Partners: UTBM (FR), Neomet(UK), RALSA (ES), Euromat (DE), ESIL (IE), RWTH (DE), IPP (CZ), Rolls-Royce (UK) and MTU (DE)

One way to improve the efficiency of gas turbine is to better control the clearance between rotating blades and engine housings and hence reduce the over-tip leakage. Current practice is to allow blade tips to cut into a relatively soft abradable coating in order to provide a self-regulating clearance control. As can be imagined, such coatings operate in a highly challenging environment under high and variable thermal, chemical and mechanical loads. This project has led to a much better understanding of this process, provided a predictive model for abradability and resulted in the development of improved abradable materials.

In aero-engines, abradable coatings are used to control the over-tip leakage of air in the compressor. They allow the blade tip to cut a track into the seal material without causing wear of the blade. To gain the combination of properties required, these coatings are generally plasma sprayed. Here powder feed material is injected into a hot plasma stream where it is heated, accelerated and projected onto the component. The resultant coating (eg fig.1) has a complex, layered structure which includes not only the powder constituents but also pores and oxides.

In the past, this strategically important area has developed largely empirically and although manufacturers have developed a suite of abradable seal coatings that are functional they are far from perfect. The aim of this project was thus to gain a much better, more fundamental understanding of abradability and at the same time design and manufacture a new family of powder/coating structures. In particular, to improve the efficiency of HP compressors. One quantifiable impact of improved seals would be on direct fuel savings. We estimate that improved abradables in the HP compressor could provide a reduction in specific fuel consumption (SFC) of up to 1%.

The SEALCOAT project contained two strands; modelling of abradability and the development and test of novel materials.

This work was in part funded by the European Commission