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The materials employed in the present experiment were a new F/M steel-SIMP designed by Institute of Modern Physics(IMP) and Institute of Metal Research(IMR), Chinese Academy of Sciences(CAS), and two kinds of ODS steels, namely commercial MA956 and Eurofer-ODS steels. Detailed thermal treatment and chemical composition for each type of steel are summarized in Table 1. It is worth further clarification that, as a new type of domestic independently developed martensitic steel, SIMP steel has better oxidation resistance and liquid metal corrosion resistance than other traditional F/M steels with the high content of Si. Moreover, the low activation characteristics of SIMP steel are realized via replacing both Mo with W and Nb with Ta.
Table 1. Details of chemical composition of SIMP, Eurofer-ODS, and MA956 steels (%).
Steels Fe Cr C Mn S W V Ta Si P Y2O3 Ni Al Ti Mo SIMP#1 Bal 10.24 0.22 0.52 0.0043 1.45 0.18 0.12 1.22 0.004 Eurofer-ODS#2 Bal 8.70 0.11 0.44 0.004 1.00 0.19 0.10 0.30 MA956#3 Bal 19.93 0.023 0.09 0.008 0.008 0.006 0.51 0.04 4.75 0.39 0.02 #1 SIMP: normalized at 1 040 °C for 30 min and tempering at 760 °C for 90 min.
#2 Eurofer-ODS: normalized at 1 150 °C for 60 min, tempering at 750 °C for 120 min.
#3MA956: canned and extruded at 1 100 °C, hot-rolled for 240 min, reheating to 1 100 °C for 30 min, hot-rolled.The samples used for the ions implantation were cut into dimensions of 3 mm×3 mm×1 mm with diamond wire cutting machine. One surface of each sample was ground into smooth surface with gradually refined sandpaper from 600 to 2 500 grades, and then was polished to a mirror-like surface by using vibration polisher.
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The implantation experiment was conducted in the Low Energy heavy ion Accelerator Facility(LEAF) at IMP, CAS. All of the materials were injected by 2 MeV He ions to a fluence of 1×1017 ions/cm2 at 500 and 600 °C. The detailed implantation parameters are shown in Table 2. The implantation temperature with a fluctuation of about
$ \pm $ 5 °C was monitored by two thermocouples near the sample. The current intensity was measured by two Faraday tubes in real time and remained at 30 μA.Table 2. Detailed parameters of He ions implantation experiment.
Sample Ion Energy/
MeVTem/℃ Fluences/
(ions·cm−2)SIMP/EU-ODS/MA956 He 2 500 1×1017 600 The depth distribution of both radiation damage level and He ions deposition concentration are obtained by SRIM 2013 calculations in “quick Kinchin-Pease calculation” mode[8]. During SRIM calculation, the density of target materials is 7.87 g/cm3, and the displacement threshold energies of both Fe and Cr are set as 40 eV[9].
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The cross-sectional TEM slices with thickness of about 70 nm were prepared by dual beams focused-ion beam(FIB) lift-out method. The microstructures were observed under the bright field image model of FEI Tecnai F20 TEM operated at 200 kV.
Irradiation induced swelling for a selected region can be calculated by Eq. (1):
$$S = \frac{{\Delta V}}{{V - \Delta V}} \times 100{\text{%}} ,$$ (1) where V is the volume of the selected region after irradiation. ∆V represents the relative change of the volume caused by bubbles in the region, that is the total volume of the bubbles in this region.
Effect of Nanostructures on Bubbles Nucleation and Growth in F/M and ODS Steels Exposed with High Helium Fluence
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摘要: 利用LEAF装置提供的2 MeV的He离子,在500和600 °C分别对新型F/M钢-SIMP钢和ODS钢(MA956和Eurofer-ODS钢)注入1×1017 ions/cm2的高通量He离子,借助透射电子显微镜,表征了辐照后三种材料的肿胀行为,验证了各材料中纳米微结构(晶界,析出相和纳米氧化物)对辐照后He泡成核和长大的影响。结果表明,基于材料中晶界和析出相对He泡生长的抑制作用,温度为500 °C时,SIMP和Eurofer-ODS钢表现出较高的抗辐照肿胀性能,而MA956中纳米界面He泡成核和长大作用不明显,表现出较差的抗辐照肿胀性能;此外,温度为600 °C时,Eurofer-ODS钢由于其晶界和氧化物界面的较强作用,表现出较好的抗辐照肿胀性能。总体来说,在高He通量注入条件下,材料中纳米结构的存在会抑制He泡长大的过程,但不同材料中纳米结构对He影响作用不同。
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关键词:
- nanostructure /
- steel /
- He bubble /
- nucleation and growth /
- TEM
Abstract: A new type of F/M steel (SIMP steel) and two kinds of ODS steels (MA956 and Eurofer-ODS steels) were irradiated by 2 MeV He ions to fluence of 1×1017 ions/cm2 at 500 and 600 °C. After irradiation, swelling behaviors and effect of nanostructures (such as grain boundaries, precipitates and nano-oxide particles) on the nucleation and growth of He bubbles were studied by transmission electron microscope. The results show that both SIMP and Eurofer-ODS steels exhibit better swelling resistance than MA956 ODS steel at 500 °C, because the grain boundaries or precipitates pronouncedly inhibit the growth of He bubbles. The Eurofer-ODS steel shows best swelling resistance due to the inhibition of He bubbles growth by the grain boundary and oxide interface at 600 °C. The present work shows that nanostructures in materials inhibit the process of He bubble growth under high He fluence conditions, but the degree of inhibition varies with different materials.-
Key words:
- nanostructure /
- steel /
- He bubble /
- nucleation and growth /
- TEM
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Figure 3. (color online)TEM images of He bubbles in the peak damage region for (a) SIMP, (b) EU-ODS, (c) MA956 under 1×1017 ions/cm2 He ions implantation conditions at 500 °C, and (d) high resolution image with its inverse Fourier transform pattern for He bubbles in SIMP steel, (e) high magnification image of He bubbles in MA956 with selected electron diffraction pattern.
Figure 4. (color online)TEM images of He bubbles in the irradiation damage zones for (a) SIMP, (b) EU-ODS, (c) MA956 under 1×1017 ions/cm2 He ions implantation conditions at 600 °C and (d) high magnification image and (e) high resolution image with its inverse Fourier transform pattern for He bubbles in Eurofer-ODS.
Table 1. Details of chemical composition of SIMP, Eurofer-ODS, and MA956 steels (%).
Steels Fe Cr C Mn S W V Ta Si P Y2O3 Ni Al Ti Mo SIMP#1 Bal 10.24 0.22 0.52 0.0043 1.45 0.18 0.12 1.22 0.004 Eurofer-ODS#2 Bal 8.70 0.11 0.44 0.004 1.00 0.19 0.10 0.30 MA956#3 Bal 19.93 0.023 0.09 0.008 0.008 0.006 0.51 0.04 4.75 0.39 0.02 #1 SIMP: normalized at 1 040 °C for 30 min and tempering at 760 °C for 90 min.
#2 Eurofer-ODS: normalized at 1 150 °C for 60 min, tempering at 750 °C for 120 min.
#3MA956: canned and extruded at 1 100 °C, hot-rolled for 240 min, reheating to 1 100 °C for 30 min, hot-rolled.Table 2. Detailed parameters of He ions implantation experiment.
Sample Ion Energy/
MeVTem/℃ Fluences/
(ions·cm−2)SIMP/EU-ODS/MA956 He 2 500 1×1017 600 -
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