Latent Hardening in Rock‐Salt Type Crystals

Abstract

AbstractThe latent hardening in nine different crystals having the rock‐salt structure was studied as a function of prestrain. The latent hardening of a LiF crystal was also measured as a function of temperature. It was found that the latent hardening ratio of a crystal increases from 1.0 at zero strain to a maximum at about 0.5 to 1.5% compressive strain, then decreases to a constant value somewhat above 1.0. The maximum latent hardening ratio varies from 3.9 for LiF to 1.2 for AgCl. The difference in stress between the latent and the primary system in LiF remained essentially constant at all temperatures from 450 to 4 °K. The latent hardening ratio at 0.5% prestrain is 3.1 at 300 °K and 1.6 at 4 °K. Latent hardening was observed even above 300 °K where the flow stresses of the primary and the latent systems are essentially independent of strain rate and temperature. Dislocation distribution, revealed by etch pitting, was uniform during the primary slip, but was confined to widely separated bands during the latent hardening test. It is concluded that latent hardening in rock‐salt type crystals is caused primarily by the interaction of the glide dislocations in the latent slip system with the dipoles and dislocations in the primary slip system according to the dislocation reaction .