Effect of Grain Boundaries on Plastic Deformation of Sodium Chloride

Sodium chloride single crystals were joined at a melt zone with a hot-wire technique to produce bicrystals of controlled crystallographic orientation. The plastic deformation properties of the bicrystals were measured in bending while the birefringence was observed with a petrographic microscope. The birefringence at the boundary was interpreted to indicate that significant deformation across the grain boundaries occurred. The stress required for deformation across the boundary was found to increase with increased angle between crystallographic axes. Twist boundaries were found to be more resistant than tilt boundaries. Behavior was consistent with the dislocation model for grain boundaries.