THE EFFECT OF AGING ON HYDROGEN TRAPPING IN BETA-TITANIUM ALLOYS

The ingress of hydrogen in three beta-titanium alloys (Beta-C, Ti-10V- 2Fe-3Al, and Ti-13V-11Cr-3Al) and an alpha-beta titanium alloy (Ti-6Al -4V) was investigated with a view to characterizing their interaction with hydrogen. A technique referred to as hydrogen ingress analysis by potentiostatic pulsing (HIAPP) was used to obtain anodic current tran sients for the unaged and aged beta-Ti alloys and as-received Ti-6-4 i n an acetate buffer (1 mol L-1 HAc/l mol L-1 NaAc, where Ac = acetate) . The transients were analyzed using a diffusion/trapping model under interface control conditions to evaluate the trapping constants and hy drogen entry flux in each case. A marked increase in irreversible trap ping was observed for the beta-titanium alloys with aging and was attr ibuted to precipitation of secondary a phase. Aging also induced chang es in the passive film and hence the hydrogen entry flux. Ti-13-11-3 a nd Ti-10-2-3 are predicted to become less resistant to hydrogen embrit tlement with aging as a result of increases in both the trapping const ant (at least for Ti-13-11-3) and the flux. In contrast, the change in resistance of Beta-C Ti with aging is subject to the opposing effects of a reduced flux and an enhanced trapping capability, though the lat ter appears to have the primary effect, rendering aged Beta-C Ti less resistant to hydrogen embrittlement than the unaged alloy.