Topography changes and microstructural evolution of nuclear graphite (IG-110) induced by Xe26+ irradiation
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摘要: 核石墨作为核反应堆的关键材料，受到核反应堆内的高通量辐照后其微观结构会产生损伤，直接影响反应堆的安全运行。为研究核石墨的辐照损伤行为，以IG-110核石墨为研究对象，研究了7 MeV Xe26+辐照对核石墨的形貌和微观结构影响。采用扫描电子显微镜、原子力显微镜、掠入射X射线衍射仪、拉曼光谱仪和纳米压痕仪对IG-110核石墨的形貌和微观结构进行了表征。结果表明，在0.11 dpa剂量辐照后，IG-110核石墨表面出现“ridge-like”结构，该结构主要在黏结剂区出现，且表面粗糙度略有增加。随着剂量的进一步增加，填料区也出现“ridge-like”结构。在0.55 dpa的剂量下，因表面孔结构的闭合而引起的新孔增多，表面粗糙度增加。这种形貌和微观结构的变化归因于石墨沿C轴方向的膨胀，且石墨薄片中的缺陷密度和面内无序度随剂量的增加而增加，但力学性能呈先增加后降低的趋势。前者是由位错钉扎和微孔闭合引起的，而高剂量辐照后力学性能下降归因于孔隙率的增加和非晶结构的产生。Abstract: The microstructure of nuclear graphite, a key material in nuclear reactors, is affected by the high-flux irradiation. The damage to the graphite by irradiation is important for reactor safety. To understand the damage of nuclear graphite by irradiation, IG-110 nuclear graphite, a representative nuclear graphite, was chosen to investigate the change in morphology and microstructure caused by 7 MeV Xe26+ irradiation with peak damage doses of 0.1-5.0 displacements per atom (dpa) for samples of a size of 40.0 mm×40.0 mm×2.0 mm. The topography and microstructure of IG-110 were characterized by SEM, AFM, grazing incidence XRD, Raman spectroscopy and nano-indentation. Results indicate that after 7 MeV Xe26+ irradiation at a dose of 0. 11 dpa, a ridge-like structure appears on the surface of the IG-110 graphite, mainly in the binder region, and the surface roughness increases slightly. With a further increase of the irradiation dose, the ridge-like structure also appears in the filler region. At a dose of 0.55 dpa, pore shrinkage increases accompanied by pore closure, and the surface roughness also increases. The changes in topography and microstructure caused by irradiation are attributed to the expansion of graphite along the c-axis direction. With increasing irradiation dose the defect density and the degree of in-plane disorder in the graphene sheets increases, while the modulus and hardness of the graphite first increase and then decrease. Their increase is caused by dislocation pinning and closure of fine pores, while their decrease is attributed to an increase in porosity and the generation of an amorphous structure.
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Key words:
- IG-110 /
- Nuclear graphite /
- Ion irradiation /
- Morphology /
- Microstructure.
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Figure 1. SEM images of IG-110 graphite (a, c, e and g) before and after irradiation at surface damage doses of (b) 0.02 dpa, (d) 0.11 dpa, (f) 0.55 dpa and (h) 1.25 dpa. (F, B, P and R refer to filler particle, binder phase, pores and ridge-like structures, respectively)
Figure 3. Magnified SEM images of IG-110 graphite (a, c, e and g) before and after irradiation at surface damage doses of (b) 0.02 dpa, (d) 0.11 dpa, (f) 0.55 dpa and (h) 1.25 dpa (F, B, C and H refer to filler particle, binder phase and crack, respectively)
Figure 4. AFM images of IG-110 graphite (a) before and after irradiation at surface damage dose of (b) 0.02 dpa, (c) 0.11 dpa, (d) 0.55 dpa and (e) 1.25 dpa. (f) The surface roughness and peak-to-peak distance varies with the surface damage dose
Figure 5. GIXRD patterns and (002) peaks of IG-110 graphite (a) before and (b) after irradiation. (c) Lc and d002 as functions of the irradiation damage dose
Figure 6. Raman spectra with linear background subtraction of IG-110 graphite (a) before and after irradiation at surface damage doses of (b) 0.02 dpa and (c) 0.11 dpa. All spectra are fitted with the Lorentz line shape. (d) ID/IG and (e) position and FWHM of the G peak as functions of the irradiation damage dose
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