Effects of substrate and friction on Vickers indentation of electroplated coatings

Abstract

The effects of the mechanical properties of the substrate and the thickness of the coating on the Vickers indentation are studied for soft and hard coatings. Surface profiles of the Vickers indentations of electroplated nickel on 70-30 brass and maraging steel are measured using a 3D laser profilometer, and are also numerically simulated using an elastoplastic finite-element method. The experimental results show that the influence of substrate on the Vickers indentation begins to appear when the ratio, δ/h, of the indentation depth to the coating thickness exceeds 0.1, under which the substrate does not influence the hardness. In the case of a soft coating on a harder substrate, the ratio hm/d of the height of the maximum pile-up to the diagonal of the indentation increases with increasing δ/h and hm/d takes the maximum value at δ/h ≅ 1.0. On the other hand, in the case of a hard coating on a softer substrate, the value of hm/d decreases and then increases with increasing δ/h. The numerical results show that in the case of a soft coating on a harder substrate, the indentation could be markedly affected by the friction between the indenter and the coatings. By comparing the numerical results with the experimental ones, it becomes clear that the effects of friction should be taken into account to analyse surface profiles of the indentations.