Process for coating substrates made of high melting metals.

p0001The present invention relates to a method for coating an article from a high melting metal with a metal or a ceramic. Refractory metals, also known as refractory metals, eg. As niobium, molybdenum, tantalum and tungsten have not only the direction indicated by its name excellent heat resistance to a good corrosion resistance to a wide range of aggressive media. This is essentially due to the fact that forms on them in the air a dense, adherent oxide layer. This oxide layer, in turn, is the reason that do not adhere to them by means of known methods, for. Example, CVD or PVD method, applied layers of other materials. The application of such a layer is, however, often required, such. As in electrical engineering when the refractory metal to be used because of its corrosion resistance as a substrate for an electrically conductive (metal) layer or an insulating (ceramic) layer. Another disadvantage of the oxide layer on the refractory metal to their high electrical resistance affects which leads to electrical contact difficulties between this metal and the coating.

p0002Object of the present invention is to provide a method which makes it possible to provide an article of a refractory metal, depending on the choice of having an electrically conductive or insulating surface layer.

p0003This object is inventively characterized in that on the subject first anaerobically a bonding layer is applied and only after that is actually desired layer is deposited.

p0004Bonding layers are basically in a variety of applications known for example the establishment of durable paints. they are, however, not yet used in the coating of refractory metals because of the possibility of its application has not been recognized in the art.

p0005In particular, niobium, molybdenum, tantalum and / or tungsten is used for the object to be coated.

p0006As inventive adhesion promoting layer preferably niobium, molybdenum, tantalum, tungsten, titanium, zirconium, chromium and / or hafnium is used. It can be used in a further embodiment of the invention for the bonding layer of the same material as for the particular article to be coated.

p0007Set on the base metal, an electrically conductive layer to be obtained, according to the invention a metal layer of gold, silver, copper, platinum, aluminum and / or nickel on the adhesion promoting layer.

p0008In contrast, preferably a ceramic layer from aluminum oxide, zirconium oxide, silicon oxide, silicon carbide, silicon nitride, boron carbide, boron nitride and / or magnesium oxide is applied for producing an electrically non-conductive layer on the adhesion promoting layer.

p0009According to the invention is suitable for applying the adhesive layer, in particular an arc-PVD process in which the coating material is deposited from a plasma on the object. In such a method one or more existing components of the desired alloy cathode are evaporated in vacuum in an arc discharge; if necessary, the composition of the coating still dosed by the addition amounts of reacting with the plasma gas can be influenced.

p0010Specifically, a thickness range of the adhesive layer of 5 to 500 nm gives very good results. The to be selected layer thickness is bounded below by the surface roughness of the object to be coated or of him covering oxide layer. The layer has to ensure complete coverage. Top the layer thickness is limited by the fact that should make no inhomogeneities or other structural defects in the bonding layer, which could make an internal disintegration of layer feed.

p0011In experiments it was found that z. B. Gold and platinum layers adhere excellently on niobium, when previously a 50 to 200 nm thick titanium or zirconium layer was deposited on this. Another very good adhesion to niobium was obtained for aluminum oxide. Similarly good results were achieved when initially niobium is applied as adhesion-promoting layer and then gold as a surface layer on the niobium surface. Without the intermediate layer of niobium gold adheres poorly.