Protium absorption-desorption properties of Ti-V-Cr alloys with a BCC structure

Vanadium-based BCC alloys are known to absorb a high amount of protium. But, they do not desorb absorbed-protium completely. This paper aims to clarify the effects of alloy composition and heat-treatment on the protium absorption-desorption properties of Ti-(0-35) at%V-Cr alloys. A Ti-35V-40Cr alloy was chosen as the starting composition. The plateau pressure of the Ti-35V-(40+x)Cr (x = -3, 0, 3) alloys increased with increasing Cr content. For the alloys containing more than 15 at%V, a BCC phase was formed in the as-cast state, which was found to have an effective protium capacity of about 2.4 mass%H. However, a Laves phase was formed for alloys containing less than 10 at%V, which only had an effective protium capacity of about 1.8 mass%H. The effect of heat-treatment on the microstructures and protium absorption-desorption properties of the Ti-35V-40Cr alloy were studied. It was found that the optimum condition for heat-treatment was annealing at 1573 K for 1 min. The Ti-35V-40Cr alloy heat-treated under this condition exhibited the highest effective protium capacity of 2.6 mass%H. This effective protium capacity is higher than any other reported values at 313 K. However, further annealing at 1573 K led to a decrease in protium capacity, which may result from an increase in the amount of a Ti-rich phase. A Ti-10V-55.4Cr alloy, which contained a Laves phase in the as-cast state, became single-phase BCC after heat-treatment. Even though the alloy contains only 10 at%V, this heat-treated alloy showed an effective protium capacity of 2.5 mass%H, which is higher than any other reported values for BCC alloys.