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
  • 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
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/02—Selection of particular materials
  • F04D29/023—Selection of particular materials especially adapted for elastic fluid pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/26—Rotors specially for elastic fluids
  • F04D29/32—Rotors specially for elastic fluids for axial flow pumps
  • F04D29/321—Rotors specially for elastic fluids for axial flow pumps for axial flow compressors
  • F04D29/324—Blades

Definitions

• This invention relates, in general, to coatings for metallic substrates and more particularly to novel two-layered erosion-resistant coatings which may be applied to gas turbine engine compressor blades without an attendant loss in fatigue life.
• Gas turbine engine compressor blades are conventionally fabricated from metallic substrates such as stainless steel or titanium alloys. The blades are subjected to severe erosion when operated in sand and dust environments. Blade erosion reduces compressor efficiency, requiring premature blade replacement.
• erosion resistant coatings such as tungsten and carbon (U.S. 4,147,820), platinum metals (U.S. 3,309,292; U.S. 3,890,456) and boron (U.S. 2,822,302).
• these coatings which have been identified by the art for imparting erosion resistance to substrates such as titanium and stainless steel alloy compressor blades promote sharp drops in fatigue properties of the substrates creating the initiation of cracks and fractures with an attendant reduction in the service life of the substrate. This effect of the fatigue life of the coated substrate is believed due to the fact that the erosion-resistant coatings of the prior art are hard materials which produce residual stress and accompanying strains in the substrate thereby accelerating a reduction in fatigue strength of the substrate.
• first layer which is applied directly to a substrate comprises palladium, platinum or nickel and the second layer, which overlies said first layer, comprises tantalum or chromium boride.
• first layer which is applied directly to a substrate
• second layer which overlies said first layer
• the coefficients of thermal expansion of the whole system, i.e., substrate, first layer and over layer, are matched closely to reduce residual stress and accompanying strains, whereby the fatigue life of the coated substrate is not deleteriously affected. Additional gains in fatigue life retention are achieved by using low coating deposition temperatures.
• Fatigue failure is believed to be the result of the application of fluctuating stresses over a long period of time.
• a major source of stress results from the difference in the coefficient of thermal expansion between the substrate material and the coating material. This difference in the coefficient of thermal expansion results in the coating being stressed by the substrate during thermal coating process cycling.
• the erosion-resistant coatings of the present invention ameliorate the problem of thermal expansion by using coating layers which have closely matched coefficients of thermal expansion so that it approaches the coefficient of thermal expansion of typical metallic alloy substrate materials. This is illustrated in the Table below which contains the coefficient of thermal expansion of several different coating materials and commonly used substrate materials.
• Ni, Pt, Pd, TaB 2 and CrB 2 have coefficients of thermal expansion which are closely matched to each other and also closely approach the coefficient of thermal expansion of a variety of stainless steel and titanium alloy substrates commonly used in gas turbine engine components.
• the coated substrates of the present invention exhibit excellent erosion- resistance with no deleterious reduction in fatigue life and this result is believed to be due to the close matching of the coefficient of thermal expansion between the coating layers and the substrate composition.
• the coatings of the present invention are thus distinguished from erosion resistant coatings of the prior art which exhibit sharp drops in fatigue properties, thus creating the initiation of cracks and fractures.
• Illustrative of this prior art is McCaughna, U.S. Patent No. 2,882,302 which discloses the plating of a refractory metal (e.g., tungsten, molybdenum or tantalum) with boron.
• a platinum interlayer may be placed between the refractory metal and the boride layer to act as a barrier.
• palladium or nickel acts as an interlayer between the substrate material (e.g., stainless steel) and the overlayer (i.e. boron and tantalum or chromium).
• D ils U.S. Patent No. 3,890,456 discloses a coating technique for depositing layers of various materials on turbine blades. At column 3, lines 44-47, Dils discusses deposition of a noble metal, such as platinum, rhodium or palladium.
• the layers comprising the coating of this invention may be of any suitable thickness. Particularly good results are obtained with the palladium, platinum or nickel-containing layer being between about 0.0001 inches to about 0.002 inches and the tantalum or chromium diboride layer being between about 0.001 inches and 0.003 inches. Optimum results are obtained when the palladium or nickel-containing layer is about between 0.0003 and about 0.001 inches and the tantalum or chromium boride overlayer is about 0.002 inches.
• Any suitable coating technique may be used to apply the first layer of the coating to the substrate material.
• Typical methods include electroplating, sputtering, ion-plating, pack coating, and vapor deposition, among others. While any suitable technique may be used, it is preferred to employ an electroplating, ion plating, sputtering or chemical vapor deposition (CV D ) process. Any suitable technique, likewise, may be used to apply the erosion-resistant tantalum or chromium boride layer to the palladium or nickel interlayer, a CVD or sputtering process being preferred.
• the surface of the substrate to be coated is first shot peened to provide compressive stresses therein.
• the shot peened surface is then thoroughly cleaned with a detergent, chlorinated solvent, or acidic or alkaline cleaning reagent to remove any remaining oil or light metal oxides, scale or other contaminants.
• the cleaned substrate is activated to effect final removal of adsorbed oxygen.
• the first layer is applied to the surface of the substrate by such conventional coating techniques as electroless-plating, CVD or sputtering. If electroplating is the coating method chosen, then activation of the substrate surface is conveniently accomplished by anodic or cathodic electrocleaning in an alkaline or acidic cleaning bath by the passage therethrough of the required electrical current. Plating is then accomplished using conventional plating baths such as a Watts nickel sulfate-chloride bath or a palladium diamino nitrite bath.
• CVD is elected for the coating application, then activation is accomplished by the passage of a hydrogen gas over the substrate surface. CVD is then accomplished using the volatilizable halide salt of the metal to be deposited and reacting these gases with hydrogen or other games at the appropriate temperature, e.g. 500° to 1850Qr to effect deposition of the metallic layer.
• bias sputtering can be used to activate the substrate.
• Deposition of the first metallic interlayer is accomplished with sputtering or ion-vapor plating using high purity targets of the desired metal coating material.
• Coating application of the second layer of tantalum or chromium boride over the first metallic layer preferably is accomplished at a temperature not exceeding 1900°F by CVD, sputtering, pack or other conventional coating processes.
• stress in the coating system is a function of the difference in the coefficients of thermal expansion between coating ( ⁇ ) and the difference in temperature between the substrate (room temperature) and the coating deposition temperature (A T).
• stress in the coating can be reduced by reducing the ⁇ ⁇ by using a coating material having a coefficient of expansion closely corresponding to that of the substrate and reducing the AT by using a lower temperature at which the coating is deposited.
• Tantalum or chromium boride coatings are conventionally applied at 1000 - 1900°F.
• the tantalum or chromium boride erosion-resistant coating is applied at a lower temperature i.e. a temperature between about 800°F and about 1400°F whereby improved fatigue life of the substrate is achieved.
• a gaseous mixture of a tantalum halide, e.g. TaCl 5 , a boron halide, e.g. BC1 3 , hydrogen gas and an inert gaseous diluent such as argon is flowed into a reaction chamber containing the first layer coated substrate heated to a temperature of about 1800 - 2000°F and the gaseous mixture is allowed to react and deposit on the heated substrate.
• the surfaces of individual C450 stainless steel substrates were first thoroughly cleaned free of all dirt, grease and other objectionable foreign matter followed by conditioning by means of shot peening.
• the cleaned surface of the substrate was then electroplated with a 0.5 - 1.5 mil coating of nickel using a Watts nickel sulfanate plating bath.
• the reaction chamber was maintained at 200 torr.
• the deposit was made at a rate of 0.0003 to O.OOlin/hr to the required coating thickness.
• a second coating consisting of a 0.5 to 1.5 mil thick Cr-B alloy was applied to the nickel plated substrate surface using a packing technique.
• the nickel plated substrate was successively put in a Cr powder pack and heated to about 1900°F followed by a boron powder pack at about 1400°F.
• the coated substrate specimens were tested for erosion- resistance using S.S. White erosion testing equipment. When using this equipment, the coated specimen is subjected to a pressurized blast of sand, which is impinged on the specimen from a 0.5 inch diameter nozzle spaced from the specimen.
• the conditions under which the erosion testing was performed were as follows:
• the specimens were blasted with sand at 30° and 90° sand impingement angles for 5 minutes.
• the erosive wear was measured as the volume of coating material lost per minute of sand impingement.
• the results of the erosive wear tests are recorded in Table I below.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Chemical Vapour Deposition (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Physical Vapour Deposition (AREA)
• Laminated Bodies (AREA)
• Electroplating Methods And Accessories (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)

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Cited By (10)

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Citations (6)

• 1985
  • 1985-10-03 EP EP85307106A patent/EP0188057A1/de not_active Withdrawn
  • 1985-10-24 JP JP60236536A patent/JPS61127872A/ja active Pending
  • 1985-11-07 BR BR8505579A patent/BR8505579A/pt unknown

Patent Citations (6)

Non-Patent Citations (1)

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