Berkovich nanoindentation study of monocrystalline tungsten: a crystal plasticity study of surface pile-up deformation

Abstract

In this paper, it was investigated whether Berkovich indentation test with a triangular-based pyramidal imprint would exhibit the same surface pile-up deformation behaviour as in Vickers or spherical indentation tests. The characteristic correlation between the pile-up patterns of monocrystalline tungsten and the geometry of slip systems was examined both experimentally and computationally. Surface pile-up patterns for three different crystallographic orientations of specimens with corresponding rotational crystal symmetry were characterised. In addition, the effect of the varying azimuthal orientation of the indenter on the pile-up patterns was also discussed. Predictions from finite element simulation based on the crystal plasticity theory are also presented and compared with the measured results. It was found that the surface pile-up patterns of Berkovich indentation did not necessarily reflect the rotational crystal symmetry of tungsten single crystal specimens. The pile-up patterns were affected by the variation of the indenter’s azimuthal orientation. The height of the pile-up hillocks was often highly non-uniform even on the same surface plane indicating strong influence of slip geometry leading to the plastic anisotropy.

Keywords:

• Crystal plasticity
• nanoindentation
• tungsten
• finite-element modelling
• pile-up
• plastic deformation

Acknowledgements

One of the authors (W.Z. Yao) is grateful to the Chinese Scholarship Council (CSC) for the financial support.