Hardening and Microstructure of Model Reactor Pressure Vessel Steel Alloys Using Proton Irradiation
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Hardening and Microstructure of Model Reactor Pressure Vessel Steel Alloys Using Proton Irradiation Q. Yu1, G. S. Was1, L. M. Wang1, R. Odette2 and D. E. Alexander3 1 Department of Nuclear Engineering and Radiological Sciences, University of Michigan 2 Department of Mechanical and Environmental Engineering, University of California at Santa Barbara 3 Materail Science Division, Argonne National Laboratory ABSTRACT As part of a broad effort to understand the mechanisms of irradiation embrittlement in reactor pressure vessels steels, irradiation hardening and microstructural evolution in simple model Fe-0.9Cu-1.0Mn, Fe-0.9Cu and Fe alloys irradiated with 3.2 MeV protons at 300°C are compared to the corresponding changes in hardening produced by neutron irradiation over a similar dose range of 0.0004 to 0.015 dpa. In the case of the proton irradiated samples, Vickers hardness was measured at a 25 g load and the microstructures were characterized using small angle x-ray scattering (SAXS). In spite of the much higher dpa rate for protons (3 x 10-7 dpa/s compared to neutron rates of about 10-9 to 10-10 dpa/s) as well as very different primary recoil spectra, the observed hardening-dose response is very similar in both cases. The large increase in hardness in the alloys with 0.9% copper, and the SAXS data are consistent with precipitation of coherent copper-rich features accelerated by irradiation enhanced diffusion, as well as a much smaller contribution presumably from defect clusters that do not require the presence of copper. INTRODUCTION Irradiation hardening and consequential embrittlement of reactor pressure vessel (RPV) steels is a complicated function of dose, dose rate, temperature and alloy composition [1]. A key to understanding hardening and embrittlement is characterizing the formation and evolution of nanometer scale features composed of coherent precipitate phases and defect-solute cluster complexes. Proton irradiation has been shown to be highly effective in emulating the effects of neutron irradiation on microstructure, microchemistry, hardening and stress corrosion cracking susceptibility of austenitic stainless steels used in LWR core components [2]. Thus the objective of this research is to explore a similar use of protons to provide basic information on processes and mechanisms pertinent to the effects of neutron exposure. Advantages of proton irradiation include highly accelerated exposure rates, minimization of complications associated with handling radioactive specimens and consequently, a significantly lower cost to obtain the data. Further, comparisons of proton, neutron and electron irradiation data can provide insight into the effects of primary recoil spectra on microstructural evolution and mechanical property changes. The initial assessment of the use of proton irradiation in this role focuses on the effects in simple ferritic alloys containing various alloy additions of copper and manganese. It is well established that the hardening in copper bearing steels and iron alloys is primarily assoc
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