Kinematic and dynamic characterization of plastic instabilities occurring in nano- and microindentation tests

This paper surveys the phenomenon of plastic instabilities occurring in depth sensing indentation measurements, during which a stepwise increase has been observed in the indentation depth-load (F-h) curves measured in constant loading rate mode. In these measurements, plastic instability - serrated indentation - manifests itself as hardness oscillations around a nearly constant value of the conventional dynamic microhardness. Investigations presented here are focused on both kinematic and dynamic characterization of Portevin-Le Châtelier type indentation instabilities. The effect of important factors such as solute concentration and polycrystalline grain size is described and discussed. Taking into account the experimental observations, a macro-mechanical dynamic model was also proposed for the characterization of indentation instabilities.