Gradient W+Cu coatings fabricated by plasma spraying method
Artur Rusowicz, Elżbieta Fortuna, Wojciech Lisowski, Tomasz Wolski 1 Politechnika Warszawska, Wydział Mechaniczny Energetyki i Lotnictwa, Instytut Techniki Cieplnej, ul. Nowowiejska 21/25, 00-665 Warszawa, Poland 2, 3 Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa, Poland 4 Zakład Systemów Pomiarowych, ul. Kościelna 31, 05-426 Wiązowna, Poland
Quarterly No. 2, 2007 pages 99-104
DOI:
keywords: W+Cu composites, plasma spraying
abstract The W+Cu composites of different composition were produced by plasma spraying. The process was conducted at the atmospheric pressure using plasmotron PN 120. The coatings were deposited at the copper substrates (35 mm x 60 mm x 3 mm). Before spraying the substrates were degreased and vapour blasted. The substrates during plasma spraying were air-cooled. The surface temperature during the process was measured by pyrometer. The powders before the spraying were reduced in the hydrogen atmosphere to remove oxides from their surfaces. In the first experiments the coatings from the powder mixtures containing 20, 40, 60 and 80 wt. % of W were fabricated. In the case of two coatings, cracks at the interface between the substrate and the coating were observed. In order to reduce the access of air to the plasma stream, the tests plasma spraying processes of copper and tungsten deposition, were carried out with screening the plasma stream by inert gas. Some tests aiming at increasing the amount of hydrogen in the plasmagenic gases were performed. The increase of the hydrogen fraction causes, however, the increase of electric power of plasmotron and in consequences, the plasma temperature. The increase of substrate surface temperature was observed. In the consecutive experiments the previous amount of the hydrogen in the plasmagenic gases (Ar+10%H2) was used. The application of plasma stream screening by inner gas reduced the coatings oxidation. In the next step the plasma spraying of the coatings with gradient composition were carried out. Two zone coatings (the powder mixtures containing 20 and 40 wt. % of W) of 600 µm thickness were produced. Afterwards, the gradient coatings with three zones (the powder mixtures containing 20, 40 and 60 wt. % of W) were fabricated. The powders were fed from one channel, during the process the powder mixtures in feeder were changed. The thickness of coatings was 1 mm. The thickness of the first zone was increased in order to reduce the stresses at the coating/substrate interface. No delimitations or cracks at the coating/substrate interface was observed.