Hydrogen cracking in titanium-based alloys

Abstract

In this paper the phenomena of hydrogen cracking and hydrogen-induced second phases formation in titanium based alloys is discussed in detail, addressing to three different alloys; the alpha + beta Ti–6Al–4V alloy, the metastable Beta-21S 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 β phase in the microstructure due to a more rapid diffusion transport of hydrogen in the bcc β phase. On the other hand, the Timetal Beta-21S β alloy, exposed to the electrochemical (high fugacity) hydrogen environment at room temperature, exhibits a fair resistance to hydrogen. 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.