Phase development in titanium by mechanical alloying under hydrogen atmosphere

Titanium hydride was successfully synthesized at room temperature by ball m illing. X-ray diffraction patterns demonstrated that a transformation of el emental Ti powders into TiH2 could be induced at room temperature by ball m illing under a hydrogen atmosphere. Almost no hydrogen absorption was obser ved during the initial few minutes of the milling process on the basis of x -ray diffraction patterns and hydrogen pressure in the reservoir system, al though the grain size of Ti decreased significantly. A non-stoichiometric t itanium hydride with an approximate composition of TiH1.9 was first formed after about 7 min of milling and existed together with unhydrided Ti flakes . The stoichiometric hydride phase TiH2 was developed after further milling at room temperature. Due to the trapping of hydrogen by numerous defects a nd grain boundaries, the dilute solution Ti(H) does not exist in the nanogr ain milled metal powders.