Using the P-delta(2) analysis to deconvolute the nanoindentation response of hard-coated systems

The continuously recording indentation responses of a number of coated syst ems, mainly thin (<10 mu m) hard nitride coatings on stainless steels and a powder metallurgy tool steel, have been explored using nanoindentation wit h indenter displacements increasing progressively to values greater than th e coating thickness. The resultant load-displacement data have been analyze d not only to produce conventional load-displacement (P-delta) plots but al so to examine the relationship between P and delta(2). Recent models have p roposed that there should be a linear P-delta(2) relationship for homogeneo us systems and that such plots have the potential to reveal the load/displa cement regimes in which either the coating or the substrate, or both, are d ominant in controlling the overall behavior of the coated system.. By utili zing point-to-point differentiation of the P-delta(2) relationship, this pa per extends this approach to confirm not only that these different regimes of behavior may be readily experimentally identified in this way, but also that further details, such as the propagation of cracks, may be recognized. Our analysis also provides a valuable experimental link to models describi ng the near-surface deformation behavior of coated systems.