irradiated two reduced activation ferritic martensitic steels (EU-ODS EUROFER and EUROFER97). Both steels contain complex microstructures that serve as barriers for bubbles.…”

“…Hence, nano/micro-mechanical tests are widely adopted to evaluate He bubble induced hardening in these sample. Nanoindentation [63,116,117], and in situ mechanical testing in SEM [118,119,120,121] and TEM [122,123,124,125,126,127] are widely performed to investigate the effect of He bubbles on the mechanical properties of various metals. We mainly focus on three parts next: He irradiation hardening in single-phase metals, He irradiation hardening in metallic multilayers and theoretical modeling of He irradiation hardening.…”

“…Several studies are performed on He irradiated steel [63], Ni [120], Cu [118,122,123,124,125,126] and Al–4Cu alloy [127] to evaluate He radiation hardening and interactions of He bubble with dislocations/deformation twin [63,120,121,122,123,124,125,126,127]. Using nanoindentation teats, Roldan et al [63] found that He-irradiated steels after annealing demonstrate much higher hardness compared with as-received samples. We [122] demonstrated that He bubbles with an equilibrium internal pressure slightly less than 1 GPa serve as shearable obstacles and internal dislocation sources in single-crystal Cu pillars.…”

Grain Refinement and Improved Mechanical Properties of EUROFER97 by Thermo-Mechanical Treatments

“…Under irradiation EUROFER97 steel has good mechanical performances in the temperature range between 350 • C and 550 • C [23][24][25] and several studies have been performed aimed to extend the operating temperature range. A possible solution to raise the maximum operating temperature, above 550 • C, is a variant of EUROFER97 steel reinforced by dispersion of oxide (ODS) [26].…”

Editorial for the Special Issue on Small-Scale Deformation using Advanced Nanoindentation Techniques

“…Müller et al [1] developed a new nanoindentation method to evaluate the influence of hydrogen on the plastic deformation of nickel. Effects of radiation on ferritic-martensitic steels were studied by Roldán et al [2]. The applications of the depth-sensing indentation method in the mechanical reliability of microelectronic packaging products, such as through-silicon via (TSV) structures and lead-free solder, were performed by Wu et al [3] and Long et al [4], respectively.…”