Defect Retention and Irradiation-Assisted Recovery in High-Purity Aluminum under Low-Dose Proton Irradiation

This thesis reviews the literature and presents a fundamental investigation of irradiation-induced defect evolution in 106 μm thick 99.997 at.% aluminum using low-dose proton irradiation to study defect retention, defect self-organization, and recrystallization. The study is divided into two phases. In Phase I, recrystallized foils were produced with a strong Cube texture by annealing at 803 K for 8 hours, providing a baseline microstructure. Proton irradiation experiments were designed from SRIM calculations and performed at low dpa levels using focused and defocused 4 MeV proton beams to examine whether measurable residual defects can persist despite the inherently high defect mobility of aluminum. A key experimental challenge was minimizing irradiation-induced thermal recovery by maintaining the lowest practical irradiation temperature. The baseline reference state, used for all comparisons, and irradiated samples were characterized using X-ray diffraction peak analysis, 78 K tensile testing, and electron microscopy to assess lattice strain, mechanical response, spatial heterogeneity, and defect structures. Focused-beam irradiation to 0.013 dpa reached an average temperature of 316 K and resulted in X-ray peak narrowing, while dislocation loops were observed by TEM. Focused-beam irradiation to 0.13 dpa reached 348 K and resulted in X-ray peak broadening and the presence of dislocation loops. The defocused 0.13 dpa exposure reached 404 K and showed peak narrowing, similar yield stress and Haasen slope, and dislocation loops. Phase II focuses on irradiation-assisted recrystallization kinetics. The same aluminum foils in the as-rolled state were irradiated using a defocused 4 MeV proton beam such that irradiation acted as a coupled source of heat and continuously generated point defects. To isolate irradiation effects, thermal-control experiments were conducted under matched temperature–time conditions. Irradiation-assisted recrystallization was evaluated using X-ray macrotexture measurements. Irradiation to 0.062 and 0.13 dpa over 774 and 1576 min reached mean temperatures of 583 and 555 K and resulted in Cube volume fractions of 30.4% and 32.4%, respectively, compared with 51.8% and 30.3% after the corresponding thermal-control treatments. This work provides insight into defect retention in aluminum at low irradiation doses and clarifies the role of irradiation as an energy input that can influence microstructural evolution.