Elastic and plastic accommodation effects on metal-hydride solubility

Abstract

A model is presented that is capable of accounting for the hysteresis observed in the measured terminal solid solubilities (TSS) of metal hydride systems. Two distinct TSS are identified: 1. (i) a TSS determined on cool-down governed by hydride nucleation and the elastic accommodation energy arising from the hydride-matrix misfit; 2. (ii) a TSS determined on heat-up and dominated by plastic accommodation effects. The energy associated with the plastic accommodation effects is expected to be much smaller than that due to elastic accommodation. The heat-up TSS is therefore expected to be a good approximation to the “equilibrium”, or stress-free, TSS. It follows that the hysteresis between the activation energies of the heat-up and cool-down TSS is approximately equal to the elastic accommodation energy. The predictions of the model are tested with reference to TSS data derived from measurements on the V, Nb, Zr and Ti-H systems and are found to be in reasonable agreement with the data. Possible effects that the hysteresis of the TSS may have on the hydrogen-induced delayed cracking mechanism are discussed.