The Influence of Thickness on the Complex Modulus of Air Plasma Sprayed Ceramic Blend Coatings

Previous research suggests that damping of metallic beams that have a hard ceramic coating applied on them is proportional to the coating thickness. This indicates that the damping is a volume dependent material property. Since thickness variations are likely in an actual application, it is essential to understand the role that coating thickness plays in damping effectiveness. For this research, a series of tests were conducted using substrate beams of 90 mil Ti-6Al-4V, coated with 3 mils of an air plasma sprayed NiCrAlY bond coat followed by a Titania-Alumina ceramic blend coating applied via air plasma spray in one of three thicknesses (5 mil, 10 mil and 15 mil). Four specimens were coated at each thickness for a total of 12 specimens. The system loss factor and natural frequencies were measured for each specimen at each stage to determine the material properties of the bare beam, the bond coat and the ceramic coating. This information was used with the dimensions at each stage to determine the material properties (storage modulus, loss modulus and loss factor) for the bond coat and the ceramic. Differences in the results of different thickness specimens allow the ability to determine and quantify a thickness effect.