Dislocation nucleation in bcc Ta single crystals studied by nanoindentation

The study of dislocation nucleation in close-packed metals by nanoindentation has recently attracted much interest. Here, we address the peculiarities of the incipient plasticity in body centered cubic bcc metals using low index Ta single crystals as a model system. The combination of nanoindentation with high-resolution atomic force microscopy provides us with experimental atomic-scale information on the process of dislocation nucleation and multiplication. Our results reveal a unique deformation behavior of bcc Ta at the onset of plasticity, which is distinctly different from that of close-packed metals. Most noticeably, we observe only one rather than a sequence of discontinuities in the load-displacement curves. This and other differences are discussed in the context of the characteristic plastic deformation behavior of bcc metals.