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In this work, the self-ion irradiation behavior of nanocrystalline copper-tantalum alloys was investigated. In particular, the microstructural evolution of Cu-3at.%Ta and Cu-10at.%Ta was evaluated under the fluence of 2 × 1017 ions/cm2 of 4 MeV Cu-ions at different temperatures. Results revealed that despite the ability of Cu-10Ta to reprecipitate new nanoclusters and thereby increase the sink density by ∼17%, it undergoes significant microstructural evolution. On the other hand, Cu-3Ta exhibits a relatively more stable microstructural response and 3.5 times less swelling over the same conditions. This result illustrates the premise that irradiation and deformation may be coupled to stabilize/rejuvenate Ta-nanoclusters in extreme-environments. [Display omitted] [ABSTRACT FROM AUTHOR]

The 12Cr1MoWV (wt%) ferritic/martensitic steel HT9 is a candidate material for fuel cladding in advanced nuclear reactors, such as the Versatile Test Reactor currently under development. As such, understanding the relationship between microstructure and mechanical properties in the context of irradiation environments for these steels is critical. N content, and more specifically interstitial N, has been hypothesized to be detrimental to irradiated properties at lower temperatures (less than 0.3T m) to a total of 6 dpa; however, in this work at a dose of 1 dpa the irradiated microstructure was improved with added N, leading to less irradiation hardening. Three variants of HT9 were irradiated with 1.5 MeV protons to a dose of 1 dpa at 300 ˚C. The HT9 variants included Low (10 ppm), Mid (190 ppm), and High (440 ppm) N alloys that were otherwise nearly identical. Changing the N content had a variety of effects on the irradiated defect structures. As N content increased, the average dislocation loop diameter decreased, while the number density of loops increased. Additionally, extensive Ni clustering was observed on dislocations and interfaces. The Mid and High N specimens exhibited significantly less hardening (ΔHV ≅ 100) relative to the Low N specimen (Δ HV ≅ 160). The decrease in hardening is attributed to vanadium carbonitride acting as a sink for Ni clusters that would otherwise form on dislocations. Under the irradiation conditions used, these results suggest increasing the N content in HT9 may have a desirable effect on the irradiated structure and properties at the dose studied, as well as the swelling resistance at higher doses. In other words, N content appears to be a powerful tool for tailoring the self-interstitial atom cluster mobility in F/M steels for different temperature and dose applications. [ABSTRACT FROM AUTHOR]

In this work, a nanocrystalline (NC) Cu-10at.%Ta alloy is irradiated with helium at different temperatures to assess the stability and effectiveness of Ta nanoclusters in trapping helium and suppressing swelling. Advanced microstructural characterization of the room-temperature irradiated specimens indicated the presence of small He-bubbles (∼1-2 nm) at the peak damage depth mainly at the core and along the interface of Ta nanoclusters with Cu matrix. Few bubbles were found along grain boundaries, with much smaller bubbles homogenously distributed within the copper lattice. High-temperature irradiation exhibited bubbles of ∼3-5 nm, which were primarily associated with nanoclusters as compared to other locations, with no observed faceting of the bubbles. Atom probe analysis confirmed helium partitioning to the Ta nanoclusters indicating the effective entrapment of these He atoms. [Display omitted] [ABSTRACT FROM AUTHOR]