Atom probe study of irradiation-enhanced α′ precipitation in neutron-irradiated Fe–Cr model alloys

Abstract

Atom probe tomography (APT) was performed to study the effects of Cr concentrations, irradiation doses and irradiation temperatures on α′ phase formation in Fe-Cr model alloys (10-16 at.%) irradiated at 300 and 450°C to 0.01, 0.1 and 1 dpa. For 1 dpa specimens, α′ precipitates with an average radius of 1.0-1.3 nm were observed. The precipitate density varied significantly from 1.1x10 23 to 2.7x10 24 1/m 3 , depending on Cr concentrations and irradiation temperatures. The volume fraction of α′ phase in 1 dpa specimens qualitatively agreed with the phase diagram prediction. For 0.01 dpa and 0.1 dpa, frequency distribution analysis detected slight Cr segregation in high-Cr specimens, but not in Fe-10Cr specimens. Proximity histogram analysis showed that the radial Cr concentration was highest at the center of α′ precipitates. For most precipitates, the Cr contents were significantly lower than that predicted by the phase diagram. The Cr concentration at precipitate center increased with increasing precipitate size.

Comparison between SANS and APT measurements in a thermally aged Fe-19 at.%Cr alloy

“…Moreover, particles presenting the highest Cr content are among the smallest one [11]. Conversely to what is shown here, Chen et al [45] observed that core Cr concentration increases with cluster size in Fe-Cr alloys neutron irradiated at 300°C and 450°C. They also noticed that no concentration plateau in Cr was observed in the core of the precipitates.…”

Flux effects in precipitation under irradiation – Simulation of Fe-Cr alloys

“…Other data in literature shows a wide variety of Cr compositions ranging from 40-80 [15] and 55-60% [8,12] for neutron irradiations, which is much less than predicted by the phase-field simulations. However, the APT compositions are strongly dependent of the precipitate size, especially below 1.5 nm [15,81]. The Fe content α' in precipitates less than 1-2 nm in radius is overestimated in APT, primarily due to so-called trajectory aberrations, that result in an interface mixing zone containing both matrix and precipitate atoms [82,83].…”

“…[43]. Other data in literature shows a wide variety of Cr compositions ranging from 40-80 [15] and 55-60% [8,12] for neutron irradiations, which is much less than predicted by the phase-field simulations. However, the APT compositions are strongly dependent of the precipitate size, especially below 1.5 nm [15,81].…”

“…Small-angle neutron scattering (SANS) measurements by Mathon et al showed the formation of α' in neutron-irradiated F/M commercial steels containing ≥ ~9% Cr at even lower temperatures of 250 and 325 °C [7]. Precipitation of α' at 300 °C has also been observed in neutron irradiations of Fe-Cr model alloys containing ≥ 9% Cr, based on atom probe tomography (APT) and SANS characterization techniques [8][9][10][11][12][13][14][15][16]. Alternatively, Horton et al did not observe α' precipitation in a Fe-10Cr irradiated 4 thermodynamically driven Cr clustering occurs at rates controlled by RED, which has less than linear scaling with the flux when recombination is important.…”

Influence of injected interstitials on α′ precipitation in Fe–Cr alloys under self-ion irradiation

“…The same Fe-12at.%Cr and Fe-9at.%Cr alloys were irradiated at 300°C using Fe ions at a dose rate of 2 × 10 −4 dpa/s and using neutrons at a dose rate of 10 −7 dpa/s and analysed using atom probe tomography (APT) [9,10]: α particles were only observed under neutron irradiation. To the best of our knowledge, α precipitation has never been reported after heavy ion irradiation at high-dose rates (10 −3 -10 −4 dpa/s), whereas α precipitation has been shown to occur via an enhanced mechanism under neutron irradiation at low-dose rates ( ∼ 10 −7 dpa/s) [9][10][11][12][13][14][15][16]. Nevertheless, the difference in dose rate cannot explain by itself the difference in α precipitation.…”