ACCOMMODATION EFFECTS DURING ROOM-TEMPERATURE HYDROGEN TRANSFORMATIONS IN THE NIOBIUM HYDROGEN SYSTEM

The free energy loss has been theoretically evaluated in the model Nb-H system at 313 K for the solid solution --> monohydride and monohydride --> dihydride transformations. The origin for this hysteresis loss has been explained by considering the elasto-plastic accommodation processes that occur in the Nb-H system during these hydrogen transformations. The calculated free energy loss for the solid solution --> monohydride transformation shows excellent agreement with experimental results. Possible sources of error in the calculations have been elucidated. The present elasto-plastic approach is compared with previous theories of hysteresis. It is found that the elasto-plastic accommodation theory offers the best explanation for the hysteresis phenomenon observed in metal-hydrogen systems.