Grain growth inhibited during grain size-sensitive creep in polycrystalline ice: an energy dissipation-rate perspective

Experiments in which two identical polycrystalline ice Ih specimens are simultaneously subjected to the same time–temperature history while one of the specimens is actively deformed via grain size-sensitive (GSS) creep demonstrate distinctly different microstructural evolution: for particular ranges of starting grain size and differential stress, grains do not grow in the deforming specimen. Ice Ih specimens having initial, uniform grain sizes in the range d = 6–63 μm were tested in pairs that were subjected to identical time–temperature conditions (durations t = 4–12 days; T = 240 K) but of which only one was subjected to differential stress (σ₁ = 0.25–1.85 MPa; σ₃ = 0). Comparing specimens within a pair, for those with coarser initial grain size, the deformed specimens exhibit suppressed or no grain growth. Our results are interpreted from the perspective of nonequilibrium thermodynamics, specifically comparing the energy dissipation rates associated with both grain growth and plastic flow: if the rate of energy dissipation associated with flow exceeds that of grain growth, the grains will not grow. An examination of the limited database on GSS flow and grain growth in silicates conforms to our analysis. The results are applied to the question of the mechanical evolution of terrestrial glaciers and to the ice-rich shells of the outer satellites.