Precipitation in NaCl-KCl Mixed Crystals

The mechanical properties of precipitation-hardened dilute mixtures of KCl in NaCl were studied. Two peaks in the flow stress occur. The suggested sequence of events is growth of coherent KCl-rich platelets, loss of coherence, growth of incoherent KCl-rich platelets, and finally recrystallization. The fracture stress is maximum for a long aging time considerably beyond the second hardness peak where the presence of rather coarse precipitates interferes with the cleavage process and increases the energy to propagate a fracture. This is an important principle for increasing the fracture strength of ceramics.