Micro-to-Nano Indentation and Scratch Hardness in the Ni–Co System: Depth Dependence and Implications for Tribological Behavior

Abstract

Although size effects in hardness have been extensively reported and analyzed for the static (indentation) case, much less attention has been given to these effects in non-static (scratch) hardness measurements. In the present work, size effects in the indentation and scratch hardness response of the Ni–Co system are evaluated by performing tests at several penetration depths, from the micro to the nanometer range. It is shown that, for all the range of compositions, the hardness response of these materials is strongly affected by the depth of penetration of the indenter: when the depth decreases, both the indentation and scratch hardness increase several times. This result denotes that, when studying the wear behavior of materials, special care must be taken concerning the scale one is dealing with, since the tribo-mechanical response of the material may change significantly from the micrometric to the nanometric contact scale.