The influence of water on deformation microstructures and textures in synthetic NaCl measured using EBSD

Abstract

Wet NaCl with >10–15 ppm water shows weakening behaviour compared with dry NaCl containing <5 ppm of water. At strains greater than about 0.1 this weakening is associated with recrystallization but at lower strains there is also considerable weakening that is thought to be associated with pressure solution creep. The development of textures and microstructures in wet, synthetic NaCl polycrystals deformed at elevated temperatures has been investigated using electron backscattered diffraction (EBSD). At very low natural strains (0.07), textures, grain shapes and average misorientations of subgrain boundaries in wet NaCl differ to those found in dry NaCl deformed under similar conditions. In wet NaCl, cube shaped grains, oriented in a hard orientation for slip on the 〈110〉{110) system, grow and produce a well defined sub texture, with 〈100〉 poles at 45° to the compression axis. An estimation of strain in wet NaCl was made using average misorientation values of subgrain boundaries. We estimate about 55% of the total strain was accommodated by dislocation creep in wet NaCl at 0.07 strain, the remaining strain being accommodated by pressure solution. At higher strains dynamic recrystallization occurs forming a 〈100〉 fibre texture. This texture can be explained by preferential nucleation of initially strain free grains, which occurs after a critical strain in the most highly deformed, soft-orientation grains, that is grains which have 〈100〉 parallel to the compression axis.