Analysis of the Vickers hardness of electroplated coatings

The Vickers hardness of electroplated nickel is analysed using the finite-element method. The effects of the mechanical properties of the substrate and the thickness of the coating on the effective hardness are studied. The predicted values are compared with experimental results for electroplated nickel on 70-30 brass and maraging steel. The influence of substrate on the hardness begins to appear when the indentation depth is approximately one tenth of the coating thickness. The critical indentation depth, below which the substrate does not influence the hardness, is independent of the type of substrate but depends on the size of the plastic zone in the coating. The effect of friction between the indenter and coating surface is also investigated. In the case of a hard coating on a softer substrate, the friction has very little influence on the hardness. However, in the case of a soft coating on a harder substrate, the hardness is markedly affected by the friction, except where the indentation depth is less than one tenth of the coating thickness or is large enough for the coating to be negligible.