UC Berkeley

Ion beam implantations are widely performed to understand the effects of radiation damage such as He bubbles on nuclear structural materials. This work investigates near-surface changes caused by low energy ion implantations, as well as deep ion implantations leading to bulk-property changes.

The near-surface interactions of low energy (25-60 keV) He ions with Ti and Cu targets were investigated by atomic force microscopy (AFM), nanoindentation, Transmission Electron Microscopy (TEM), and Positron Annihilation Spectroscopy (PAS). AFM showed a linear increase in swelling with respect to dose for all materials, and blistering onset doses of 5 × 1017 ions/cm2, 8 × 1017 ions/cm2, and 1 × 1018 ions/cm2 for Ti(0001), Ti(10¯10), and Cu(100), respectively. Cavities on the order of 287 nm diameter were observed in Cu, and surface blisters formed from the intersection of these large cavities. He bubbles observed in Ti were around 1 nm diameter, and surface blisters formed from inter-bubble fracture. PAS showed an increase in defect concentration with respect to depth and dose, agreeing well with AFM and TEM results. An additional PAS measurement determined that shock loading can lead to a decrease in vacancy concentration in a pre-implanted material.

To fill the gap between widely available low energy ion implantations and difficult-to-achieve bulk implantations, this work aimed to establish the use of the 88-Inch Cyclotron for nuclear materials studies. Four HT-9 SS-J-geometry tensile specimens were irradiated with high energy (19-25 MeV) deuterons at the 88-Inch Cyclotron to doses of approximately 0.2 dpa prior to small scale tensile testing. The results from this study showed irradiation hardening characterized by black dot irradiation defects, and the tensile test results were in agreement with the available data. To support future deep ion implantation campaigns, a novel ion beam degrader capable of uniformly implanting bulk-scale materials with He ions was designed.