Lanthanum hexaaluminate thermal barrier coatings

State-of-the-art thermal barrier coatings (TBC) consisting of Yttria partially stabilized zirconia (Y-PSZ) are restricted to long term application temperatures below 1100 degreesC. Exposed to higher temperatures their thermally insulating properties decline due to densification. Moreover Y-PSZ becomes an oxygen ion conductor at elevated temperatures. Lanthanum hexaaluminate (LHA) is a novel thermal barrier material which is able to overcome these problems associated with the use of Y-PSZ at higher temperatures. LHA crystallizes in magnetoplumbite structure and shows an outstanding thermal stability up to 1600 degreesC and insulating properties comparable to Y-PSZ. The low thermal conductivity of LHA is caused by its microstructure - a random arrangement of LHA platelets which builds up a microporous coating - and the insulating properties of the material with its crystallographic features itself. This study describes the development of an optimized procedure for the processing, manufacturing and application of LHA as TBC-material. The plasma spray powders were produced by spray-drying of aqueous ceramic slurries. The Atmospheric Plasma Spray (APS) deposition process was optimized to yield an homogenous coating with controlled microporosity and residual stresses. The crystalline phases were characterized by X-ray diffraction (XRD).