Pakhomova I. Internal stress relaxation in alkali-halide single crystals with NaCl-type lattice in an initial stage of high-temperature creep

Object of research: the high-temperature relaxation of internal back stresses in alkali-halide crystals NaCl and KCl during transient creep. Using methods of high-temperature dilatometry, strain transient dip tests, X-ray diffraction microscopy, etching and computer modeling the basic ways of relaxation of internal stresses in alkali-halide single crystals NaCl and KCl in temperature range are determined. The anisotropy of high-temperature creep rate in single crystals with NaCl-type lattice is found out. The internal stress dependence on external applied stress value, on temperature, and on crystal orientation relative to external force direction is experimentally determined. The conditions of time-stable well-ordered dislocation structure formation are found out. The dislocation ensemble evolution at high temperature is modeled. It was shown that if dislocation movement in easy slip system is difficult the new slip system is activated starting with some temperature decreasing with growth of external stress value. It is true both for crystals with uniform and with non-uniform stress distribution.