Titanium (Ti) alloys are widely used in the biomedical, aerospace and automobile industry thanks to their high specific strength, excellent fatigue and creep properties, corrosion resistance, high workability, good weldability as well as their commercial availability. Ti-alloys are also currently investigated for several applications in the nuclear industry and especially as a structural material for the beam dump for the Facility for Rare Isotope Beams (FRIB) at Michigan State University due to their low activation in radioactive environments. This dissertation investigates the effect of heavy ion radiation damage on the microstructure and the nano-hardness in Ti and Ti alloys, namely commercially pure (CP) Ti and a two-phase α+β Ti-6Al-4V alloy processed through two different methods: conventional powder metallurgy rolling (PM) and additive manufacturing (AM).The microstructures of the as-received materials are characterized using scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Nano-indentation was performed on samples irradiated ex situ with Ar ion beams at 30 °C and 350 °C to investigate the change in mechanical properties in the three materials. Additionally, a study of the evolution of radiation damage in CP Ti irradiated in situ with krypton (Kr) ion beams was performed at the IVEM-Tandem facility at Argonne National Laboratory, USA. The results of the observations of the nucleation and growth of dislocation loops using transmission electron microscopy (TEM) are reported.Radiation hardening was observed in all materials irradiated ex situ at 30 °C and 360 °C. This hardening was insensitive to electronic excitation and was caused by ballistic effects. A strong dose dependence was observed mainly for the PM α+β Ti-alloy. The resistance to radiation hardening in the AM Ti-alloy was higher than that for the PM rolled alloy due to the significant α-phase grain refinement. The current study is the first to quantify the radiation-induced dislocation loop evolution at different temperatures and doses in Ti and AM Ti-6Al-4V (wt.%). The primary mechanism of loop growth was coalescence and their size increased proportionally with the irradiation dose. In situ TEM irradiation observation shows that c-component loops were only observed after reaching a threshold incubation dose (TID). In CP Ti, these loops nucleated at much lower doses than Zr, and the TID decreased with increasing temperature: 1.4 dpa, 0.6 dpa and 0.24 dpa for irradiation temperatures of 30 °C, 360 °C and 430 °C, respectively. The TID for AM Ti-6Al-4V (wt.%) at 360 °C was lower than for CP Ti, confirming previous observations where alloying elements assisted c-component loop nucleation. The dispersed barrier hardening model is used to analyze structure-mechanics relationships after irradiation in CP Ti. A good agreement between the experimental measurements of the hardening in irradiated CP Ti and the calculated contributions from dislocation loops is found. Through this work, an improved understanding of the influence of radiation-induced dislocation loops on the mechanical properties, and in particular, the hardness of Ti alloys as a function of the irradiation conditions and the alloy microstructure is gained. These insights can further the development of radiation-resistant Ti-alloys for use in radioactive environments.
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