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

Definitions

• This invention relates, in general, to coatings for steel and titanium substrates and more particularly to novel two-layered erosion-resistant coatings which may be applied to steel and titanium gas turbine engine compressor blades without an attendant loss in fatigue life.
• Gas turbine engine compressor blades are conventionally fabricated from 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.
• an erosion-resistant coating system comprising two successively applied layers of different respective materials.
• the second-applied coating layer is formed of a tungsten-carbon alloy erosion-resistant material.
• the first-applied layer or interlayer which is applied directly to the titanium or steel substrate, is formed of a ductile material, such as platinum, palladium or nickel which is capable of preventing diffusion of material from the second-applied layer into or completely through the first applied layer and thus into the substrate.
• the substrate is thereby protected from degradation of material or engineering properties. Residual stress and accompanying tensile strains in the coating system are minimized by applying the second layer on the first layer at a relatively low temperature, i.e. about 500° F to about 1400°F which allows for a fine grain and/or a columnar grain structured coating.
• an erosion resistant tungsten-carbon alloy coated titanium or steel alloy substrate in which the deleterious effect on the fatigue life of the substrate previously encountered with such erosion resistant coatings is substantially eliminated.
• the ductile first layer applied to the substrate acts as a barrier to the diffusion of embrittling components of the second tungsten-carbon alloy layer onto the substrate layer as well as acting as a crack arrestor, which by the retardation of the crack propagation rate results in improved fatigue life performance by the substrate.
• stress in the coating can be reduced by either reducing the ⁇ by using a coating material having a coefficient of expansion closely corresponding to that of the substrate or reducing ⁇ T by using a lower temperature at which the coating is deposited.
• Tungsten-carbon alloy erosion-resistant coatings are conventionally applied at 1800°-2000°F.
• the tungsten-carbon alloy erosion-resistant coating is applied at a temperature between about 500°F and about 1400°F whereby improved fatigue life of the substrate is achieved.
• Any suitable substrate material may be used with the two-layered coatings of the present invention.
• Typical substrate materials include steel alloys, titanium alloys, nickel base and cobalt base super-alloys, dispersion-strengthened alloys, composites, single crystal and directional eutectics. While any suitable substrate material may be used, particularly good results are obtained when stainless steel or titanium alloys are used with the novel two-layer coatings disclosed herein.
• the first layer of the coating of this invention contains palladium, platinum or nickel. While any suitable palladium, platinum or nickel-containing metal may be used, nickel or palladium is preferred, especially when stainless steel is the substrate being coated, and platinum or nickel is preferred when a titanium alloy is used as the substrate material being coated. This palladium, platinum or nickel-containing layer as already discussed, acts as a diffusion barrier and protects the substrate during further coating with the hard tungsten-carbon alloy overlayer.
• 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, electrocladding, pack coating, and chemical vapor deposition, among others. While any suitable technique may be used, it is preferred to employ an electroplating, sputtering, chemical vapor deposition, or ion-plating process. Any suitable technique, likewise, may be used to apply the erosion-resistant tungsten-carbon layer to the palladium, platinum or nickel interlayer. Preferred methods of achieving this low temperature deposition include chemical vapor deposition/controlled nucleation thermochemical deposition, sputtering, physical vapor deposition and electroplating processes.
• 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 reagents 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 electroplating, chemical vapor deposition (C V D), sputtering or ion plating. 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 platinum/palladium amino nitrite/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 gases at the appropriate temperature, e.g. below 1400° F 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 targents of the metals chosen to form the interlayer.
• Coating application of the second layer of tungsten-carbon alloy over the first metallic layer as already discussed is accomplished at a temperature not exceeding 1400°F by CVD, sputtering or other conventional coating processes.
• the substrate was preheated to 1000°F for 30 - 60 minutes before deposition was initiated and this temperature was maintained throughout the coating operation. Deposition time was controlled to obtain a coating thickness of about 1-3 mils.
• the hardness of the tungsten-carbon alloy coating was 2050 kg/mm2.
• 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 at selected impingement angles from a 1/2 inch diameter nozzle spaced from the specimen.
• the conditions under which the erosion testing using sand impingement were performed are as follows:
• powder chamber is vibrated 60 times per second to produce desired powder flow rate.
• the specimens were blasted with sand at 30° and 90° sand impingement angles for 5 minutes.
• the erosive wear of the specimen 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.
• Fatigue bend plate (modified Krause) test specimens were coated in accordance with the Example were then subjected to fatigue testing in a bend plate testing machine by clamping both ends of the specimen.
• An uncoated C 450 stainless steel substrate was used as a control for baseline determination.
• the stress level was varied from 55 to 60 ksi. Failure was indicated by breakage of the test specimen.
• First stage compressor blades fabricated from AM 350 stainless steel were coated with a Ni/W-C coating system in accordance with the Example.
• the total coating thickness was 2-3 mils with a coating hardness of 1950-2050 kg/mm 2 .
• the coated blades were evaluated for fatigue life using a Beehive tester in which the blades were air-jet excited at their fundamental bending mode frequency while rigidly clamped at the dovetail root. The test was conducted at room temperature. The conditions of the test were as follows:
• the failure point was indicated by the loss of natural frequency at the rate of 10 cycles/second. In this beehive test, an acceptable fatigue life is 300,000 cycles.
• the first coated blade was determined to have a fatigue life of 430,000 cycles and the second coated blade had a fatigue life of 385,000 cycles whereby the coated blades exceeded the fatigue life specification for the blades thereby confirming the fact that the erosion resistant coating system does not degrade the fatigue life of the substrate to which it is applied.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
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• Organic Chemistry (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Physical Vapour Deposition (AREA)
• Laminated Bodies (AREA)
• Chemically Coating (AREA)
• Electroplating Methods And Accessories (AREA)
• Chemical Vapour Deposition (AREA)

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Citations (8)

• 1985
  • 1985-10-03 EP EP85307105A patent/EP0186266A1/de not_active Withdrawn
  • 1985-10-24 JP JP23653785A patent/JPS61127873A/ja active Pending

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