Sol-gel oxide coatings can have custom functionalities and are of interest to many global players in the coating modification market, e.g. 3M Company, Akzo Nobel NV, Arkema Group, Axalta Coatings Systems Ltd., CCM GmbH, Euroglas GmbH, Henkel AG & Co . KGaA and others.

As the thickness of sol-gel coatings often does not exceed 1um, there are not many measurement techniques suitable for this purpose. In the case of commercial applications, we can focus on the properties of the modified surface and not the layer itself. However, the technique used must have the highest level of sensitivity. In this study, we present the results of testing the influence of sol-gel coating on the mechanical properties of metallic substrate carried out using modal analysis.

The modal analysis aims to find the natural frequencies and mode shapes of the examined system as well as modal damping. Modal analysis is the process of determining all the modal parameters, within the frequency range of interest. These parameters usually are used for formulating a mathematical dynamic model of examined structure.

Moreover it should be in mind that natural frequencies depends mostly on stiffness and mass distribution of the system, modal damping rely on energy dissipation connected to material properties and system construction. So any changes in material properties, and physical modifications alter the modal parameters.

We investigate silica (SiO2) coatings on metallic substrates made of 16Mo3 steel. The thickness of coating layer is in range 500nm-1µm so its contribution to the structure dimensions could be neglected in relation to modal properties. In that case, we can assume that the possible changes in modal parameters should be due to the coating presence.

We focused on modal frequency and damping coefficient observations before and after silica coating. For this purpose, the proper measurement stand was prepared to investigate modal parameters of the rectangular (150 x 20 mm) specimens, with and without sol-gel coating. A rectangular substrate thickness was in the range 0,3 – 1,0 mm. Because sol-gel coating was dried at elevated temperature additional tests for plain substrate heated at 180°C degree was conducted.

The test results may indicate whether the presented technique can be used to test the impact of the sol-gel coating on the properties of the coated object.

Dr.-Ing. Justyna Krzak