Determination of the (alpha+beta)/beta-transition temperature in the quasi-binary system Ti5Al2.5Fe-H as a function of its hydrogen content

Near net shape components of titanium and titanium alloys produced by preci sion casting often show poor mechanical properties, especially a poor fatig ue strength because of their coarse microstructure caused by the high proce ss temperature. As hydrogen can be dissolved reversibly in titanium and tit anium alloys and lowers the (alpha + beta)/beta-transition temperature, a t hermochemical treatment can provide a reduction in grain size and hence imp rove the mechanical properties. The knowledge of the exact transition tempe rature depending on the hydrogen content will allow the development of such a thermochemical treatment. In the present study, the (alpha + beta)/beta- transition temperature of the biocompatible alloy TiAl5Fe2.5 was determined as a function of the hydrogen content by isothermal metal-gas-reaction mea surements.