The effect of divalent impurity state on the microhardness of NaCl crystals

The microhardness and bulk density variations with annealing temperature have been measured in NaCl crystals doped with Ca²⁺, Cd²⁺, Ni²⁺, and Pb²⁺. Both characteristics are not affected by coherent metastable precipitation while incoherent precipitation produces either hardening or softening depending on the impurity phase type (stable or metastable). The results support the suggestion that aggregates and coherent precipitates are cut through by dislocations whereas incoherent precipitates are by-passed via the Orowan looping mechanism.