Dependence on grain boundary structure of radiation induced segregation in a 9wt.% Cr model ferritic/martensitic steel (original) (raw)
2013, Journal of Nuclear Materials
Ferritic/Martensitic (F/M) steels containing 9 wt.% Cr are candidates for structural and cladding components in the next generation of advanced nuclear fission and fusion reactors. Although it is known these alloys exhibit radiation-induced segregation (RIS) at grain boundaries (GBs) while in-service, little is known about the mechanism behind RIS in F/M steels. The classical understanding of RIS in F/M steels presents a mechanism where point defects migrate to GBs acting as perfect sinks. However, variation in grain boundary structure may influence the sink efficiency and these migration processes. A proton irradiated 9 wt.% Cr model alloy steel was investigated using STEM/EDS spectrum imaging and GB misorientation analysis to determine the role of GB structure on RIS at different GBs. An ab initio based rate theory model was developed and compared to the experimental findings. This investigation found Cr preferentially segregates to specific GB structures. The preferential segregation to specific GB structures suggests GB structure plays a key role in the mechanism behind radiation-induced segregation, showing that not all grain boundaries in F/M steels act as perfect sinks. The study also found how irradiation dose and temperature impact the radiation-induced segregation response in F/M steels.
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Journal of Nuclear Materials, 2014
Ferritic/Martensitic (F/M) steels with high Cr content posses the high temperature strength and low swelling rates required for advanced nuclear reactor designs. Radiation induced segregation (RIS) occurs in F/M steels due to solute atoms preferentially coupling to point defect fluxes which migrate to defect sinks, such as grain boundaries (GBs). The RIS response of F/M steels and austenitic steels has been shown to be dependent on the local structure of GBs where low energy structures have suppressed RIS responses. This relationship between local GB structure and RIS has been demonstrated primarily in ion-irradiated specimens. A 9 wt.% Cr model alloy steel was irradiated to 3 dpa using neutrons at the Advanced Test Reactor (ATR) to determine the effect of a neutron radiation environment on the RIS response at different GB structures. This investigation found the relationship between GB structure and RIS is also active for F/M steels irradiated using neutrons. The data generated from the neutron irradiation is also compared to RIS data generated using proton irradiations on the same heat of model alloy.
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In this work, we perform molecular dynamics simulations to study the diffusion characteristics of a self-interstitial atom (SIA) in BCC Fe-Cr alloys and corresponding mass transport of Fe and Cr atoms via SIA migration mechanism. The calculations have been performed in the temperature range 600-1000 K in the alloys with Cr content 5-25 at.%, which is relevant for ferritic/martensitic steels. The results of atomistic simulations have been applied to evaluate the contribution of SIA diffusion mechanism to radiation-induced segregation (RIS) phenomenon. An original treatment is proposed in this work to account for the contribution from both vacancy and SIA mechanisms to RIS at sinks for point defects in multi-component system. By combining available experimental data on diffusion of Fe and Cr via vacancy mechanism with the results of MD simulations for SIAs, we demonstrate that enrichment of sinks by Cr atoms is possible in the Fe-Cr alloys containing less than 13% Cr. This result is discussed in the light of available experimental data on the RIS in Fe-Cr alloys and ferritic/martensitic steels. It is predicted that the degree of the Cr enrichment goes up with decreasing Cr content in the alloy and irradiation temperature.
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Grain boundary radiation-induced segregation (RIS) in two Type 304 stainless steels neutron-irradiated at 28R"C has been investigated by analytical electron microscopy. In the conventional alloy (CP), narrow i 5 5 nm width) RIS zones depleted in chromium and iron and enriched in silicon, phosphorus, and nickel were observed near grain boundaries. For the higher purity alloy (HP), similar width ( 2 6 nm) RIS zones depleted in chromium and enriched in nickel and iron were observed at boundaries, though at reduced magnitudes relative to those in the CP material. No significant segregation of silicon or phosphorus was observed in the HP material. RIS zones associated with faulted dislocation loops in the CP material were detected and shown to be depleted in chromium and enriched in nickel and iron relative to the matrix. 0022.311S/92/$OS.O0 0 1992 -Elsevier Science Publishers B.V. All rights reserved
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