Effect of humidity and holding temperature (in the range from −13 to +60°C) on the recrystallization and aging of strontium-doped KCl crystals after plastic deformation

The effect of humidity and temperature in the range from −13 to +60°C on the processes of recrystallization and aging is studied upon holding of KCl crystals doped with 0.06 wt % Sr after plastic deformation. The crystals initially consist of a supersaturated solid solution. The presence of water is found to increase the rates of nucleation and growth of grains with twinned orientations with respect to the initial single crystal. Upon aging of these crystals in the presence of water vapor, strontium chloride crystalline-hydrate SrCl2 6H2O forms along the boundaries of recrystallized grains and crack edges. This results not only in a decreased plastic deformation-induced increment in the hardness but also in decomposition of the crystals. It is found that varying the temperature in the range from −13 to +25°C affects the recrystallization rate and aging processes much more weakly than does the presence of excess moisture. The most stable structure and properties are observed in the case where deformed crystals that are held at temperatures from −13 to +25°C remain in a solid-solution state. The possible long-term conservation of the high hardness of deformed crystals owing to an additional postdeformation treatment is discussed.