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Title: Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions

Abstract

Newly-developed precipitate-strengthened ferritic steels with and without pre-existing nanoscale precipitates were irradiated with 4 MeV protons to a dose of ~5 mdpa at 50 C and subsequently examined by nanoindentation and atom probe tomography (APT). Irradiation-enhanced precipitation and coarsening of pre-existing nanoscale precipitates were observed. Copper partitions to the precipitate core along with a segregation of Ni, Al and Mn to the precipitate/matrix interface after both thermal aging and proton irradiation. Proton irradiation induces the precipitation reaction and coarsening of pre-existing nanoscale precipitates, and these results are similar to a thermal aging process. The precipitation and coarsening of nanoscale precipitates are responsible for the changes in hardness. The observation of the radiation-induced softening is essentially due to the coarsening of the pre-existing Cu-rich nanoscale precipitates. The implication of the precipitation on the embrittlement of reactor-pressure-vessel steels after irradiation is discussed.

Authors:
 [1];  [2];  [1];  [1];  [1];  [3];  [2];  [2]
  1. ORNL
  2. Auburn University, Auburn, Alabama
  3. Nanjing University of Science and Technology
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Shared Research Equipment Collaborative Research Center
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1037657
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Acta Materialia; Journal Volume: 60; Journal Issue: 6-7
Country of Publication:
United States
Language:
English

Citation Formats

Zhang, Zhongwu, Liu, C T, Wang, Xun-Li, Miller, Michael K, Ma, Dong, Chen, Guang, Williams, J R, and Chin, Bryan. Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions. United States: N. p., 2012. Web. doi:10.1016/j.actamat.2012.02.008.
Zhang, Zhongwu, Liu, C T, Wang, Xun-Li, Miller, Michael K, Ma, Dong, Chen, Guang, Williams, J R, & Chin, Bryan. Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions. United States. doi:10.1016/j.actamat.2012.02.008.
Zhang, Zhongwu, Liu, C T, Wang, Xun-Li, Miller, Michael K, Ma, Dong, Chen, Guang, Williams, J R, and Chin, Bryan. 2012. "Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions". United States. doi:10.1016/j.actamat.2012.02.008.
@article{osti_1037657,
title = {Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions},
author = {Zhang, Zhongwu and Liu, C T and Wang, Xun-Li and Miller, Michael K and Ma, Dong and Chen, Guang and Williams, J R and Chin, Bryan},
abstractNote = {Newly-developed precipitate-strengthened ferritic steels with and without pre-existing nanoscale precipitates were irradiated with 4 MeV protons to a dose of ~5 mdpa at 50 C and subsequently examined by nanoindentation and atom probe tomography (APT). Irradiation-enhanced precipitation and coarsening of pre-existing nanoscale precipitates were observed. Copper partitions to the precipitate core along with a segregation of Ni, Al and Mn to the precipitate/matrix interface after both thermal aging and proton irradiation. Proton irradiation induces the precipitation reaction and coarsening of pre-existing nanoscale precipitates, and these results are similar to a thermal aging process. The precipitation and coarsening of nanoscale precipitates are responsible for the changes in hardness. The observation of the radiation-induced softening is essentially due to the coarsening of the pre-existing Cu-rich nanoscale precipitates. The implication of the precipitation on the embrittlement of reactor-pressure-vessel steels after irradiation is discussed.},
doi = {10.1016/j.actamat.2012.02.008},
journal = {Acta Materialia},
number = 6-7,
volume = 60,
place = {United States},
year = 2012,
month = 1
}
  • Newly-developed precipitate-strengthened ferritic steels with and without pre-existing nanoscale precipitates were irradiated with 4 MeV protons to a dose of ~5 mdpa at 50 C and subsequently examined by nanoindentation and atom probe tomography (APT). Irradiation-enhanced precipitation and coarsening of pre-existing nanoscale precipitates were observed. Copper partitions to the precipitate core along with a segregation of Ni, Al and Mn to the precipitate/matrix interface after both thermal aging and proton irradiation. Proton irradiation induces the precipitation reaction and coarsening of pre-existing nanoscale precipitates, and these results are similar to a thermal aging process. The precipitation and coarsening of nanoscale precipitatesmore » are responsible for the changes in hardness. The observation of the radiation-induced softening is essentially due to the coarsening of the pre-existing Cu-rich nanoscale precipitates. The implication of the precipitation on the embrittlement of reactor-pressure-vessel steels after irradiation is discussed.« less
  • Recent experimental results tend to indicate that embrittlement and swelling due to irradiation by fast neutrons are not so important in ferritic as in austenitic stainless steels. For this reason, it would be possible to use ferritic steels as canning or structural materials in fast reactors. In a joint program it was decided to develop a ferritic alloy, strengthened by inert phase dispersion, to be compatible with a sodium environment. This work is concerned with the results pertaining to the metallic matrix of this material. It is shown that titanium and molybdenum are interesting additions to the Fe--13 Cr ferriticmore » alloy as far as the mechanical properties at high temperature are concerned. Creep rupture strength and low cycle behavior of these ferritic alloys have been measured in the temperature range from 600 to 750 deg C. (auth)« less
  • Nanocluster-strengthened ferritic alloys are promising as structural materials because of their excellent high-temperature strength and radiation-damage resistance. Recently, Fu et al. [Phys. Rev. Lett. 99, 225502 (2007)] predicted that vacancies play an essential role in the formation and stabilization of nanoclusters in these materials. Positron-lifetime spectroscopy has been used to test this theoretical prediction in a nanocluster-strengthened Fe-based alloy. Nanoclusters (2-4 nm in diameter) containing Ti, Y, and O have been observed in a mechanically alloyed ferritic steel by atom-probe tomography. Vacancy clusters containing four to six vacancies have also been found in this material. In contrast, no vacancy clustersmore » were detected in similar alloys containing no nanoclusters. These results indicate that vacancies are a vital component of the nanoclusters in these alloys.« less
  • The effects of copper, silicon, molybdenum, and nitrogen as alloying elements on the microstructure and corrosion behavior of type 304 (UNS S30400) austenitic stainless steel (SS) in deaerated dilute acidic chloride solutions at 30 C and 60 C was investigated using potentiodynamic, scanning electron microscopy, and energy dispersive X-ray analysis techniques. The addition of 2% Cu decreased the corrosion and critical current densities sharply. Surface analysis showed the presence of insoluble cuprous chloride dispersed on the steel surface in severe conditions. The additive Cu had no measurable effect on the other passivation parameters. The presence of 3% Si promoted themore » formation of some {delta}-ferrite phase, but the Si-rich film on the surface was sufficient to improve the general and pitting corrosion resistance. A combined beneficial effect was brought about by alloying 0.8% Mo with high-nickel type 304 SS containing 2% Cu + 3% Si. SEM revealed the segregation of N-rich phases in the presence of 0.24% N in these steels. However, N addition shifted the pitting potential in the positive direction, extending the passive range of the steel.« less
  • During the up and down cycles of a fusion reactor, the first wall is exposed concomitantly to a flux of energetic neutrons that generates radiation defects and to a neutron thermal flux that induces thermal stresses. The resulting strains may exceed the elastic limit and induce a plastic deformation in the material. A similar situation occurs in the window of a spallation liquid source target and results in the same type of damage. This particular loading has been simulated in F82H martensitic ferritic steel, using a device allowing a fatigue test to be carried out during irradiation with 590 MeVmore » protons. All fatigue tests were carried out at 300?C, in a strain controlled test at strain levels around 0.8%. Two different signals have been used: a fully symmetrical triangle wave signal (R=-1) and a triangle ramp with 2 min tension holds. The fatigue was investigated under three different conditions: unirradiated , irradiated and post irradiation tested, and finally in beam tested. The main result is that the in beam tested specimens have the lowest life as compared to the post irradiation tested specimens and unirradiated specimens. Hydrogen is suspected to be the main contributor to the observed embrittlement.« less