Abstract
The results of an investigation of creep characteristics including slip pattern of copper single crystals oriented for preferred slip in two symmetrical (with respect to the tensile stress axis) slip systems subjected to creep at constant stresses ranging from 3 to 9 MPa and temperatures 873, 923, and 973 are presented. The creep test durations ranged from 1 to 8000 ks, the strains were, as a rule, smaller than 0.09. The results obtained are compared with those followed from studies of copper single crystals oriented for easy glide. Both the sets of single crystals were prepared using the same procedure and crept at the same conditions; the shear stress component in the main slip system was approximately of the same magnitude. The symmetric orientation of two slip systems characterized by high shear stress component restricts the slip in the slip bands due to a restriction of the slip bands formation in the advanced stages of creep. The submicroscopic slip represents the main component of the creep strain; it is manifested by higher creep strain rates at greater creep strains as compared to the creep strain in single crystals oriented for easy slip.
The development of the slip bands in one of the slip systems under consideration may be stimulated by shorter slip distance in the specimen of the oblong cross section and perhaps also by conditions of dislocation disappearance on the specimen surface. The geometric advantage following from the specimen cross section may be compensated by small difference of the shear stresses acting in the two slip systems.
An estimated value of the apparent activation energy of creep suggests dislocation climb as the rate controlling process. In the advanced stages of creep frequent cross slip is observed.

Key words
copper single crystals, creep, shear stress, creep frequent cross slip

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