Experimental study by Secondary Ion Mass Spectrometry focused on the relationship between hardness and sputtering rate in hard coatings

Hardness is a key property in materials' characterization, particularly regarding micro and submicron functional coating technology. Hardness definition is commonly cited as the resistance of materials to plastic deformation. To assess the hardness value of a given material different methods are available and can be defined as macro-, micro- or nano-scale according to the forces applied and the displacements obtained. Nano-hardness measurements are essential for functional thin coatings characterization. In the present work we tested the possibility to evaluate coatings hardness by using a complementary method: the ion beam sputtering by Secondary Ion Mass Spectrometry (SIMS) equipment. This approach has two evident advantages: independence of measurements from the substrate and additional compositional and structural information provided by SIMS measurements. The applicability of this approach has been experimentally tested on several kind of hard coating films (as ZrN, TiN, TiAlCN et al.), including diamond-like (DLC) carbon materials. Some initial results pointed out the possibility to find a direct relationship between hardness and sputter rate, pointing out a good agreement with previous works. Nevertheless, detailed tests showed evident problems on DLC coatings. In this case the dependence between ion beam sputter rate and hardness is not evident and far to fit other experimental data. In our hypothesis this effect is related to the different nature of hardness on DLC materials.