Birmingham Metallurgical Association Lecture

Hugh E. Evans - University of Birmingham

Ni-based superalloys, used as hot components of gas turbines, have inadequate oxidation and hot corrosion properties to operate for extended periods. Such high-temperature components are coated, usually to increase surface aluminium concentrations, so that a protective alumina layer can be both formed and maintained during service. Current coatings are produced either by diffusion or by depositing an overlay layer. In heat flux situations, a thermally insulating top coat of yttria stabilised zirconia (YSZ) is also used to form a Thermal Barrier Coating (TBC) system. These coatings degrade with continued exposure at temperature due principally to the depletion of aluminium by selective oxidation and by interdiffusion with the alloy substrate. In TBC systems, continued oxide growth can lead to stress development and to spallation of the YSZ top coat. A discussion of these degradation and failure processes is given in the talk.

A new generation of coatings will be needed to meet economic and environmental  pressures to improve fuel efficiency, to use biomass-derived fuels and to operate more flexibly. Likely candidates will be multilayered SMART coatings that can respond to local differences in oxidation and hot corrosion conditions and can provide healing capabilities. Current developments in such coating systems are described.

Lecture starts at 6.30pm with buffet available at 6.00pm

All are welcome!