Hysteresis in metal-hydrogen systems

Hysteresis in metal-hydrogen systems originates due to the presence of transformation strains during both hydride formation and decomposition. The variation of accommodation energies in the hydride and metallic phases as a function of progress of hydride formation obtained by elastic and elasto-plastic finite element analyses (FEA) have been discussed in relation to pressure hysteresis. The experimental hysteresis curve cannot be obtained by considering pure elastic accommodation. The process of accommodation is reasonably represented by the elasto-plastic analysis which reveals that the plastic energy created in the metallic phase during the course of hydride precipitation (and decomposition) is the major contributor to the accommodation energy. The FEA supports the view that hysteresis losses in metal-hydrogen systems result due to plastic deformation in the metallic matrix during hydride precipitation and decomposition. In physical terms, hysteresis energy loss is the energy expended to create dislocations in the metal phase during both hydride formation and decomposition.