Nanosized Nanocrystalline and Nanotwinned Metals

Traditionally, the most fundamental principle in materials science is that the properties of materials are strongly influenced by their internal microstructure [1]. During the plastic deformation of many metallic systems, dislocations carry most of the plasticity and hence their interactions with the internal microstructure, such as grain boundaries, solute atoms, precipitation or even other dislocations, are the most influential in determining mechanical responses of those materials [2]. However, recent studies found that the microstructure is not the only factor that affects the mechanical properties, but the external dimension of the specimen also significantly changes the mechanical behavior when it is reduced to the submicron and nanometer scale [3]. Therefore, when the effects from those two factors, microstructure and specimen size at the nanoscale, are combined, the materials often exhibit very unique properties distinguished from both of the bulk samples containing same kind of microstructure and nano-samples not containing the corresponding microstructure [3]. Especially, the homogeneous internal interfaces, such as ordinary grain boundary (GB) and coherent twin boundary (TB), are one of the most interesting microstructures as their interaction to dislocations is a key parameter in understanding plasticity of metallic materials. In this entry, the review of the recent studies investigating the mechanical properties of nano-sized metallic samples containing ordinary GBs and coherent TBs is presented. The main focus is placed on the results from uniaxial tension/compression experiments on the nanometer-sized pillar-shaped specimen (nano-pillars). Fabrication techniques to produce the nano-pillars with various internal interfaces are also introduced.