The effect of varying water contents on the creep behavior of Heavitree quartzite

Publisher Website
Google Scholar
Abstract
Creep and constant strain rate experiments have been performed on Heavitree quartzite samples with different amounts of available water, at 15 kbar confining pressure, 800°–1100°C, 10−4 to 10−7/s strain rate, and 1–10 kbar deviatoric stress. Some samples were dried by vacuum heating, others were left as is, and others had 0.1–0.5 wt % water added to them before being mechanically sealed in a Pt tube and deformed. When the creep data are fit to a power law form of flow law, they show, with increasing water available, a decrease in the activation energy from 44 to 41 to 35 kcal/mol, and a decrease in the stress exponent from 3.3 to 2.3 to 1.8. Samples deformed at 900°C and 10−6/s showed corresponding changes in preferred orientations from a diffuse maximum parallel to to a small circle girdle about σ1 and a change in deformation lamellae orientations from basal to basal plus prismatic. The samples also showed corresponding textural changes, from little recovery and no recrystallization, to greater recovery with moderate amounts of fine grain boundary recrystallization and small isolated melt pockets (<1 vol %), to even greater recovery with less continuous but coarser recrystallization and somewhat more extensive grain boundary melt (<3 vol %). The low stress exponent of the water added samples may be due to a component of grain boundary sliding, allowed by the grain boundary recrystallization and melt in these samples, but there is no microstructural evidence for such a mechanism. The change in slip systems of the original grains in the water added samples might be due in part to some relaxation of grain boundary constraints. The ease of recovery in the as is and water‐added samples suggests that deformation of these samples was glide controlled and the chief mechanical effect of the added water may be to enhance dislocation glide.