AN ELECTRON-MICROSCOPE STUDY OF THE ORIGIN OF LATENT HARDENING IN NACL

Latent hardening of NaCl single crystals, which is associated with the intersection of oblique [110] {1BAR10} slip systems, has been studied by an electron microscope replica technique. The method images both the forest dislocations and the slip lines of individual screw dislocations moving through the forest dislocations so that the dislocation mechanisms could be studied in some detail. Accordingly the latent hardening is essentially determined by the long-range elastic interaction of the intersecting dislocations and the formation of junctions. Both processes generate obstacle structures with long-range stress fields, which limit the slip path of the gliding dislocations. The overcoming of the obstacle structures results in an athermal contribution to latent hardening.