Microstructural characterization of zirconia co-doped with yttria and niobia by laser deposition on Ti-6Al-4V as a thermal barrier for application in turbines

The Ti-6Al-4V is a very important alloy in the aerospace industry in the manufacturing blades for aircrafts turbines and structural forgings. However, one of the major factors limiting the life of titanium alloys in service is their degradation due to gaseous environments especially to environments containing oxygen at elevated temperatures during long-term. Some coatings have been discovered as layers of protection called TBC (Thermal Barrier Coating). The TBC provides the protection and allows reaching the higher operating temperature to increase the efficiency of the turbines without changing the mechanical properties of the titanium. The top coat ceramic aims to protect alloys against corrosion, oxidation and thermal protection. However, because of the limitations of the composition 7 YSZ (commercial zirconia stabilized with 7.6 ± 1 mol % yttria) other stabilizing of the tetragonal phase of zirconia such as tantalum and niobium has been studied to overcome these limitations. The present study the TBC are composted with the Ti-6Al-4V (metallic substrate), NiCrAlY (bond coat), thermally grown oxide (TGO) and the ceramic topcoat ZrO₂-YO_1.5-NbO_2.5. The zirconia ceramic was co-doped with yttria and niobia with 14.5, 16.0 and 17.5 mol%. The deposition process the bond coat and power ceramic were by CO₂ laser and the TGO was forming by vacuum thermal treatment in 1100 °C. The objective of the study is the comparison for a potential protection of this ceramic coating described above with the zirconia-yttria ceramic commercial. The samples were analyzed by microscopy and EDS for the morphology analysis and chemical analysis of the layers obtained. The SEM analysis showed finer grains and nanofissures for the ceramic composition of 14.5 and 17.5 mol % and showed coarse grains for the composition of 16.0 mol %. At high temperatures the coarse grains tend to have better mechanical properties, indicating that the composition of 16.0 mol% better meets the desired application.