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.