US3442720A - Method of forming ti-modified silicide coatings on cb-base substrates and resulting articles - Google Patents

Method of forming ti-modified silicide coatings on cb-base substrates and resulting articles Download PDF

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US3442720A
US3442720A US506144A US3442720DA US3442720A US 3442720 A US3442720 A US 3442720A US 506144 A US506144 A US 506144A US 3442720D A US3442720D A US 3442720DA US 3442720 A US3442720 A US 3442720A
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coating
columbium
substrate
coatings
weight
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Elihu F Bradley
Edwin S Bartlett
Horace R Ogden
Robert I Jaffee
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Raytheon Technologies Corp
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United Aircraft Corp
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    • 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
    • C23C10/44—Siliconising
    • 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

Definitions

  • Oxidation resistant articles comprising a Cb-base alloy substrate having superimposed thereon a surface coating zone consisting essentially of columbium silicide modified by 7-35% by weight of the coating of a metal modifier selected from the group consisting of Ti, and Ti in combination with at least one of V and Cr.
  • a pack cementation process is preferably employed for depositing the silicide coating.
  • This invention relates to novel coatings for columbiumbase alloys that will protect the base metal or substrate from oxidation in high-temperature environments and to a method for creating such coatings.
  • this invention relates to modified columbium silicide coatings for columbium-base alloys in which the silicide portion of the coating is created by methods, such as vapor deposition (particularly pack-cementation), eleotrophoretic deposition, and the like, and the modifiers for the coatings are titanium or a combination of titanium and at least one of vanadium and chromium.
  • the invention also particularly relates to a method for creating such titanium-modified silicide coatings on columbium-base substrates by vapor deposition to produce a protective surface layer or zone over such substrates that provides oxidation-resistance at high temperatures, such as, for example, up to at least 2200 F. in air, or even higher for short exposure times.
  • the principal limitation in gas turbine technology today is the maximum turbine inlet temperature.
  • the maximum turbine inlet temperature is, in turn, controlled by the maximum temperature that turbine blades and vanes are able to withstand without danger of failure.
  • the best available high-temperature alloys were nickel-and cobalt-base superalloys, but critical structural components, such as turbine blades and vanes made from such alloys, are limited to maximum operating temperatures of between 1800 and 1900 F.
  • metals having high melting points are capable of forming alloys having high strength at high temperatures.
  • the need for structural materials that can be used at temperatures in excess of those obtainable with existing structural materials has stimulated interest in the metals having the highest melting points, i.e., the refractory metals, particularly, chromium, columbium, vanadium, hafnium, tantalum, molybdenum, and tungsten.
  • the refractory metals particularly, chromium, columbium, vanadium, hafnium, tantalum, molybdenum, and tungsten.
  • Molybdenum was once considered the chief candidate for use as a base metal in high-temperature alloys. At the elevated temperature service conditions needed, however, molybdenum not only oxidizes, but the oxide formed is also volatile. Once the oxidation reaction sets in, it tends to progress rapidly until molybdenum is consumed at a catastrophic rate.
  • columbium As an alloy base material for high-temperature service, columbium ultimately offers more promise, and considerable interest has been shown in its development as a structural alloy base for use in high-temperature environments. Among the technically most important physical qualities of columbium as an alloy base are its high melting temperature (about 4475 F.) and its low neutroncapture cross section. Columbium is, therefore, potentially useful in such structures as test aircraft, space flight vehicles, and nuclear reactors.
  • columbium is inherently a soft, ductile, readily fabricable material, and although it becomes too weak for practical structural uses at temperatures above 1200 B, it can be readily strengthened for use at much higher temperatures by alloying with various other metals, and particularly by alloying with other refractory metals.
  • Columbium is also a highly reactive metal in that it dissolves large quantities of oxygen and also nitrogen, upon exposure to air or to atmospheres containing even small amounts of these elements at relatively modest temperatures.
  • Cbover Mo-base alloys are relatively more ductile and workable at low temperatures and columbium has a lower density than molybdenum.
  • Cbbase alloys as dictated by economic and technological factors are in structural materials, such as turbine blades for jet engines, which are designed for exposure to oxidizing and corrosive combustion gas environments at temperatures up to about 2000 F. (a temperature that clearly establishes utility for these alloys) and higher. Concomitantly, such alloys must be able to resist mechanical stresses for appreciable periods of time at these high temperatures.
  • oxidation-resistant intermetallic coatings as exhibiting particular potential for protecting refractory metals (e.g., columbium, molybdenum, tantalum, and tungsten) from oxidation at high temperatures.
  • refractory metals e.g., columbium, molybdenum, tantalum, and tungsten
  • the more effective of these ilntermetallic coatings are silicides, aluminides, and beryllides of the base metal.
  • both the coating and substrate material importantly affect the performance of the coated systems.
  • a silicide coating over columbium may perform quite differently from one over molybdenum with the dilference in performance attributable to the substrate rather than to the coating type.
  • some species of coating that are reliably protective over certain of the refractory metals are ineffective over columbium and are susceptible to failure on columbium at high temperatures. Coating and substrate must thus be coordinated and treated as an integrated system. Success with a particular coating on a particular refractory metal base does not mean the coating will be successful when used on a different refractory metal base.
  • a vapor deposition process that can be used advantageously to achieve some types of coatings is the so called pack-cementation process, in which the object to be coated is surrounded by a particulate pack mixture containing, for example, (1) the metal to be reacted with (or deposited upon) the object to be coated (e.g., silicon, aluminum, beryllium), (2) an activator or energizer (usually a halide salt, such as, NaCl, NaF, KF, NH Cl, and the like), and (3) an inert filler material (e.g., A1 SiO BeO, MgO, and the like).
  • the metal to be reacted with (or deposited upon) the object to be coated e.g., silicon, aluminum, beryllium
  • an activator or energizer usually a halide salt, such as, NaCl, NaF, KF, NH Cl, and the like
  • an inert filler material e.g., A1 SiO BeO, MgO
  • This mixture held in a suitable container (such as, a steel box, a graphite boat, or a refractory oxide crucible), is then heated to the desired coating temperature in a prescribed atmosphere and held for a length of time suflicient to achieve the desired coating.
  • a suitable container such as, a steel box, a graphite boat, or a refractory oxide crucible
  • the pack-cementation process may be used to produce controlled-thickness coatings on columbium, the major portions of which will be compounds, such as, CbA13, CbSi and the like.
  • columbium columbium aluminides, silicides, and beryllides
  • certain intrinsic deficiencies such as rapid oxidation failure at low temperatures (in the vicinity of about 1300 F.) or at high temperatures (about 2000 F. and above).
  • the most serious deficiency of existing coatings for columbium is their propensity for failing at localized sites.
  • Silicide coatings on columbium and its structural alloys are more stable than aluminides and have a better thermal expansion match with the substrate than beryllides.
  • beryllides have such a severe thermal expansion mismatch with columbium that their use is prohibited in many applications. With columbium, the silicides are thus coating materials of primary interest.
  • silicide coatings on structural Cb alloy substrates are prone to consumption by rapid oxidation at low (about 1300 F.) temperatures. This characteristic of silicide coatings is sometimes termed the silicide pest phenomenon. Modification of silicide coatings is thus highly desirable to impart sufficient longevity and reliability to give to them a utility they do not normally possess.
  • Another object of this invention is to provide new and improved Ti-modified columbium silicide coatings for Cbbase substrates that overcome the silicide pest phenomenon characterized by rapid consumption of silicide coatings through oxidation at temperatures of about 1300 F., and that also overcome rapid consumption of columbium silicide coatings through oxidation at high temperatures of about 2000 F. or higher thereby providing coatings that give excellent oxidation resistance at temperatures up to at least 2500 F.
  • Further objects of this invention are to provide a novel and improved coating for Cb-base substrates that in addition to providing resistance to simple thermal oxidation will also be protective under other reasonably expected conditions of use, and to this end, the protective coatings of, this invention achieve good resistance to thermal cycl- 7 ing, thermal shock, formation of defects, and high velocity gas erosion, and exhibit and achieve good thermal chemical stability.
  • thermal chemical stability means the ability of a silicide coating to retain its coating integrity, adherence, and oxidation resistance at a relatively low temperature in the silicide pest phenomenon range (i.e., about 1300 F.) following a substantial exposure (e.g., hours) at relatively high temperatures, such as, for example, 2000 F. or higher.
  • a coating that in nominal thicknesses of 2 mils or more is capable of providing protection for exposures to high-temperature oxidizing environments for times in excess of 100 hours at temperatures of up to at least about 2700 F.;
  • a further object of this invention is to provide a new and improved Ti-modified silicide coating for columbium and its alloys that includes a sublayer or subzone formed from subsilicides of the substrate which subzone acts as an oxidation penetration barrier to give back-up protection to the substrate should a defect in the primary surface coating occur, and which also acts as a thermal expansion buffer and thereby prevents failure of the coating due to thermal expansion mismatch between the Timodified silicide compound of the coating surface zone and the substrate itself.
  • a still further object of this invention is to provide a new and improved method for coating Cb-base substrates with a columbium silicide coating by vapor deposition (pack-cementation) of a silicide coating over a Cb-base substrate that has been previously modified by alloying with titanium, or by alloying with titanium and at least one metal selected from the group consisting of vanadium and chromium, to create thereby a substantially homogeneous and uniformly modified columbium silicide coating.
  • Such coatings have an equiaxed structure, maintain their uniformity and homogeneity on even intricately shaped parts and at the edges and corners of parts, and resist local failure.
  • this application provides an oxidation-resistant coating for Cb-base alloys, the coating consisting essentially of columbium silicide modfied with from about 7 to 35% by weight of the coating of a metal modifier selected from the group consisting of: (a) titanium (Ti), and (b) titanium (Ti) and at least one metal selected from the group consisting of vanadium (V) and chromium (Cr).
  • a metal modifier selected from the group consisting of: (a) titanium (Ti), and (b) titanium (Ti) and at least one metal selected from the group consisting of vanadium (V) and chromium (Cr).
  • this invention in one embodiment provides an article of manufacture having good resistance to oxidation that comprises a substrate consisting essentially of Cb and from 12 to 65% by weight of the substrate of Ti, the article having an oxidation resistant surface zone consisting essentially of columbium silicide modified by a Ti content of from 7 to 35% by weight of the surface zone.
  • this invention also provides a new and improved article of manufacture having good stress-rupture strength at high temperatures, high-temperature oxidation resistance, and resistance to cyclic fatigue failure, which article comprises a substrate selected from the group consisting of: (a) columbium and an alloying addition of from 12 to 65% by weight of the substrate of titanium (Cb-(12 to 6-5) Ti), and (b) columbium and an alloying addition of from 12 to 65% by weight of the substrate of a metal modifier consisting essentially of titanium and at least one metal selected from the group consisting of vanadium and chromium [Cb- (12 to 65)(Ti-V)], [Cb-(12 to 65)(Ti-Cr)], or [Cb- (12 to 65 )(Ti-V-Cr)]; the article having a thermal cyclic failure resistant, defect resistant, and broad range oxidation-resistant coating or surface zone consisting essentially of columbium silicide modified by a metal modifier in an amount of from 7 to
  • the invention also includes an article having good resistance to oxidation at elevated temperatures which comprises a substrate consisting essentially of Cb and from 12 to 65 by weight of the substrate of an alloying addition consisting essentially of Ti and V, the article having an oxidation-resistant coating consisting essentially of a surface zone of columbium silicide modified by a metal modifier in an amount of from 7 to 35% by weight of the coating, the metal modifier consisting essentially of Ti and V.
  • this invention provides a process for producing a coated metal article having resistance to oxidation at high temperatures, the metal article comprising a substrate consisting essentially of Cb and from 12 to 65% by weight of the substrate of an alloying addition of a metal modifier selected from the group consisting of: (a) Ti, and (b) Ti and at least one metal selected from the group consisting of Cr and V; which process comprises contacting the substrate with a powdered pack of a finely ground source of Si and a small amount of a volatilizable halide salt, as active ingredients, and in inert filler; heating the substrate and powdered pack for a time period sufiicient to cause volatilization of the halide salt, producting deposition of Si on the surface of the substrate, and thereby effecting the creation of an exterior surface zone on the substrate consisting essentially of columbium silicide modified by an amount of the metal modifier consisting essentially of 7 to 35% by weight of the exterior surface zone.
  • a metal modifier selected from the group consisting of
  • the metal modifier includes V in addition to Ti.
  • Preferred results, in general, are also obtained when the metal modifier is titanium alone, and the Ti is present in amounts from 13 to 28% by weight of the surface zone or coating.
  • These coatings are produced by siliconizing Cb-alloy substrates containing 23 to 55% Ti (e.g., Cb-23Ti to Cb-55Ti).
  • the most preferred Ti-modified coating of this invention contains 14% by weight Ti and is produced by siliconizing a Cb- 25Ti alloy substrate.
  • Ti content be from 4 to 26% by weight of the coating and V content be from 2 to 6% by weight of the coating, provided the aggregate of Ti and V in the coating is at least 7% by weight of the coating.
  • Such coatings can be prepared by the proportionate modification of silicide coatings, by siliconizing, in accordance with the process of this invention Cb-base alloy substrates containing 6 to 50% by weight Ti and 3 to 12% by weight V. An aggregate Ti and V content of 12 to 16% in the alloy substrates siliconized in this manner is greatly preferred. These substrates 4 to 5% by weight of the coating of Ti and 4 to 5% by weight of the coating of V.
  • These more preferred coatings are prepared by proportionate silicide modification of Cb-(69)Ti-(69)V alloy substrates. These coatings can therefore be represented by the formula [Cb- (6-9)Ti-(6-9)V]Si Coatings produced by siliconizing the following alloys in accordance with this invention produce the best results of all: Cb-6Ti-9V, and Cb-9Ti- 6V. Of these, alloy substrate (Cb-6Ti-9V), which contains about 6% by weight of Ti and about 9% by weight of V, is the optimum alloy of this invention.
  • V (or Cr) content of the coating
  • V contents (of the coating) above about 15% should not be used.
  • V content exceeds this maximum limit, excessive diffusional growth of the subsilicide zone results and produces a corresponding depletion of the protective disilicide coating or surface zone and a shorter life of the roating;
  • V content in the substrate in excess of this maximum limit can produce V enrichment of the substrate zone immediately beneath the coating to an extent whereby any local coating failure results in formation of V 0 in large amounts, with resulting catastrophic oxidation of the coated system, thus negating one of the major advantages of Cb-base alloys over Mo-base alloys.
  • V containing coatings are applied to structural substrates it is also important that the V content not exceed this 15 maximum limit because if the applied coating has too high a V content, V will diffuse from the coating into the substrate and result in significant degradation of substrate strength.
  • Typical Cb-base structural substrates to which these coatings can be applied include V-free or low-V containing Cb-base substrates, i.e., substrates containing V only in amounts up to about 5%.
  • V may be desirable in some Cb-base structural substrates because, in low amounts, it has a modest strengthening effect on Cb-base substrates and also decreases the alloy density. In amounts above 5%, however, V tends to degrade the strength of the substrate.
  • Ti-Cr modified silicide coatings in accordance with this invention, Ti contents of 4 to 26% by weight of the coating and Cr contents of 2 to 15 by weight of the coating are preferred, provided that the aggregate of Ti and Cr is at least 7% and not in excess of 35% by weight of the coating.
  • Such coatings can be prepared by siliconizing, in accordance with this invention, an alloy substrate of the formula Cb-(650) Ti-(329)Cr with the proviso that the Ti and Cr, in the aggregate, are between 12 and 65 by weight of the substrate.
  • Even more preferred are Ti-Cr modified silicide coatings containing 4 to 6% Ti by weight of the coating and 2 to 5% Cr by weight of the coating, provided again that the aggregate of Ti and Cr is at least 7% by weight of the coating.
  • An optimum Ti-Cr modified coating is produced by siliconizing the following alloy substrate in accordance with this invention:
  • Coatings having Cr contents above 16% Cr have diffusion properties that could result in severe degradation of the ductility of the coated system when the coatings of this invention are used with structural Cb-base alloys.
  • a combination metal modifier containing Ti, V, and Cr can also be used, although the combination of all three modifiers in one coating system does not produce the superior coating properties attainable with Ti-V modifiers.
  • the aggregate amount of Ti, V, and Cr in these tri-modified coatings should be between 7 and 35% by weight of the coating.
  • These coatings can be produced by siliconizing, in accordance with this invention, Cb-Ti-V-Cr alloy substrates containing, in the aggregate, from 12 to 65% by weight of the substrate of Ti, V, and Cr.
  • Ti-V combination metal modifier is the most preferred embodiment of this invention.
  • each of Ti-V, and Cr ias modifiers lends valuable oxidation resistance and other desirable properties to the coatings of this invention, each of these modifiers, in one manner or another, is capable of adversely affecting the structural properties of the substrate.
  • Ti is the most detrimental to high-temperature structural strength of Cbbase alloys, while V is the least detrimental.
  • V is the most detrimental to high-temperature structural strength of Cbbase alloys
  • V is the least detrimental.
  • the use of V in combination with Ti permits use of lesser amounts of Ti, by substitution of less detrimental V.
  • V is less detrimental to the structural properties of Cb-base alloys than is Ti (and thus substitution of V for Ti lessens the overall detrimental effect imposed by the total modifier)
  • Ti and V modifiers when used in combination, produce a synergistic effect.
  • the coatings produced by siliconizing Cb-6Ti-9V substrates achieve equivalent oxidation resistance, erosion resistance, thermal chemical stability, and thermal shock resistance to that obtainable with high Ti-modification (e.g., Cb-SOTi or Cb-25Ti), at much lower aggregate amounts of Ti-V modifier, and even lower amounts of the more deleterious Ti.
  • this invention comprehends the production of the instant coating by siliconizing Cb-Ti, Cb-Ti-V, Cb-Ti-Cr, or Cb-Ti-V-Cr alloy substrates, resulting in the formation of proportionately modi fied columbium silicide coatings, it will be understood that, in its broader aspects, this invention comprehends application of the oxidation-resistant coatings of this invention to other Cb-base structural alloy substrates, such as, for example, Cb-ZOTa-ISW-SMO, and the like.
  • Such application could be accomplished, for example, either by incorporating a metal modifier (Ti, Ti-V, etc.), in accordance with this invention in the substrate, or by physically adhering thin sheets or foils of the Cb-base alloy substrates of the coatings of this invention (e.g., Cb- 6Ti-9V, Cb-9Ti-6V, etc.) to structural alloy substrates before, or possibly even after, siliconizing.
  • a metal modifier Ti, Ti-V, etc.
  • Such adherance also could be achieved, for example, by a combination of physical and chemical means.
  • an alloy substrate consisting essentially of 8 Cb-20Ta-l5W-5Mo-21Ti when siliconized in accordance with this invention, achieves a modified silicide coating exhibiting the improved oxidation resistance and other benefits provided by this invention.
  • coatings of this invention can be desirable in some instances for structural reasons; hence, such means, rather than direct inclusion of the modifiers of this invention in the substrate can be used to achieve the beneficial results of this invention.
  • the coatings of this invention can be removed from the substrates of this invention by grinding, machining, etc., and applied to structural Cb-base alloy substrates by plasma or flame spraying, electrophoretic deposition, powder or slurry processes, or the like.
  • silicide coatings on structural Cb-base alloy substrates are prone to rapid consumption through oxidation at low (about 1300 F.) temperatures (this tendency is sometimes referred to as the silicide pest phenomenon) and at high (about 2000 F. or higher) temperatures. At the latter temperatures a rapid oxidation mechanism occurs which, though different from the pest phenomenon, is similar in its harmful end result.
  • silicide coatings for columbium and its structural alloys are modified through substrate modifications of:
  • Titanium (Ti) titanium
  • Titanium and chromium (Ti-Cr), or
  • the Ti-modified silicide coatings of this invention are thus particularly outstanding in their ability to protect columbium and its alloys from oxidation under a wide variety of conditions of use and at temperatures ranging from room temperature up to about 2700 F. These coatings possess distinctly superior oxidation resistance and superior defect insensitivity up to at least about 2700" F. and overcome and counteract the tendency of unmodified or Ti-free silicide coatings on Cb-base substrates to fail at critical temperatures of about 1300 F. and about 2000 F. or above.
  • Coating failure at low temperatures occurs by rapid disintegration of the coating to a fine, intermetallic powder that spalls from the surface of the substrate, leaving it unprotected against subsequent oxidation attack.
  • the normal disilicide structure shown in FIG. 1 (photomicrograph of a disilicide coating over alloy showing structure enlarged 500 times), consists predominantly of columnar grains with axes oriented normal to the substrate surface.
  • the grain boundaries disclose areas of atomistic imperfection that are highly susceptible to failure by either chemical or mechanical forces. With either of the two mechanisms just described, such a structure presents the least resistance to failure.
  • the predominant resulting coating phase is CbSi
  • a Cb-base alloy such as, Cb-20Ta-15W-5Mo (additions expressed in percent by weight)
  • Cb-20Ta-15W-5Mo additions expressed in percent by weight
  • the resulting coating can thus also be modified in chemical composition.
  • specific elemental modifiers within specific ranges ofalloy content may be used to homogeneously and uniformly modify columbium silicide coatings to improve significantly coating performance over that attainable with unmodified columbium silicide coatings.
  • the Cb-base alloy substrates set forth below most of which consist essentially of Cb and various amounts of alloying elemental additions of Ti, Ti-V, Ti-Cr, and Ti-V-Cr, were prepared as set forth in the description that follows this enumeration of the alloys.
  • the as-cast buttons were machined to provide a number of nominal X A x 4 inch rectangular tabs. Sharp corners and edges were rounded off by filing.
  • Si powder 17 NaF powder 3 A1 powder 80 These packs, contained in covered steel or graphite cans, were then subjected to a temperature of about 2200 F in an argon atmosphere for about 4 hours, Mter this treatment, the specimens were cooled and recovered from the first pack, repacked in a fresh pack mix of the same composition as the first pack mix, and recycled for times ranging /2 to 12 hours at about 2200 F.
  • the resulting modified disilicide coatings were homogeneous, sound, and uniform. They ranged in thickness from 3 to 6 mils.
  • compositions of the modified silicide coatings created by such treatment were determined or controlled by substrate composition.
  • the improved behavior displayed by such modified coatings primarily resulted from the chemical modification achieved and was dependent upon proportions of modifying ingredients in the coating.
  • the proportions of modifiers in each coating were determined in turn largely by the proportions of elemental modifiers in the substrate.
  • Oxidation tests were conducted in ambient air without forced air flow. During testing, specimens, supported on refractory oxide boats, were inserted in an electrically heated mufile furnace preset at the desired temperature. Specimens were removed periodically from the furnace, and cooled to room temperature for visual examination and weighing, after which they were returned to the furnace for additional oxidation exposure.
  • columbium d1s1l1c1de Cb1 modlfied by an addltlon in Table 4 and related data, the following conclusions of about 1% of chromium in the coating (photomlcroon improvement in 1300 F. oxidation performance of graph enlarged 500 times). 15 columbium disilicide coatings are apparent:
  • Morediiferent crystallographic types Morediiferent crystallographic types. Broad, diffused grain over, within this range, the use of combined modifiers, boundaries are particularly evident in the Ti-, Ti-V, Ti-Cr and particularly V, was unusually beneficial and in some and Ti-V-Cr-modified coatings of this invention, which cases achieved results improved even beyond those atsuggests that important and beneficial chemical segregatainable with the primary single Ti-modification. In many tion effects take place at grain boundaries. 35 cases it was thus possible to use lesser amounts of Ti At modification levels above about 60% by weight of and V, or Ti and Cr, or Ti, V and Cr, than would have Ti in the substrate, the desired improved behavior in been necessary if Ti alone had been used as a modifier.
  • Ti-modification, Ti-V-modification, and Ti-Cr-modification of the disilicide structure achieved improvements of primary significance, with certain Ti-V- modifications producing coatings exceeding all others tested in oxidation resistance.
  • the thermal expansion of the subsilicide (M Si is less than that of either CbSi or (Cb- 20Ta-15W-5Mo)Si and therefore the subsilicide zone is in compression at low temperatures, i.e., below the coating temperature or higher exposure temperatures. Exposure at higher temperatures permits growth of M Si as pointed out above, and as this zone becomes thicker it TABLE 5.
  • Subsilicides are defined as the phase or phases of the coating having substantially less Si than CbSi which phase or phases can be determined by X-ray d'iifraction to be crystallographically distinct from the most protective CbSi phase.
  • the subsilicides were found to be not completely oxidationresistant after hours of exposure.
  • the 7Timodification thus did not prevent some undesirable contamination of the alloy substrate after 100 hours at 2200 F.
  • an important attribute of this invention is its capability of enhancing oxidation resistance of the subsilicide region through co-modification of low level Ti-modified silicide coatings by V or Cr. This effect is shown in the photomicrographs of FIGS. 4-6.
  • any of the modifications of this invention i.e., Ti, Ti-V, Ti-Cr, or Ti-V-Cr produce greatly improved 300-hour protection over unmodified silicide coatings or coatings modified by Ti, V, or Cr in amounts outside the limits of this invention.
  • the thermal chemical stability of the coatings of this invention was tested by subjecting certain of the abovelisted alloys to a standard 100 hour, 8-cycle exposure at 2200" F., then slow cooling the specimens by a standard slow cool cycle, and then subjecting the specimens to a standard 8-cycle, up to 100 hour exposure at 1300 F.
  • thermal chemical stability tests are indicated in Table 7 below. These tests were designed to simulate certain operating conditions to which parts coated with the alloys of this invention would be likely to be subjected. For example, a part in a gas turbine or jet aircraft engine may be subjected to exposure to high temperatures (above 2000 F.) for extended periods during operation, and then to cooling and resulting intermittent exposures at low temperatures (around 1300 F.) during slowdown or shut-down of the turbine or engine.
  • the slow-cool resistance was of great interest because some coatings have a tendency to exhibit powdering during slow cool cycles.
  • the most preferred coating of this invention i.e., the coating produced by siliconizing a Cb-6Ti-9V alloy substrate, was also tested for thermal shock resistance and diffusional stability.
  • the sample was subjected to air-quench cycles during 100 hours at 2200 F.
  • the thermal shock resistance of this sample was excellent.
  • the coating was not degraded and 100-hour weight gain was only 0.73 mg./cm.
  • Oxidation tests of the most preferred coating (Cb-6Ti-9V)Si were also conducted at higher temperatures. These cyclic tests were conducted for 100 hours on duplicate specimens at 2500 F. and 2700 F., respectively, and produced no failures of the test specimens. Weight gains after 100 hours of testing, using the standard eight cycles between room and test temperatures, were 0.54 mg./cm. and 0.69 mg./c m. respectively, for the specimens oxidized at 2500 F., and 0.90 mg./cm. and 156 mg./cm. respectively, for the specimens oxidized at 2700 F.
  • this invention is directed to protective coatings for Cb-base substrates based on modified columbium silicide structures.
  • the primary structure of the coating comprises a vapor-deposited columbium silicide surface zone, but in accordance with the invention this surface zone is Ti-modified.
  • Ti-modification the basic chemical and microstructural characteristics of the columbium silicide coating are changed, and these changes result in a pronounced improvement in coating behavior at both low and high temperatures.
  • the Timodification is combined with V or Cr, or with both V and Cr modification. The very best results are achieved with a combination of Tiand V-modification.
  • modification of basic columbium silicide coatings with the following elements and combinations of elements at levels in the aggregate of from 7 to 35% by weight of the silicide coating are particularly etfective in promoting significantly improved coating behavior at both low and high temperatures: Ti, Ti-V, Ti-Cr, and Ti-V-Cr.
  • An article of manufacture comprising a Cb-base alloy substrate having superimposed thereon a thermalcyclic-failure resistant, defect resistant and broad range oxidation resistant surface coating zone consisting essentially of columbium silicide modified by 7 to 35% by Weight of the coating of a metal modifier selected from the group consisting of: (a) Ti, and (b) Ti and at least one of V and Cr.
  • said surface coating zone consists essentially of columbium silicide modified by from 4 to 26% of Ti and 2 to 15% of Cr, the aggregate Ti and Cr in said coating not exceeding 35% by weight thereof.
  • An article of manufacture having good resistance to oxidation at elevated temperatures which comprises: a substrate consisting essentially of Cb and an alloying addition of from 12 to 65% by weight of the substrate of a metal modifier selected from the group consisting of (a) Ti, and (b) Ti and at least one of V and Cr; and a thermal-cyclic-failure resistant, defect resistant, and broad range oxidation resistant coating on the surface of said substrate, said coating consisting essentially of columbium silicide modified by from 7 to 35% by weight of the coating of the selected metal modifier.
  • metal modifier consists essentially of Ti and at least one of V and Cr.
  • the substrate consists essentially of Cb modified by an alloying addition of from 6 to 50% by weight of the substrate of Ti and from 3 to 12% by weight of the substrate of V, and the coating essentially of columbium silicide modified by from 4 to 26% by weight of the coating of Ti and from 2 to 6% by weight of the coating of V.
  • the article of claim 12 wherein the substrate consists essentially of 6 to 9% by weight of Ti, 6 to 9% by weight of V, balance essentially Cb, and the coating consists essentially of columbium silicide modified by 4 to 5% by weight of the coating of Ti and 4 to 5% by weight of the coating of V.
  • the substrate consists essentially of about 6% by weight of Ti, about 9% by weight of V, balance essentially Cb, and the coating consists essentially of columbium silicide modified by about 4% by weight of the coating of Ti, and about 5% by weight of the coating of V.
  • the substrate consists essentially of about 9% by weight of Ti, about 6% by weight of V, balance essentially Cb, and the coating consists essentially of columbium silicide modified by about 5% by weight of the coating of Ti and about 4% by weight of the coating of V.
  • the substrate consists essentially of from 23 to 55% by weight of Ti, balance essentially Cb, and the coating consists essentially of columbium silicide modified by 13 to 28% by weight of the coating of Ti.
  • the substrate consists essentially of about 25% by weight of Ti, balance essentially Cb, and the coating consists essentially of columbium silicide modified by about 14% by weight of the coating of Ti.
  • the substrate consists essentially of at least 35 by weight of Cb, from 6 to 50% by weight of Ti, and from 3 to 29% by weight of Cr
  • the coating consists essentially of columbium silicide modified by from 4 to 26% by weight of the coating of Ti and 2 to 15% by weight of the coating of Cr, the aggregate Ti and Cr in said coating not exceeding 35% by weight thereof.
  • the substrate consists essentially of at least 35% by weight of Cb, from 3 to 25% by weight of Ti, from 4 to 29% by weight of Cr, and from 3 to 12% by weight of V, the aggregate Ti, Cr and V being at least 12% by weight of the substrate, and the coatng consists essentially of columbium silicide modified by 2 to 13% by weight of the coating of Ti, 3 to 16% by weight of the coating of Cr, and 2 to 6% by weight of the coating of V.
  • a method of producing a coated metal article having resistance to oxidation at elevated temperatures the metal article having a substrate consisting essentially of Cb and an alloying addition of from 12 to 65% by weight, in aggregate, of a metal modifier selected from the group consisting of (a) Ti, and (b) Ti and at least one of V and Cr, which process comprises subjecting the substrate to an environment produced by heating a mixture of powders comprising a finely ground source of Si and a small amount of a volatilizable halide salt, as active ingredients, and an inert filler; heating the substrate and powder mixture for a time sufficient to cause volatilization of the halide salt and deposition of Si on the surface of the substrate, thereby effecting the creation of an exterior coating on the surface of the substrate consisting essentially of columbium silicide modified by the selected 23 metal modifier in an amount of from 7 to 35% by weight of the coating.
  • a metal modifier selected from the group consisting of (a) Ti, and (b) Ti and at least one of V and Cr
  • the metal modifier consists essentially of from 6 to 50% by weight of the substrate of Ti and from 3 to 12% by weight of the substrate of V.
  • the metal modifier consists essentially of from 6 to 50% by weight of the substrate of Ti and from 3 to 29% by weight of the substrate of Cr, the aggregate Ti and Cr not exceeding 65 by weight of the substrate.

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US506144A 1965-10-23 1965-10-23 Method of forming ti-modified silicide coatings on cb-base substrates and resulting articles Expired - Lifetime US3442720A (en)

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BE (1) BE688653A (de)
DE (1) DE1521572B1 (de)
FR (1) FR1497819A (de)
GB (1) GB1163615A (de)
SE (1) SE324270B (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3643658A (en) * 1968-09-03 1972-02-22 Straumann Inst Ag Implants of titanium or a titanium alloy for the surgical treatment of bones
US3931447A (en) * 1973-05-04 1976-01-06 The United States Of America As Represented By The United States National Aeronautics And Space Administration Fused silicide coatings containing discrete particles for protecting niobium alloys
JPS52114023U (de) * 1976-02-25 1977-08-30
US4413302A (en) * 1978-07-19 1983-11-01 Gesellschaft Fuer Kernenergieverwertung In Schiffbau Und Schiffahrt Gmbh Structural member made from a metallic material having an upper surface exposed to the danger of electric charge building-up thereon and the use of such structural member
US4713134A (en) * 1982-09-30 1987-12-15 Chicopee Double belt bonding of fibrous web comprising thermoplastic fibers on steam cans
CN115821258A (zh) * 2022-12-06 2023-03-21 西北有色金属研究院 一种耐热冲刷抗热震硅化物涂层及其制备方法

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3015579A (en) * 1959-06-15 1962-01-02 Chromizing Corp Metal coating process
US3037883A (en) * 1959-02-18 1962-06-05 Chromalloy Corp Diffusion coating of non-ferrous metals
US3090702A (en) * 1961-01-23 1963-05-21 Chromizing Corp Protective coating of refractory metals
US3219474A (en) * 1962-05-11 1965-11-23 Priceman Seymour Protective coatings for columbium and its alloys
US3307964A (en) * 1963-05-07 1967-03-07 Du Pont Process of forming protective coatings on columbium and tantalum using a fluidized bed
US3317343A (en) * 1963-02-01 1967-05-02 Richard A Jefferys Activated coating of columbium metal
US3337363A (en) * 1965-03-15 1967-08-22 Ritter Pfaudler Corp High temperature coatings for columbium alloys

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3037883A (en) * 1959-02-18 1962-06-05 Chromalloy Corp Diffusion coating of non-ferrous metals
US3015579A (en) * 1959-06-15 1962-01-02 Chromizing Corp Metal coating process
US3090702A (en) * 1961-01-23 1963-05-21 Chromizing Corp Protective coating of refractory metals
US3219474A (en) * 1962-05-11 1965-11-23 Priceman Seymour Protective coatings for columbium and its alloys
US3317343A (en) * 1963-02-01 1967-05-02 Richard A Jefferys Activated coating of columbium metal
US3307964A (en) * 1963-05-07 1967-03-07 Du Pont Process of forming protective coatings on columbium and tantalum using a fluidized bed
US3337363A (en) * 1965-03-15 1967-08-22 Ritter Pfaudler Corp High temperature coatings for columbium alloys

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3643658A (en) * 1968-09-03 1972-02-22 Straumann Inst Ag Implants of titanium or a titanium alloy for the surgical treatment of bones
US3931447A (en) * 1973-05-04 1976-01-06 The United States Of America As Represented By The United States National Aeronautics And Space Administration Fused silicide coatings containing discrete particles for protecting niobium alloys
JPS52114023U (de) * 1976-02-25 1977-08-30
JPS6030786Y2 (ja) * 1976-02-25 1985-09-14 株式会社河合楽器製作所 鍵のストツパ装置
US4413302A (en) * 1978-07-19 1983-11-01 Gesellschaft Fuer Kernenergieverwertung In Schiffbau Und Schiffahrt Gmbh Structural member made from a metallic material having an upper surface exposed to the danger of electric charge building-up thereon and the use of such structural member
US4713134A (en) * 1982-09-30 1987-12-15 Chicopee Double belt bonding of fibrous web comprising thermoplastic fibers on steam cans
CN115821258A (zh) * 2022-12-06 2023-03-21 西北有色金属研究院 一种耐热冲刷抗热震硅化物涂层及其制备方法
CN115821258B (zh) * 2022-12-06 2024-05-03 西北有色金属研究院 一种耐热冲刷抗热震硅化物涂层及其制备方法

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Publication number Publication date
FR1497819A (fr) 1967-10-13
GB1163615A (en) 1969-09-10
DE1521572B1 (de) 1971-03-04
BE688653A (de) 1967-03-31
SE324270B (de) 1970-05-25

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