The objective of this present work is to obtain preliminary data to check the validity of the current 1300 °C upper temperature limit of atmospheric plasma sprayed (APS) YSZ thermal barrier coatings (TBCs). To accomplish this objective, optimized YSZ coating systems were sprayed onto CMSX-4 substrate pucks and their thermal cycling performance was evaluated using a laser rig. Test samples were operated under a temperature gradient of 1500 °C at the coating frontside and 1000 °C at the substrate backside. Two heating-cooling sequences were applied: 5 min of heating and 2 min of cooling for 1000 cycles and 1 h of heating and 2 min of cooling for 10 cycles. In both cases, no TBC failures were observed.

Different thermal spray technologies were used to apply CoNiCrAlY bond coats to Inconel substrates. Powder compositions were the same in all cases and particle size recommendations were followed for each torch. YSZ topcoats were deposited via APS on bond coat samples selected based on roughness, porosity, residual stress, oxidation, and isothermal TGO growth. The TBCs were furnace cycle tested for 10-1400 cycles as well as to failure and changes in bond strength and TGO thickness were recorded. It was observed that bond strength values, which are relatively stable during thermal cycling, decrease significantly just before failure brought on by topcoat spall off.

In this study, the influence of spray parameters on the electrical resistivity of thermally sprayed ceramic coatings from the system Cr 2 O 3 -TiO 2 was investigated. Fused and crushed feedstock powders with contents of 10 wt. % and 20 wt. % chromium oxide were deposited by APS and HVOF. Temperature and velocity of the particles in the spray jet as well as the coating surface temperature were analyzed during the deposition process. Impedance spectroscopy was used to investigate the electrical resistivity of the coatings and the results were correlated to coating microstructure and phase composition. It was found that phase transformations occur during the spray process. In the coatings a high temperature phase (n-phase) and rutile were observed. Though, the ratio of rutile depends on the spray methods employed for coating deposition. The electrical resistivity of coatings obtained by HVOF can be correlated to the content of chromium oxide. Furthermore, the surface temperature of the coating during deposition also shows some influence. Concerning the coatings resulting from APS, the different mixtures of the plasma gases (Ar-H 2 and Ar-N 2 ) are supposed to have the most important influence on the electric resistivity.