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
  • C23C10/28—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

Definitions

• the present invention relates generally to the protective coating art and is more particularly concerned with a new diffusion-coating method of providing oxidation resistant aluminum alloy coatings on nickel-base superalloy bodies, and with a novel composition for use in carrying out that method.
• the charge material will desirably be of substantially smaller particle size than that heretofore preferred in practice, and will comprise a relatively small proportion of the diffusion-coating bed, being admixed with an inexpensive inert material such as alumina so that sticking of the sintered charge is prevented and the cost of the charge is reduced to the point that the economic necessity of recovery and reuse is eliminated.
• this invention consists in the step of heating a nickel-base superalloy article to be provided with a protective coating to the temperature range of 900 to 1, 100C in the presence of hydrogen, an aluminum source and a halide carrier in particulate form. More specifically, this process includes as additional and preliminary steps the mixing of the aluminum source and carrier in the form of minus 100- mesh particle size to provide a bed and the placing of the superalloy article to be coated by the diffusion coating process within that bed.
• the carrier is sodium fluoride or ammonium fluoride and the aluminum source is FeAl Fe Al or FeAl or a mixture thereof.
• the aluminum source and carrier of minus 325-mesh size are admixed with alumina of similar particle size to provide a diffusion-coating bed made up of from five to 40 percent of the aluminum source, from 0.1 to 0.4 percent carrier and from about 60 to percent alumina.
• my invention concept in general terms takes the form of a substantially uniform mixture of minus IOO-mesh size fines of alumina, aluminum source and halide carrier in which the aluminum source comprises from 5 to 40 percent of the mixture and the carrier is present in amount from 0.1 to 0.4 percent, the balance being alumina.
• the aluminum source is FeAI Fe- Al or FeAl and is present in amounts of about 40 percent in the case of either FeAl or Fe Al and about eight per cent in the case of FeAl
• the carrier is preferably ammonium fluoride or sodium fluoride and is present in the mixture in amount about 0.2 percent.
• the process is conducted at a temperature from 900C to 1,100C with l,050C at present representing the best practice of the invention.
• the results which are obtained in using temperatures outside this range, and particularly below the lower end of it, are not as consistently good as usually desired, while temperatures above the upper end of the range do not afford a sufficient advantage of greater diffusion-coating rates or efficiencies to warrant the increased equipment and operating costs.
• any convenient halide or halide mixture may be used in this process.
• ammonium halide or an alkali metal halide a convenient halide or halide mixture
• Another halide such as aluminum chloride or aluminum fluoride may be used although it is neither as economical or easy to use as the corresponding ammonium or sodium or potassium salts.
• the thickness of the diffusion coating produced in accordance with this process will depend mainly upon the temperature at which the process is carried out and the length of the diffusion-coating period. Because of the high degree of uniformity of the resulting diffusion coatings and the freedom of these coatings from breaks and flaws, I prefer to limit their thickness to a total of 10 to microns. Coatings of such thickness will provide oxidation resistance to the extent that only much thicker coatings of the prior art afford, and there is normally no significant advantage in prolonging the process to obtain diffusion coatings of such greater thickness.
• aluminide diffusion coatings on a number of nickel and nickel-base superalloy articles using ammonium fluoride or sodium fluoride as the carrier and FeAI or Fe Al or FeAl as the aluminum source or charge material.
• alumina was used as an inert filler to make up a treating bed consisting of a substantially uniform mixture of about 0.2 percent of carrier, from eight to 40 percent charge alloy and balance alumina, all of particle size of minus IOO-mesh and in several instances minus 325-mesh.
• the treating temperature was maintained substantially constant in every case for a full three-hour period and in most runs was l.050C.
• the articles to be coated were buried in the bed contained in a box-like retort, then the retort was flushed with pure, dry hydrogen (dew point approximating 80C) and closed to maintain a hydrogen atmosphere substantially free from air throughout the treating period.
• the retort was then brought to temperature in an electric oven and furnace-cooled beginning at a time 3 hours later. Thereafter, the nickel or nickelbase superalloy parts were removed from the retort and examined with the results set forth in the following tables:
• the coating on the test specimen was uniform in thickness and consisted of nickel aluminides of aluminum content decreasing with depth in the coating. Bonding of the coating consequently was consistently good and the coatings were all continuous and hole-free and resistant to oxidation at elevated temperature. The gain in weight in all cases is attributable to the deposition of aluminum which is in contrast to the prior art practice of carrying out the diffusion-coating operation in such a way as to codeposit iron and aluminum.
• the hydrogen pressure within the retort before the heating step is begun is not critical in terms of this diffusion-coating method and neither is the presence in the bed of an excess of carrier.
• the diffusion-coating method of providing an aluminum-containing, oxidation-resistant protective coating on a nickel-base superalloy article which comprises the steps of providing a diffusion-coating bed of a mixture of-l00 mesh size particles of from 5 to 40 percent of an aluminum source and from 0.1 to 0.4 per cent ofa halide carrier and from about 60 to percent of a filler material said aluminum source being selected from the group consisting of FeAl I e- A1 and FeAl and mixtures thereof and said halide carrier being selected from the group consisting of ammonium fluoride, aluminum chloride and sodium fluoride. embedding the superalloy articles in the diffusion-coating bed, flushing the bed with hydrogen, and heating the bed and article therein to 900 to 1,100C while maintaining a hydrogen atmosphere in the bed until a coating of the desired thickness has been formed on the article.

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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)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Powder Metallurgy (AREA)

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

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Cited By (15)

Families Citing this family (4)

Citations (8)

Family Cites Families (5)

• 1970
  • 1970-08-21 US US00066069A patent/US3837901A/en not_active Expired - Lifetime
• 1971
  • 1971-07-23 GB GB3465071A patent/GB1333271A/en not_active Expired
  • 1971-08-20 FR FR7130460A patent/FR2103440B1/fr not_active Expired
  • 1971-08-20 DE DE2141924A patent/DE2141924C3/de not_active Expired
  • 1971-08-20 JP JP6302771A patent/JPS5511742B1/ja active Pending
  • 1971-08-20 BE BE771587A patent/BE771587A/xx unknown

Patent Citations (8)

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