Reduction of hydrogen content in pure Ti

Pure Ti is adopted as a material for ducts and bellows at the proton accelerator 3 GeV-RCS in J-PARC project, because of its small residual radioactivity. In the particle accelerator, the H2 outgassing due to ion impact is often the dominant source of gas release. As the reduction of hydrogen content will probably suppress ion induced desorption, we attempted to reduce the hydrogen content in the Ti by in-situ vacuum baking. First, thermal desorption behavior and the change in hydrogen content after the heat treatment were investigated. Vacuum firing at temperatures higher than 550°C was effective in reducing the hydrogen content in the Ti. At the same time, the mechanical properties were monitored because grain growth leads to decrease in mechanical strength. Even after treatment at 750°C for 12 hr, the decreases in tensile and yield strength were so small (~10%) that we have no anxiety about the reduction of mechanical strength. Based upon the results of this study, vacuum firing has been applied to reduce the hydrogen content in the Ti bellows and ducts of the RCS machine.