The contribution of pyramidal forest dislocations to the hardening of zinc single crystals

Abstract

Abstract The influence of a pyramidal dislocation forest on basal-glide critical stress of zinc single crystals has been studied at 77, 198 and 298 K. The experiments gave the usual relationship τ0 = aKebρf 1/2 , where Ke is an elastic constant function, b the basal Burgers vector, ρf the forest density and a is a coefficient. The coefficient values are, at the three temperatures respectively, 1.46, 1.35 and 1.23 when the dislocation reaction is a3 + (c-a3 ) and 1.13 at 298 K in the case al + (c + a3 ). A model has been developed which consists of the following. (i) Calculation of the stress needed to break a junction created by a tree and a basal dislocation, in the different geometric cases. The reduced breaking stress γM is introduced. (ii) Calculation of the mean breaking stress y M. It is shown that a cubic average of the γm values gives the best result. (iii) Deduction of the relationship between the macroscopic critical stress of the crystal τ0, the local stress y M and the forest density ρf. The calculated and measured a values are in good agreement.