US 3198653 A
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Description (OCR text may contain errors)
Aug- 3, 1965 w. B. HALL 3,198,653
COATED GOLUMBIUM ARTICLE Filed Aug. 2, 1962 United States Patent Office y Patented Aug. 3, i965 This invention relates generally to a coated article and a method for preparing the same. More particularly, this invention is concerned with providing protection for columbium and columbium alloys against oxidative degradation at high temperatures.
High speed jet aircraft engines, especially in the afterburner section, achieve temperatures in excess of that which normally causes oxidation of columbium metal when such metal is exposed to an oxidizing atmosphere thereby precluding the utilization of the refractory characteristics of this metal in such applications. In addition, the high temperatures in jet aircraft engines causes minute amounts of gas to diffuse into the metal thereby causing severe embrittlernent defects.
The `solutions to the aforementioned problems `are provided by this invention in order to allow for the utilization of refractory metal columbium, with its high melting point, in the construction of jet engines and turbines.
In addition, a simple, easily produced coated article is provided which has utility in jet afterburner linings, 'turbine blades, etc., or wherever a refractory metal is subjected to high temperatures during use. The coating of this invention provides a coated base which is substantially resistant to thermal shock, gas embrittlement and oxidative degradation.
Columbium is a refractory metal having a melting point of 4380" F.; however, exposure to temperatures of about 1000 F. in an oxidizing atmosphere causes severe oxidation of the metal and diffusion of gas into the metal thereby causing embrittlement.
To overcome this problem a structure of columbium or `one of its alloys is provided with a first coating of alumina and a second coating of a slip sprayed glasslike metal oxide which protects the metal from contamination and oxidation up to a temperature of 2500 F. The drawing illustrates the coated article of this invention and the best method of carrying the invention into effect.
In the drawings:
FIGURE 1 is an isometric View in cross-section and exploded form of the coated oclumbium base of this invention; and
FIGURE 2 is a ow lsheet diagram showing the various process steps involved in the production of the coated article of FIGURE 1.
In order to coat columbium or its alloys, the metallic structure must rst be cleaned, for example, by grit blasting. A ten mil layer of alumina is then deposited onV that portion of the surface to which would be exposed to high temperature conditions in an oxidizing atmosphere. Flame spraying of alumina is the method chosen for applying the coating While alumina is utilized because of its inertness with respect to columbium and, with ilame spraying, provides superior adherence to columbium.
A glass-like metal oxide which forms the `second coating is slip sprayed over the alumina and tired in a purified argon atmosphere. The metal oxides utilized in accordance with the teachings of this invention are selected from the group consisting of MgO, BaO, and SiO2.
A columbium alloy article coated by the above-described method provides constant protection of the base metal from oxidation and contamination for 200 hours at a temperature of 2300 F. Testing further indicated that no failure due to thermal shock of thermal cycles of 1000 F. to 2300 F. in two minute cycles occurs to the coating.
Thus, the coated columbium or columbium alloy articles described provides protection for a longer period of time by means of a single, low cost process against the deleterious effects to which refractory materials are subjected at high temperatures.
Although the invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.
1. A coated metal article comprising a base of columbium metal, a first layer of llame sprayed alumina bonded to said base and a second layer of a fired, slip sprayed metallic oxide bonded to said first layer in which said metallic oxide is selected from the group consisting of MgO, BaO, and SiO2.
2. A coated metal article in accordance with claim 1 wherein said second layer is MgO.
3. A coated metal article in accordance with claim 1 wherein said second layer is BaO.
4. A coated metal article in accordance with claim 1 wherein said second layer is Si02.
References Cited by the Examiner UNITED STATES PATENTS 3,038,817 6/62 Day et al 117-70 X 3,054,694 9/ 62 Aves 117-46 X 3,057,048 10/ 62 Hirakis 29-194 FOREIGN PATENTS 895,848 11/53 Germany.
RICHARD D. NEVIUS, Primary Examiner.
WILLIAM D. MARTIN, Examiner.