An investigation of the mechanical behaviors of micro-sized tungsten whiskers using nanoindentation

The mechanical behaviors of single crystalline micro-sized tungsten whiskers were experimentally characterized using nanoindentation. Nucleation and multiplication of dislocations were seen as displacement burst or pop-in events in the load-displacement curves during loading segment. The Hertzian contact theory and Kick's law were used to describe the elastic deformation of the material, whereas the theoretical strength of the perfect tungsten whiskers can be derived from the critical pop-in load. The elastic-plastic deformation after the pop-in agrees well with the Taylor relation. Either only one major pop-in or a series of discontinuities was observed in the experiments, attributed to the different critical loads at which the first pop-in occurs. Creep behaviors of the whiskers were also investigated under a constant load for 600 s. The stress exponent n was calculated using the displacement-time curve and agrees well with the value obtained using the traditional tensile creep testing method. The creep behavior is dominated by the dislocation-controlled (power-law) mechanism with an n of ~5. Additionally, the stress exponent n is proved to increase with increasing the holding load, and remains stable with increasing the loading rate in the range of testing parameters selected in the experiments.