Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of coating supply or source outside of primary...
Reexamination Certificate
2001-03-20
2002-02-12
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of coating supply or source outside of primary...
C427S573000, C427S576000, C427S255310, C427S255320, C427S255360, C427S295000, C427S422000
Reexamination Certificate
active
06346301
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a coating apparatus for producing a heat-insulating layer, in particular a heat-insulating-layer system, on a base and to a method of coating a base under vacuum with a heat-insulating layer.
U.S. Pat. No. 5,238,752 discloses a heat-insulating-layer system having an intermediate bond coating. The heat-insulating-layer system is applied to a metallic substrate, in particular a Cr—Co steel for an aircraft powerplant blade. Cobalt- or nickel-based alloys are specified as further materials for the substrate. Applied directly to this metallic substrate is an intermediate layer, in particular consisting of a nickel aluminide or a platinum aluminide.
Adjoining this intermediate coating is a thin ceramic layer of aluminum oxide, to which the actual heat-insulating layer, in particular consisting of zirconium oxide stabilized with yttrium oxide, is applied. This ceramic heat-insulating layer of zirconium oxide has a rod-shaped structure, the rod-shaped stems being oriented essentially perpendicularly to the surface of the substrate. This is intended to ensure an improvement in the cyclic thermal loading capacity. The heat-insulating layer is deposited on the substrate by means of an electron-beam PVD (physical vapor deposition) method, in the course of which zirconium oxide and yttrium oxide are evaporated from a metal-oxide body by means of an electron-beam gun. The method is carried out in an apparatus in which the substrate is preheated to a temperature of about 950° C. to 1000° C. The substrate is rotated in the stream of metal oxide during the coating operation. Details of the rod-shaped grain structure and its properties cannot be gathered from U.S. Pat. No. 5,238,752. The electron-beam PVD method of producing ceramic coatings having a rod-shaped grain structure is also described. In U.S. Pat. No. 5,087,477 and U.S. Pat. No. 5,262,245, the deposition of zirconium oxide on a substrate being effected in an oxygen atmosphere.
Further methods and examples of applying a heat-insulating-layer system to a gas-turbine blade are described in U.S. Pat. No. 5,514,482 and U.S. Pat. No. 4,405,659.
According to U.S. Pat. No. 4,405,659, it is supposed to be possible with the electron-beam PVD method to apply a heat-insulating layer of zirconium oxide which is stabilized with yttrium oxide and has a thickness of about 125 &mgr;m and a columnar structure. The average cross-sectional area of a stem is said to be in the order of magnitude of 6.5 &mgr;m
2
.
U.S. Pat. No. 4,321,310 and U.S. Pat. No. 4,321,311 each describe heat-insulating-layer systems which have an adherent layer between the zirconium oxide and the metallic substrate with an alloy of the MCrAlY type. Here, “M” stands for one of the metals cobalt, nickel or iron, “Cr” stands for chromium, “Al” stands for aluminum and “Y” stands for yttrium. A PVD (physical vapor deposition) method is disclosed as a possible method for producing a heat-insulating layer of zirconium oxide.
The coating of metallic components, in particular gas-turbine blades consisting of a superalloy, from a composite system having an adhesive layer and a heat-insulating layer is likewise described in International patent Application WO 93/18199 A1. Here, the heat-insulating layer is preferably applied by the electron-beam PVD method, although other PVD methods, such as sputtering and arc deposition, could also be suitable for this purpose.
In the article “Zirconia thin film deposition on silicon by reactive gas flow sputtering: the influence of low energy particle bombardment” by T. Jung and A.Westphal, in Material Science and Engineering, A 140, 191, pages 528 to 533, the so-called reactive gas-flow sputtering method is disclosed for producing zirconium-oxide layers on semiconductor substrates, in particular on a silicon basis. Here, the method relates to the cold deposition of zirconium oxide, which leads to an amorphous growth of the zirconium oxide. This amorphous deposition is effected at substrate temperatures of markedly less than 800° C., heating of the substrate being effected directly, with losses by the substrate carrier. For this purpose, the substrate carrier itself can be heated up to at most a temperature of about 800° C., so that, with due allowance for the heat losses which occur, heating of the substrate to over 400° C. can be achieved.
In German Democratic Republic Patent No. DD 294 511 A5, corresponding to this article, an inert gas, in particular argon, is passed through a hollow cathode, in the interior of which an anode is arranged, so that ionization of argon atoms takes place. The latter strike the cathode, as a result of which cathode material passes into the interior of the hollow cathode and is passed out of the latter with the inert-gas flow. The cathode material is a pure metal, to which oxygen is fed outside the hollow cathode, so that complete oxidation of the metal, in particular zirconium, takes place. Here, the partial pressure of the fed oxygen is in the order of magnitude of 10
−4
Pa. The total dynamic pressure in the vicinity of the semiconductor to be coated is about 13 Pa to 24 Pa. The deposition rate is about 15 nm/min, the substrate having a temperature of about 400° C. The hollow cathode is designed as a cylindrical tube of zirconium having a percentage purity of 99.7%.
An alternative design of the hollow cathode for achieving a larger coating area and a higher coating rate is described in the article “High rated deposition of alumina films by reactive gas flow sputtering” by T. Jung and A. Westphal, in Surface and Coatings Technology, 59,1993, pages 171 to 176 (corresponding to German patent Application DE 42 35 953 A1). The hollow cathode disclosed is of linear construction in the sense that plates of zirconium are arranged next to one another in a housing. An inert-gas flow can be passed between each two adjacent plates, so that a plasma of inert-gas atoms forms between adjacent plates. In addition, the plates may have a cooling feature, in particular cooling passages. Test bodies of silicon, stainless steel and glass were coated by the hollow cathode and the strength of the aluminum-oxide layer was tested up to around 200° C. Nothing is said in the two articles mentioned, concerning the structural properties of the oxide layers with regard to crystallite size and orientation.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a coating apparatus for producing a heat-insulating layer, in particular a heat-insulating-layer system, on a base and to a method of coating a base under vacuum with a heat-insulating layer, that overcome the above-mentioned disadvantages of the prior art components, apparatus, and methods.
With the foregoing and other objects in view there is provided a heat resistant component comprising a substrate and a ceramic heat-insulating layer which is arranged thereon and has a structure having ceramic stems which are oriented mainly normal to the surface of the substrate and have an average stem diameter not exceeding 2.5 &mgr;m and preferably 0.5 to 2.0 &mgr;m.
There is also provided a coating apparatus for producing a heat-insulating layer on a substrate, comprising a) a holding device for positioning the substrate, b) a hollow-cathode arrangement through which an inert gas can flow and which comprises a cathode material and an anode and has a gas-outlet opening facing the holding device, and a gas-inlet opening for inert gas, and c) a separate heating device for directly heating the substrate with heat radiation and/or convection.
There is moreover provided a method of coating a substrate under vacuum with a heat-insulating layer, in which method an inert gas is ionized in an essentially oxygen-free atmosphere, and the ionized inert gas releases from a metallic cathode material metal atoms, which are carried along with the inert gas in the direction of the substrate and to which oxygen is fed before the substrate is reached, so that a metal oxide forms and is deposited on the substrate, or
Beele Wolfram
Brand Peter-Jochen
Jung Thomas
Greenberg Laurence A.
Lerner Herbert L.
Pianalto Bernard
Siemens Aktiengesellschaft
Stemer Werner H.
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