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Title: Structural and chemical evolution in neutron irradiated and helium-injected ferritic ODS PM2000 alloy

Abstract

An investigation of the influence of helium on damage evolution under neutron irradiation of an 11 at% Al, 19 at% Cr ODS ferritic PM2000 alloy was carried out in the High Flux Isotope Reactor (HFIR) using a novel in situ helium injection (ISHI) technique. Helium was injected into adjacent TEM discs from thermal neutron 59Ni(nth, 59Ni(nth,α) reactions in a thin NiAl layer. The PM2000 undergoes concurrent displacement damage from the high-energy neutrons. The ISHI technique allows direct comparisons of regions with and without high concentrations of helium since only the side coated with the NiAl experiences helium injection. The corresponding microstructural and microchemical evolutions were characterized using both conventional and scanning transmission electron microscopy techniques. The evolutions observed include formation of dislocation loops and associated helium bubbles, precipitation of a variety of phases, amorphization of the Al2YO3 oxides (which also variously contained internal voids), and several manifestations of solute segregation. Notably, high concentrations of helium had a significant effect on many of these diverse phenomena. These results on PM2000 are compared and contrasted to the evolution of so-called nanostructured ferritic alloys (NFA).

Authors:
ORCiD logo; ORCiD logo; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1347849
Report Number(s):
PNNL-SA-122149
Journal ID: ISSN 0022-3115; 49137; AT2030110
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Nuclear Materials; Journal Volume: 484
Country of Publication:
United States
Language:
English
Subject:
Dual Helium and Neutron Irradiation; Ferritic ODS Alloy; Transmission electron microscopy; Environmental Molecular Sciences Laboratory

Citation Formats

Jung, Hee Joon, Edwards, Dan J., Kurtz, Richard J., Yamamoto, Takuya, Wu, Yuan, and Odette, G. Robert. Structural and chemical evolution in neutron irradiated and helium-injected ferritic ODS PM2000 alloy. United States: N. p., 2017. Web. doi:10.1016/j.jnucmat.2016.11.022.
Jung, Hee Joon, Edwards, Dan J., Kurtz, Richard J., Yamamoto, Takuya, Wu, Yuan, & Odette, G. Robert. Structural and chemical evolution in neutron irradiated and helium-injected ferritic ODS PM2000 alloy. United States. doi:10.1016/j.jnucmat.2016.11.022.
Jung, Hee Joon, Edwards, Dan J., Kurtz, Richard J., Yamamoto, Takuya, Wu, Yuan, and Odette, G. Robert. Wed . "Structural and chemical evolution in neutron irradiated and helium-injected ferritic ODS PM2000 alloy". United States. doi:10.1016/j.jnucmat.2016.11.022.
@article{osti_1347849,
title = {Structural and chemical evolution in neutron irradiated and helium-injected ferritic ODS PM2000 alloy},
author = {Jung, Hee Joon and Edwards, Dan J. and Kurtz, Richard J. and Yamamoto, Takuya and Wu, Yuan and Odette, G. Robert},
abstractNote = {An investigation of the influence of helium on damage evolution under neutron irradiation of an 11 at% Al, 19 at% Cr ODS ferritic PM2000 alloy was carried out in the High Flux Isotope Reactor (HFIR) using a novel in situ helium injection (ISHI) technique. Helium was injected into adjacent TEM discs from thermal neutron 59Ni(nth, 59Ni(nth,α) reactions in a thin NiAl layer. The PM2000 undergoes concurrent displacement damage from the high-energy neutrons. The ISHI technique allows direct comparisons of regions with and without high concentrations of helium since only the side coated with the NiAl experiences helium injection. The corresponding microstructural and microchemical evolutions were characterized using both conventional and scanning transmission electron microscopy techniques. The evolutions observed include formation of dislocation loops and associated helium bubbles, precipitation of a variety of phases, amorphization of the Al2YO3 oxides (which also variously contained internal voids), and several manifestations of solute segregation. Notably, high concentrations of helium had a significant effect on many of these diverse phenomena. These results on PM2000 are compared and contrasted to the evolution of so-called nanostructured ferritic alloys (NFA).},
doi = {10.1016/j.jnucmat.2016.11.022},
journal = {Journal of Nuclear Materials},
number = ,
volume = 484,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • Transmission electron microscopy (TEM) discs of PM2000 were coated on one side with a ~4 µm thick NiAl film and irradiated in HFIR to a neutron displacement damage dose of 21.2 dpa at 500°C. The dpa are primarily produced by fast neutrons, while the in situ He injection (ISHI) to 1230 appm derives from the thermal neutron two-step 59Ni(n,α) reaction. A uniform He injection profile extends up to about 8 µm below the NiAl coating, hence the remaining material experiences only dpa damage (21.2 dpa at 500°C). This report summarizes analytical TEM analyses to compare the two different regions, i.e.,more » simultaneous He-injection/displacement damage versus displacement damage only, or high and very low He/dpa ratios, respectively. TEM analyses of the He implanted region reveals a high density of small (<2 nm) He bubbles predominantly associated with dislocation loops in the matrix. Because of a very large grain size, no grain or subgrain boundaries were observed in the samples prepared by focused ion beam (FIB) micromachining. The only voids formed were associated with large ODS particles, all of which were amorphous, irrespective of particle size and level of He. The ODS particles range in size from 15-30 nm, and most particles have a single faceted void attached to it that ranges in size from 5 to 15 nm. On the non-implanted side of the sample, no He bubbles could be detected, and faceted voids were found on ~10% of the ODS particles. The He-implanted side contains both <100>{100} and ½<111>{111} dislocation loops and a low density of line dislocations, whereas the un-implanted side possesses predominantly line dislocations with a lower density of dislocation loops. In both regions, nanoscale fcc precipitates exhibiting a cube-on-cube orientation relationship with the bcc matrix were observed. Chemical analysis using energy dispersive x-ray spectroscopy (EDS) indicates this phase is rich in Al and Ti. It was also noted that substantial Cr segregation occurs around the dislocation loops, concurrent with Fe depletion. The clusters of fcc precipitates that do not appear to be associated with the existing loops or line dislocations. The amorphous Y-Al-O particles contain a high Al concentration (>20 at%) and Cr segregation/Fe-depletion at the periphery.« less
  • This report summaries TEM characterization of 14YWT and 12YWT, ODS ferritic alloys with 14 and 12 wt % of Cr respectively, to compare the effect of neutron irradiation with and without concurrent He injection using ISHI. The density and average size of <100>/{100} type dislocation loops are always larger than those of 1/2<111>/{111} type, but this difference is significantly affected by He implantation. The density of dislocation loops of both types ranges from ~1 to 4x1021 m-3 with average size ranging from 5~20 nm. 14YWT has lower density but larger size dislocation loops than 12YWT, while the line dislocation densitymore » of 14YWT is 3 times lower than that of 12YWT. Helium bubble densities of both 14YWT and 12YWT are 1.9x1023 m-3, the average He bubbles size of 14YWT and 12YWT are 1.4 and 1.2 nm, respectively. 14YWT exhibits α-α’ phase separation, Y-rich particles and uniformly distributed W. In addition to those features, 12YWT exhibits Y-Ti-O particles (not Y-O rich) and elongated Cr-rich phases.« less