  A high-intensity proton beam exposure with 181 MeV energy has been conducted
at Brookhaven Linac Isotope Producer facility on various material specimens for
accelerator targetry applications, including titanium alloys as a beam window
material. The radiation damage level of the analyzed capsule was 0.25 dpa at
beam center region with an irradiation temperature around 120 degree C. Tensile
tests showed increased hardness and a large decrease in ductility for the dual
alpha+beta-phase Ti-6Al-4V Grade-5 and Grade-23 extra low interstitial alloys,
with the near alpha-phase Ti-3Al-2.5V Grade-9 alloy still exhibiting uniform
elongation of a few % after irradiation. Transmission Electron Microscope
analyses on Ti-6Al-4V indicated clear evidence of a high-density of defect
clusters with size less than 2 nm in each alpha-phase grain. The beta-phase
grains did not contain any visible defects such as loops or black dots, while
the diffraction patterns clearly indicated omega-phase precipitation in an
advanced formation stage. The radiation-induced omega-phase transformation in
the beta-phase could lead to greater loss of ductility in Ti-6Al-4V alloys in
comparison with Ti-3Al-2.5V alloy with less beta-phase.
