Irradiation Induced Precipitation in Model Alloys with Systematic Variation of Cu, Ni and P Content: A Small Angle Neutron Scattering Study

Abstract

Trends in the properties of defects, reflecting the role of Ni and P in the enhanced precipitation of copper during irradiation, have been studied by small angle neutron scattering (SANS) in a set of 8 model RPV steels. The alloys in the set contain different, selected amounts of Cu, Ni and P, while the composition of all the 8 samples concerning the rest of the alloying elements, the ‘RPV steel background’, was invariant throughout the series. The irradiation was done in a test reactor at 290C, at controlled radiation conditions, for two neutron fluences of 5∙1018 and 5∙1019 n/cm2. The SANS data show an approximately quadratic relationship between the precipitated volume fraction fm of damage particles and the nickel content cNi of the sample for the medium-copper cCu = 0.16% alloys, with a nearly zero initial slope of fm; the coefficients in the equation vary substantially with the fluence. A nearly perfect correlation of fm with the increase of microhardness was found for all alloys. The size distribution, as deduced from magnetic scattering, differs systematically from that found by analysis of the nuclear scattering; this difference correlates with both cCu and cNi. For the two low-copper alloys, phosphorus is seen to enhance production of radiation damage centers, whereas for the medium-copper alloys a refinement of the precipitated phase occurs.

Flux dependence of cluster formation in neutron-irradiated weld material

“…According to our standard analysis we have assumed that the system consists of isolated scattering particles in a homogeneous matrix (twophase approach) and that the particles are spherical and nonmagnetic. The A-ratio, originally defined as the ratio of the scattering cross-sections perpendicular and parallel to the magnetic field direction [22], was calculated in the size space after performing the transformation according to the relation, A = 1 + M/N, where M and N denote the area under the size distribution curve obtained from the magnetic and nuclear scattering contributions, respectively.…”

Characterization of neutron-irradiated ferritic model alloys and a RPV steel from combined APT, SANS, TEM and PAS analyses

“…The total volume fraction of clusters, the estimated number density (integrated from the lower detection limit, 0.5 nm, upwards), the radius at the peak of the size distribution and the A-ratio, found for each investigated alloy and condition according to Ref. [42], are summarized in Figs. 2-5.…”

Embrittlement of nuclear reactor pressure vessels

“…The primary consequence of RED is the formation of fine-scale CRPs. 6,8,9,[14][15][16][20][21][22] The maximum effective concentration of supersaturated copper in the iron matrix is about 0.3%. This upper limit is imposed by coarse-scale copper preprecipitation during the final stress relief treatment.…”