Characterization of the effects of 3-MeV proton irradiation on fine-grained isotropic nuclear graphite

The irradiation-induced damage on the fine-grained isotropic nuclear graphite, IG-110, was investigated by 3-MeV proton irradiation at room temperature. The irradiation effects were characterized using scanning electron microscopy, transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), and nano-indentation. The surface morphology showed a fragmented shape after irradiation, indicating that the surface microstructure of the graphite was damaged by proton bombardment. The TEM images revealed clear and convincing evidence for the increase in defect clusters (probably interstitial clusters), basal plane bending, and basal plane dislocations, which might be the main reason for property changes. Raman studies indicated a rapid increase in the interstitial and vacancy defects, and decrease of in-plane “crystallite size”. The XRD results indicated a slight increase in the interlayer spacing and decrease in crystallite size. The enhancement in the hardness and modulus can be attributed to the pinning of basal plane dislocations by lattice defects produced by proton irradiation.