In this study, a novel self-healing concept is considered in order to increase the lifetime of thermal barrier coatings (TBCs) in modern gas turbines. For that purpose, SiC healing particles were introduced to conventional 8YSZ topcoats by using various plasma spray concepts, i.e., composite or multilayered coatings. All topcoats were sprayed by SG-100 plasma torch on previously deposited NiCrAlY bondcoats produced by conventional atmospheric plasma spraying. Coatings were subjected to thermal conductivity measurements by laser flash method up to 1000°C, isothermal oxidation testing up to 200h at 1100°C and finally thermal cyclic fatigue (TCF) lifetime testing at 1100°C. Microstructural coating evaluation was performed by scanning electronic microscope (SEM), in the as-produced and post high-temperature tested states. This was done to analyze the self-healing phenomena and its influence on the high-temperature performance of the newly developed TBCs.

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.

This study investigates the correlation between thermal barrier coating (TBC) lifetime and thermally grown oxide (TGO) layer thickness. YSZ TBCs were deposited by atmospheric plasma spraying on Ni-base substrates and subjected to burner cycling tests with a thermal gradient and isothermal furnace testing. Both tests revealed that thermal cycling lifetime decreases with increasing TGO thickness, following a power law function, and for a critical TGO thickness of 5-6 μm, the failure mode changes from cracking within the YSZ layer to interface cracking around the TGO. Although either test can be used to evaluate TBC performance, burner cycling tests are better suited for evaluating ceramic topcoats, while furnace cycling test results integrate the effects of bond coat properties, especially oxidation resistance, as well as ceramic topcoat cracking resistance. The two tests can thus be used together to assess the factors that control TBC failure.

TiAl 3 -Al composite coatings are believed to hold promise for extending the service temperature range of titanium alloys used as structural materials. In this study, 0.6 x 40 mm Ti-6Al-4V specimens are coated with a 30 μm thick layer of TiAl 3 -Al by low-temperature HVOF spraying. Cross-sectional imaging shows that the as-sprayed coatings have a dense laminar microstructure and are well bonded to the substrate. Following the initial examination, the coating samples were placed in a muffle furnace, where they were held at 700 °C for up to 1000 h. Mass gain was detected starting at 200 h and remained nearly constant for the remainder of the test. This is an indication of excellent corrosion resistance, which is verified by SEM cross-sectioning and elemental EDS analysis. A brief explanation of the protective mechanism of the coating is provided.