Incipient plasticity of potassium-doped tungsten under nanoindentation: A comparison between experiments and defect dynamics simulations

• Nano-sized K-bubbles are formed inside grains of tungsten during sintering process. • Nanoindentation tests indicate K-bubbles reduce the critical stress for dislocation nucleation. • Simulations show stress concentration near K-bubbles facilitates dislocation nucleation and enhances plasticity in tungsten. • With increasing dislocation density, the mechanism for incipient plasticity of tungsten transitions from dislocation nucleation to dislocation source activation. The effects of potassium (K) doping on the incipient plasticity of tungsten (W) under nanoindentation were investigated using a combination of experiments and mesoscale defects dynamic simulations. The transmission electron microscopy study reveal that nanometer-sized bubbles were formed through the vaporization of K in specimens prepared by spark plasma sintering. In order to investigate the mechanical properties of the K-doped W specimens, nano-characterization experiments and defect dynamics simulations were conducted, comparing with those in pure W. Nanoindentation tests reveal that the maximum shear yield stress approaches the theoretical strength in annealed pure W, while K-doped W samples exhibit significant yield drop accompanied with stochastic variations. A newly developed mesoscale defect dynamics model to concurrently couple dislocation dynamics with finite element method has been also employed to investigate micro-mechanisms of plasticity under nanoindentation and the effects of K-bubbles on the plastic deformation. The simulations revealed that the localized stress concentration induced by the K-bubbles promoted dislocation nucleation and enhanced plastic deformation, thereby reducing the yield stress, showing good agreement with the experiment.