Thomas Melonie, Oh Hajin, Schoell Ryan, House Stephen, Crespillo Miguel, Hattar Khalid, Windes William, Haque Aman
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, NM 87185, USA.
Materials (Basel). 2024 Sep 14;17(18):4530. doi: 10.3390/ma17184530.
Time-dependent deformation in nuclear graphite is influenced by the creation and migration of radiation-induced defects in the reactor environment. This study investigates the role of pre-existing defects such as point defect clusters and Mrozowski cracks in nuclear graphite IG-110. Separate specimens were irradiated with a 2.8 MeV Au beam with a fluence of 4.38 × 10 cm and an 8 MeV C beam with a fluence of 1.24 × 10 cm. Microscopic specimens were either mechanically loaded inside a transmission electron microscope (TEM) or subjected to ex situ indentation-based creep loading. In situ TEM tests showed significant plasticity in regions highly localized around the Mrozowski cracks, resembling slip or ripplocation bands. Slip bands were also seen near regions without pre-existing defects but at very high stresses. Ex situ self-ion irradiation embrittled the specimens and decreased the creep displacement and rate, while heavy ion irradiation resulted in the opposite behavior. We hypothesize that the large-sized gold ions (compared to the carbon atoms) induced interplanar swelling as well as cross-plane channels for increased defect mobility. These findings illustrate the role of pre-existing defects in the dynamic relaxation of stresses during irradiation and the need for more studies into the radiation environment's impact on the mechanical response of nuclear graphite.
核石墨中的时间相关变形受反应堆环境中辐射诱导缺陷的产生和迁移影响。本研究调查了诸如点缺陷簇和姆罗佐夫斯基裂纹等预先存在的缺陷在核石墨IG - 110中的作用。分别用通量为4.38×10/cm的2.8 MeV金束和通量为1.24×10/cm的8 MeV碳束辐照不同的试样。微观试样要么在透射电子显微镜（TEM）内进行机械加载，要么进行基于压痕的异位蠕变加载。原位TEM测试表明，在姆罗佐夫斯基裂纹高度局部化的区域出现了显著的塑性，类似于滑移或位错带。在没有预先存在缺陷的区域附近也观察到了滑移带，但应力非常高。异位自离子辐照使试样脆化，降低了蠕变位移和速率，而重离子辐照则产生相反的效果。我们推测，大尺寸的金离子（与碳原子相比）会引起层间肿胀以及增加缺陷迁移率的跨平面通道。这些发现说明了预先存在的缺陷在辐照过程中应力动态松弛中的作用，以及需要更多地研究辐射环境对核石墨力学响应的影响。
