Plasticity initiation and subsequent deformation behavior in the vicinity of single grain boundary investigated through nanoindentation technique

The initiation of plasticity and the subsequent state in the vicinity of a single grain boundary during indentation-induced deformation were investigated to understand an elementary step of a stress-strain behavior of polycrystalline materials. Nanoindentation measurements on several points on a single grain boundary and the grain interior of an interstitial-free steel and an analysis on the pop-in behavior and the plastic nanohardness were carried out. The pop-in load Pc that was obtained on the loading curve is different for each measurement. However, the loading curves overlap one another and the unloading curves coincide as well after the pop-in event. The nanohardness Hn has no dependence on the Pc in the range of 150–550 μN. The relation between Pc and Δh can be expressed as a simple cubic polynomial function based on a geometrically necessary dislocation loop model. The fitted function differed for various grains with different crystallographic orientations.