The effects of intrinsic properties and defect structures on the indentation size effect in metals

Abstract

The indentation size effect has been linked to the generation of geometrically necessary dislocations that may be impacted by intrinsic materials properties, such as stacking fault energy, and extrinsic defects, such as statistically stored dislocations. Nanoindentation was carried out at room temperature and elevated temperatures on four different metals in a variety of microstructural conditions. A size effect parameter was determined for each material set combining the effects of temperature and existing dislocation structure. Extrinsic defects, particularly dislocation density, dominate the size effect parameter over those due to intrinsic properties such as stacking fault energy. A multi-mechanism description using a series of mechanisms, rather than a single mechanism, is presented as a phenomenological explanation for the observed size effect in these materials. In this description, the size effect begins with a volume scale dominated by sparse sources, next is controlled by the ability of dislocations to cross-slip and multiply, and then finally at larger length scales work hardening and recovery dominate the effect.

Keywords:

• Indentation size effect
• high-temperature deformation
• stacking fault energy

Acknowledgements

The authors wish to thank S. Lynch, of Defence Science and Technology Organisation, Melbourne 3001, Australia for providing the single crystal Ir sample on loan, and Raheleh Mohamad Rahimi for confirming experimental behaviour on some samples.