He Transport and Fate of Tempered Martensitic Steels: Summary of Recent TEM Observations
As an extension of prior work [1-4], we summarize recent observations made on a He-implanted tempered martensitic steel (TMS), F82H mod 3, irradiated in the HFIR, in both as-tempered (AT) and cold-worked (CW) conditions. A novel implantation technique was used to uniformly inject He into 3-mm diameter TEM discs to depths ranging from ≈ 5-8 µm. The He is generated by two-step transmutation reactions in Ni contained in a NiAl coating layer adjacent to paired 3 mm TEM discs. NiAl layers from 1 to 4 μm thick produced He/dpa ratios between 5 and 40 appm/dpa. The irradiations were at temperatures of 300, 400 and 500°C from 3.9 to 9 dpa and 90 to 380 appm He. Electron transparent samples were prepared by a cross-sectional thinning technique that allowed investigating microstructural evolution over a range of implantation depths. Irradiation of the AT alloy to 9 dpa at 500°C and 380 appm He resulted in relatively large, faceted cavities, that are likely voids, along with a much higher density of smaller He bubbles. The cavities were most often aligned in pearl necklace like strings, presumably due to their formation on pre-existing dislocations. A finer distribution of cavities was also present on precipitate interfaces, lath and grain boundaries. Nine dpa irradiations that produced 190 appm He resulted in a somewhat more random distribution and lower density of smaller matrix cavities; but lower He levels had a less noticeable effect on bubbles in the lath and precipitate boundaries. Corresponding irradiations of the CW F82H produced a larger number of smaller cavities. Irradiation of the AT alloy to 3.9 dpa and 90 ppm He at 400°C produced a similar cavity population to that observed at 500°C at 190 appm He, while the corresponding cavities at 500°C are slightly larger and more numerous at 380 appm He. The cavity strings were less obvious for the 400°C irradiations, and the bubble distribution appeared to be more random. No cavities were observed in the case of the 300°C irradiations. Overall the cavity number densities compare favorably with those previously reported [4], but details, including size distributions, are still under investigation. Dislocation structures were complex and varied greatly as a function of irradiation dose and temperature, and will be more thoroughly characterized in the next phase of the work.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1072915
- Report Number(s):
- PNNL-19198; AT6020100
- Country of Publication:
- United States
- Language:
- English
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