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Towards a substitution of PVD by PS – Coatings

Towards a substitution of PVD by PS – Coatings

The aim of this project is to make significant improvements to thermal barrier coating (TBC) systems used for gas turbine applications by introducing a number of key innovations. TBC’s consist of an oxidation resistant (Co,Ni)CrAlY bond coat and a insulating yttria stabilized zirconia top coat.

The top coat is deposited by air plasma-spraying (APS) or by electron-beam physical vapour deposition (EB-PVD). The use of the much more expensive EBPVD process has been due largely to the columnar structure of the coatings resulting in improved strain tolerance and improved reliability.

The in-service life of these coatings is now around 8000 hours. Conventional APS coatings are deposited onto a random, rough grit blasted surface. A new method which produces a controlled, 3D surface morphology has been used to both improve bonding and, crucially, enable control of the TBC microstructure., in particular, providing a much higher segmentation crack density. Most failures in TBC systems occur at the interface between the topcoat and the bond coat. Interfacial adhesion has been improved by the introduction of interface with regular 3D pattern. Finally, new processes for the deposition of the TBC have be developed.

These include; thin film – LPPS, plasma enhanced CVD, nano-phase suspension PS and high speed PVD. The project provided significant improvements to TBC systems using a number of innovative steps. This work will not only extend the life of conventional TBC’s but also provides the breakthrough necessary to achieve ‘next generation’ TBC systems.