This dissertation comprises a systematic study of boron (B) addition and processing on the microstructure, tensile behavior, 455°C fatigue behavior, and elevated-temperature creep behavior of two α+β alloys systems, namely Ti-6Al-4V (wt.%) (Ti-64) and Ti-6Al-2Sn-4Zr-2Mo-0.1 Si (wt.%) (Ti-6242S). As-cast Ti-64-xB (x=0, 0.1, and 1 wt.%) and Ti-6242S-xB (x=0, 0.1, 0.4, and 1 wt.%) alloys were evaluated. For the Ti-64-1B alloy, the processing effects (including cast, cast-and-extruded, powder metallurgy (PM) rolled, and PM extruded) were investigated. For the as-cast processing condition, B-additions did not degrade the 455°C fatigue resistance of Ti-64 and Ti-6242S alloys, and the B content which resulted in the greatest average fatigue life and elongation-to-failure (8f) was 0.1 wt.% in both alloy systems. The creep resistance of the as-cast alloys was significantly improved with increased B concentration in the as-cast Ti-64-xB alloy system due to the load sharing effect of the strong and stiff TiB phase. However B-additions did not result in as significant of an improvement in the creep resistance of the Ti-6242S alloy system. The cast-and-extruded Ti-64-xB alloys exhibited significantly higher 455°C yield strengths, ultimate tensile strengths, and fatigue strengths than the as- cast Ti-64-xB alloys due to their smaller grain size, a smaller a-colony size, finer a-lath width, and strongly textured a-phase For the same nominal B contents, the cast-and-extruded alloys also exhibited significantly greater creep resistance and tensile strength than the as-cast alloys. The fatigue resistance of the PM processed Ti-64-1B alloys were superior to the as-cast and cast-and-extruded Ti-64-1B alloys due to the equiaxed a morphology in these alloys. The PM extruded Ti-64-1B exhibited a fine equiaxed α-phase morphology and strong α-texture, enabling it to exhibit even longer fatigue life than that of the PM rolled Ti-64-1B alloy. However, the creep resistance of the PM processed Ti-64-1B was worse than the cast-and-extruded Ti-64-1B alloy since creep property is favored by lenticular a morphology instead of equiaxed a morphology. Creep-fatigue interactions were also evaluated for the 455°C fatigue experiments. The large amount of dislocations generated by the fatigue process may have facilitated the creep deformation process and increased the strain rate. It is possible that the defects induced by fatigue (such as micro-voids) also increased the creep rate. The strong α-phase texture in the cast-and-extruded Ti-64-xB alloys and the PM extruded Ti-64-1B alloy resulted in the anisotropy of tensile strength. The YS and UTS for these alloys in the transverse direction were lower than in the longitudinal (extrusion) direction. As the α-phase texture became weaker with higher B content in the cast-and-extruded Ti-64-xB alloys, the tensile anisotropy became weaker. However, the tensile strength in the transverse direction was still much higher than that of the as-cast Ti-64 alloy. Overall, this dissertation work has shown that B-modified Ti-64 alloys show promise for fatigue-driven and creep-driven applications and have the potential to replace Ti-64 for both RT and elevated-temperature structural applications.