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The nanocontact plastic behaviour of single-crystalline Ta (1 0 0), Ta (1 1 0) and Ta (1 1 1) 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 °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 °C is related to differences in the quasi-elastic reloading originating from changes in the defect mechanism. [ABSTRACT FROM PUBLISHER]

Nanoindention has been used to study the plastic flow behavior of bcc Ta(001) in the temperature range 25-200°C. Most notably, it is found that the shape of the load-displacement curves changes with increasing temperature. Only one large discontinuity marking the onset of plasticity is observed in room-temperature experiments, whereas multiple pop-ins separated by elastic reloading segments were observed at 200°C. Detailed analysis of the load-displacement curves indicates that the lattice resistance decreases with increasing temperature, consistent with the mobilization of screw dislocations by thermal activation. Contributions from the oxide layer and/or thermal drift can be excluded. [ABSTRACT FROM AUTHOR]