Abstract
In the present paper creep of copper single crystals with the crystallographic directions <001> or <111> parallel to the tensile stress axis was investigated. The constant stress creep tests were performed at stresses ranging from 3 to 9 MPa and temperatures 873, 923, and 973 K. The creep testing times ranged from 8 to 7000 ks and 7 to 8000 ks and the total creep strains ranged to 0.085 and 0.02 for the orientation <001> and <111>, respectively. The "minimum" creep strain rates ranged from 10^-10 s^-1 to 3 × 10^-5 s^-1 depending on testing conditions. The main attention was paid to the changes of morphology as observed on the crept specimen surfaces.
The slip pattern on the surface of specimens with <001> orientation has an appearance of fine waves oriented in parallel with the lines of intersections of {111} planes with the specimen surface. The generation of these fine waves is attributed to the local microscopic slip of one slip system with the identical shear stress. The creep strain rate attains maximum values at the creep strains less than 0.01 and with the strain increasing in time above this value it continuously decreases. In this respect, the creep strain rate behaviour is similar to that of single crystals oriented for easy glide as well as for double slip. On the surfaces of single crystals of <111> orientation no microscopic changes were observed. The maximum creep strain rate is observed at the beginning of creep tests; with increasing creep strain, the creep strain rate quickly decreases. This specific creep strain rate behaviour is due to different geometric condition for development of slip bands in both microscopic and submicroscopic scale.

Key words
creep, Cu, single crystal, multiple slip

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