Nanoindentation of a hard ceramic coating formed on a soft substrate

The hardness and Young’s modulus of the thin hydroxyapatite-based coatings deposited by RF magnetron sputtering onto magnesium alloy, titanium, and steel substrates are studied. As the penetration depth increases, the hardness and Young’s modulus of these coatings are found to tend toward the values that are characteristic of the substrates. It is shown that the difference between the values of hardness and Young’s modulus at small penetration depths ($h<$ 80–100 nm) can be caused by the difference between the physicomechanical properties inside the coatings and that this difference at large penetration depths ($h>$ 100 nm) can be induced by an additional effect of the strength properties of the substrate material.