TiCrV hydrogen storage alloy studied by positron annihilation spectroscopy

We have studied the structural changes of Ti24Cr36V40 alloy prepared by arc-melting using positron annihilation spectroscopy and X-ray diffraction (XRD) as functions of the number of hydrogen pressure swing cycles and degassing temperature. As the hydrogen storage capacity decreased with the number of pressure swing cycles, both positron lifetime and XRD peak width increased. Upon hydriding, the crystal structure changed from bcc to bct with increased lattice constants. The increase in positron lifetime is due to the volume expansion caused by hydride formation. After degassing at 500 degrees C, the hydrogen storage capacity recovered to 95% of the initial level, and the XRD peak width and the lattice constants nearly completely returned to their initial values. However, the positron lifetime was still longer than the initial level suggesting the survival of dislocations. The degradation of hydrogen storage capacity is probably caused by both hydride formation and the generation of dislocations. (C) 2009 Elsevier B.V. All rights reserved.