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
  • C23C10/02—Pretreatment of the material to be coated

Definitions

• the particulate mixture includes, along with the alloy and an inert filler, about 0.l-l weight percent of a halide salt activator which will react with a metallic element in the ternary alloy to form a halide of such metallic element under sufficient time and temperature conditions in a nonoxidizing atmosphere.
• a halide salt activator which will react with a metallic element in the ternary alloy to form a halide of such metallic element under sufficient time and temperature conditions in a nonoxidizing atmosphere.
• chlorides and fluorides of ammonium and of the alkali metals of Group I A of the Periodic Table of Elements Specifically preferred is about 0.l-2 percent of halides selected from NaF, KF, NH,C1 and N H F.
• Another object is to provide such an improved coating having an outer portion which will act as an interdiffusion barrier between oxidizing and sulfidizing environments around a coated article and the article basis metal.
• an improved combination of oxidation and sulfidation resistance can be obtained in a diffusion bonded coating of about 1-5 mils as measured in the ascoated condition by embedding in an outer portion of the coating, such as the one described in the above identified copending application, about 5-50 volume percent of entrapped oxide particles of about lmicrons in size and thermally stable to at least about 2000 F.
• Such dispersion in the outer portion can be accomplished, according to the method form of the present invention, by first applying to a surface of an article to be coated an interim coating of about 1-25 mils in thickness of such oxide particles in a nonfused, loosely held, vapor permeable condition and of a type which will not enter into the reaction of the metallic diffusion coating.
• the metallic diffusion coating such as defined by the aboveidentified copending application, penetrates through the particles of the interim coating entrapping the particles in the coating outer portion during the heating cycle. Because the oxide particles are about 1-20 microns in size and thus are larger than a size which would allow them to move interstitially into the basis metal or alloy, the oxide particles are confined to the coating outer portion.
• the useful life of metallic diffusion coatings applied to high temperature operating components such as of a gas turbine engine is dependent in a significant amount on the stability of the interface between the coating and the basis metal to which it has been applied.
• coating life is further dependent upon coating surface degradation resulting from contact with erosive, corrosive or oxidizing environments.
• inhibition of diffusion through the coating of oxidizing and sulfidizing agents toward the coating basis metal interface can significantly lengthen the useful life of the coating.
• the present invention recognizes that the introduction of the above defined oxide particles in an outer portion of the coating results in such a barrier to that undesirable migration.
• one form of the above described ternary alloy powder used in the evaluation of the present invention consisted nominally, by weight, of 61 percent Ti, 34 percent Al, and about 4.5 percent combined carbon.
• This ternary alloy in powder form will be hereinafter identified as Alloy C.”
• Alloy C a ternary alloy in powder form
• a blend of about 40 weight percent Alloy C powder and about 60 weight percent AI,O, powder was mixed with about 0.2 weight percent NHJ.
• the Algoa powder acts to inhibit sintering of the Alloy C powders but does not enter into the coating process.
• the method of the present invention contemplates the application to the surface of an article to be diffusion coated of oxide particles, stable both to the processing temperature and mechanism, as an interim or preliminary coating in a nonfused, loosely held vapor permeable condition.
• This can be and was in this example accomplished by first making a slurry of the oxide particles and a liquid binder which will decompose without residue upon heating.
• a slurry of the oxide particles and a liquid binder which will decompose without residue upon heating.
• an acrylic resin in toluene or acetone can be used.
• the thickness of the interim coating is not critical. Therefore, the slurry can be adjusted in concentration to provide, for example, from about l25 mils of oxide on the surface. However, from a practical viewpoint no more than about l5 mils is necessary.
• the oxide particles are no more than about 20 microns in size, it is preferred that a variety in size of particles be present rather than particles all of the same size.
• TIOg or A1 0 or their mixtures in particle sizes of about 1-20 microns be used in the present invention when coating surfaces based on one of the elements Fe, Ni or C0.
• the slurry can be applied to the article surface by a variety of methods such as brushing, dipping, spraying, etc.
• a paint spray gun was used with a slurry to apply a coating of a powder mixture of about 50 weight percent each of AIgog and After application of the oxide coating to the article surface to be coated, the article was placed in a container, such as retort, along with the previously described particulate mixture. including powdered Alloy C. It should be recognized, however, that as indicated before, the Ase, in the particulate mix is included as a filler and does not enter into the coating reaction. Therefore, if a method such as is described in copending application Ser. No.
• the retort enclosing the particulate mixture and the article surface including the interim oxide coating was provided with a nonoxidizing atmosphere, in this example hydrogen, and was heated in the range of l400-2 F. for 1-4 hours, for example, about 1950" F. for 3-4 hours. This time and temperature was sufficient to allow deposition of such elements as aluminum and titanium from powdered ternary Alloy C, through their halide vapor state, onto the article surface by first penetrating through and subsequently entrapping the particles of the oxide of the interim coating. The time and temperature selected must be sufficient to allow further interdiffusion between the deposited elements and the article surface.
• the treated article surface was removed from the retort. Loosely adhering excess powders either from the particulate mix, if the article contacted such mix, or from the interim oxide coating, or both, were removed from the coated surface. It has been found that although relatively thick interim coatings of oxides can be applied to the surface, the titanium or aluminum or both from the ternary alloy powder will penetrate through the excess oxides to leave them only loosely adherent and readily removable from the surface after processing. Thus a reasonable excess thickness of the interim coating is not critical. It is preferred that about 2-10 mils of oxide be applied as the loosely adherent, nonfused, vapor permeable particles comprising the interim coating.
• Practice of the method of the present invention provides an article surface, particularly one based on Fe, Ni or Co, with a diffusion bonded, two portion coating: a coating outer portion and a coating inner interdifi'usion portion.
• Each portion includes primarily intermetallics formed from the basis element, for example, Ni, Co or Fe, and certain of any alloying elements of the article surface, with metallic diffusion coating elements such as titanium, aluminum, etc.
• the interrnetallics result from interdiffusion between elements of the coating and of the basis metal or alloy.
• the entrapped oxide particles in the coating outer portion because of their size in the range of about 1-20 microns, cannot move interstitially with respect to the basis metal in the formation of coating inner diffusion portion between the outer portion of the coating and the article surface. Therefore only the coating outer portion includes, in addition to the intermetallics, entrapped oxide particles.
• the coating inner interdiffusion portion and the coating outer portion together in the as-coated condition must represent a thickness no greater than about mils. Thicknesses in excess of that amount result in coatings having poor adherence properties.
• the present invention contemplates a coating the outer portion of which includes, in addition to the above described intermetallics and diffusion products, about 5-50 volume percent of dispersed oxides.
• the oxides preferred for dispersion in the outer portion of the coating in the practice of the method of the present invention in coating Fe, Ni or C0 base alloys include A1 0 or TiO or their mixtures. if such a mixture of oxides is used, it has been found that about 50 percent by weight of each is a satisfactory mixture and that a varied size mixture of particles is preferred in the range of l-l 0 microns.
• the type of diffusion coating with which this invention is particularly concerned can be applied to alloy surfaces based on elements selected from Ni, Co and Fe.
• Typical of data generated in the evaluation of the present invention is that relating to high temperature nickel base superalloys, the compositions for which are shown in the following Table I as including such alloying elements as Cr, Co, Mo, W, Al, Ti, Fe, etc.
• Specimens of each of the nickel base alloys listed in Table l were coated in the manner described in the above specific example: A mixture of 50 percent by volume each of A1 0 and of 'liO of particle size in the range of l-lO microns was applied as an interim coating by spraying from a slurry of the oxide particles and acrylic resin in acetone. The coating 'method was conducted at about l950 F. for 3-4 hours in a TABLE ll STATIC OXIDATION: 2 1 00 F.-l00 hrs.
• the life of the coating of the present invention is significantly better than the same coating without entrapped oxides, even though both coatings were capable of withstanding more than 100 hours under oxidizing conditions alone as shown by the data from which table ll was selected.
• the oxide particles are oxides selected from the group consisting of oxides of Al, Ti and their mixtures; and the metallic diffusion coating is applied by:
• a ternary alloy consisting essentially of, by weight, about 50-70 percent Ti, 20-48 percent Al and 0.5-9 percent combined carbon, the alloy having a dispersion of Ti AlC complex carbide in a matrix selected from the group consisting of Ti, Al and their alloys, and
• a halide salt activator which will react with a metallic element in the ternary alloy to form a halide of the metallic ele- 3 and then heating the surface and the mixture in the nonoxidizing atmosphere at a temperature and for a time sufficient 1) to form a halide vapor of at least one metallic component of the ternary alloy, (2) to allow penetration of the vapor through the interim coating to the metallic article surface to deposit the metallic component on the surface and (3) to allow both i. diffusion of the deposited metallic component with the article surface and ii. entrapment of particles of the interim coating by the deposited metallic component to provide the metallic coating comprising a coating outer portion including the entrapped oxides and a coating inner interdiffusion portion intermediate of and diffusion bonded with both the article surface and the coating outer portion.
• the basis element is Ni
• the interim coating is about l-l5 mils in thickness
• the halide salt activator is selected from the group consisting of chlorides and fluorides of ammonium and of the alkali metals of Group I A of the Periodic Table of Elements;
• the article surface and mixture are heated at a temperature of about 1400-2100F. for about [-4 hours.
• the mixture consists essentially of, by weight:

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Catalysts (AREA)

Applications Claiming Priority (1)

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Cited By (4)

Citations (2)

• 1968
  • 1968-11-29 US US780177A patent/US3617360A/en not_active Expired - Lifetime
• 1969
  • 1969-06-09 GB GB1250247D patent/GB1250247A/en not_active Expired
  • 1969-06-11 IL IL32374A patent/IL32374A/xx unknown
  • 1969-07-15 BE BE736134D patent/BE736134A/xx not_active IP Right Cessation
  • 1969-08-01 DE DE1939115A patent/DE1939115C3/de not_active Expired
  • 1969-08-19 CH CH1263969A patent/CH543595A/de not_active IP Right Cessation
  • 1969-08-28 SE SE11941/69A patent/SE350536B/xx unknown
  • 1969-08-28 FR FR6929541A patent/FR2024462A1/fr active Pending
  • 1969-08-28 ES ES370956A patent/ES370956A1/es not_active Expired

Patent Citations (2)

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