US3729295A - Corrosion resistant coating system - Google Patents

Corrosion resistant coating system Download PDF

Info

Publication number
US3729295A
US3729295A US00143842A US3729295DA US3729295A US 3729295 A US3729295 A US 3729295A US 00143842 A US00143842 A US 00143842A US 3729295D A US3729295D A US 3729295DA US 3729295 A US3729295 A US 3729295A
Authority
US
United States
Prior art keywords
silicate
coating
aluminized
corrosion
solution
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00143842A
Other languages
English (en)
Inventor
M Weinstein
K Speirs
R Baer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Chromalloy Gas Turbine Corp
Original Assignee
Chromalloy American Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Chromalloy American Corp filed Critical Chromalloy American Corp
Application granted granted Critical
Publication of US3729295A publication Critical patent/US3729295A/en
Assigned to CHROMALLOY GAS TURBINE CORPORATION, A DE. CORP. reassignment CHROMALLOY GAS TURBINE CORPORATION, A DE. CORP. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: CHROMALLOY AMERICAN CORPORATION
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

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
    • C23C10/60—After-treatment
    • 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
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
    • C23C22/74—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process for obtaining burned-in conversion coatings
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft
    • 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
    • Y10S428/9265—Special properties
    • Y10S428/933—Sacrificial 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
    • 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
    • Y10S428/934—Electrical process
    • Y10S428/935—Electroplating
    • 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.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12556—Organic 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.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12583—Component contains compound of adjacent metal
    • 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
    • Y10T428/12861—Group VIII or IB metal-base component
    • Y10T428/12951—Fe-base component
    • Y10T428/12958—Next to Fe-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.]
    • Y10T428/12986—Adjacent functionally defined components

Definitions

  • Ferrous metal articles having improved resistance to corrosion in highly saline and/or marine atmospheres, the articles being characterized by a protective duplex coating comprised of a sacrificial thermally aluminized ferrous metal surface in a combination with a special barrier type non-metallic overcoat.
  • a protective duplex coating comprised of a sacrificial thermally aluminized ferrous metal surface in a combination with a special barrier type non-metallic overcoat.
  • One method of providing the foregoing system is to apply an adherent layer from a liquid of a soluble silicate salt or compound onto a thermally aluminized layer, the silicate layer being preferably thereafter cured.
  • a conversion coating is applied to the silicate layer and cured in situ to further enhance the resistance to corro- SlOIl.
  • This invention relates to the protection of ferrous metal articles from corrosion in highly saline and/or marine atmospheres by employing a protective duplex coating compound of a sacrificial thermally aluminized ferrous metal surface in combination with a special barrier-type non-metallic overcoat.
  • Jet and gas turbine engine compressor components are subject to corrosion in highly saline atmosphere at the air intake end of the engine and also to direct impact of abrasive particulate matter, such as coral dust. Additionally, the compressor blades are subjected to tremendous mechanical stresses from centrifugal forces, thermal shock, vibration and other sources of stresses. Thus, corrosion can accelerate catastrophic failure, since pits and other corrosion defects can act as stress raisers.
  • High strength ferrous alloys are employed in the construction of compressor blades and other aircraft engine components (e.g. Society of Automotive Engineers alloy designation AMS 5508, AMS 5616, AMS 6304 and others) but, because of their low resistance to saline corrosion, they are generally subjected to a protective surface treatment.
  • One, in particular, is the provision of an aluminum-base diffusion coating on the ferrous substrate by pack-aluminizing at coating temperatures ranging up to 1000 F. and preferably not higher so as to avoid undesired crystallographic or metallurgical changes in the substrate during coating, which might have an adverse or undesired effect on the mechanical properties of the parts.
  • Such coatings have provided advantageous oxidation and erosion resistance and have minimized the production of pulverous corrosion products and have been very useful in extending the operating life of jet engine components.
  • Another object is to provide a method for further enhancing the corrosion resistance of ferrous metal substrates by applying thereto a protective duplex coating comprising a sacrificial thermally aluminized coating in combination with a special barrier type non-metallic overcoat.
  • This invention is based on the discovery that the corrosion resistance of ferrous metal articles can be unexpectedly enhanced by providing the ferrous article with a protective duplex coating system comprising thermally aluminizing the ferrous substrate and then applying thereto a highly adherent barrier type non-metallic overcoat containing a silicate salt or compound as an essential ingredient.
  • the intermetallic iron aluminide produced by the pack aluminizing of ferrous articles in a bed containing essentially alumina, some aluminum powder and a small but effective amount of a halide, e.g. AlCl and the like is characterized by the ability to absorb readily a silicate liquid, such as an aqueous solution of sodium silicate. It is believed that the high afiinity of the aluminized coating for the silicate is associated with the physicalchemical character of the aluminized surface arising out of the method of growth of the aluminide. Observations have indicated that the iron aluminide formed at the surface is characterized by an exceptionally high surface area, high degree of chemical cleanliness and chemical activity. Itis believed that the foregoing characteristics provide for synergistic effects which lead to unexpected improved results.
  • the expression thermally aluminized surface is meant to cover the thermal diffusion of aluminum in a ferrous surface in which iron aluminide is formed at the surface.
  • One embodiment of the invention resides in a method which comprises applying to the thermally aluminized surface of the article a solution of a soluble silicate salt at a temperature ranging up to about C., for example, about 70 C. to 95 C. (about F. to 200 F.), removing excess liquid from the surface, such as by blowing it off with air, to form a uniform layer of said silicate salt, and then drying the layer on said surface
  • a typical salt spray test shows that sacrificial products form after approximately 15 hours of testing, whereas times in excess of 200 hours have been repeatedly obtained when the aluminized surface is coated with a uniform silicate layer. This result appears to confirm the synergistic effects which accrue when the silicate contacts the iron aluminide at the interface.
  • sodium silicate solutions can be employed in carrying out the invention.
  • the solutions can be prepared from solutions of 50 to 100% concentrations of Na O-3.22 SiO
  • Various other sodium silicates can be employed to prepare solutions such as Baum 40, 45, 47 and 50.
  • Potassium silicate may be similarly employed.
  • Lithium silicate and also organic silicates can be used, such as ethyl silicate.
  • a preferred solution for producing a uniform pre-coat on the intermetallic iron aluminide substrate is on containing by weight about 0.05 to 2% SiO equivalent, for example, a soluble silicate in the form of Na O-3.22 Si
  • the temperature of the substrate during application should preferably range from about 70 C. to 95 C.
  • a preferred method for applying the silicate solution pre-coat at the foregoing concentration comprises immersing the thermally aluminized ferrous article (e.g. a compressor blade) in a tank maintained at a temperature of about 70 C. to 95 C. with suflicient time in the bath to bring the article to temperature and assure absorption of the solution into the aluminized surface.'The excess liquid is then blown off with air and the part allowed to dry. It is immersed again for a brief period for a time suflicient to allow the article to be covered with liquid, after which it is removed, blown off with air and air dried. The steps may be repeated until the desired thickness is obtained.
  • the thermally aluminized ferrous article e.g. a compressor blade
  • an anionic surfactant or wetting agent may be employed, for example, an anionic phosphate surfactant, such as Triton QS-30 (manufactured by Rohm & Haas).
  • An alternate method which yields a more stable silicate coating resides in applying a succession of layers as described hereinabove followed by curing in an oven. Infra-red or forced air heated ovens may be employed in the temperature range of about 150 C. to 430 C. (about 300 F. to 805 F.) with enhanced corrosion protection.
  • the silicate coating applied by any of the methods described herein will produce a uniform layer with a thickness of approximately 0.0001 inch (0.1 mil) while avoiding as far as is possible areas of excess silicate on the surface.
  • a preferred method is to apply at least one precoat from a dilute silicate bath containing 0.05% to 2% by weight of SiO equivalent by a series of dipping, drying and curing steps followed by at least one spray coating of silicate from a more concentrated solution containing about 2.5% to 17.5% (e.g. 6.8%) by weight of SiO equivalent.
  • the advantage of curing the silicate coating which allows multiple layers to be formed is that the cured coating can withstand ten oxidation-corrosion cycles comprising heating the coated substrate to 1000 F. (about 538 C.) for 1 hour followed by 5 hours of salt spray testing, the foregoing test being repeated for ten cycles.
  • the intermetallic layer on a stainless steel substrate without the silicate coating provides protection for only 3 cycles, withv pitting occurring in the stainless steel substrate.
  • Applications of the silicate coating followed by curing at about 400 F. (205 C.) have yielded high degrees of protection and, in many cases, very little sacrificial products have been observed after cycles of heati g 1 00 (538 Q) fol owed y h sa t. p ay t st- 4
  • the foregoing tests are helpful as controls in assuring the quality of the silicate coating before the next coating treatment is applied.
  • the corrosion resistance of the intermetallic layer is further enhanced by applying a conversion coating to the cured silicate layer.
  • the conversion coating in turn may be covered by a silicate layer.
  • the conversion coating may be applied by spraying, using commercially available reciprocating guns.
  • the silicate solution containing 6.8% by weight equivalent of SiO and containing about 0.002% by weight of an anionic phosphate surfactant may optionally be sprayed over the conversion coating having a surface temperature not exceeding about F. (65 C.) followed by curing at temperatures from about 300 F. (150 C.) to about 805 F. (430 C. for 10 minutes in an infra-red furnace.
  • Another method of covering the conversion coating is to dip the article in a hot solution of about 180 F. to 200 F. (82 C. to 93 C.), using a sodium silicate concentration of about 0.9% to 2.4% by weight of SiO equivalent with a 0.002% addition of an anionic phosphate surfactant.
  • the article is immersed in the bath and allowed to come to temperature and excess liquid removed rapidly by means of an air gun. It is then immersed again and immediately pulled out of the solution and air dried.
  • a third application is made in the same manner. It is important that excess liquid be removed from the part to avoid foaming during curing.
  • the purpose of repeated immersion and drying is to assure uniform coating of the surface.
  • the curing is preferably carried out at about 800 F. in an infra-red furnace.
  • Compressor blades of AMS 5616 steel are subjected to 4 cycles of treatment in the solution by supporting the blades on a rack which is immersed in the solution and immediately withdrawn. The liquid is allowed to drain for approximately 15 seconds, after which it is immersed again and withdrawn. Following the second dip, an annular air collar (air pressure at about 70 p.s.i.) is disposed about the rack of blades to blow off the excess liquid. This is achieved by raising the rack through and above the air collar to allow the parts to drain, the air valve opened, and the rack then caused to be lowered through the collar. This group of steps constitutes one cycle. Four cycles are employed to produce the desired silicate layer. If necessary, an air gun can be used to remove excess liquid from the root of the blades.
  • the blades are dried free of moisture by, for example, blowing with air.
  • the temperature at which the silicate layers are applied may range from about F. (70 C.) to 200 F. (90 C.).
  • the coating on the dried blade is then cured at about 800 F. (425 C.) in an infra-red oven.
  • aqueous conversion coating solution which is preferred may range by weight from about 5% to 30% phosphoric acid (preferably 10% to 30%), about 0.0235% to 3% aluminum, about 3% to 8% chromic a id (Cr0 about 0.75% to 6% magnesium. and th balance essentially water.
  • a formulation found particularly preferred in producing the solution is as follows:
  • a non-anionic surfactant comprising a condensation product of ethylene oxide with an alkylphenol (Triton X100 by Rohm & Haas) 0.1 Water 78.175
  • the aluminum and magnesium are dissolved in the solution by virtue of the free acid present.
  • the application of the conversion coating as described above results in a smooth uniform surface layer which provides oxidation-corrosion protection without the need for supplementary surface finishing.
  • a build-up of approximately 0.1 mil can be obtained by employing a plurality of silicate and conversion coating applications.
  • EXAMPLE 1 A group of compressor blades is first aluminized by preparing an aluminizing pack comprised of 800 lbs. of 60+140 mesh aluminum powder blended with 200 lbs. of A1 also 60+140 mesh size. To the 1000 lb. mixture is added 30 lbs. of dry AlCl under a humidity preferably not exceeding 45%.
  • the pack is mixed in a vibrating blender from about 5 to minutes. If the charge is a fresh charge, it is subjected to burn-out at 795-825 F. (425 C. to 440 C.) for 36 hours. However, where a charge has already been used, burn-out is not required.
  • the pack is placed in a dry condition in a retort with the compressor blades of AMS 5616 steel to be treated, the blades being completely embedded in the pack.
  • the cover is sealed to the retort body with multiple layers of aluminum foil in the form of a gasket sufficient to prevent air from getting in but to allow out-gassing of gaseous by-products.
  • the retort is placed in an oven at ambient temperature and the temperature allowed to rise to the desired coating temperature by the application of heat. As the temperature rises, it goes through an endothermic arrest at about 350 F. (176 C.) due to vaporization of AlCl and then allowed to reach a range of about 795 F. to 825 F. (425 C. to 440 C.) and the retort maintained at substantially that temperature range for about 36 hours. Upon completion of the heating cycle, the retort is removed from the oven and allowed to cool approximately to 400 F. (205 C.), after which it is placed in a dry environment for cooling to ambient temperature.
  • the cooled retort is then placed in a humidity control cabinet, the cover removed and the compressor blades taken out of the cementation pack.
  • the blades are cleaned of adhering coating compound by blowing with dry air and immersed in water to remove fine dust and other residues to provide a very clean aluminum deposit containing an iron aluminide intermetallic compound, such as FeAl
  • the aluminized surface like other thermally diffused aluminum coatings, has some sacrificial properties in that it will corrode in preference to the ferrous substrate in saline environments and, therefore, provide some measure of protection of the ferrous substrate against corrosion.
  • a characteristic of thermally diffused aluminum coatings is that it readily absorbs dilute liquid silicate solutions due to its microporosity and apparently synergistically reacts with the silicate to provide an adherent protective pre-coat.
  • the blades are racked and the rack immersed in a tank containing an aqueous sodium silicate solution containing by weight about 0.1% to 2% SiO equivalent maintained at a temperature ranging from about 160 F. to 200 F. (70 C. to C.).
  • the bath also contained a small but effective amount of an anionic phosphate surfactant.
  • the blades are immersed for a time sufficient to reach the temperature of the bath and then withdrawn, the excess liquid being blown off with air and the blades allowed to then dry. The process is repeated a number of times until a desired thickness is obtained, e.g. 0.05 mil.
  • Several blades coated in this manner exhibited improved resistance to corrosion. The resistance to corrosion was even further improved by subjecting the silicated thermally aluminized blades to an oven cure at a temperature within the range of about 300 F. (150 C.) to 800 F. 430 c.).
  • the blade test specimens in the series outside the invention include (A) the bare steel substrate; (B) the bare steel substrate with a cured sodium silicate pre-coat; (C) the bare steel substrate with alternate cured layers of sodium silicate and a cured conversion coating; (D) the bare steel surface with only a cured conversion coating; (E) a bare steel specimen with a cured conversion coat containing about 0.1% by weight of SiO equivalent (as sodium silicate); (F) the steel substrate with only a thermally aluminized surface containing iron aluminide; and (G) the steel substrate with the thermally aluminized surface and with a cured overcoat of the conversion coating.
  • the series within the invention included (1) the steel substrate with the thermally aluminized surface with a cured overcoat of sodium silicate; (2) the steel substrate with the thermally aluminized surface which in turn has the overcoat as in (C); and (3) the steel substrate with the thermally aluminized surface covered with an overcoat of the conversion coating containing about 0.1% by Weight of SiO equivalent as sodium silicate.
  • the corrosion testing cycle comprised heating the blade specimens for 1 hour at 900 F. followed by cooling and then subjecting the cooled specimen to 5 hours of salt spray in accordance with ASTM B 117-64.
  • the foregoing, which is considered one cycle, is repeated generally 10 times or more to obtain an evaluation of the relative quality of each of the coating systems.
  • the results and details of the tests are given in the following table:
  • C Baresteel surface coated as follpws (a) precoat of sodium silicate from 36 to 1 vol. percent solution (about 0.15 to 0.3 wt. percent SiOz) and cured; (b) spray coat with 25 vol. percent sodium silicate solution (7.3% by wt. S102) and cured; (c) spray coat with conversion coat 1 and cured; (d) spray coat with 25 vol. percent sodium silicate (7.3 wt. percent 3102) and cured.
  • sion coat 1 containing 0.1% by wt. of SiOz equivalent as sodium silicate.
  • test specimens A to F (outside the invention) showed deterioration much sooner than specimens 1 to 3 (within the invention).
  • Tcst No. 1 (aluminized surface plus cured sodium silicate) exhibits nine times the improvement over Test NO. P )aluminized only) after the eighth cycle on the amount of area corroded.
  • Test Nos. 1 and 2 showed very little corrosion all after the 12th cycle.
  • the duplex coating system of Test No. 2 is particularly advantageous.
  • the non-metallic overcoat is applied (as described in Test No. C) in a series of steps as follows: (1) The aluminized steel surface is provided with a pro-coat of sodium silicate applied by a, series of dips in a solution containing by weight about 0.15% to 0.3% Si0 equivalent and then cured; (2) a spray coat of silicate is applied containing vol. percent of sodium silicate (obtained from 41.5 Baum solution) corresponding to 7 .3 wt. percent of SiO equivalent followed by curing; (3) the conversion coat is then sprayedonto the cured silicate layer; and (4) lastly, sodium silicate of about 25 vol. percent concentration (about 7.3 wt. percent Si0 equivalent) is sprayed over the conversion coat and thereafter cured.
  • the sodium silicate solutions were prepared from Baum 41.5 solutions.
  • the concentration of the dip solution generally ranges by weight from about 0.05% to 2% SiO equivalent.
  • the concentration may range by weight from about 2.5% to 17.5% of Si0 equivalent.
  • Example 8 EXAMPLE 2 The method of aluminizing described in Example 1 is repeated in the coating of a vane shroud made of 17-4 pH stainless steel (17% Cr, 4% Ni, 3% Cu and the balance essentially iron). Because of the configuration of the shroud, special care is taken in preparing the shroud for pack aluminizing using substantially the same pack and conditions described in Example 1. Following the pack aluminizing step, the shroud is cleaned of adhering pack material and then coated with the silicate salt which is thereafter cured and the conversion coating applied and cured in the manner similarly herein.
  • the baking of the duplex silicate conversion coating results in a reaction product which provides new and improved resistance to corrosion in saline environments.
  • the silicate is preferably first applied to the thermally aluminizcd surface, it is appreciated that it can be applied as a solution together with the conversion coating materials.
  • the conversion coating solution prior to spraying may contain about 0.05 to 2% by weight SiO equivalent as sodium silicate, potassium silicate, ethyl silicate, and the like.
  • the amount of silicate dissolved in the conversion coating solution will depend upon the prevailing pH of the solution, and therefore, the amount of silicate dissolved therein will be limited to some extent.
  • the silicate dissolved in the solution will generally be sufiicient to enhance the corrosion resistance of the ferrous article, since the silicate during the coating process tends to migrate to the aluminized surface and provide the necessary barrier function and to react with the conversion coating during the curing cycle.
  • Test No. 3 in which the conversion coat applied to the specimen also contains sodium silicate.
  • the conversion coating comprises phosphates and chromates of at least one metal, for example, Al, Mg, Zn, Be, Ba, Sr, Ce, group metals and other metals.
  • a conversion coat containing phosphates and chromates of aluminum and magnesium has been found very desirable.
  • a phosphatc-chromatc solution X of beryllium is produced by starting with 200 ml. of phosphoric acid (1.6 grams/mil) which is diluted with water to a pH f 1.01. To the solution is added 62.5 grams of chromic acid (99% CrO and 40 grams of beryllium phosphate (Be (PO) This solution has a density of about 1.2 grams/mil and provides a conversion coating by spraying the solution onto the aluminized surface and curing at tempcraturcs ranging [from 300 F. (150 C.) to 800 F. or 900 F. (425 C.-482 C.), the spraying and curing being repeated about three times or more, if necessary.
  • the foregoing solution may be used as a base to which other soluble metal salts or compounds can be added.
  • a preferred formulation is to add 0.69 gram of the other metal salt or compound to grams of solution X.
  • the conversion solutions may range in composition by weight of at least about 0.5% of at least one phosphate and chromate-forming metal, e.g. about 0.5 to about 5% to 30% phosphoric acid, about 3% to 8% chromic acid (CrO and the balance essentially water.
  • a preferred conversion solution is one containing by weight about 0.02% to 3% dissolved aluminum, about 0.75% to 6% dissolved magnesium, about 5% to 30% phosphoric acid (preferably to 30%), about 3% to 8% chromic acid and the balance essentially water.
  • a more specific composition is one containing by weight about aluminum, about 1.5% magnesium, about 15% phosphoric acid, about 5% chromic acid and the balance essentially water.
  • the silicate salt may be selected from the group consisting of sodium silicate, potassium silicate, lithium silicate, and organic silicates, such as ethyl silicate.
  • the ASTM salt spray test (Designation B 117-64) employed in testing the resistance to corrosion of the various coating systems disclosed herein comprises a fog chamber, a salt solution reservoir, a supply of suitably conditioned compressed air, one or more fog nozzles, specimen supports, provisions for heating the chamber and control means.
  • the specimens are supported or suspended between 15 and 30 degrees from the vertical (out of contact with each other) and preferably parallel to the principal direction of horizontal flow of fog through the chamber.
  • the salt solution is made up of 5 i1 parts of salt to 95 parts of distilled water containing not more than 200 p.p.m. of total solids.
  • the condensed fog should have a pH of about 6.5 to 7.2.
  • the temperature within the chamber is maintained at 95 F. plus 2 or minus 3 F.
  • the salt spray testing is carried out for a period of 5 hours, precautions being taken to avoid dripping of condensed solution from one specimen to another.
  • a ferrous metal substrate characterized by an adherent protective duplex coating comprised of a sacrificial thermally aluminized surface containing iron aluminide, said aluminized surface of the substrate having bonded thereto a cured non-metallic barrier layer obtained from a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate and ethyl silicate.
  • a ferrous metal substrate characterized by an adherent protective duplex coat ing comprised of a sacrificial thermally aluminized surface containing iron aluminide, said aluminized surface of the substrate having bonded thereto a cured reaction product comprising a non-metallic barrier layer formed from a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate and ethyl' silicate reacted with a chromate and a phosphate of at least one metal.
  • a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate and ethyl' silicate reacted with a chromate and a phosphate of at least one metal.
  • a ferrous metal substrate characterized by an adherent protective duplex coating comprised of a sacrificial thermally aluminized surface containing iron aluminide, said aluminized surface of the substrate having bonded thereto a non-metallic barrier layer comprising a cured reaction product formed from a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate and ethyl silicate reacted with chromates and phosphates of aluminum and magnesium.
  • a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate and ethyl silicate reacted with chromates and phosphates of aluminum and magnesium.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Chemical Treatment Of Metals (AREA)
US00143842A 1971-05-17 1971-05-17 Corrosion resistant coating system Expired - Lifetime US3729295A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US14384271A 1971-05-17 1971-05-17

Publications (1)

Publication Number Publication Date
US3729295A true US3729295A (en) 1973-04-24

Family

ID=22505907

Family Applications (1)

Application Number Title Priority Date Filing Date
US00143842A Expired - Lifetime US3729295A (en) 1971-05-17 1971-05-17 Corrosion resistant coating system

Country Status (14)

Country Link
US (1) US3729295A (xx)
JP (1) JPS525051B1 (xx)
AU (1) AU467810B2 (xx)
BE (1) BE782151A (xx)
CA (1) CA967463A (xx)
CH (1) CH558838A (xx)
DE (1) DE2218175A1 (xx)
FR (1) FR2137488B1 (xx)
GB (1) GB1345128A (xx)
IL (1) IL39217A (xx)
IT (1) IT953364B (xx)
LU (1) LU65164A1 (xx)
NL (1) NL7205010A (xx)
SE (3) SE383003B (xx)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3859061A (en) * 1973-04-23 1975-01-07 Chromalloy American Corp Corrosion resistant coating system for ferrous metal articles having brazed joints
US4429019A (en) 1980-01-03 1984-01-31 Bulten-Kanthal Ab Heat-resistant machine component
US4600662A (en) * 1985-03-18 1986-07-15 Illinois Tool Works Inc. Ferrous article layered with ion vapor deposited non-oxidized aluminum

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2228863B1 (xx) * 1973-05-07 1978-06-02 Alloy Surfaces Co Inc

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB614120A (en) * 1946-07-08 1948-12-09 Int Comb Ltd A process for protecting the heating surfaces of boiler and superheater tubes and economisers and oil and tar stills
GB639676A (en) * 1947-08-29 1950-07-05 William Edward Ballard Improvements in the protection of ferrous metal surfaces subject to contact with hotfurnace gases

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3859061A (en) * 1973-04-23 1975-01-07 Chromalloy American Corp Corrosion resistant coating system for ferrous metal articles having brazed joints
US4429019A (en) 1980-01-03 1984-01-31 Bulten-Kanthal Ab Heat-resistant machine component
US4600662A (en) * 1985-03-18 1986-07-15 Illinois Tool Works Inc. Ferrous article layered with ion vapor deposited non-oxidized aluminum

Also Published As

Publication number Publication date
SE7415179L (xx) 1974-12-04
IL39217A (en) 1975-08-31
DE2218175A1 (de) 1972-11-30
FR2137488B1 (xx) 1975-03-21
CH558838A (de) 1975-02-14
CA967463A (en) 1975-05-13
GB1345128A (en) 1974-01-30
IL39217A0 (en) 1972-08-30
NL7205010A (xx) 1972-11-21
JPS525051B1 (xx) 1977-02-09
FR2137488A1 (xx) 1972-12-29
BE782151A (fr) 1972-07-31
SE383003B (sv) 1976-02-23
IT953364B (it) 1973-08-10
SE379061B (xx) 1975-09-22
LU65164A1 (xx) 1972-07-13
AU4110772A (en) 1973-10-18
AU467810B2 (en) 1973-10-18

Similar Documents

Publication Publication Date Title
US3922396A (en) Corrosion resistant coating system for ferrous metal articles having brazed joints
US3874901A (en) Coating system for superalloys
US5098797A (en) Steel articles having protective duplex coatings and method of production
CA1222719A (en) Methods of forming a protective diffusion layer on nickel, cobalt and iron base alloys
US3873347A (en) Coating system for superalloys
US3859061A (en) Corrosion resistant coating system for ferrous metal articles having brazed joints
US2763919A (en) Coated refractory body
US2927043A (en) Aluminum coating processes and compositions
US3741791A (en) Slurry coating superalloys with fecraiy coatings
US4009146A (en) Method of and mixture for aluminizing a metal surface
US3748110A (en) Ductile corrosion resistant coating for nickel base alloy articles
US3904789A (en) Masking method for use in aluminizing selected portions of metal substrates
US5260099A (en) Method of making a gas turbine blade having a duplex coating
US3862851A (en) Method of producing Magnesium-Based coating for the sacrificial protection of metals
US4141760A (en) Stainless steel coated with aluminum
US2970065A (en) Forming an aluminum-containing alloy protective layer on metals
US4241113A (en) Process for producing protective coatings on metals and metal alloys for use at high temperatures
US4036602A (en) Diffusion coating of magnesium in metal substrates
CN112323014A (zh) 一种渗铝硅-预氧化制备扩散阻挡层的方法
US3748172A (en) Magnesium based coating for the sacrificial protection of metals
US4260654A (en) Smooth coating
US3729295A (en) Corrosion resistant coating system
US2788290A (en) Method of forming a protective coating on a molybdenum-base article
US2988807A (en) Method of aluminizing cobalt base alloys and article resulting therefrom
US3898052A (en) Corrosion resistant coating system for ferrous metal articles having brazed joints

Legal Events

Date Code Title Description
AS Assignment

Owner name: CHROMALLOY GAS TURBINE CORPORATION, A DE. CORP., N

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CHROMALLOY AMERICAN CORPORATION;REEL/FRAME:004862/0635

Effective date: 19880311

Owner name: CHROMALLOY GAS TURBINE CORPORATION, BLAISDELL ROAD

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:CHROMALLOY AMERICAN CORPORATION;REEL/FRAME:004862/0635

Effective date: 19880311