Length scale plasticity: A review from the perspective of dislocation nucleation

Abstract

Sub-micron and nano-size material systems and components are now regularly being fabricated for use in a wide variety of new applications. These systems exhibit mechanical properties that can be drastically different from their macroscopic counterparts and recently much work has focused on the size effects on the mechanical behaviour of materials. Although the size dependent behaviour has been observed in all of the crystal structures, the governing mechanisms have been found to be different. Different theories have been proposed to describe the size dependent behaviour of metallic samples and the governing mechanisms and it is well known that the surface plays an important role in the plasticity of small scales. Some of the theories indicate the importance of surface in nucleating dislocation and some other ones consider the surface importance as its effect on truncating dislocation loops and activation of internal sources. Moreover, recent studies have revealed that while dislocation based deformation in fcc metals is not very sensitive to temperature, deformation is strongly temperature dependent in bcc metals. The effect of orientation is more clear in the size scale behavior of hcp metals. This review covers recent literature that has focused on uniaxial compression of single crystals at the sub-micron and nanometer scale. The fundamental mechanisms governing the size dependent mechanical behaviour of different crystal structures are described. The effect of fabrication process and current experimental techniques for micro and nano-compression are studied as well.