Ultra-large elongation and dislocation behavior of nano-sized tantalum single crystals

Although extensive simulations and experimental investigations have been carried out, the plastic deformation mechanism of body-centered-cubic (BCC) metals is still unclear. With our home-made device, the in situ tensile tests of single crystal tantalum (Ta) nanoplates with a lateral dimension of ∼200 nm in width and ∼100 nm in thickness were conducted inside a transmission electron microscope. We discovered an unusual ambient temperature (below ∼60°C) ultra-large elongation which could be as large as 63% on Ta nanoplates. The in situ observations revealed that the continuous and homogeneous dislocation nucleation and fast dislocation escape lead to the ultra-large elongation in BCC Ta nanoplates. Besides commonly believed screw dislocations, a large amount of mixed dislocation with b=12<111> were also found during the tensile loading, indicating the dislocation process can be significantly influenced by the small sizes of BCC metals. These results provide basic understanding of plastic deformation in BCC metallic nanomaterials.