Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C29/00—Joining metals with the aid of glass
• • 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
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/02—Pretreatment of the material to be coated
  • C23C14/024—Deposition of sublayers, e.g. to promote adhesion of the coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/14—Layered products comprising a layer of metal next to a fibrous or filamentary layer
• • 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
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/02—Pretreatment of the material to be coated
  • C23C14/024—Deposition of sublayers, e.g. to promote adhesion of the coating
  • C23C14/025—Metallic sublayers
• • 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
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/02—Pretreatment of the material to be coated
  • C23C14/028—Physical treatment to alter the texture of the substrate surface, e.g. grinding, polishing
• • 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
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/08—Oxides
  • C23C14/083—Oxides of refractory metals or yttrium
• • 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
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
  • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
  • F01D5/12—Blades
  • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
  • F01D5/284—Selection of ceramic materials
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
  • F05D2250/00—Geometry
  • F05D2250/60—Structure; Surface texture
  • F05D2250/62—Structure; Surface texture smooth or fine
  • F05D2250/621—Structure; Surface texture smooth or fine polished
• • 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
  • Y10S428/923—Physical dimension
  • Y10S428/924—Composite
  • Y10S428/926—Thickness of individual layer specified
• • 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
  • Y10T428/12472—Microscopic interfacial wave or roughness
• • 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.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12542—More than one such component
  • Y10T428/12549—Adjacent to each other
• • 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.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12583—Component contains compound of adjacent metal
  • Y10T428/1259—Oxide
• • 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.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12611—Oxide-containing 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.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12611—Oxide-containing component
  • Y10T428/12618—Plural oxides
• • 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
  • Y10T428/12861—Group VIII or IB metal-base component
  • Y10T428/12931—Co-, Fe-, or Ni-base components, alternative to each other

Definitions

• This invention is concerned with the field of ceramic coatings on metal substrates.
• the coating and method described in the present application are useful for the application of protective ceramic thermal barrier coatings to gas turbine engine components. Through the use of the present coating, substantial increases in turbine operating temperatures may be possible.
• the superalloy art has long sought to combine the properties of ceramics with the properties of metals.
• many attempts have been made to provide protective ceramic coatings to metal articles which find application at elevated temperatures so as to combine the thermal properties of ceramics with the ductility of metals.
• the primary problem which has not been successfully solved heretofore is that the substantial difference in the coefficient of thermal expansion of metals and ceramics invariably leads to failure of ceramic coatings under conditions of severe thermal cycling.
• One approach which has been employed in an effort to overcome this problem is that of grading the coating from essentially all metal at the metal surface to all ceramic at the outer surface of the coating. In this way it is believed that the coefficient of thermal expansion will change gradually through the coating thickness and the stress resulting from thermal cycling will not be sufficient to cause damage to the coating.
• the article to be coated is held over a molten pool of material of appropriate composition which evaporates, and the vapor condenses on and coats the article.
• This process is used in a variety of applications including the application of metallic coatings to gas turbine engine parts.
• the application to gas turbine engine parts is described in the "Journal of Vacuum Science of Technology," Vol. 11, No. 4, July/August 1974, pgs. 641 through 646 in an article by Boone et al.
• This article also describes the types of defects which can occur in vapor deposited coatings.
• the most significant defect described is termed a "columnar defect" in which the coating forms as columnar grains which are poorly bonded to each other.
• Such a structure is described as being detrimental because the exposed columnar surface greatly increased the surface exposed to the environment and because the gaps between the columns may adversely affect mechanical properties.
• the article indicates that practical uses of vapor deposited coatings requires that the columnar type of structure be minimized.
• Ceramic coatings have also been applied by a plasma spray process.
• the most successful plasma spray coatings to date have been applied to articles which have been previously coated with a metallic bond coat.
• the bond coats investigated have been the MCrAlY class of materials. In this situation, the bond coat appears to function by acting as a soft, rough layer in which the plasma spray particles are embedded forming a mechanical bond. This is described in U.S. Patent No. 4,055,705 and pending application U.S. Serial No.
• the present invention includes a composite coating system which protects metallic articles from environmental damage especially under conditions of high temperature.
• the novel application method also forms a part of the present invention.
• the article to be protected is supplied with a uniform adherent MCrAlY layer. On this MCrAlY layer, there is applied a ceramic coating having a particular novel columnar microstructure.
• the ceramic coating is comprised of many individual columnar segments which are firmly bonded to the article to be protected, but not to each other. By providing gaps between the columnar segments, the metallic substrate may expand without causing damaging stresses in the ceramic.
• the ceramic coating is applied by a vapor deposition process.
• a continuous alumina layer is present between the MCrAlY component and the columnar ceramic coating. This alumina layer plays a crucial role in bonding the ceramic coating to the MCrAlY layer.
• a significant feature of the present invention is that the interface between the MCrAlY layer and the alumina layer is polished so as to have a low surface roughness and this polished interface is shown to provide substantial improvements in coating performance.
• Figure 1 is a cross sectional drawing showing the invention coating
• Figure 2 is a photomicrograph which shows an experimental coating.
• the thermal barrier coating system of the present invention is a composite coating which includes three interrelated elements which perform different functions.
• the performance of the coating system is superior to that of any other known high temperature coating when evaluated in gas turbine engine environments.
• the invention coating system provides oxidation and corrosion protection equal to that of best current coatings in combination with significant thermal barrier or insulating capabilities.
• the major use of the invention coating is in the protection of superalloy articles.
• Superalloys are nickel, cobalt, and iron base alloys which have exceptional properties at elevated temperatures. Typical compositions are listed in Table 1.
• thermal barrier coating has a major use in gas turbine engines and was developed with this application in mind. However, there are many other potential applications for which this coating or some variation thereof would be well-suited.
• the coating consists of a metallic layer of a MCrAlY alloy, having a polished surface, a continuous adherent alumina layer (formed in situ) on the metallic layer and a discontinuous pure ceramic layer of a particular columnar morphology on the alumina layer.
• the metallic layer is comprised of a MCrAlY alloy.
• MCrAlY alloys have a broad composition of 10 to 30% chromium, 5 to 15% aluminum, .01 to 1% yttrium (or hafnium, lanthanum, cerium and scandium) and a balance selected from the group consisting of iron, cobalt, nickel and mixtures thereof. Minor amounts of other elements may also be present.
• Such alloys are known in the prior art for use alone as a protective coating and are described in various U. S. patents including 3,542,530; 3,676,085; 3,754,903 and 3,928,026 which are incorporated herein by reference.
• This invention also contemplates the use of various interlayers between the superalloy substrate and the MCrAlY layer.
• various interlayers between the superalloy substrate and the MCrAlY layer.
• U. S. Patent No. 4,005,989 it is known from U. S. Patent No. 4,005,989 that the use of an aluminide layer (produced by aluminizing) between a substrate and a MCrAlY layer can provide improved coating durability.
• Other materials such as platinum have also been proposed for interlayer use.
• interlayers will be used only where necessary and only where they do not adversely affect the bond between the substrate and the MCrAlY.
• this MCrAlY layer be applied by vapor deposition.
• Such a deposition process in combination with peening and heat treating provides a dense adherent layer of relatively uniform thickness which is basically free from defects. A thickness of 1 - 10 mils is suitable.
• a key feature of the invention is that the MCrAlY surface is treated, by polishing or the like, to have a very smooth finish.
• Other deposition processes may be employed for producing the MCrAlY layer including sputtering and plasma spraying, possibly with associated post coating treatments, so long as they produce a uniform thickness high integrity coating of the desired composition which has or can be treated to have a polished surface.
• the alumina layer on the MCrAlY layer is produced by oxidation of the MCrAlY layer.
• This oxide layer is relatively thin (.01 - .1 mil), uniform and adherent.
• the oxide layer will also be smooth.
• Adherence of the oxide layer is greatly improved in MCrAlY alloys compared to that of similar alloys which do not contain yttrium or similar active elements. This improved adherence results from the formation of yttrium oxides which extend into the MCrAlY and are bonded to the alumina surface layer thus anchoring the surface layer and minimizing spalling.
• the adherence of the alumina layer is essential to the adherence of the columnar ceramic layer and the presence of yttrium or equivalent oxygen active elements such as lanthanum, cerium, hafnium, and scandium or mixtures of oxide particles thereof, in the metallic coating is important to the proper functioning of the invention coating system.
• the final component of the thermal barrier coating is a unique columnar grained ceramic surface coating which is tightly bonded to the alumina layer.
• the columnar grains are oriented substantially perpendicular to the surface of the substrate with free surfaces between the individual columns extending down to the aluminum oxide layer.
• the ceramic surface layer is a pure ceramic as distinguished from some prior art which has suggested the use of a graded layer incorporating substantial amounts of metal in the coating.
• the columnar nature of the surface layer circumvents the difference in the coefficients of thermal expansion between the substrate and the coating which is believed responsible for failure in prior art ceramic thermal barrier coatings.
• the substrate expands at a greater rate than the ceramic surface coating and the columnar boundaries between the individual ceramic columns open to accommodate mismatch strains. This reduces the stress at the interface between the substrate and the columnar ceramic to a level below that which will produce a fracture of a columnar surface layer.
• the columns have dimensions on the order of .1 mil in cross section.
• the columnar surface layer may be one of many ceramic compositions. Most of the experimental work to date has been performed with a ceramic composed of cubic zirconia stabilized by the addition of either 20 or 35% yttria.
• the columnar ceramic material should not form low melting compounds (e.g. eutectics) when in contact with alumina at elevated temperatures.
• the melting point (and sublimation point) of the columnar ceramic material should be substantially greater than the service temperature.
• the columnar ceramic material should be stable in the intended environment; i.e., the material should not oxidize or otherwise react with the environment to any significant extent (some ceramics such as Si 3 N 4 will oxidize at elevated temperatures but the oxidation is self limiting since the oxidize produced (SiO 2 ) protects against further oxidation) .
• the following ceramics are believed to have utility as the columnar coating material of the present invention: zirconia
• the columnar ceramic material should have some degree of solid solubility in alumina and should be stable in the intended use environment. We believe that the skilled artisan will have no difficulty in selecting an appropriate ceramic based on the previous guidelines.
• the function of the MCrAlY layer is to adhere strongly to the substrate and to produce a strong adherent continuous oxide surface layer.
• the alumina surface layer so-produced protects the underlying MCrAlY layer and substrate against oxidation and hot corrosion and provides a firm foundation for the columnar grain ceramic surface layer.
• the columnar grain ceramic surface layer reduces the temperature of the underlying substrate and coating layers. Because of the nature of many ceramics and the existence of open boundaries between the columns, the ceramic surface layer is relatively transparent to oxygen and does not play a major role in reducing the oxidation of the underlying layers except to the extent that the reduction in the temperature of the underlying layers reduces the rate of oxidation.
• the alumina layer on the MCrAlY is the major barrier to oxidation. Preliminary indications are that a 5 mil thick ZrO 2 base coating can reduce substrate temperatures by from 50 to 200°F under conditions typical of those found in current gas turbine engines with cooled blades.
• the ceramic surface layer may play a role in reducing hot corrosion by acting as a barrier between the underlying MCrAlY layer and the various liquid and solid combustion products which have been observed to cause hot corrosion.
• the ceramic layer is also believed to be beneficial in protecting against hot corrosion by acting to increase the rate of evaporation of surface deposits in certain circumstances as a result of the high surface temperature of the ceramic which results from its thermal insulation capabilities.
• the provision of a polished MCrAlY surface dramatically improves the adherence of the columnar ceramic coating.
• Figure 1 shows a cross sectional view of a coating according to the present invention.
• the substrate material 1 is coated with an MCrAlY layer 2.
• This MCrAlY layer has a polished outer surface 3.
• On this surface 3 there is formed an adherent alumina layer 4.
• a columnar ceramic layer 5 adheres to the alumina layer 4.
• the initial step in the coating application sequence is the preparation of the surface to be coated.
• the surface must be clean of all dirt, grease, oxides and the like.
• the cleaning method we have used is vapor honing which employs an aqueous abrasive slurry which is propelled against the surface to be cleaned with the sufficient force to remove all extraneous material from the surface.
• the surface is preferably vapor degreased. While this is a satisfactory cleaning process, numerous alternative processes are possible so long as they produce a satisfactory cleaned surface.
• the MCrAlY layer is applied. It is preferred that this MCrAlY layer be applied by vapor deposition.
• the deposition process is performed by holding the surface to be coated over a pool of molten MCrAlY material in a vacuum chamber.
• the heat source used to keep the MCrAlY molten is usually an electron beam.
• the surface to be coated is preferably maintained at a temperature of about 1600 - 1800°F during the MCrAlY deposition process. It is preferred that the MCrAlY layer have a thickness of about 1 to about 10 mils. MCrAlY thicknesses below about 1 mil do not provide adequate protection to the surface (especially if the MCrAlY is subsequently polished) and thicknesses in excess of about 10 mils are prone to rippling during repeated thermal cycling.
• the coatings are dry glass bead peened to densify any voids and to improve the coating structure. Such peening is preferred, but has not been found essential, in the present invention process.
• the coating is then preferably heat treated at 1975 ⁇ F in hydrogen, however, neither the time or temperature is particularly critical.
• dramatic improvements in coating performance are obtained by polishing the MCrAlY surface.
• Such a polishing step is an important part of the invention. The exact method employed does not appear to be significant.
• Other polishing techniques such as purely chemical methods may also be applicable.
• the surface roughness of the subsequently developed aluminum layer is also reduced.
• This improved alumina surface finish improves the perfection of the initial portion of the subsequently deposited columnar ceramic.
• the initial portion of the columnar ceramic consists of many smallcolumnar grains which appear to grow in a competitive fashion withsome more favorably oriented grains dominating less favorably oriented grains. Eventually, the more favorably oriented grains prevail so that the number of grains at the free surface is substantially less than the number of initially nucleated grains.
• polishing the MCrAlY the perfection of the competitive growth is increased and its perfection increased. Failure of the coating occurs in the columnar layer near the alumina interface.
• the columnar ceramic displays greatly improved adhesion to the alumina when the alumina has a smooth surface.
• the end result must be an alumina layer on a polished MCrAlY surface. Because the alumina faithfully follows the underlying surface the surface finish of the alumina will be essentially the same as the MCrAlY surface finish on which it is developed.
• the exact processing sequence employed does not appear to be critical. For example, if the peening step is omitted, the parts may be polished immediately after MCrAlYdeposition and then heat treated. Even if peening is employed, the parts may be polished immediately after peening and the post peening heat treatment may be combined with the alumina forming heat treatment. Following the application of the MCrAlY layer and the development of the oxide layer, the columnar grained ceramic surface layer is applied by a vapor deposition process.
• the ceramic to be deposited is melted and maintained as a molten pool or evaporation source.
• the substrate to be coated is positioned over the evaporation source and is manipulated to produce a uniform coating thickness and to enhance the production of a columnar structure.
• the ceramic coating thickness may range from abcut 1 to about 50 mils.
• the as deposited ceramic may be oxygen deficient.
• a heat treatment in air maybe used to achieve stoichiometry.
• the coating of the invention is novel in the sense that the prior art has, in general, gone to some lengths to avoid the production of a columnar structure which has been regarded as a coating defect. This invention utilizes what has heretofore been regarded as a coating defect to provide improved coating performance.
• Example 1 A nickel base superalloy substrate formed of alloy MAR-M-200 (nominal composition shown in Table 1) was provided with a NiCoCrAlY coating having a nominal composition of 18% chromium, 23% cobalt, 12.5% aluminum, .3% yttrium, balance nickel.
• a plasma spray process was used to deposit the NiCoCrAlY.
• the surface roughness of the as deposited plasma spray NiCoCrAlY was 280 - 350 microinches RMS.
• a similar plasma spray process was used to deposit a yttria stabilized zirconia layer 5 mils thick.
• the details of the ceramic deposition process and resultant layer are also within the teachings of allowed U. S. application Serial No. 811,807.
• This plasma sprayed thermal barrier system is a state-of-the-art system.
• a second set of samples was prepared according to the teachings of ⁇ . S. application Serial No.109,956 by Strangman filed on even date herewith. This preparation sequence is similar to that described in the present application except that the MCrAlY is not polished prior to the development of the alumina layer and the deposition of the columnar ceramic layer.
• a superalloy substrate of Mar-M-200 was cleaned and given a 5 mil coating of NiCoCrAlY by vapor deposition. The vapor deposition was performed in vacuum chamber and the substrate was maintained at a temperature of 1500°F during the deposition process.
• the NiCoCrAlY was glass bead peened and heat treated (4 hours at 1975°F). After peening the surface roughness was 35-50 microinches RMS.
• the second set of samples was mechanically polished with 600 grit silicon carbide paper to reduce the surface roughness to a value of 6 - 14 microinch RMS.
• the polished NiCoCrAlY samples were heat treated to produce an alumina layer (1975°F/4 hrs./H 2 ) and a 5 mil thick coating of yttria stabilized zirconia was applied by vapor deposition under the same conditions as described in Example 1.
• the ceramic coating thus applied had a columnar structure which was usually indistinguishable from that shown in Fig. 2.
• Both sets of samples were processed in the same fashion except for the inclusion of the polishing step in the processing of the second set of samples.
• the second set of samples represents the present invention.
• the plasma sprayed coating in Example 1 is a state-of- the-art thermal barrier coating.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Metallurgy (AREA)
• Ceramic Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Coating By Spraying Or Casting (AREA)
• Physical Vapour Deposition (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=22330483

Family Applications (1)

Country Status (13)

Cited By (14)

Families Citing this family (111)

Citations (8)

Family Cites Families (25)

• 1980
  • 1980-01-07 US US06/109,955 patent/US4321310A/en not_active Expired - Lifetime
  • 1980-12-17 CA CA000367035A patent/CA1167328A/en not_active Expired
• 1981
  • 1981-01-06 BE BE0/203410A patent/BE886974A/fr not_active IP Right Cessation
  • 1981-01-07 DE DE8181900392T patent/DE3162618D1/de not_active Expired
  • 1981-01-07 JP JP56500661A patent/JPH0118994B2/ja not_active Expired
  • 1981-01-07 IL IL61877A patent/IL61877A/xx not_active IP Right Cessation
  • 1981-01-07 IT IT19031/81A patent/IT1134958B/it active
  • 1981-01-07 BR BR8105749A patent/BR8105749A/pt not_active IP Right Cessation
  • 1981-01-07 AU AU67732/81A patent/AU543682B2/en not_active Expired
  • 1981-01-07 WO PCT/US1981/000022 patent/WO1981001983A1/en active IP Right Grant
  • 1981-01-07 KR KR1019810000023A patent/KR840001682B1/ko active
  • 1981-01-07 EP EP81900392A patent/EP0044329B1/en not_active Expired
  • 1981-09-04 NO NO81812999A patent/NO156747C/no unknown

Patent Citations (8)

Non-Patent Citations (4)

Also Published As

Similar Documents

Legal Events