TRIBOLOGICAL BEHAVIOR OF Al-Si POLYESTER ABRADABLE COATINGS (original) (raw)

Abstract

1 ABSTRACT Abradable seal coatings are engineered to minimise the clearance between blade tips and casing to enhance gas-turbine performance. The gas path sealing has become an important method for this purpose. Abradable seals act as sacrificial layers between the blades and the casing, and are soft enough to avoid significant wear to blade tips, thus allowing much smaller clearances. The thermal sprayed abradable seal coating has been used because of its simple manufacturing processes, easy repair of the components, easy adjustment of its properties and good sealing effectiveness. In the present paper, we report on the surface microstructure and the tribological behavior of the widely used, abradable coating Al-Si polyester. Coatings were produced by using fully-automated atmospheric thermal spraying (APS) equipment. Microscopic examination revealed rounded polyester particles embedded in the Al-Si phase without forming any interfacial product. Porosity was estimated to be about 3 %, while the coating-substrate interface was coherent. For the evaluation of the coatings tribological performance, sliding friction tests were performed on a pinon-disc apparatus with SiC as counterbody. Three normal loads (5 N, 7 N and 10 N) were used, in order to examine the influence of the contact stress on tribosystem. Abrasion was identified as the dominant wear mechanism of the coating, whilst secondary microcracking was activated when applying more severe sliding conditions. During testing, the friction coefficient remained constant, ranging from 0.21 to 0.27, for all the loads applied, and the wear volume was increasing proportionally with the applied load.

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