This paper presents an overview of current research activities regarding the properties and functionalities of finely structured alumina (Al 2 O 3 ) and titania (TiO 2 ) coatings prepared by suspension plasma spraying and suspension HVOF spraying. A selection of new experimental results obtained by the authors is also included. In the case of Al 2 O 3 , focus was on the retention of a higher content of the a-phase in the coatings without any post-treatment or alloying. For TiO 2 , the goal was to preserve the initial anatase phase in order to obtain photocatalytically active titania coatings. Coating microstructures, phase compositions, and functionalities resulting from the interactions between different working parameters are discussed.

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The composition WC-(W,Cr) 2 C-Ni is one of the standard compositions used for the preparation of thermally sprayed coatings by high velocity oxy-fuel (HVOF) spraying. Surprisingly, this composition has been poorly investigated in the past. Frequent use of commercial designations WC-ÔCrCÕ-Ni, WC-Cr 3 C 2 -Ni, and WC-NiCr indicates the insufficient knowledge about the phase compositions of these powders and coatings. The properties of these coatings differ significantly from those of WC-Co and WC-CoCr coatings. In this paper, the results of different series of experiments conducted on HVOFsprayed WC-(W,Cr) 2 C-Ni coatings are compiled and their specific benefits pointed out. The focus of this study is on the analysis of the microstructures and phase compositions of the feedstock powders and coatings. Unlike WC-Co and Cr 3 C 2 -NiCr, WC-(W,Cr) 2 C-Ni is not a simple binary hard phase-binder metal composite. The phase (W,Cr) 2 C with unknown physical and mechanical properties appears as a second hard phase, which is inhomogeneously distributed in the feedstock powders and coatings. As examples of coating properties, the oxidation resistance and dry sliding wear properties are compared with those of WC-10%Co-4%Cr coatings.

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