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
  • C23C10/50—Aluminising of ferrous surfaces
• • 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
• • 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
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/922—Static electricity metal bleed-off metallic stock
  • Y10S428/923—Physical dimension
  • Y10S428/924—Composite
  • Y10S428/926—Thickness of individual layer specified
• • 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
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/922—Static electricity metal bleed-off metallic stock
  • Y10S428/9335—Product by special process
  • Y10S428/938—Vapor deposition or gas diffusion
• • 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
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/922—Static electricity metal bleed-off metallic stock
  • Y10S428/9335—Product by special process
  • Y10S428/941—Solid state alloying, e.g. diffusion, to disappearance of an original layer
• • 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
• • 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
  • Y10T428/12778—Alternative base metals from diverse categories
• • 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
  • Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
  • Y10T428/12826—Group VIB metal-base component
  • Y10T428/12847—Cr-base component
• • 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
  • Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
  • Y10T428/263—Coating layer not in excess of 5 mils thick or equivalent
  • Y10T428/264—Up to 3 mils
• • 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
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31678—Of metal

Definitions

• This invention relates to the diffusion coating of metal articles for the production thereon of an outer coating or layer of enhanced oxidation and corrosion or erosion and thermal shock resistance at high temperatures, as well as other enhanced surface characteristics, in which the article to be coated is heated as embedded in or otherwise in surface contact with a powdered pack or mixture including a metallic coating material, and, more particularly, to the production of such diffusion coatings where the coating pack or mixture includes at least one ingredient other than the primary coating material for controlling the rate at which the coating material is presented to the surface of the article to be coated for diffusion thereinto.
• the various chemical reactions involved e.g.', between the carrier and the coating material, between the coating material -and the metal or other components of the article to be coated, among whatever ingredients are in the pack, between coating material and whatever inter-metallics or alloys may have already been formed at or in the surface of the article being coated, etc.
• the various chemical reactions involved occur more or less simultaneously during the heating treatment and are mostly of a reversible nature, so that the net result of the coating step and the chemical reactions therein involved may depend predominantly upon the various equilibria achieved.
• ingredients in the coating pack may be inclined to combine with each other .at the same time (and, perhaps, even at the same rate) as one or another thereof may diffuse into the surface of the metal article; while (if the equilibrium conditions are appropriate) some portion of the metal from the article itself, or one or another component thereof, may also diffuse out of the article and into the pack ingredients.
• the chemistry within the coating pack may determine, for a specific temperature, the rate at which coating material is delivered to the surface of a coated article for diffusion thereinto, yet this delivery rate may not necessarily be directly related to the rate of diffusion of the same coating material into the article after having penetrated the surface thereof.
• the situation may arise where a particular high temperature is adequate for forcing a particular coating material to begin to diffuse into the surface of the article, but yet so high, with respect to the'diffusion rate of the material inside the article, that the coating material will be driven on into the center of the article and away from the surface thereof under prolonged exposure to the same high temperature.
• preliminary diffusion of some coating material into the article surface may so inhibit the penetration of additional coating material sufiicient to form thedesired thickness of coating as to be incompatible with a treating temperature consistent with forcing the reversible reactions in the coating pack toward the desired equilibrium result.
• the composition ofv the article being coated may be subject to crystallographic or metallog-raphi-c changes at different-temperatures under circumstances which are completely unrelated to the reaction rates of the various reactions in the coating pack itself so that treating temperatures sufficient to induce diffusion of the coating material toward or into the surface of the article being coated are too low to achieve the desired temperature or metallographic thermal condition of the article being coated to receive the coating material in the desired manner.
• the article to be coated may appr-oximate-a molten condition before thermal conditions can be established promoting the desired diffusion from the coating materials in the pack.
• the treating temperature is controlled to no more than will force diffusion of aluminum at a fairly moderate rate (so as to avoid deep diffusion of the aluminum and retain a surface coating or layer), it may be found that the particularcopper aluminide formed in the coating is not the one desired; whereas, on the other hand, if the treating temperature is raised to the point Where the desired particular copper aluminide is formed in the surface of the article, such higher temperature may produce an aluminum diffusion rate greatly in excess of that desired and/ or so as to produce too deep penetration of the aluminum into the article being coated.
• the particular temperature levels which must be obtained to instigate and maintain the initial reactions between the particular carrier material and the source of coating material in the pack and/or the thermal conditions and temperature levels which must be maintained in order to drive such reactions to completion within any commercially tolerable length of time may have no direct relation at all (indeed, they usually do not have) with the chemical characteristics and/ or diffusion rates of the coating material at or into the surface of different articles being coated.
• the complexity of the alloy or inter-metallic surface of the article being coated adds a further complication or additional factor, at least from the standpoint of predicting a set of operating conditions which will in all cases produce a satisfactory diffusion coating and/or permitting conditions which will drive one of the various possible reactions desirably toward the particular result desired.
• the particular intermetallic resultant desired Will be formed in the article surface, to the exclusion of other possible resultants, and/or that presentation of the coating material to the article surface in view of the diffusion rate thereof into the article neither inhibits nor excessively accelerates diffusion or reactions within the article inimical to or inconsistent with the formation at the surface thereof of a diffusion coating layer of the desired thickness, composition, and protective characteristics.
• one or more extra ingredients are added to or included in the coating pack for combination or interaction with the material to be coated and/ or the carrier component of the pack for forming a rate-controlling intermetallic or other compound with the coating material or otherwise altering the normal transfer rate of such material through the pack at the particular temperature being used, with such extra ingredients usually being metallic (by which term is meant to include elements such as silicon or boron as well as elements usually considered as metals) and even may itself not be diffused into'the metal article to form a significant or contributing part of the ultimately desired coating thereon.
• the selection of the particular extra ingredient hereof, with due regard to the particular car- 'er component being utilized, is specifically correlated to the metallic or chemical characteristics of the article being coated and the diffusion or reaction rates of the coating material therein and the variety of possible intermetallic compounds which may be formed between the coating material and components of the coated article of to the end of regulating or controlling the transfer rate of the coating material from the-pack to the surface of the article being coated to conform to predetermined temperature and other operating conditions so as to provide in the finished coating the particular intermetallic or alloy or other composition desired notwithstanding the fact that the normal or inherent forming of such desired composition may be quite inimical to or incompatible with the predetermined temperature or other operating conditions desired and/ or, indeed, impossible of formation under any operating conditions without the provision of the added rate-controlling ingredients.
• this invention and the teachings thereof are applicable to a wide variety of different coating situations utilizing different coating materials and different compositions of articles to be coated, it may generally be convenient initially to describe techniques and compositions embodying and for practicing this invention as particularly, although merely illustratively, applied to forming an essentially aluminide coating on high-nickel and high-cobalt superalloys and utilizing a coating pack containing, in addition to the aluminum to be coated, an inert filler, a volatilizable halide material such as ammonium fluoride as the carrier component, and metallic chromium as the extra rate-controlling ingredient.
• the oxidation resistance and/or corrosion resistance of the surface of such alloys may be less than desired for prolonged or severe use. If it is attempted to increase the oxidation and corrosion resistance of the surface of such high-nickel or high-cobalt alloys by diffusion coating thereinto of a metal such as chromium according to contions to which the article may be subjected in use.
• a diffusion coating of aluminum produces, at the surface of ,such alloy articles, a layer of substantially enhanced resistance to oxidation and erosion, as well as a casing of good and uniform adherence to the article, even during thermal shocks and deforma-
• This latter characteristic is ofparticular importance in the production of oxidation-resistant coatings on high temperatu're alloys subjected to severe thermal conditions because, if the supposedly oxidation-resistant coating or outer casing is not maintained uniformly continuous and firmly adhered to the article during thermal deformations thereof, fissures or other discontinuities may occur in the oxidation-resistant coating as a result of thermal shock, which fissures, once having occurred, readily present easy access to the base metalof the article for oxidation corrosion or erosion thereof.
• base metal alloys containing a substantial or preponderant proportion of nickel or cobalt and chromiu'me such alloys as are particularly formulated for high temperature use and having physical properties and a useful life as desired when subjected for prolonged duration to both very high temperatures 7 and to severe thermal shocks and rapid changes of temperature over wide ranges.
• superalloys may have small amounts (e.-g., usually less than 10%) of iron, they are composed primarily of a substantial proportion of chromium (e.g., about 10%- 20%), with at least about 50% or more of the composition being made up of nickel or cobalt and/or mixtures thereof.
• High nickel alloy Percent Carbon 0.12 Chromium 19 Cobalt 19 Iron 1 Molybdenum 4 Aluminum 3 Titanium 3 Nickel balance High cobalt alloy: Percent Carbon 0.50 Chromium 24.5 Nickel 10.5 .Tungsten 7.4
• Iron 1 Cobalt balance Also illustrative of the type of superalloy materials with which satisfactory results are achieved with this invention are the alloy high temperature steels and alloys having about equal proportions of nickel, cobalt and iron.
• articles of such high temperature alloys for which this invention is particularly adapted are satisfactorily coated by procedures including embedding the article to be coated in a dry powder pack including an inert mineral material, a source of the metallic elements to be diffusion coated, and a source of a vaporizable or diffusible halogen.
• the articles are heated to a substantial temperature for a number of hours to cause diffusion coating of the desired metals, in conjunction with the elemental halogen, into the surface of the articles being treated.
• the diffusion coating is carried out, preferably, at the lower temperatures and/or for shorter times within the foregoing ranges, and, where thicker cases may be desired (e.g., where oxidation and erosion resistance is of more importance than resistance to the possible disruption of the coating layer or casing by thermal shock), the diffusion coating step is conducted at higher temperatures and/or for longer times, thereby appropriately controlling the thickness of the diffused coating layer or casing produced in accordance with this invention.
• the proportions of materials, and the materials themselves, suggested in the above mentioned pack may be varied over fairly wide ranges.
• the proportion of inert filler is not critical and, although alumina is a preferred filler material for such a pack,
• thicker coatings may be ⁇ sisting thermal shock and thermally induced dimensional variations to which the finished article will be subjected in use.
• the aluminum coatings, according to this invention in addition to being oxidation-resistant, also exhibit good resistance to chemical corrosion attack, other than oxidation, at high temperature, as well as resistance to thermally induced metallurgical changes even after prolonged exposure to very high temperatures. Such coatings also exhibit good continued adherence to the coated article despite rapid and severe temperature changes to which the article may be subjected in use.
• an article composed of one of the highcobalt alloys to which this invention relates exhibits a satisfactory life of no more than about hours when continuously exposed to a temperature of about 2000 F.
• the same alloy with a protective coating of aluminum alone exhibits a satisfactory life of only about 20 to 30 hours under exposure to the same high temperature, with a coating of chromium alone affording less protection than the aluminum coating.
• the same highcobalt alloy having a diffusion coating of aluminum according to this invention exhibits a satisfactory life of 150 hours or more under continuous exposure to a temperature of 2000 F.
• One of the high-nickel alloys may exhibit a satisfactory life of up to 100 hours at 2000 F., with little or no extension of such life when the alloy is provided with a coating of aluminum alone or chromium alone. By contrast, however, satisfactory life of 150 hours or more at 2000 F. is achieved by such a high-nickel alloy when provided with an aluminum diffusion coating according to this invention.
• the rate controlling or inhibiting mechanism of a material such as chromium in an aluminizing pack may be related to the preliminary formation within the pack of a chromium aluminide at temperatures perhaps below the ultimate treating temperature.
• chromium and aluminum may be initially present in the pack in elemental form, chromium aluminides may be formed during heating the pack and preferentially or prior to transfer or diffusion of the aluminum component into the surface of the article being coated.
• the medium from which aluminum is to be transferred to-the article being coated is not metallic or elemental aluminum, but the chromium aluminide, which may require decomposition in order to diffuse aluminum into the surface of the article, especially if the diffusion rates (or even the possibility of diffusion) of the chromium aluminide is not thermodynamically effective or achievable at the particular treating temperature.
• the availability or transfer of the aluminum component in the pack for diffusion into the surface of the article is readily inhibited or controlled so that the temperature levels or other thermodynamic conditions necessary to break down the preliminary chromium aluminide sufficiently for aluminum to be diffused will produce the desired conditions for the formation of the particular nickel aluminide desired in the surface of the article.
• an inhibiting or rate controlling component such as chromium in an aluminum pack-for preliminary formation therein of a chromium aluminide has been found to produce satisfactory results in that temperatures high enough to break down the chromium aluminide for diffusion coating of aluminum are at levels where the desired particular nickel aluminide will be formed in the surface of a nickel-containing alloy (and substantially the same considerations have been found to apply to highcobalt alloys).
• a chromium aluminide is formed in the pack ingredients, it may be necessary, in addition to temperature control, to utilize an extremely aggressive carrier material (e.g., a fluoride instead of an elemental halogen or a chloride or iodide) for sufficiently aggressive attack to break up a preliminarily formed intermetallic (somewhat along the lines as disclosed in Patent No. 3,096,205).
• an extremely aggressive carrier material e.g., a fluoride instead of an elemental halogen or a chloride or iodide
• the inhibiting chromium aluminide may be formed preliminarily to the actual coating operation and the pack composed of such intermetallic, or elemental chromium and aluminum may be added to the pack originally with the article therein, since the preliminary formation of the inhibiting aluminide occurs during heating of the pack and, generally, prior to any significant diffusion of aluminum (or simultaneously with preliminary diffusion) in accordance with the various inherent equilibria and thermodynamic conditions of the pack ingredients.
• inert filler may interfere with any diffusion coating mere-- hereof, it will be understood that mere dilution of the diffusible ingredients of the pack, without other controls, may produce unsatisfactory results regardless of how effective it is for inhibiting the transfer or presentation of the diffusible metallic component to the surface of the article being coated.
• inert filler or diluent such as alumina
• the coating thickness achieved may generally increase as the metallic components of the pack increase, yet purely economic considerations may indicate the desirability for a substantial proportion of filler in any case.
• chromium-aluminum proportionings in the pack ingredients above 90% chromium are not preferred (although they may be operative) in accordance herewith primarily because of the thermodynamically engendered .difficulty of driving the aluminum component of such compositions adequately or controllably into diffusion relation with the article being coated, although such commercial difficulties may primarily relate to sintering of the pack ingredients around or to the surface being coated or similar purely mechanical side effects which can, if desired, be controlled by other techniques.
• chromium-to-aluminum ratios (by weight) in the pack ingredients substantially less than 0.5 may include so little chromiurn that the ratecontrolling effect thereof is either negligible or less than to be desired as compared with a straight aluminum pack; whereas, chromium-to-aluminum ratios substantially above 4.6 may produce an ultimate product having less than optimum oxidation resistance, perhaps because of too great an inhibition of aluminum available for diffusion coating or because of some actual diffusion coating of chromium instead of aluminum.
• chromium-to-aluminum ratios within the broad ranges of from about 0.1 to 8 may be considered operative, although such chromium-to-aluminum ratios in the pack ingredients initially beyond the range of about from 0.5 to 4.6 are generally not preferred for standard commercial operations with most types of superalloy and other articles to be aluminized in accordance herewith.
• chromium-to-aluminum ratios within the broad ranges of from about 0.1 to 8 may be considered operative, although such chromium-to-aluminum ratios in the pack ingredients initially beyond the range of about from 0.5 to 4.6 are generally not preferred for standard commercial operations with most types of superalloy and other articles to be aluminized in accordance herewith.
• the character of the particular coating actually diffused into the surface of the article changes substantially little throughout a very wide range of chromium-to-aluminum ratios in the pack, although the depth of coating and other operating characteristics may be predictably and controllably varied for commercial production reasons Within suchranges.
• the chromium component of the coating pack is as high as 92% by weight, it is primarily aluminum which is diffused intothe surface of the article (although such aluminum diffusion may be excessively inhibited by reaction or merely dilution at such high chromiurn levels).
• high-cobalt alloys such as that designated as WI-52 and containing approximately 63% cobalt, 20% chromium, 11% tungsten, 2% nickel, 1.5% colombium, 0.4% carbon, and the balance iron.
• WI-52 high-cobalt alloys
• chromium chromium
• nickel nickel
• colombium 0.4% carbon
• the coating ack initially contained metallic chromium metal and metallic aluminum metal approximately in the ratios by Weight of chromium in the amount of 24 times the amount of aluminum and with the aluminum comprising about 3% to 20% by weight of the coating pack, with a substantial amount of the pack (e.g., 60%70%) being made up of powdered alumina and with about 1% of ammonium fluoride as the carrier component.
• a substantial amount of the pack e.g., 60%70% being made up of powdered alumina and with about 1% of ammonium fluoride as the carrier component.
• One satisfactory composition is that noted above for all of these commercial treatments of the various metals noted-Le, 69% alumina, 22% metallic chromium, 8% aluminum metal, and 1% ammonium fluoride.
• coating pack composition may be included in the coating pack composition to achieve the desired rate-controlling or inhibiting action therein for systems providing an aluminized diffusioncoating, as
• such materials as cobalt, vanadium, carbon, silicon, and even, in some cases, iron, produce satisfactory results in accordance herewith, as rate-controlling ingredients for diffusion coating packs where aluminum and/or various other metals are being diffused into the surface of a variety of materials.
• the metals such as nickel and chromium, among other materials, are also satisfactory for inhibiting the transfer rate of lower melting coating materials (e.g., copper or iron) in the transfer and diffusion thereof from a coating pack into the surface of an article being coated and especially where the composition of the article and/or the thermal characteristics of the coating material are such as to promote too rapid transfer or diffusion at treating temperatures as high as may be desired in standard commercial operations.
• lower melting coating materials e.g., copper or iron
• cobalt may be considered as satisfactory rate-controlling ingredients for diffusion coatings of aluminum or silicon, while such materials as silicon or iron or carbon satisfactorily control the transfer of chromium, while silicon also is useful with aluminum coatings and iron similarly for silicon or aluminum, etc.
• rate-controlling or inhibiting ingredients in the various coating packs mentioned or included in accordance herewith does not necessarily exclude some diffusion of the rate-controlling ingredient itself, although usually of a minor and/ or ancillary nature, and such operations are generally to be distinguished from situations where an additional ingredient is actually added to the pack purposefully to be diffused along with the primary coating metal as, for example, the addition of carbon to the pack for carburizing or controlling the decarburizing of a ferrous alloy (and within the article, not by reaction in the pack) during the heating treatment for diffusing some other primary coating metal into the article.
• one or another of the materials noted may be used primarily as a getter for one or another of the possible resultants of one or another of the concurrent reversible reactions (e.g., to getter iron halide in the diffusion coating if iron materials using a halide carrier component) for accelerating or otherwise controlling which one of the several possible reactions goes farthest to completion.
• the foregoing disclosure is to be understood as relating primarily to rate-controlling techniques involving inhibiting the transfer of the coating material from the pack to the surface of the article by chemical reaction thereof with other ingredients in the pack (and/ or, as noted, by controlling the decomposition of any resultants of such chemical reaction by a selected degree of aggressiveness of the carrier component), rather than to such mechanical expedients of rate control as simple dilution of the pack with inert ingredients and/ or such techniques as may involve actual preliminary treatment of the surface of the article being coated for inhibiting penetration thereto (or thereinto) of pack ingredients (such as the techniques disclosed in the co-pending application of Martin Epner relating to preliminary coating or masking of the article surface for mechanical or chemical interference with transfer or diffusion of coating'materials from the pack, or that of Walter Butler relating to preliminary or simultaneous coating of the article itself with one diffusion material for altering the acceptance charac teristics of the article surface for another or primary diffusion material).
• the temperature and time ranges noted above may also be preferred as a standard commercial operating condition, it is to be understood that, especially with chromium-aluminum packs in the aluminizing treatment of high-nickel and high-cobalt superalloys, satisfactory results are also obtained by holding the articles to be coated embedded in the pack at temperature (i.e., after heating the retort up to temperature) for a time range of approximately -%-40 hours within a temperature range of about l400-2200 F., depending, of course, on the particular material being coated and the depth or thickness of coating case desired.
• a diffusion coating of the character described on the surface of an alloy base metal having high temperature resistant characteristics and having a substantial proportion of approximately half of a metal of the group consisting of nickel and cobalt and a substantial proportion of chromium the steps which comprise embedding said alloy base metal in a diffusion coating pack including a source of chromium metal and sufficient aluminum metal for effecting diffusion coating thereof into the surface of said base alloy and a source of vaporizable halogen as a carrier for said aluminum in the diffusion coating thereof and powdered filler material, heating said base alloy in said pack effecting diffusion coating of said aluminum into the surface of said article, said aluminum comprising about 3%-20% of said pack by 'weight and said chromium being present in an amount about 2-4 times by weight the amount of said aluminum.
• a metal article of the character described and susceptibleto long exposure to an oxidizing and corrosive atmosphere at high temperature and resistant to the thermal shock incident to repeated heating and cooling between ambient temperature to high temperature and comprising a base alloy including a substantial proportion of aproximately half of at least one of the metals selected from the group consisting of nickel and cobalt and a substantial proportion of chromium, which article is enclosed within a diffused outer layer case including aluminum. and said outer layer case having been formed on said article in accordance with the method recited in claim 1.
• a diffusion coating of the character described on the surface of an alloy base metal having high temperature resistant characteristics and a substantial proportion of approximately half of a metal selected from the group consisting of nickel and cobalt, and a substantial proportion of chromium the steps which comprise embedding said alloy base metal article in a diffusion coating pack including a source of chromium metal and sufiicient aluminum metal for eflfecting diffusion coating thereof into the surface ofsaid base alloy and a source of vaporizable halogen as a carrier for said aluminum in said diffusion coating thereof, the weight ratio of said chromium to said aluminum in said powdered pack being substantially within the range of about 0.5 to 4.6, and heating said basemetal alloy in said pack effecting diffusion coating of said aluminum into the surface of said article.
• a method as recited in claim 7 in which said heating step is accomplished at temperatures within the range of about 1400-2200 F. and prolonged for a time at said temperature within the range of about 4-40 hours.
• a metallic coating is diffused into the surface of a metal article by heating such metal article in a non-oxidizing atmosphere in a sealed powdered diffusion coating pack including the metallic coating material to be diffused into said article and a carrier component for effecting the transfer of said metallic coating material from said pack to the surface of said article
• a process as recited in claim 9 in which said metallic coating material to be diffused into said article is selected from the group consisting of aluminum, chromium, iron, silicon, and mixtures thereof.
• a process as recited in claim 9 in which said metal article to be coated comprises a substantial proportion of a metal selected from the group consisting of chromium, cobalt, copper, iron, nickel, the refractory metals, and alloys and mixtures thereof.
• said additional metallic ingredient added to said pack for combining chemically with said coating material comprises a material selected from the group consisting of aluminum, beryllium, boron, carbon, chromium, cobalt, iron, nickel, the refractory metals, silicon, and mixtures and alloys thereof.
• a process as recited in claim 9 in which said metal article to be coated comprises a substantial proportion of a metal selected from the group consisting of chromium, cobalt, copper, iron, nickel, the refractory metals, and alloys and mixtures thereof; and in which said metallic coating material to be diffused into said article is selected from the group consisting of aluminum, chromium, iron, silicon, and alloys and mixtures thereof; and in which said additional metallic ingredient added to said pack for combining chemically with said coating material is selected from the group consisting of aluminum, beryllium, boron, carbon, chromium, cobalt, iron, nickel, the refractory metals, silicon, and alloys and mixtures thereof.
• a diffusion coating of the character described on the surface of an alloy base metal having high temperature resistant characteristics and a substantial proportion of approximately half of a metal selected from the group consisting of nickel and cobalt, and a substantial proportion of chromium the steps which comprise embedding said alloy base metal article in a diffusion coating pack including a source of sufficient aluminum for effecting ditfusion coating thereof into the surface of said base alloy and a source of vaporizable halogen as a carrier for said aluminum in said diffusion coating thereof and an additional separate metallic ingredient for combining chemically with said aluminum in said pack for inhibiting and controlling said transfer thereof to the surface of said alloy base metal, and heating said alloy base metal in said pack effecting diffusion coating of said aluminum only into the surface of said article substantially in the absence of diffusion of said separate metallic ingredient thereinto.

Landscapes

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

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23393345

Family Applications (1)

Country Status (4)

Cited By (49)

Citations (17)

• 1964
  • 1964-03-24 US US354440A patent/US3257230A/en not_active Expired - Lifetime
• 1965
  • 1965-03-22 GB GB12100/65A patent/GB1102076A/en not_active Expired
  • 1965-03-22 CH CH393765A patent/CH490512A/de not_active IP Right Cessation
  • 1965-03-24 SE SE03792/65A patent/SE326620B/xx unknown

Patent Citations (17)

Also Published As

Similar Documents