Dislocation distributions during stage I deformation of silver single crystals

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Abstract
The development of the arrangement of primary dislocations as a function of strain in the easy glide deformation of silver single crystals was investigated by means of the etch pitting technique. At the smallest strain increments (∼0·1%) loose clusters grew in size and number, the dislocation density within them increased and near the end of stage I they began to link together to form a more or less homogeneous cellular array of dense dislocation groups surrounding dislocation free areas. The attainment of the cellular structure throughout the specimen gauge length was found to be a necessary but not a sufficient condition for the end of easy glide. Sequential polishing and straining of the specimen as well as intermittent sprinkling of the crystal surface with silicon carbide powder increased the length of stage I by a factor of two over that of an identical crystal strained directly into stage II without interruption or treatment. It is suggested that these effects are best explained in terms of surface dislocation sources rather than ‘debris layers', and that surface sources play a significant role in easy glide deformation.