Analysis of crystallographic preferred orientations of experimentally deformed Black Hills Quartzite

The crystallographic preferred orientations (textures) of three samples of Black Hills Quartzite (BHQ) deformed experimentally in the dislocation creep regimes 1, 2 and 3 (according to Hirth and Tullis, 1992) have been analyzed using electron backscatter diffraction (EBSD). All samples were deformed to relatively high strain at temperatures of 850 to 915 °C and are almost completely dynamically recrystallized. A texture transition from peripheral [c] axes in regime 1 to a central [c] maximum in regime 3 is observed. Separate pole figures are calculated for different grain sizes, aspect ratios and long-axis trends of grains, and high and low levels of intragranular deformation intensity as measured by the mean grain kernel average misorientation (gKAM). Misorientation relations are analyzed for grains of different texture components (named Y, B, R and σ grains, with reference to previously published prism, basal, rhomb and σ1 grains). Results show that regimes 1 and 3 correspond to clear end-member textures, with regime 2 being transitional. Texture strength and the development of a central [c]-axis maximum from a girdle distribution depend on deformation intensity at the grain scale and on the contribution of dislocation creep, which increases towards regime 3. Adding to this calculations of resolved shear stresses and misorientation analysis, it becomes clear that the peripheral [c]-axis maximum in regime 1 is not due to deformation by basal 〈a〉 slip. Instead, we interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses (nucleation or growth of grains with peripheral [c] axes), the other depending on strain (dislocation glide involving prism and rhomb 〈a〉 slip systems), and not as a result of temperature-dependent activity of different slip systems.

Texture analysis of experimentally deformed Black Hills Quartzite

The textures of three samples of Black Hills quartzite (BHQ) deformed experimentally in the dislocation creep regime 1, 2 and 3 (according to Hirth and Tullis, 1992) have been analysed by EBSD. All samples were deformed to relatively high strain, within a temperature range of 65° and identical displacement rates and are almost entirely composed of dynamically recrystallized grains. A texture transition from peripheral c-axes in regime 1 to a central c-axis maximum in regime 3 is observed. Separate pole figures are calculated for different grain sizes, aspect ratios and long axis trend (θ) of grains, and high and low levels of intragranular deformation intensity as measured by the grain kernel average misorientation (gKAM). Misorientation relations are analysed for different texture components (named Y- B- R- and σ, with reference to previously published prism, basal, rhomb and σ1 – grains). Results show that regime 1 and 3 correspond to clear end member textures with regime 2 being transitional. Texture strength and the development of a central c-axis maximum from a girdle distribution depends on deformation intensity at the grain scale and on the contribution of dislocation creep which increases towards regime 3. Combined with calculations of resolved shear stresses and misorientation analysis, it becomes clear that the peripheral c-axis maximum in regime 1 is not due to deformation by basal –<a> slip. We interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses (formation of grains with peripheral c-axes), the other depending on strain (dislocation glide involving prism and rhomb slip systems), and not as a result of a temperature dependent activity of different slip systems.