Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
  • C23C10/28—Solid state diffusion of only metal elements or silicon into metallic material surfaces using solids, e.g. powders, pastes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/66—Electroplating: Baths therefor from melts
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T50/00—Aeronautics or air transport
  • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/922—Static electricity metal bleed-off metallic stock
  • Y10S428/9335—Product by special process
  • Y10S428/934—Electrical process
  • Y10S428/935—Electroplating
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12639—Adjacent, identical composition, components
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12736—Al-base component
  • Y10T428/12743—Next to refractory [Group IVB, VB, or VIB] metal-base component
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
  • Y10T428/12819—Group VB metal-base component

Definitions

• This invention relates to a novel coating of columbium, cobalt, and nickel base alloys that will protect the base metal or alloy from oxidation in very high temperature environments. More particularly, this invention relates to electrodeposited coatings of aluminum on columbium, cobalt, or nickel base alloys, and a method for electrodepositing the aluminum on these alloys to produce compounds of the aluminum with the base metal of the alloys that provide an oxidation resistant coating for the alloys at very high temperatures.
• the principal limitation in gas turbine technology today is the maximum turbine inlet temperature.
• the turbine inlet temperature is in turn limited by the temperature that the turbine vanes and blades are able to Withstand without danger of failure.
• the best available high temperature alloys in the prior art are nickel and cobalt base superalloys, but critical structural components, such as turbine vanes and blades constructed from such alloys are limited to maximum operating temperatures of between 1600 and 1900" F.
• columbium is, therefore, potentially useful for fast aircraft and space flight vehicles and in nuclear reactors.
• Columbium is inherently a soft, ductile, readily fabricable material. Although its melting temperature is about 4474 F., pure columbium becomes too weak for structural use at temperatures above 1200 F. Columbium is also a very reactive metal in that it dissolves large quantities of oxygen, and probably nitrogen, on exposure; .to atmospheres containing even small amounts of these elements at modest temperatures.
• columbium suffersvfrom oxidation, its oxide does not volatilize, and it is thus potentially possible to localize oxygen attack on columbium by coating the metal.
• columbium base alloys as compared with molybdenum base alloys are that colum-. bium alloys are relatively more ductile and workable at low temperatures and columbium has a lower density than molybdenum. v 0 Until recent years, estimated ore reserves of colum bium were so small that there was only a mild interest in columbium base alloys. However, with the discovery I 3206,29 Patented Sept-14, 1965 ice of substantial ore bodies the potential availability of columbium has become so great that scarcity is no longer a restriction on its use.
• columbium base alloys that are suitable for use under high temperature service conditions about 2000 F.
• the coatings of the present invention may be used with such columbium base alloys.
• the coatings of the present invention are also useful with columbium base alloys earlier developed by others, such as Du Pont 31 (columbium-l0%molybdenuml0% titanium, by Weight).
• the coatings and methods of coating of the present invention are not restricted to use with columbium base alloys, but may also be used with nickel and cobalt base alloys.
• the latter alloys are generally described as superalloys, and a number of them are well-known in the art of high-temperature technology. Indeed, these so-called superalloys are thought to have stretched the iron, nickel, cobalt group of alloys to the upper limits of possible highternperature applications.
• Both cobalt and nickel base alloys of the type discussed above can be successfully plated with the coatings and by the method of the present invention.
• the coatings and the method of this invention may thus be successfully used to deposit aluminum on a base metal in the form of aluminum compounds with a base metal that is a member of the group consisting of columbium base alloys, nickel base alloys and cobalt base alloys.
• a base metal that is a member of the group consisting of columbium base alloys, nickel base alloys and cobalt base alloys.
• Additional objects of this invention are to provide a coating on columbium, nickel, and cobalt base alloys that, in addition to protecting the alloys from oxidation at high temperatures, is also capable of withstanding severe mechanical and thermal stresses, such as are encountered in jet engine service.
• the coating must also be compatible with the base metal of the alloy, so that the coating will not form low-melting phases or phase mixtures, volatile compounds, or a thick brittle layer. Also, the thermal expansion and mechanical properties of the coating must be reasonably matched to the base metal.
• Further objects of this invention are to provide a coating for columbium, nickel, and cobalt base alloys that will provide good oxidation resistance at high temperatures through the formation of an adherent, continuous coating.
• the coating method provides some initial diffusion between the coating and the base metal but the resultant coating exhibits stability at operating temperatures to both oxidation and further diffusion.
• the coating of-this invention is relatively ductile at all temperatures of use.
• Another objects of this invention are to provide a coating on columbium, nickel and cobalt base alloys that will provide control of the uniformity of the coating and yield an essentially uniform coating on even intricately shaped parts and at the edges and corners of parts.
• the electrodeposition method of applying the'coatings of the present invention to parts formed from columbium, nickel, or cobalt base alloys provides a practical method for achieving uniformity in the coating.
• a still further object of the present invention is to provide a method for electrodepositing aluminum on columbium, nickel, or cobalt base alloys to form a chemical compound of aluminum with a base metal of the 4 alloy that will provide an oxidation resistant coating for the columbium, nickel, and cobalt base alloys.
• the aluminum is electrodeposited on the base alloy from a molten salt bath.
• the foregoing and other objects of this invention are realized by the coating of a columbium, nickel, or cobalt base alloy with an aluminum compound of the base metal that is resistant to oxidation.
• the coatings of this invention are useful for coatings on a base metal that is a member of the group consisting of columbium base alloys, nickel base alloys and cobalt base alloys that contain at least 40% by weight of columbium, nickel and cobalt, respectively.
• the compounds formed are columbium aluminides, e.g., CbAl with cobalt base alloys, the aluminum compounds formed are cobalt aluminides, e.g., Co Al and CoAl, and with nickel base alloys, the aluminum compounds formed are the nickel aluminides, e.g., NiAl and Ni Al.
• the coatings of the present invention protect columbium base alloys from oxidation at high temperatures by a diffusion coating consisting of columbium aluminides, such as CbAl at the outer surface that are bonded to a Cb-Al solid solution.
• the excellent oxidation re sistance of CbAl for example, is apparent from its oxidation rate.
• this compound increases in weight, as the result of reaction with oxygen, at a rate of only 0.001 mg./mm. /hr.
• Specimens of columbium base alloys coated with aluminum by the method of this invention demonstrate a similar low oxidation rate at temperatures up to 2550 F.
• Effective life of Temperature in F. coating in hours 2550 25. 2375 More than 50. 2190 More than 170.
• the oxidation rate curve rises steeply during the first few hours but subsequently undergoes a sharp transition to a low rate of oxidation; the oxidation curve thus appears to be parabolic. Elim ination of, or a sharp decrease in, the rapid initial oxidation rate may be accomplished by treating coated columbium base alloy specimens in an inert atmosphere to diffuse the coating prior to exposure in air.
• the last high temperature oxidation resistance is obtained within the range 2150 through 2550 F.
• the surface of the base metal may be prepared for coating in a conventional manner, but preferably it is prepared by degreasing with a conventional organic solvent then etched by dipping in a combined solution of nitric and hydrofluoric acid, and finally it is immersed in the molten salt bath for from two to five minutes to flux it before electrodeposition is commenced.
• the specimen to be plated is wired as a cathode, inserted into a molten salt bath containing the electrolyte and a composition containing the plating metal. Current is then applied to a suitable anode and to the specimen to be plated as the cathode.
• Aluminum may be deposited from a great variety of molten salt baths operated over the temperature range from 300 F. to 1900 F.
• a bath operating Well above the melting point of alumimum is desired, and the baths used in the coating process are preferably operated within a temperature range of from 1350 to 1900 F.
• the molten salt baths are also preferably based on the system NaF-AlF with A1 0 used as the electrolyte. In this NaF-A11 system, two
• l eutectics occur: one at 1625 F. and 23% AlF and the other at 1265" F. and 63% by weight AlF
• the higher melting mixture may be made most conveniently by blending NaF and cryolite (Na AlF and the lower melting mixture by combining AIR and cryolite (Na AlF Bath compositions having greater than 63% by weight A1F have been found impractical to prepare, because the volatility of the mixture of cryolite with aluminum fluoride (A11 increases too rapidly with increase of the aluminum fluoride content above 63%.
• the bath compositions of this invention used to coat columbium, nickel, or cobalt alloys thus comprise cryolite (Na AlF and A1 0 and may optionally include one or more compounds selected from the group consisting of NaF and AlF
• cryolite Na AlF and A1 0
• the range of cryolite may be from to 95% by weight and the range of A1 0 may be from 5 to 25 o by weight.
• the bath comprises to by weight cryolite and 10 to 20% by weight A1 0
• the preferred operating temperature for these baths is from 1600 to 1900 F.
• the bath may comprise from 55 to 65% by Weight of cryolite, from 15 to 35% by weight of NaF and from 5 to 25% by weight of A1 0
• the bath comprises about 60% by Weight of cryolite, 20 to 30% by weight NaF, and 10 to 20% by Weight of A1 0
• the preferred operating temperature for these baths is from l600 to 1800 F.
• the bath may comprise from 50 to 75% by weight of cryolite, and from 15 to 40% by weight of MR, and from 5 to 15% by Weight of A1 0
• the bath comprises 55 to 70% by Weight of cryolite, 20 to 35% by Weight of MB, and about 10% by weight of Al O
• the preferred operating temperature for these baths is from 1350 to 1700 F.
• the bath may also comprise all four compounds in the ranges of from 65 to 75% by Weight of cryolite, 5 to 20% by weight of NaF, and 5 to 20% by weight of All-"' and 5 to 15 by weight of A1 0
• a preferred proportion of compounds for such a bath is 70% by Weight of cryolite, 12% by weight of NaF, 8% by weight of AlF and 10% by weight of A1 0
• any conventional DC. power source may be used, such as a 0 to 20 volt rectifier with a plating circuit consisting of copper lead wires connected directly from the rectifier to the anode and cathode.
• Anodes suitable for use with molten salt baths may be used, preferably, however, the anode comprises a graphite crucible that also serves as a container for the bath.
• Current densities may vary from 0.15 to 3.0 amps/cm and preferably are Within the range 0.15 to 1.5 amps./ cm.
• Plating time may vary from 2 to 90 minutes or more depending upon the thickness of coating desired. Preferably, a plating time of from 5 to 40 minutes is used.
• the specimens being plated Upon completion of electrodeposition, the specimens being plated will be found to be coated with a layer of salt comprising mainly cryolite and NaF. These salts should be removed, and this can be accomplished in a variety of ways.
• a preferred technique is to place the specimen in a molten bath comprising a mixture of sodium chloride and lithium chloride and operated at a temperature of approximately 1200 F. This results in substitution of the fluoride salts with chloride salts, and the chloride salts can be easily removed by ultra-sonic cleanby Weight ing under water or by light brushing.
• Another preferred technique is to immerse the specimens in a solution of chromium oxide in dilute phosphoric acid and subject them to ultrasonic vibration.
• electrodeposition of aluminum onto columbium base alloys is conducted at 1800 F. and a current density of 1 amp/cm. for 10 minutes. Also, it is desirable to subject the columbium base alloys plated with aluminum using the process of this invention to diffusion in air at 1600 to 1300. F. after plating for a period of from one to eight hours. Preferably, the specimens are diffused at 1700 F. for four hours.
• Example I A protective oxidation resistant coating of columbium aluminide (CbAl on a columbium base alloy, as an example of this invention, was prepared by electrodeposition of aluminum on columbium from a molten salt bath having the following composition:
• the bath was operated at a temperature of 1800 F. and electrodeposition occurred at current densities varying between 0.1 and 0.3 amp./cm.
• a graphite crucible was used both as a container for the bath and as the anode.
• a specimen of a columbium base alloy to be coated was made the cathode of the electroplating apparatus. The aluminum was then deposited directly on the columbium base alloy cathode.
• a plating time of thirty (30) minutes at an average current density of 0.15 amp/cm. caused an increase in thickness on the columbium base alloy of approximately 0.0003 in. or 0.3 mil on each surface of the specimen that was plated.
• This increase in thickness of the plated specimen was accompanied by an increase in weight of about 3 mg./cm.
• the aluminum was found to have penetrated into the specimen to a maximum depth of 2 to 4 mils.
• the plated specimens of the columbium base alloy were removed from the molten salt bath, they were found to be coated with a layer of salt comprising mainly Na AlF and NaF. These salts had to be removed before the sample could be exposed to an oxidizing environment at temperatures above 1800 F., or the salt would dissolve the coating at these high temperatures.
• the samples were immersed in a solution of 20 g. of CrO +27 ml. H PO +973 ml. H 0 and subjected to ultrasonic vibration.
• Example 11 Specimens of columbium base alloys coated with aluminum to provide a columbium aluminide (CbAl coating on the specimens were prepared in the same manner as described in Example I, except that the molten salt bath comprised the following composition:
• Example III Percent by weight Na AlF (cryolite) 55 AlF 35 A1 0 (alumina) 10 In this instance the bath was operated at a temperature of 1600" F., but otherwise all conditions remained the same as for Example I.
• the samples of coated columbium base alloys produced according to Example III also yielded the same test results as those obtained for samples prepared as described in Example I.
• Example IV A cobalt base alloy containing by weight 20% chromium, 20% nickel, 4% molybdenum, 4% tungsten, 4% columbium, and the balance cobalt in the form of a wrought ingot divided into approximately one (1) inch square specimens was plated with aluminum in a molten salt bath of the following composition:
• Example IV Percent by weight Na A1F (cryolite) 59 A1123 A1 0 (alumina) 2
• the bath was operated at 1500 F. and a current Example V
• An article of manufacture having good stress-rupture strength at high temperatures and high-temperature oxidation resistance which comprises a core of metal selected from the group consisting of columbium and columbium-base alloys, the articles having a ditfusionally stable, mechanically stress resistant and oxidation resistant surface zone consisting essentially of CbAlg.
• An article of manufacture having good stress-rupture strength at high temperatures and high-temperature oxidation resistance which comprises a core of metal se- 'lected from the group consisting of columbiurn and colurnbium-base alloys, the article having a surface layer consisting essentially of CbA1 and a sublayer consisting essentially of a Cb-Al solid solution, the sublayer being between the surface layer and the core.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Electrochemistry (AREA)
• Electrolytic Production Of Metals (AREA)
• Coating With Molten Metal (AREA)
• Electroplating Methods And Accessories (AREA)

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Citations (12)

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• 1961
  • 1961-11-07 US US150628A patent/US3206289A/en not_active Expired - Lifetime
• 1962
  • 1962-10-29 GB GB40770/62A patent/GB1024613A/en not_active Expired
  • 1962-10-30 DE DEU9349A patent/DE1246348B/de active Pending
  • 1962-10-31 FR FR914137A patent/FR1343084A/fr not_active Expired
  • 1962-11-02 SE SE11783/62A patent/SE303911B/xx unknown

Patent Citations (12)

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