Raman spectra and modulus measurement on the cross section of proton-irradiated graphite

A method combining proton irradiation and nano-indentation was explored in this study to measure the modulus of irradiated graphite. A IG-110 graphite sample was irradiated with 2.5-MeV protons to a fluence of 1.2 × 1018 ions/cm2 at room temperature. Proton irradiation produced a damaged layer with a thickness of ∼75 μm. A scan of Raman spectrum was performed on cross section of irradiated sample. Analysis of the Raman spectra indicates that the graphite breaks into nano-crystalline graphite at very low dose (0.02-0.04 dpa) during room-temperature irradiation. Nano-indentation tests were performed on the cross section of irradiated sample so that the damage along the loading direction is uniform. Thus, it was able to identify a dpa value for the nano-indentation tests. Using this method, the modulus at 0.015 dpa was deduced to be 2.39 times that of the un-irradiated graphite. The hardness is also more than doubled after irradiation to 0.015 dpa.