Improvement of thermally sprayed abradable coating by microstructure control

The aim of this work was to characterise the microstructure of recently developed abradable materials for providing a sealing between rotating and stationary parts in aerospace turbine engines. The investigated materials were two coatings obtained by thermal spraying of composite powder particles from the AlSi–hBN and NiCrAl–bentonite systems. X-ray diffraction and scanning electron microscopy were used to analyse the microstructure and identify the structural elements of the coatings. These structural elements: the coarse porosities, the metallic binding phase and the embedded “abradable” particles were analysed by quantitative metallography. In particular, an image analysis procedure has been established to quantify different geometrical parameters related to the shape, size and orientation distribution, of these structural elements.