Yttria stabilized zirconia thermal barrier coatings (TBCs) produced by air plasma spraying on Ni-based superalloys with MCrAlY (M = Ni, Co) bondcoats were studied. The specimens were subjected to cyclic oxidation testing in laboratory air at temperatures between 1000 and 1100°C under various cyclic conditions. It was observed that the lifetime of the TBC-system was about 30% shorter when tested with hot-dwell times in the order of 2 hours than when tested with hot-dwells in the order of 20 hours. Analytical studies of the polished cross-sections of the exposed specimens by optical metallography and scanning electron microscopy (SEM) indicated that TBC-failure was initiated by delaminations at the alumina scale/bondcoat interface in the convex regions of the rough bondcoat surfaces, which then propagated through the TBC. Independent of the testing procedure the absolute values of the TBC lifetime were found to depend strongly on the TBC-microstructure and especially the morphology of the TBC/bondcoat interface. Comparison of two TBC systems with nominally the same base material, bondcoat and TBC chemical compositions revealed that these properties crucially determine the rate of crack propagation through the TBC.

Several different single-crystal superalloys were coated with different bond coatings to study the effect of composition on the cyclic oxidation lifetime of an yttria-stabilized zirconia (YSZ) top coating. Three different superalloys were coated with a 7µm Pt layer that was diffused into the surface prior to YSZ deposition by physical vapor deposition from a commercial source. One of the superalloys was coated with a standard Pt-modified aluminide coating and Pt-diffusion coatings with 3 or 7µm of Pt. Three coatings of each type were cycled to failure in 1h cycles at 1150°C to get an average coating lifetime. The Pt-diffusion bond coating on the superalloy containing Ti exhibited the shortest YSZ coating lifetime. Initial characterization has been conducted to understand the role of Ti in the coating system.

TBCs are ceramic protective coatings designed to withstand extreme environmental conditions such as high temperatures, thermal shock and possibly corrosion attack. Over the past decades a tremendous effort has been put into the development and understanding of thermal barrier coatings as their application in the gas turbine industry promises higher operational efficiency, longer life of components and hence lower fuel bills and maintenance bills. As the effort of the turbine industry is focused on lowering carbon emissions a drive for even higher operating temperatures is foreseen. This will require new approaches in regard to component monitoring to reduce maintenance costs and to permit maximum utilisation of engine components in the hot section.

The paper looks into the design of materials suitable to manufacture EBPVD and APS sensor coating systems. Different aspect will be highlighted such as suitable dopants, two phase systems and layered coatings. Selected systems were manufactured and characterised using industrial standard coating techniques. These systems were studied on luminescence from room temperature to temperatures in excess of 1400oC. Further, some systems have shown very promising durability properties when tested alongside standard thermal barrier coatings.

In addition to the thermal sensing properties the paper will demonstrate the potential to measure other properties such as ageing of the material or hot corrosion effects.

Thermal properties and failure mechanisms of thermal barrier coatings (TBCs) are closely related with its microstructure. Numerous factors, besides the thermo-mechanical properties, have to be considered in practical applications of TBCs, such as erosion and wear resistance. There is therefore a need to improve the adhesive strength and mechanical characteristics, which are essential to improving the reliability and lifetime performance of the air-plasma sprayed (APS) TBC system. In this study, the microstructures in the top and bond coats of TBCs have been designed as a new strategy for the advanced coatings, and we prepared the layered TBC with three coating layers in both the top and coats using a specialized coating system (TriplexPro-200). In order to determine and to understand the effects of the microstructure design on the fracture behavior and the mechanical properties, the adhesive strength and sharp indentation tests were conducted. Results were compared with the common TBC systems with single layer in each coat. In the layered TBCs, more dense coating could be possible due to an higher flame velocity compared to a conventional APS system (9MB), and semi-graded coating also possible using a multi-hopper system. The bond and top coats were coated with 100 and 200 mm for each feedstock, resulting in 300 and 600 mm in the bond and top coats, respectively. The microstructure of the top coat could be controlled by changing the feedstock—dense/intermediate/porous layers from surface to interface or reverse microstructure. The adhesive strength values of the bond and top coats were about 80 and 10 MPa, respectively, independent of microstructure, which are higher values than those of TBC system prepared by the 9MB system. The hardness and toughness values were gradually changed from surface to interface, indicating that the mechanical properties are well corresponded with the microstructure of TBCs.