Incipient plasticity of single-crystal tantalum as a function of temperature and orientation

The nanocontact plastic behaviour of single-crystalline Ta (100), Ta (110) and Ta (111) was studied as a function of temperature and indentation rate. Tantalum, a representative body centred cubic (BCC) metal, reveals a unique deformation behaviour dominated by twinning and the generation of stacking faults. Experiments performed at room temperature exhibit a single pop-in event, while at 200 degrees C, above the critical temperature, a transition to multiple pop-ins was observed. The experimental results are discussed with respect to the orientation as well as temperature and correlated to the defect structures using both anisotropic finite element and MD simulations. The serrated flow observed at 200 degrees C is related to differences in the quasi-elastic reloading originating from changes in the defect mechanism.