HYDROGEN EMBRITTLEMENT IN TITANIUM ALLOYS

In this paper the phenomena of hydrogen cracking and hydrogen-induced second phases formation in titanium based alloys is discussed, addressing to two different alloys; the alpha+beta Ti-6Al-4V alloy and the Ti-20 wt.%Nb refractory alloy. The prior microstructure of the alloy plays a very significant role on its behavior under exposure to a hydrogen-containing environment. In the Ti-6Al-4V alloy the main mechanism of hydrogen cracking is the formation and rupture of brittle titanium hydride phases. The severity of hydrogen degradation in the Ti-6Al-4V alloy depends on the amount and distribution of the beta phase in the microstructure due to a more rapid diffusion transport of hydrogen in the bcc beta phase. In the Ti-20 wt.%Nb alloy hydrogen-induced phase transitions and hydrides formation were followed by an interesting softening effect, irrespective of the charging procedure.