Tomographic atom probe characterization of the microstructure of a cold worked 316 austenitic stainless steel after neutron irradiation

Abstract

a b s t r a c tFor the first time, chemical analyses using Atom Probe Tomography were performed on a bolt made of cold worked 316 austenitic stainless steel, extracted from the internal structures of a pressurized water reactor after 17 years of reactor service. The irradiation temperature of these samples was 633 K and the irradiation dose was estimated to 12 dpa (7.81 Â 10 25 neutrons.m À2 , E > 1 MeV). The samples were analysed with a laser assisted tomographic atom probe. These analyses have shown that neutron irradiation has a strong effect on the intragranular distribution of solute atoms. A high number density (6 Â 10 23 m À3 ) of Ni-Si enriched and Cr-Fe depleted clusters was detected after irradiation. Mo and P segregations at the interfaces of these clusters were also observed. Finally, Si enriched atmospheres were seen.

Experimental atomic scale investigation of irradiation effects in CW 316SS and UFG-CW 316SS

“…As reported in Ref. [30], the similarity between the number density and size of Ni-Si clusters measured in this work and the number density and size of interstitial dislocation loops observed by TEM in the already referenced literature (i.e. Frank loop number density of the order of: 10 23 m À3 and diameter of 9 ± 2 nm) strongly supports the radiation induced segregation mechanism of Ni and Si solutes towards dislocation loops as already reported in [20,24,31].…”

“…The same value is found either the calculation is based on mass balance (taking into account the reported composition of phases, with Ni and Si for example) or with number density and size of clusters. A detailed description of these data may be seen in reference [30]. As reported in Ref.…”

“…The irradiation temperature was estimated to be 633 K. The neutron dose rate was 2.2  10 À8 dpa s À1 (dpa s À1 = r  U where r = 1500 barn is the displacement cross section and U is the flux of neutrons with energy higher than 1 MeV) and the dose was about 12 dpa (8  10 25 n m À2 ). TEM microstructural examinations on different parts of this bolt [30,31] show interstitial Frank loops and small 'black dots'. The number density and the diameter of Frank loops and black dots were not measured for this dpa level and exact location of extraction of atom probe samples.…”

Atomic scale investigation of radiation-induced segregation in austenitic stainless steels

“…It has been shown recently that neutron irradiation induces the formation of Ni-Si enriched clusters in a 316 SS [15]. The authors suggest that the solute clusters are formed by radiation-induced segregation to dislocation loops.…”

Microstructural and Stress Corrosion Cracking Characteristics of Austenitic Stainless Steels Containing Silicon

“…A high concentration of Si has been reported on the grain boundaries of the parts of SSs exposed to neutron irradiation in nuclear reactors. [2,4,16] The following two types of Tohoku samples were studied: (1) those in the SA condition and (2) those in the WR condition, in which a deformation of 15 pct was introduced by cross rolling at 200°C to 250°C. [9] Metallographic studies (Figures 8 and 9) show that the microstructure of both samples was equiaxed austenite with a grain size between 4 and 5.…”