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
  • C23C10/60—After-treatment
• • 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
  • C23C10/34—Embedding in a powder mixture, i.e. pack cementation
  • C23C10/36—Embedding in a powder mixture, i.e. pack cementation only one element being diffused
  • C23C10/48—Aluminising
• • 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
  • F01D5/005—Repairing methods or devices
• • 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
  • F01D5/288—Protective coatings for blades
• • 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
  • 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
  • Y10T428/1275—Next to Group VIII or IB metal-base component
  • Y10T428/12757—Fe
• • 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
  • Y10T428/12937—Co- or Ni-base component next to Fe-base component

Definitions

• the present practice with salvageable parts following a coating deterioration or breakdown is to: remove all of the original coating; rework the part as necessary; and then recoat utilizing one of the standard techniques such as slurry-diffusion.
• These current salvage operations are not without drawback however.
• Most aluminide coatings are produced by or involve a diffusion mechanism whereby the coating is formed by reaction of the coating material with the substrate elements. Therefore, the formation of the usual 3 mil coating involves consumption of at least 2 mils of the substrate alloy.
• the removal of the old coating even from areas where a coating failure has not occurred, necessarily results in the loss of some substrate material and a reduction in the thickness of the part.
• a particularly preferred process comprises the steps of: removing the part to be processed from its oxidizing environment prior to the onset of any substantial oxidative attack on the superalloy substrate elements; superficially cleaning the oxide layer therefrom; recoating the part in a pack aluminizing process utliizing a pack mix of sulficiently high aluminum activity at the coating temperature to preferentially form the nickel aluminides having an aluminum content equal to or greater than that corresponding to Ni Al and subsequently heat treating the coated components to cause further diffusion thereby converting at least a portion of the aluminides to those having an aluminum content less than that of the Ni Al phase.
• Diffused aluminum coatings for the protection of various metals from high temperature oxidation have been in use for over fifty years.
• Two major processes are generally used for the application of such coatings to nickelbase gas turbine hardware. The first involves covering the surface of the metal to be protected with a slurry of aluminum in a liquid vehicle, followed by drying and firing at an elevated temperature.
• the second process comprises the steps of embedding the article in a dry powder mix of aluminum, an inert filler such as powdered alumina, and an activator such as ammonium chloride, and heating the pack to some elevated temperature for a period of time suflicient to form a coating of the desired thickness.
• pack aluminizing This latter process is typically referred to as pack aluminizing or pack cementation aluminizing. While various other elements may be added to the pack mix either as rate-controllers or to impart some additional specific property to the coating, nevertheless all such coatings consist primarily of intermetallic compounds, such as nickel aluminides derived from the aluminum in the pack and elements from the substrate and from which the basic oxidation resistance is derived.
• the thickness, composition and structure of a pack cementation coating are determined by the follow; ing controllable variables: (a) pack mix composition; (b) processing temperatures; (c) time at temperature; and (d), any subsequent heat treatment of the coated component.
• pack cementation processes have been performed in large retorts necessitating the use of long times at temperature to obtain thermal equilibrium
• a pack mix of low time-sensitivity is generally employed, such a mix being characterized by a low aluminum activity.
• the coating comprising the Ni Al phase generated-in a pack of high aluminum activity cannot be practically employed in many cases because of its brittleness. Therefore, the coated alloy is normally subsequently heat treated to cause further diffusion to occur which promotes the formation of the more ductile NiAl phase. Because the driving force of high aluminum activity is no longer present, nickel diffusion from the substrate now occurs in combination with diffusion of the aluminum from the Ni Al phase to form a layer of NiAl beneath the original Ni Al coating.
• the aluminide coatings derive their protectivity from the intermetallic compounds of aluminum which in turn are protected by a thin layer of aluminum oxide formed by high temperature oxidation of the coating. Gradually, however, the oxide is lost by a process of erosive spalling, but a reoxidation occurs and the protective function is reestablished. Accordingly, the substrate remains protected as long as sufiicient aluminum is retained in the coating to provide for the preferential oxidation to aluminum oxide, and a coating failure or rapid degradation occurs when one or more of the substrate metals commences to oxidize.
• the protective function of the coating is, hence, a direct function of its aluminum content.
• a major factor contributing to the success of the present invention involves recognition of the fact that aluminide coatings may be formed on the superalloys by an inward diffusion of aluminum provided the aluminum activity of the pack mix is sufiiciently high to form equilibrium aluminide phases of high aluminum content as previously described.
• the aluminum activity of the pack mix is sufiiciently high to form equilibrium aluminide phases of high aluminum content as previously described.
• there is a parabolic relationship between coating thickness and time Thus, a part with no coating in an eroded zone and a retained coating of 3 mils in a cooler zone will, during such a recoating process, form a new coating of Ni Al or phases of higher aluminum content, of the required thickness in all zones but in so doing will absorb considerably less aluminum in the undegraded zones than in the degraded or eroded zone.
• the aluminum content in the undegraded zones the aluminum content, before recoating amounts to about 30%, corresponding to the ,3 (NiAl) phase, whereas in the degraded zone the aluminum content may be as low as 5%. That is to say, that in being transformed to the Ni A1 phase, which contains 40% aluminum, the undegraded zones absorb the equivalent of about aluminum while the degraded zone absorbs as much as the equivalent of 35% aluminum.
• the coating on the previously undegraded zones exhibits minimal new growth because these zones have absorbed relatively small amounts of aluminum during the recoating process, whereas a completely new coating has formed on the previously degraded zone because this zone has absorbed a relatively large amount of aluminum.
• the net result is that new coating of the required thickness has been formed on the previously eroded area of the part with insignificant increase in coating thickness in the cooler, undegraded zones thereby eliminating the necessity of performing the expensive and otherwise undesirable stripping operation of the current processes wherein the old coating is totally removed.
• the particular pack aluminizing process preferred in the present overhaul and repair process is one selected to provide for the incorporation of the desirable substrate alloying elements in the coating while minimizing the formation of deleterious phases.
• the article to be coated is embedded in a pack mix containing 5-20 Weight percent aluminum, 0.5-3 percent ammonium chloride, balance alumina.
• the pack is then heated to a relatively low temperature 1200-1600 F. in an inert atmosphere and coating growth is allowed to proceed for 1-4 hours.
• a minimum coating thickness of 0.003 inch is effected.
• the recoated article is subjected to a ductilizing heat treatment in the temperature range of l900-2200 F. usually matched to the strengthening heattreatments specified for the superalloy substrate.
• pack composition and coating parameters employed in a given case are, of course, dependent upon the particular component being processed and the particular end result desired. In each case, however, the pack of the present invention will be characterized by a high aluminum activity, and will tend to yield coatings high in aluminum content for a given time at temperature. Those skilled in the art will readily recognize the variety of alternative techniques and compositions adapted to provide the requisite high aluminum activity.
• nickel-base superalloys will be understood to have reference to those multiphase alloys of the 'y'y' type which are characterized by high strengths at temperatures of 1500" F. and higher.
• Several represeriative alloys of this type are listed in the following ta e.
• an erosion bar formed of the B-1900 alloy was coated by slurry techniques to a thickness of about 3 mils and run in an oxidation-erosion environment at 2100 F. for hours.
• the bar was removed from test at the first sign of coating penetration and substrate oxidation as evidenced by the appearance of the blue-green, nickel-rich oxide.
• the specimen was sectioned through the eroded zone and one half was examined metallographically as a control specimen while the other half was recoated in a pack of high aluminum activity for 1 /2 hours at 1400 F., followed by a heat treatment of 4 hours at 2000 F. This specimen was then examined metallographically to determine coating uniformity, thickness and structure.
• control specimen revealed pitting through the coating at the eroded zone which resulted in the formation of the blue-green oxide.
• the uneroded portion of the coating in the hot zone of bar contained no ,0 (NiAl) aluminide and a thin layer of carbides was observed to be in the process of resolutioning in the 'y (nickel solid solution)-'y (Ni Al) phases of the coating layer.
• the recoating process uniformly covered the defect area and the remaining 'y'y' phase layer with but a slight depression in the coating surface at the eroded zone, but otherwise little difference was noted in the coating structure or thickness after recoating.
• the cooler zones of specimen before recoating showed some effects of aluminum depletion with the presence of the 7' phase of the aluminide at the grain boundaries of the ,9 (NiAl) aluminide.
• the recoated structure after diffusion heat treatment was all aluminide with a slightly different carbide morphology than in the original specimen, but no unusual or detrimental phases were present. As indicated by the absence of a hyper-stoichiometric aluminum rich ,6 phase layer, the recoated structure was not excessive high in aluminum content.
• a second B-1900 alloy erosion bar was coated in a process similar to that used with the first specimen and was run in an oxidation-erosion test at 2100 F. Although the specimen failed at about 50 hours by pitting through the coating to the substrate, the test was run to 100 hours. As a result, some excessive substrate damage in hot zone on the trailing surface was noted because of the excessive time in test. However, the specimen was lightly cleaned with a vapor blast and recoated by a pack aluminizing process of high aluminum activity. This recoated specimen was then retested for an additional 60 hours at 2100 F. until coating failure again occurred.
• the specimen was again cleaned and recoated, this time to produce a coating of 3 /2 mils thickness.
• a third oxidation erosion cycle at 2100 F. was run and coating failure did not occur for an additional 80 hours.
• aluminide-coated alloy systems can be recoated several times by the disclosed pack cementation process without the necessity of prior coating stripping.
• the principal considerations are the removal of the specimen from its oxidizing environment prior to coating breakthrough and significant substrate attack, and the use of a pack aluminizing process utilizing a pack mix of high aluminum activity.
• An overhaul and repair procedure for aluminidecoated gas turbine engine components formed from the nickel-base superalloys which comprises:
• An overhaul and repair procedure for aluminide coated gas turbine engine components formed from the nickel-base superalloys which comprises:

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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Cited By (41)

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Citations (7)

• 1968
  • 1968-10-25 US US770853A patent/US3544348A/en not_active Expired - Lifetime
• 1969
  • 1969-10-17 GB GB1258833D patent/GB1258833A/en not_active Expired
  • 1969-10-21 CH CH1569069A patent/CH540346A/de not_active IP Right Cessation
  • 1969-10-21 NL NL696915857A patent/NL153276B/xx not_active IP Right Cessation
  • 1969-10-21 FR FR6936133A patent/FR2021543A1/fr active Pending
  • 1969-10-23 SE SE14558/69A patent/SE344767B/xx unknown
  • 1969-10-24 BE BE740776D patent/BE740776A/xx not_active IP Right Cessation
  • 1969-10-25 ES ES372871A patent/ES372871A1/es not_active Expired

Patent Citations (7)

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