Experimental and theoretical analysis of equilibrium segregation and radiation-induced segregation of Cr at grain bounda
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ORIGINAL PAPER
Experimental and theoretical analysis of equilibrium segregation and radiation-induced segregation of Cr at grain boundaries in a reduced activation ferritic/martensitic (RAFM) steel Li-dong Xia1 • Hao Chen1 • Zhi-gang Yang1 • Chi Zhang1 Received: 17 January 2020 / Revised: 8 April 2020 / Accepted: 13 April 2020 China Iron and Steel Research Institute Group 2020
Abstract Helium ion irradiation at 350 C was performed to study equilibrium segregation and radiation-induced segregation (RIS) of Cr at grain boundaries in reduced activation ferritic/martensitic steels. Cr concentration at grain boundary was measured by scanning transmission electron microscopy with an energy-dispersive spectrometer. The measured Cr concentration at grain boundaries in heat treated zone was 11.7 and 12.8 wt.% in irradiated zone, respectively, which matched well to the calculated results from Mclean and modified Perk model. Equilibrium segregation and RIS of Cr mechanisms were theoretically analysed. The analysis indicates that as temperature rises, equilibrium Cr segregation decreases monotonically, while RIS of Cr has a bell-shape profile, which increases first and then decreases. It is also shown that at low and high temperatures, equilibrium segregation of Cr is higher than that of RIS; at intermediate temperatures, equilibrium Cr segregation is lower than RIS. Keywords Reduced activation ferritic/martensitic steel Equilibrium Cr segregation Radiation-induced segregation Grain boundary Rate theory Mclean equation
1 Introduction Reduced activation ferritic/martensitic (RAFM) steels can be used in the next generation of fusion nuclear reactors as structural materials [1–4]. It is known that the segregation of Cr at grain boundaries plays important roles in determining the mechanical properties of RAFM steels [5], which may enhance precipitate or embrittle the grain boundaries, depending on Cr concentration at grain boundaries. When in applications, RAFM steels must withstand not only radiation damage, but also high temperatures for long time. Therefore, it is essential to have an exhaustive knowledge of Cr segregation mechanisms under heat treatment as well as irradiation. Equilibrium Cr segregation has been reported in many literatures after heat treatment in ferritic/martensitic steels & Chi Zhang [email protected] 1
Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
[6–8]. It was reported that Cr concentration at grain boundaries in a 9.16 wt.% Cr ferritic steel after heat treatment at 300 C was 12.90 wt.% [8] and that in a 14.25 wt.% Cr steel after 350 C heat treatment was 17.31 wt.% [7]. Radiation-induced segregation (RIS) of Cr at different temperatures has also been reported [9–11]. Lu et al. [12] summarized some experimental literatures and found that both Cr enrichment and depletion could be observed. Wharry et al. [13, 14] have recently pointed
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