It has been a long standing mystery why cavities nucleate during materials' creep even when the applied stresses are much smaller (<1/100) than those required either to break crystal bonds or to induce, thermodynamically, vacancy accumulations convertible to stable cavities. It is shown, in the present work, that the incorporation of the cavity formation entropy-never done before-in the equations for the creep driven thermodynamic nucleation of a 'void phase,' i.e., of a cavity or pore out of a crystal/'matrix phase,' can provide the appropriate explanation. Additionally, a novel possible mode of growth/survival of sub-critical creep cavities beyond the sintering limit is presented. Based on the above two main results-viability of cavity nucleation and feasibility of sub-critical growth-it is pointed out that a strong case can be made for a recently proposed methodology where long-term brittle creep rupture times can be predicted via short-term cavity density measurements.
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