Development and investigation of SiC-based thermal spray powders with alumina-yttria binder matrix

The combination of excellent mechanical, thermal and chemical properties of silicon carbide (SiC) ant titanium carbide (TiC) has made these materials very attractive both for structural ceramics applications and for thermal sprayed coatings. To suppress oxidation and to avoid the formation of silicides during spraying of SiC-based composites, feedstock spray powders have been developed containing 32 wt.-% of an alumina-yttrium ceramic binder matrix. The spray posers are prepared by spray-drying and sintering (a&s). Also, TiC-based composite spray powders showing the same matrix material and content have been developed and produced. Thermal spray processing of the described powders by atmospheric plasma spraying (APS) using an F6 APS torch and high velocity oxygen fuel spraying (HVOF) with the Top Gun G acetylene torch is carried out. Both the produced coatings and feedstock powder are characterized by optical microscopy, Xray diffractometry (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray analyses (EDXS). The volumetric content of the carbide phase is 73 vol.-%, that corresponds to 67 wt.-% of SiC and 76 wt.-% of TiC within the composite powders. The carbide grain size is 2.5 microns and 1.5 microns respectively. The oxide-ceramic matrix phase mainly contains yttrium-aluminum-garnet (Y3Al5O12) and a smaller amount of corundum (Al2O3). The powder particles show globular shapes. All components are homogeneously distributed within the powder microstructures. While APS coatings show high porosities in the lower coating areas so far, all produced HVOF coatings show higher densities and continuously developed coatings-substrate interfaces. Further investigations will deal with powder and spray parameter optimization, including profound metallographical examinations. Entnommen aus <a_href="http://www.fiz-technik.de/db/b_tema.htm" target="_blank">TEMA</a>