Lattice defects in V–Ti BCC alloys before and after hydrogenation

abstract Microstructures of V–Ti BCC alloys before and after hydrogenation/dehydrogenation are investigatedusing transmission electron microscopy. Strain contrast with spacing smaller than 20 nm is observedboth in the as-cast alloys and hydrogenated alloys. Twin boundaries and stacking faults with spacingof 5–20 nm are introduced into the V–Ti BCC alloys after hydrogenation. These are parallel to {1 11}planes of FCC hydrides. The twin boundaries and stacking faults are formed due to the accommodationof shear stress during hydrogenation accompanied by large anisotropic expansion along the c-axis direc-tion in V–Ti BCC alloys. Density of twin boundaries is high in the alloys with small contents of V, whichhave a small effective hydrogen capacity at ambient condition. Dependence of microstructure evolutionin the V–Ti alloys during hydrogenation on the V/Ti ratio is also discussed with the thermodynamic sta-bilities from measurements of Pressure–Composition isotherms and mechanical properties. 2013 Elsevier B.V. All rights reserved.