SCS have identified a coating composition based on luminescence dopants that has shown superior durability in comparison to a standard thermal barrier coating (TBC) This could enable higher operating temperatures which can improve efficiency and reduce maintenance costs.

The coating has been trialled in a large gas turbine for power generation in the UK where it served for 4000 hours. The SCS coatings passed the maintenance checks whilst the standard reference coatings failed, indicating the potential reduction in maintenance costs if employed on existing engines.

The novel coating composition was discovered as a by-product of the sensor coating development which is the core technology of the business. The composition has been shown to reduce the development of cracks caused by severe thermal exposure. The coating can be deposited using standard industrial techniques and is only a slight modification from the widely used coating technology at present.

The current material of choice for a TBC is based on yttrium stabilised zirconia (YSZ). This material has numerous technical advantages, but when it is exposed to temperatures above 1250ºC it becomes unstable.

SCS has developed an intelligent coating imaging system which enables maintenance engineers to quickly assess damage to a coated surface in high resolution with wide viewing angles. This technology can be applied in areas where the thickness of a protection layer is critical for example in manufacturing processes or in gas turbines.

The coating is layered so that it appears to have different colours at different thicknesses, which enables the erosion detection. It allows identification and quantification of the areas that have reached critical erosion levels in real time, even in dark environments where no other light source is available eg. inside processing reactors or turbines. The evaluation can be done on the engine or in other machinery where optical access is difficult using borescope-like devices. This is cost effective as engine components can be checked without dismantling the engine. The coating is based on industrial thermal barrier coating architecture and hence is very robust in challenging high temperature environments.

The new method applied by SCS enables high precision erosion measurements down to a micrometre scale, but with large viewing angles so that large parts of a component can be monitored. This technique will enable the degradation of the coating to be monitored and erosion patterns to be mapped in-situ.

Online temperature measurement – when temperature transients are important SCS coatings can also be produced so that there is no thermal history effect! In this case, the luminescence in the coatings changes reversibly with temperature so that measurements are recorded while the material is at temperature. On-line phosphorescence temperature measurements can be useful when other technologies such as infrared detectors are disturbed by the vicinity of combustion flames or unknown and changing surface emissivity. This technique, termed phosphor thermometry, has been known for many years. Southside Thermal Sciences (now New STS Ltd) has pioneered its practical application on gas turbines using patented robust coatings and applied the technology successfully in the hot section of a Rolls-Royce Viper 201 engine. Sensor Coating Systems spun out of Southside Thermal Sciences in 2012. However, the expertise to apply the on-line temperature technology is still in Sensor Coating Systems Ltd. The application of the on-line temperature system was published in peer reviewed scientific journals and presented at several conferences. The work was acknowledged with several best paper awards and the John P Davies award from the ASME Turbo Expo in 2014.

Measurements carried out on a Rolls-Royce Viper 201 jet engine:

• Nozzle guide vanes
• Combustion chamber wall (looking through a flame)
• Rotating turbine blade (at ca 350m/s speed)
• Sub-surface measurements performed close to the bondcoat.

Contact SCS if you are interested into a specific application.