Dislocation Activity Under Nanoscale Contacts Prior to Discontinuous Yield

Abstract

In nanoindentation, when stresses near the theoretical strength are reached, it is commonly assumed that the volume tested is dislocation free. This study examines the case where permanent deformation occurs prior to an apparent yield point. Force-modulated creep and quasi-static (QS) nanoindentation tests were conducted on Co, W, Ir, and Pt. Statistical comparisons show that the percentage of tests displaying creep correlates with the percentage of QS tests displaying plasticity prior to pop-in. This is evident that apparent plastic behavior prior to pop-in is due to dislocation motion, and permanent deformation can and does occur at extremely small indenter displacements before pop-in.

Keywords:

• Nanoindentation
• Plasticity
• Creep
• Dislocation Nucleation
• Theoretical Shear Strength

Acknowledgements

The authors would like to thank Samantha K. Lawrence for the surface roughness measurement of the Co, and for the financial support of the National Science Foundation's CMMI program under grant #1030843.