Effect of interstitial boron and carbon on the hydrogenation properties of Ti25V35Cr40 alloy

Doping of interstitial elements B or C into a BCC-type Ti25V35Cr40 alloy to raise effective desorption hydrogenation capacity was investigated. Ti25V35Cr40Mx alloys (M = B or C and x = 0, 0.1, 1, or 5) were prepared by arc-melting followed by homogenization treatment. X-ray diffraction shows that the as-cast specimens have a BCC structure, but they contain some amount of precipitates that increases with the doping concentration of B and C. Doping-induced precipitates can be greatly eliminated by annealing treatment at 1200 °C, indicating that B or C might have been partially dissolved into the interstitial sites in the BCC lattice of matrix phase of specimens. With the doping of C, the second plateau pressure of annealed specimens in the PCI curves at T = 30 °C significantly increases with the amount of C, but the maximum hydrogenation capacity is reduced. On the other hand, the second plateau pressure and maximum hydrogenation capacity are only slightly affected by the B doping. Under optimum doping conditions, the effective hydrogen desorption capacities are increased from 0.80 H/M of the sample without doping to 0.86 H/M and 0.87 H/M for Ti25V35Cr40B1 and Ti25V35Cr40C0.1, respectively. The improvement might be ascribed to the increase in second plateau pressure caused by less stable hydrogen atoms at the lattice sites of Ti25V35Cr40 containing interstitial B or C.