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
  • C23C12/00—Solid state diffusion of at least one non-metal element other than silicon and at least one metal element or silicon into metallic material surfaces
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
  • F28F19/02—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings
  • F28F19/04—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings of rubber; of plastics material; of varnish
• • 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
  • Y10T428/12576—Boride, carbide or nitride 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.]
  • Y10T428/12771—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

Definitions

• the chromium layer and the diffusion zone between the chromium and substrate serve as a thermal expansion mismatch accommodation region to minimize cracking of the chromium boride layer.
• the chromium layer serves as a secondary corrosion barrier at the base of minor cracks sometimes formed in the outer chromium boride layer.
• we produce a crack-free chromium boride layer by selecting a substrate material which is expansion matched therewith.
• the present materials have particular utility on temperature sensing devices in molten aluminum.
• Our invention is directed to a material which is essentially a tricomponent member having namely, a substrate, a chromium layer adherent thereto and a chromium boride reaction zone formed on the chromium.
• the chromium intermediate layer be used.
• such layer may be partially or completely boronized to form chromium boride.
• the chromium be only partially boronized.
• such chromium layer be formed and used as an independent member and not as a mere diffusion zone on the surface of the substrate.
• a principal object of our invention is to provide a new article of manufacture consisting essentially of a substrate having a chromium layer formed thereon which chromium layer is preferrably surface boronized, or completely boronized, to provide a chromium boride protective coating on said substrate.
• Another object of our invention is to provide a chro- States Patent O hoe mium boride coating on a substrate wherein both coating and substrate are closely thermal expansion matched.
• a further object of our invention is to provide a chromium boride coating on a chromium interlayer afiixed to a substrate wherein there is provided a thermal expansion mismatch accommodation region to minimize cracking of the chromium boride layer.
• the substrate is first coated with a layer of chromium.
• chromium may be deposited by various methods known to those skilled in the art such as electroplating, physical or chemical vapor deposition, and others.
• the thickness of the chromium layer may be varied to accomplish specific objectives as later described herein, but it is essential that there be a discrete chromium layer and not merely, for example, the interdiffusion of the chromium into the substrate. The latter leads to the subsequent formation of mixed borides which we avoid.
• the chromium layer is then surface impregnated with boron at elevated temperature to form a coating thereon consisting essentially of chromium boride.
• a coating thereon consisting essentially of chromium boride.
• Such chromium has excellent corrosion resistance in a variety of environments, and thus acts as a secondary corrosion barrier if cracks exist in the outer boride which penetrate into the chromium region.
• a crack-free chromium boride layer on certain substrate materials. To accomplish this it is necessary to use a substrate material with a coefiicient of thermal expansion closely matched to that of the chromium boride. We also find that materials with somewhat less favorably matched expansion behavior can be used to produce a crack-free chromium boride layer by controlling the relative thicknesses of the chromium boride, the residual chromium, and the chromium-substrate interditfusion zone.
• the crack-free chromium boride coatings have particular utility protecting substrate materials from corrosion in molten aluminum. We have also found that such chromium boride coated articles have adequate oxidation resistance at temperatures above the melting point of aluminum such that they may be used as immersion devices in which both resistance to attack by air and molten aluminum is necessary.
• Specimens of AISI type 1020 and 4130 steel, type 310, 410, 430 and 446 stainless steel, and an alloy of were electroplated with chromium to thicknesses of 0.8 to 1.5 mils. These were subsequently surface impregnated with boron in a fused mixture of 60 weight percent Na B O 40 weight percent B 0. It will of course be understood that other boronizing treatments could also be employed. The boronizing was carried out at 1900 to 1950 F. for two to four hours. Lower temperatures may be used if a longer time is provided to produce boride diffusion coatings of comparable thickness.
• the chromium boride coating formed on the chromium plated 1020, 4130 and type 310 stainless was cracked with the extent of cracking being most severe on the austenitic stainless steel.
• These specimens were then immersed in commercial purity aluminum at a temperature of l300 to 1400 F. for one hour. After this exposure, a dendritic growth was observed on all of the specimens which simulated the crack pattern that existed in the chromium boride coating.
• This dendritic growth, formed in the boride cracks was composed of aluminides of chromium or of chromium and iron. After four hours of exposure to molten aluminum there was rapid disintegration of the coating.
• the chromium boride layer formed on the chromium plated 400 series stainless steels and Fe-25-Cr5-Al alloy was crack-free. These alloys are essentially ferritic from room temperature to 1900 F., and thus have no transformation strains upon cooling, and have a close thermal expansion match with chromium boride.
• the chromium boride layers on chromium plated type 410 and 430 stainless steels and on the alloy afforded complete protection of the underlying substrate.
• Specimens of chromium boride on chromium plated type 446 stainless steel made as herein taught were exposed for over 100 hours in molten aluminum without evidence of corrosion.
• Other materials such as the commercial nickel base alloy Mar M200 which is reported to have an expansion coefiicient about 10% greater than the chromium containing ferritic steels should also be an acceptable substrate material for use herein.
• defect tolerance can be usefully employed, particularly if the underlying materials are not rapidly attacked by molten aluminum.
• the defect tolerance also makes practical multiple chromium boride layer devices in which each layer provides a finite life; the total life of such device being considerable since such random defects are not likely to superimpose on each other.
• the latter two zones provided an expansion mismatch accommodation region between the chromium boride and Armco iron.
• the iron undergoes an allotropic transformation at 1670 F. which on heating results in a decrease in volume. Above this temperature the austenitic form of iron has a higher expansion coefiicient than chromium boride.
• This same expansion mismatch accommodation region can be usefully employed on other materials to avoid or minimize cracking of the chromium boride layer.
• a chromium boride coating of 0.6 mil thickness was produced on a 1018 steel substrate which had been electroplated with 3 mils of chromium. Boronizing was carried out at 1950 F. for two hours in the previously described fused mixture. The residual chromium layer was 2.2 mils thick and the interdifiusion zone between the chromium and substrate had a thickness of 0.5 mil.
• the chromium boride layer contained slight cracks normal to the surface, which extended to the residual chromium layer.
• the cracks were very narrow and spaced about 7 mils apart. Such minor cracks are not expected to significantly detract from the utility of the chromium boride layer as a wear or abrasion resistant surface.
• the chromium boride layer has a hardness in excess of 3000 Diamond Pyramid Numerals (DPN) as measured by SO-gram load microhardness readings on a metallographically polished cross-section of such layer. This is significantly harder than the readings obtained on 1018 steel in which iron boride layers are formed. Such readings normally average 2200 DPN when measured by the above technique.
• the hardness of the chromium boride layer is also significantly higher than those obtained on boronized Fe-Cr alloys containing from 20-25% chromium. The hardness of the Fe-Cr layers on such materials averages approximately 2400 DPN.
• the hardness of the chromium boride layer is considerably greater than that obtained for carburized chromium plated materials or carburized stainless steels.
• the chromium boride layer formed on chromium has a very smooth external surface resembling the original surface finish of the chromium deposit. Such surface is much smoother than that obtainable when iron or most iron-base alloys are boronized.
• This very hard chromium boride layer has utility for a variety of products that require wear and abrasion resistance, such as pump components, shears, scrapers, gripper dogs and chucks, engine components such as piston rings, cams, stems, and rods, chains and sprockets, gears, impellers, knife, razor edges, and slitters, glass cutters, saws, chain saw cutters, routers drills and taps.
• the surface finish can be controlled by, for example, varying the chromium plated finish prior to boronizing which is of considerable importance for applications such as dies, thread and wire guides, capstans, thread, plug and ring gages, mechanical seals such as rotary seals and valve components, forming rolls, cylinder liners, nozzles, bearings and bushings.
• chromium layer affords useful corrosion protectionin environments less aggressive than molten aluminum-at the base of minor cracks that could exist in the boride.
• This offers significant advantage over the iron boride that forms without the chromium interlayer and which exhibits significant rusting.
• the chromium boride layer has excellent corrosion resistance in strong acids. Thus these materials have further utility for use in the wear and abrasion resistant applications previously described, when such applications further involve use in a corrosive environment.
• the thickness of the chromium deposit prior to boronizing can be varied over wide limits in the practice of our invention. It is only essential that the thickness be adequate to provide an outer surface layer which is essentially chromium boride having its excellent corrosion resistance and high hardness. For practical purposes the chromium layer can be as thin as 0.1 mil. We are aware of no practical limitation on the maximum thickness of chromium. However, the difiiculty of fabricating chromium metal to shape by methods other than deposition techniques is well known. Thus, the use of chromium as an interlayer on another structural material is of obvious advantage.
• a tricomponent article of manufacture consisting essentially of:
• sub strate is an alloy steel, essentially ferritic at temperatures from room temperature to at least 1900 F., and having a thermal expansion coefiicient closely matched to that of chromium boride.
• said substrate member is an alloy steel which is essentially ferritic at temperatures from room temperature to at least 1900 F.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Electroplating Methods And Accessories (AREA)
• Physical Vapour Deposition (AREA)

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• 1970
  • 1970-01-06 US US00001054A patent/US3712798A/en not_active Expired - Lifetime
  • 1970-12-19 DE DE19702062777 patent/DE2062777A1/de active Pending
• 1971
  • 1971-01-01 GB GB2571A patent/GB1338641A/en not_active Expired
  • 1971-01-05 FR FR7100166A patent/FR2075946B1/fr not_active Expired

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