Typical coatings for high-temperature applications involve an oxidation resistant coating and a thermal barrier coating (TBC). The oxidation resistant coating is also called bond coat because it provides a layer on which the ceramic TBC can adhere.

In many papers, TBC is used to refer to the ensemble bond-coat+TBC, in the following, I will use TBC only to refer to the ceramic thermal barrier.

Illustration of a typical coating system in a high-pressure turbine blade. Clockwise, a TBC coated high-pressure turbine blade, view from top showing the cooling systems (image courtesy Michael Cervenka, Rolls-Royce Plc), and schematic profile temperature, note the drop of temperature close to the blade surface due to the presence of a thin cooling air film (SEM picture courtesy M. Pusch).

As noted in the introduction, the TBC is oxygen transparent and therefore does not provide any oxydation resistance.

Note: the following will make extensive use of these abbreviations:

• TGO:thermally grown oxide
• TBC:thermal barrier coating
• APS:air plasma spray
• LPPS:low pressure plasma spray
• EBPVD:electron beam physical vapour deposition

Bibliography

1. Padture et al., Science, 296:2002, 280-284, 'Themal barrier coatings for gas-turbine engine applications'.