Abstract
One of the main application fields of the thermal spraying process are thermal barrier coatings (TBC). Today partially stabilised zirconia (YSZ or MSZ) is mainly used as TBC material. At temperatures above 1000°C, zirconia layers ages distinctively including shrinkage and microcrack formation. Therefore there is a considerable interest in TBCs for higher temperature application. In this paper lanthanum aluminate, a newly developed TBC material with long term stability up to 1400 °C, is presented. It ages significantly slower at these high temperatures than commercial zirconia based TBCs. Its composition favors the formation of platelets, which prevent a densification of the coating by postsintering. It consists of La2O3, AI2O3 and MgO. Its crystal structure corresponds to lanthanum aluminate powders were produced using two different fabrication routes, one based on salts, the other one based on oxides. To optimise the granulate various raw materials and additives were tested. The slurry was spray dried in a laboratory spray drier and calcined at 1650°C. Using these two powders, coatings were produced by atmospheric plasma spraying (APS). The residual stresses of the coatings were measured by the hole drilling method and the deposition process was optimised with respect to the residual stresses of the TBC. The coatings were extensively analysed regarding phase composition, thermal expansion, long term stability as well as microstructural properties.
