The development of dislocation substructure in hydrogen embrittled niobium-8 to 10 at % vanadium alloy

Abstract

The development of dislocation substructure in niobium-8 to 10 at % vanadium alloy single and polycrystals is presented to emphasize the effect of interstitial hydrogen and substitutional vanadium. The formation of cross grid of straight long screw dislocations in the initial stages of deformation is associated with a high lattice frictional stress caused by the substitutional vanadium. Similarly, the presence of non-screw segments, edge dipoles and loop debris at higher strains is also considered to arise from the high lattice frictional stress. On the other hand, the formation of cell structure at 195 K in both single and polycrystals tested in tension is related to the presence of hydrogen. In addition, the nucleation of cracks along the active {1 0 1} or {1 1 2} type slip planes is related to the accumulation of hydrogen atoms along cell walls. Furthermore, the stress concentration due to the array of long straight dislocations is believed responsible for twinning observed at 77 K in the presence of hydrogen. The dislocation substructure associated with deformation twins indicates that hydrogen embrittlement through crack nucleation cannot be linked with deformation twinning in this alloy.