Effect of hydrogen on the β transus temperature of TC21 alloy

Effect of hydrogen on the β transus temperature of TC21 alloy was investigated by metallographic technique and dilatometry. It is found that the β transus temperature is closely related to the hydrogen content. For the hydrogenated TC21 alloy, the starting and finishing temperatures of α → β phase transition decrease with the increasing of hydrogen content before the hydride precipitates. And the finishing temperature of α → β phase transition increases as the hydrogen content increases after the hydride precipitates. Furthermore, corresponding inherent mechanisms of the above-mentioned phenomena have been presented according to atomic diffusivity, interface migration and the precipitation of hydride.