CA1068453A - Composite interlayer for diffusion bonding - Google Patents
Composite interlayer for diffusion bondingInfo
- Publication number
- CA1068453A CA1068453A CA268,544A CA268544A CA1068453A CA 1068453 A CA1068453 A CA 1068453A CA 268544 A CA268544 A CA 268544A CA 1068453 A CA1068453 A CA 1068453A
- Authority
- CA
- Canada
- Prior art keywords
- interlayer
- ductile
- brittle
- lamellae
- lamellar
- 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
Links
- 239000011229 interlayer Substances 0.000 title claims abstract description 87
- 238000009792 diffusion process Methods 0.000 title description 17
- 239000002131 composite material Substances 0.000 title description 5
- 230000008018 melting Effects 0.000 claims abstract description 29
- 238000002844 melting Methods 0.000 claims abstract description 29
- 239000000203 mixture Substances 0.000 claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 21
- 230000000994 depressogenic effect Effects 0.000 claims abstract description 19
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052751 metal Inorganic materials 0.000 claims abstract description 7
- 239000002184 metal Substances 0.000 claims abstract description 7
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 6
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 4
- 239000010941 cobalt Substances 0.000 claims abstract description 4
- 229910017052 cobalt Inorganic materials 0.000 claims abstract description 4
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims abstract description 4
- 229910052742 iron Inorganic materials 0.000 claims abstract description 4
- 229910045601 alloy Inorganic materials 0.000 claims description 22
- 239000000956 alloy Substances 0.000 claims description 22
- 239000012071 phase Substances 0.000 claims description 12
- 239000007791 liquid phase Substances 0.000 claims description 9
- 230000001052 transient effect Effects 0.000 claims description 9
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 7
- 229910052804 chromium Inorganic materials 0.000 claims description 7
- 239000011651 chromium Substances 0.000 claims description 7
- 239000000463 material Substances 0.000 claims description 7
- 238000005096 rolling process Methods 0.000 claims description 7
- 229910052721 tungsten Inorganic materials 0.000 claims description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 6
- 229910052799 carbon Inorganic materials 0.000 claims description 6
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 6
- 239000010937 tungsten Substances 0.000 claims description 6
- 238000007740 vapor deposition Methods 0.000 claims description 5
- 241000446313 Lamella Species 0.000 claims description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 4
- 239000000758 substrate Substances 0.000 claims description 4
- 229910052719 titanium Inorganic materials 0.000 claims description 4
- 239000010936 titanium Substances 0.000 claims description 4
- 230000001464 adherent effect Effects 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 238000000151 deposition Methods 0.000 claims description 3
- 238000007772 electroless plating Methods 0.000 claims description 3
- 239000000155 melt Substances 0.000 claims description 3
- 229910052726 zirconium Inorganic materials 0.000 claims description 3
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims description 2
- 229910052735 hafnium Inorganic materials 0.000 claims description 2
- 239000010955 niobium Substances 0.000 claims description 2
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 2
- 229910052715 tantalum Inorganic materials 0.000 claims description 2
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 claims description 2
- 238000005137 deposition process Methods 0.000 claims 3
- 230000000875 corresponding effect Effects 0.000 claims 1
- 238000009713 electroplating Methods 0.000 claims 1
- VBJZVLUMGGDVMO-UHFFFAOYSA-N hafnium atom Chemical compound [Hf] VBJZVLUMGGDVMO-UHFFFAOYSA-N 0.000 claims 1
- 239000011888 foil Substances 0.000 description 21
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 14
- 229910052796 boron Inorganic materials 0.000 description 14
- 239000010410 layer Substances 0.000 description 10
- 229910052782 aluminium Inorganic materials 0.000 description 9
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 9
- 229910000601 superalloy Inorganic materials 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 7
- 229910000521 B alloy Inorganic materials 0.000 description 4
- 238000005304 joining Methods 0.000 description 4
- 230000004927 fusion Effects 0.000 description 3
- 238000007747 plating Methods 0.000 description 3
- 239000003870 refractory metal Substances 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- 238000007792 addition Methods 0.000 description 2
- QDWJUBJKEHXSMT-UHFFFAOYSA-N boranylidynenickel Chemical compound [Ni]#B QDWJUBJKEHXSMT-UHFFFAOYSA-N 0.000 description 2
- 238000005271 boronizing Methods 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 229910001005 Ni3Al Inorganic materials 0.000 description 1
- JJFNJZGXHWYGMQ-UHFFFAOYSA-N [Ni].B#[Co] Chemical compound [Ni].B#[Co] JJFNJZGXHWYGMQ-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical compound [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 description 1
- 238000005219 brazing Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000002939 deleterious effect Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- -1 nickel-chromium-aluminum Chemical compound 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 description 1
Landscapes
- Pressure Welding/Diffusion-Bonding (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The disclosure teaches an improvement in an interlayer for bonding metallic articles. The articles are based on a metal chosen from the group consisting of nickel, cobalt, and iron, and the interlayer has a composition similar to that of the articles being joined, except for the addition of a quantity of at least one melting point depressant. The interlayer also has a brittle characteristic because of the formation of brittle phases. In accordance with the invention, the interlayer is provided in the form of a plurality of lamellae, each of the lamellae being free from those combinations of elements which form brittle phases. Thus, the lamellar interlayer is ductile even though its overall composition is one which would be brittle if produced in a homogeneous form. The invention also relates to a process for producing a ductile lamellar interlayer.
The disclosure teaches an improvement in an interlayer for bonding metallic articles. The articles are based on a metal chosen from the group consisting of nickel, cobalt, and iron, and the interlayer has a composition similar to that of the articles being joined, except for the addition of a quantity of at least one melting point depressant. The interlayer also has a brittle characteristic because of the formation of brittle phases. In accordance with the invention, the interlayer is provided in the form of a plurality of lamellae, each of the lamellae being free from those combinations of elements which form brittle phases. Thus, the lamellar interlayer is ductile even though its overall composition is one which would be brittle if produced in a homogeneous form. The invention also relates to a process for producing a ductile lamellar interlayer.
Description
BACKGROUND OF THE INVENTION
.
The present lnvention relates in general to the art of diffusion bonding and, more particularly, to diffusion bonding of the superalloys utilizing a transient liquid phase in the bonding process.
Transient liquid phase diffusion bonding has been shown to be a very useful method for produclng high quality dlffusion bonds in the high temperature superalloys, such as those utilized in the manufacture of gas turbine en8ine hardware. Such bonding is described in detail in the U.S. Patent No. 3,678,570 to D.F. Paulonis et al, of common assignee herewith, and whose teachings are incorporated herein by reference.
The superalloys are recognized as those alloys, usually having their basis in nickel, cobalt or iron, or some combination thereof exhibiting good high temperature strength and oxidation resistance in environments such as gas turbine engines. Usually, these alloys also contain substantial quantities of chromium and other elements such as aluminum, titanium and the refractory metals.
It is frequently desirable to make certain gas turbine engine components by joining easily fabricable segments together into the desired configurations. However, the limited weldability of many of these superalloys has severely limited the applicability of conventional joining techniques,
.
The present lnvention relates in general to the art of diffusion bonding and, more particularly, to diffusion bonding of the superalloys utilizing a transient liquid phase in the bonding process.
Transient liquid phase diffusion bonding has been shown to be a very useful method for produclng high quality dlffusion bonds in the high temperature superalloys, such as those utilized in the manufacture of gas turbine en8ine hardware. Such bonding is described in detail in the U.S. Patent No. 3,678,570 to D.F. Paulonis et al, of common assignee herewith, and whose teachings are incorporated herein by reference.
The superalloys are recognized as those alloys, usually having their basis in nickel, cobalt or iron, or some combination thereof exhibiting good high temperature strength and oxidation resistance in environments such as gas turbine engines. Usually, these alloys also contain substantial quantities of chromium and other elements such as aluminum, titanium and the refractory metals.
It is frequently desirable to make certain gas turbine engine components by joining easily fabricable segments together into the desired configurations. However, the limited weldability of many of these superalloys has severely limited the applicability of conventional joining techniques,
-2-such as fusion welding, in the production of structural hardware. Further, many components because of their design are simply not adapted to the utilization of fusion welding. Brazing, while offering a number of advantages over fusion welding, has very limited application because of the penalties associated with the relatively low strengths and low melting points of typical brazed joints.
The relative simplicity and reproducibility of the transient liquid phase diffusion bonding technique in the production of high quality bonds in sensitive hardware has led to substantial usage thereof. This is particularly true in the gas turbine engine industry although the invention described herein is obviously not limited thereto.
One key element in the transient liquid phase diffusion bonding technique is the provision between the surfaces to be joined of a thin alloy interlayer. This interlayer melts at a temperature below the melting temperature of the materials being joined, and through diffusion, solidifies at the joining temperature to form a bond. The composition of the interlayer preferably should be tailored to the al}oys being joined, particularly with respect to the inclusion therein of those elements whose presence is required in the finished bond area and whose solid state diffusion rates are slow. It is also desirable to exclude from the interlayer alloy those elements which may adversely affect the bonding process or the quality of the finished joint. A melting point depressant (usually boron) is added to reduce the melting point of the interlayer to the desired point.
Since the amount of melting point depressant (boron) added to an interlayer to allow it to sufficiently melt at the bonding temperature also renders it extremely brittle, and therefore unrollable in homogeneous forml other methods of applying such interlayers have been devised.
One method of getting the interlayer alloy species 1~ between the faying surfaces is through the use of a thin ductile foil of the type described in the U.S. Patent No.
The relative simplicity and reproducibility of the transient liquid phase diffusion bonding technique in the production of high quality bonds in sensitive hardware has led to substantial usage thereof. This is particularly true in the gas turbine engine industry although the invention described herein is obviously not limited thereto.
One key element in the transient liquid phase diffusion bonding technique is the provision between the surfaces to be joined of a thin alloy interlayer. This interlayer melts at a temperature below the melting temperature of the materials being joined, and through diffusion, solidifies at the joining temperature to form a bond. The composition of the interlayer preferably should be tailored to the al}oys being joined, particularly with respect to the inclusion therein of those elements whose presence is required in the finished bond area and whose solid state diffusion rates are slow. It is also desirable to exclude from the interlayer alloy those elements which may adversely affect the bonding process or the quality of the finished joint. A melting point depressant (usually boron) is added to reduce the melting point of the interlayer to the desired point.
Since the amount of melting point depressant (boron) added to an interlayer to allow it to sufficiently melt at the bonding temperature also renders it extremely brittle, and therefore unrollable in homogeneous forml other methods of applying such interlayers have been devised.
One method of getting the interlayer alloy species 1~ between the faying surfaces is through the use of a thin ductile foil of the type described in the U.S. Patent No.
3,753,794 to D. F. Paulonis et al, which also shares a common assignee herewith. Ductile interlayer foil as described in this patent is manufactured by rolling the interlayer com-position (minus the boron) into foil of the desired thickness and subsequently adding boron to the surfaces of the foil through a boronizing process. Another method is by providing an interlayer composition as a plate or coating (containing boron) on one or more of the faying surfaces themselves, as described in Canadian Application Serial No. 268,015. As previously mentioned it is generally important that at the completion of the diffusion bonding operation the composition across the bond area include those elements whose presence is advantageous for optimum strength. In the case of some ~; i ,s .., of the elements whose solid state diffusion rates are slow, it is desirable to provide these elements between the surfaces to be joined so that sole reliance on diffusion from the parent metal is not necessary. This is particularly true in the case of bonding gaps of substantial width because of the extended bonding cycle which would be required to provide difusion over the greater distance.
In some cases, it is not feasible to provide all of the desired components in a single homogeneous interlayer foil (prior to boronizing) for several reasons. Principally, such complex alloys would either be physically impossible to roll into the thin foil required or would not melt sufficiently at the bonding temperature.
SUMMARY OF THE INVENTION
According to the present invention an interlayer alloy is provided as a thin lamellar composite which will be positioned between the surfaces to be joined. This composite comprises a single foil of one distinct composition in combination with one or more other foils also of distinct composition and/or one or more directly deposited metallic layers on any of the foils or the surfaces to be bonded.
The amounts and distinct compositions of the individual lamellar are such that the overall composition of the composite is equivalent to the desired interlayer composition.
~ -5-1~6B453 In accordance wi~h an embodiment of the invention, there is provided, in an interlayer for bonding metallic articles which are based on a metal chosen from the group consisting of nickel, cobalt, and iron, said interlayer having a composition similar to that of the articles being joined, except for the addition of a quantity of at least one melting point depressant, said interlayer having a brittle characteristic because of the formation of brittle phases, the improvement which comprises:
providing the interlayer in the form of a plurality of lamellae, each of said lamellae being free from those combinations of elements which form brittle phases: whereby the lamellar inter-layer is ductile even though its overall composition is one which would be brittle if produced in a homogeneous form.
From a different aspect, and in accordance with the invention, a process for producing a ductile lamellar interlayer, useful in the transient liquid phase bonding of metallic articles, containing a melting point depressant, and containing combinations of elements which form brittle phases, includes the steps of:
a) providing a ductile lamellar substrate, with each ductile lamella being free from those combinations of elements which form significant amounts of brittle phases, b) depositing at least one adherent coating on the surface of the lamellar sub-strate.
-Sa-iO~;84~3 DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following description, all compositions are given in weight percent unless otherwise specified.
The transient liquid phase bonding technique utilizes an interlayer between the articles being ~oined which contains a melting point depressant in an alloy which ideally is similar to the alloys being ~oined. Certain elements present in the alloy being ~oined are excluded from the interlayer to prevent the formation of brittle, difficult-to-eliminate phases in the bond. Also, a melting point depressant which has a high diffusion coefficient in thea~oy which comprises the articles being joined is required so that after the joint is heated above the interlayer melting point, solidifcation will occur isothermally as the concentration of the melting point depressant in the interlayer is reduced by diffusion into the articles being joined.
In order to insure proper bonding, and to minimize the total amount of melting poin~ depressant in the finished bond, thin uniform interlayers are required and these are most advantageously produced by rolling to foil form. The current commercial practice is to prepare the interlayer without the melting point depressant, and to subsequently add the melting point depressant (usually boron) to the surfaces of the foil by a diffusion process (boronizLng~.
~CIG8453 It is preferred that the interlayer composition be as similar as possible to the alloys being joined (excluding the melting point depressant) so that the finished bond will be as similar as possible to the parent metal. Unfortunately, in some cases difficulties are encountered in the preparation of interlayers for joining the high strength superalloys because certain combinations o alloy constituents react and severely impair the interlayer material ductility and fabricability.
A majority of nickel base superalloys contain gamma prime as a strengthening agent, which is an intermetallic phase between aluminum and nickel with the approximate formula Ni3Al (often titaniu~ is substituted in part for the aluminum). Many superalloys contain upwards of 5%
aluminum and it would be desirable to produce interlayers with 5% (and greater) aluminum levels. Four percent is generally the upper limit for the production of homogeneous interlayers of complex alloys by rolling, and production is easier and more consistent if the aluminum level is limited to about two percent. Any deviation of the interlayer composition (except melting point depressant) from the alloys being joined can be e~ualized by extended diffusion heat treatments, but this is not desirable, particularly with the thicker interlayers. Also, aluminum raises the melting point of the interlayer to the point where the interlayer could not be used to join certain alloys. Thus, from both a technical and manufacturing standpoint, it would be desirable to be able to produce interlayers containing relatively hiBh aluminum levels without the penalties of makin8 the foil difficult to roll or raising the melting point excessively.
A similar problem is presented by a combination of carbon with carbide formers such as hafnlum, chromium, tantalum, columbium, titanium, zirconium, tangsten, etc., which together with carbon may form brittle carbides.
Current practice is to limit the percentage~added of these elements in interlayers, but of course, bonds could more closely approximate the composition of the parent metal if greater amounts of these elements could be incorporated into the interlayer.
The basis of this invention`is the production of an interlayer in lamellar form. Each of the lamellae or parts of the interlayer differ significantly in chemistry from the ad~acent lamellae. Those lamellae provided in foil are free from those combinations of elements which cause brittle phases and other problems, thus the lamellar interlayer material is relatively ductile and may be fabricated by rolling. The overall composition of the interlayer (excluding the melting point depressant) is adjusted to be close to the composition of the materials being ~oined.
~368453 This concept may be employed in several different ways including the following:
A. Use of two or more separate foils, produced by rolling, with adjacent foils having distinct chemical compositions. These foils may be stacked in sandwich form to produce an interlayer of the desired thickness. Even though only two distinct compositions are required to produce the desired interlayer chemistry, it may be desirable to use several sets of the two foils to reduce diffusion distances and shorten the bonding cycle, the time required to produce a homogeneous bond, especially if a thick interlayer is desired.
B. Use of an interlayer is described in A above wherein the separate ductile foils have been bonded together, for example by co-rolling, to produce an integral lamellar interlayer material.
C. Use of at least one rolled ductile interlayer foil in combination with at least one directly deposited layer on at least one of the surfaces to be joined.
The layer would usually be metallic but might contain nonmetallic elements such as boron. An example might be one in which the reaction of chromium and carbon was a problem, in which case a layer of chromium could be directly applied to the surfaces to be bonded (plating, vapor ~68453 deposition, etc.) with a wrought ductile interlayer foil containing carbon. Such a directly deposited layer need not be as ductile as the underlying foil, provided that the directly deposited layer were sufficiently adherent. That is to say, if the composite interlayer were deformed, cracking of the surface layer is not deleterious, so long as the surface layer does not spall off the interlayer surface D. Use of one or more ductile rolled interlayers with a directly applied layer on at least one surface of the rolled interlayer. The layer would usually be metallic, but might contain nonmetallic elements such as boron. For example an electroless plating scheme could be used to apply a nickel boron alloy to the two surfaces of the interlayer, and the interlayer could be a (ductile) nickel-chromium-aluminum alloy. The same comments made above with reference to ductility of surface layers also apply to this embodiment.
In the above schemes boron would normally be used as the melting point depressant, although other depressants might be used. The boron could be applied by conventional boron~zing; by vapor deposition, either pure boron or a boron metallic mixture; or by electroless plating, for example of a ~06845.3 nickel boron alloy or nickel-cobalt-boron alloy. Other elements include alumin~lm which is desirable for precipitation strengthening and might be supplied in pure form, as part of a ductile alloy, or by various vapor deposition methods.
Chromium is desirable since it lowers the melting point of some alloy interlayers, and because it increases the oxidation and corrosion resistance of the bond region;
chromium ~ight be applied as part o a ductile alloy or by plating or vapor deposition. Various refractory elements such as W and Mo, and carbide formers, such as Zr and Hf are desirable for high strength and creep resistance; these materials may also be applied as part of a ductile alloy or by plating and/or vapor deposition. In general these elements (except boron) would be desirable in substantially the same concentration as in the base alloy, and sufficient melting point additions would be used to depress the melting point as desired.
Another embodiment of the invention which should be discussed is an embodiment in which not all of the interlayer parts melt. For example the refractory metals such as tungsten are present in many superalloys and would be desirable in the interlayer but for the fact that they act to increase the interlayer melting point. It is desirable that bonding be performed at a low temperature so that minimal metallurgical changes occur in the articles being bonded. If a three part interlayer were utilized with the central alloy interlayer containing tungsten and the outer parts being fabricated from a Ni-15% Cr-3.5% B alloy(melting point 1930F), the transient liquid phase bonding process could be performed at a temperature just slightly in excess of 1930F. The tungsten free portions of the interlayer would melt at this temperature, and, although the tungsten containing layer would not melt it would be partially dissolved by the melted layers and permit satisfactory bonding. If however one unitary interlayer containing all of the tungsten was utilized, the process temperature required would be much greater Another similar embodiment involves the preparation of interlayers for wide gap bonding in which a lamellar interlayer is utilized to provide elements such as aluminum, titanium, carbon and the refractory metals within the bond area so that homogeneous bonds can be developed with only short diffusion times. For example, one of the interlayer components might have a composition close to that of the parent metal.
Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be under-stood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and the scope of the invention.
In some cases, it is not feasible to provide all of the desired components in a single homogeneous interlayer foil (prior to boronizing) for several reasons. Principally, such complex alloys would either be physically impossible to roll into the thin foil required or would not melt sufficiently at the bonding temperature.
SUMMARY OF THE INVENTION
According to the present invention an interlayer alloy is provided as a thin lamellar composite which will be positioned between the surfaces to be joined. This composite comprises a single foil of one distinct composition in combination with one or more other foils also of distinct composition and/or one or more directly deposited metallic layers on any of the foils or the surfaces to be bonded.
The amounts and distinct compositions of the individual lamellar are such that the overall composition of the composite is equivalent to the desired interlayer composition.
~ -5-1~6B453 In accordance wi~h an embodiment of the invention, there is provided, in an interlayer for bonding metallic articles which are based on a metal chosen from the group consisting of nickel, cobalt, and iron, said interlayer having a composition similar to that of the articles being joined, except for the addition of a quantity of at least one melting point depressant, said interlayer having a brittle characteristic because of the formation of brittle phases, the improvement which comprises:
providing the interlayer in the form of a plurality of lamellae, each of said lamellae being free from those combinations of elements which form brittle phases: whereby the lamellar inter-layer is ductile even though its overall composition is one which would be brittle if produced in a homogeneous form.
From a different aspect, and in accordance with the invention, a process for producing a ductile lamellar interlayer, useful in the transient liquid phase bonding of metallic articles, containing a melting point depressant, and containing combinations of elements which form brittle phases, includes the steps of:
a) providing a ductile lamellar substrate, with each ductile lamella being free from those combinations of elements which form significant amounts of brittle phases, b) depositing at least one adherent coating on the surface of the lamellar sub-strate.
-Sa-iO~;84~3 DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following description, all compositions are given in weight percent unless otherwise specified.
The transient liquid phase bonding technique utilizes an interlayer between the articles being ~oined which contains a melting point depressant in an alloy which ideally is similar to the alloys being ~oined. Certain elements present in the alloy being ~oined are excluded from the interlayer to prevent the formation of brittle, difficult-to-eliminate phases in the bond. Also, a melting point depressant which has a high diffusion coefficient in thea~oy which comprises the articles being joined is required so that after the joint is heated above the interlayer melting point, solidifcation will occur isothermally as the concentration of the melting point depressant in the interlayer is reduced by diffusion into the articles being joined.
In order to insure proper bonding, and to minimize the total amount of melting poin~ depressant in the finished bond, thin uniform interlayers are required and these are most advantageously produced by rolling to foil form. The current commercial practice is to prepare the interlayer without the melting point depressant, and to subsequently add the melting point depressant (usually boron) to the surfaces of the foil by a diffusion process (boronizLng~.
~CIG8453 It is preferred that the interlayer composition be as similar as possible to the alloys being joined (excluding the melting point depressant) so that the finished bond will be as similar as possible to the parent metal. Unfortunately, in some cases difficulties are encountered in the preparation of interlayers for joining the high strength superalloys because certain combinations o alloy constituents react and severely impair the interlayer material ductility and fabricability.
A majority of nickel base superalloys contain gamma prime as a strengthening agent, which is an intermetallic phase between aluminum and nickel with the approximate formula Ni3Al (often titaniu~ is substituted in part for the aluminum). Many superalloys contain upwards of 5%
aluminum and it would be desirable to produce interlayers with 5% (and greater) aluminum levels. Four percent is generally the upper limit for the production of homogeneous interlayers of complex alloys by rolling, and production is easier and more consistent if the aluminum level is limited to about two percent. Any deviation of the interlayer composition (except melting point depressant) from the alloys being joined can be e~ualized by extended diffusion heat treatments, but this is not desirable, particularly with the thicker interlayers. Also, aluminum raises the melting point of the interlayer to the point where the interlayer could not be used to join certain alloys. Thus, from both a technical and manufacturing standpoint, it would be desirable to be able to produce interlayers containing relatively hiBh aluminum levels without the penalties of makin8 the foil difficult to roll or raising the melting point excessively.
A similar problem is presented by a combination of carbon with carbide formers such as hafnlum, chromium, tantalum, columbium, titanium, zirconium, tangsten, etc., which together with carbon may form brittle carbides.
Current practice is to limit the percentage~added of these elements in interlayers, but of course, bonds could more closely approximate the composition of the parent metal if greater amounts of these elements could be incorporated into the interlayer.
The basis of this invention`is the production of an interlayer in lamellar form. Each of the lamellae or parts of the interlayer differ significantly in chemistry from the ad~acent lamellae. Those lamellae provided in foil are free from those combinations of elements which cause brittle phases and other problems, thus the lamellar interlayer material is relatively ductile and may be fabricated by rolling. The overall composition of the interlayer (excluding the melting point depressant) is adjusted to be close to the composition of the materials being ~oined.
~368453 This concept may be employed in several different ways including the following:
A. Use of two or more separate foils, produced by rolling, with adjacent foils having distinct chemical compositions. These foils may be stacked in sandwich form to produce an interlayer of the desired thickness. Even though only two distinct compositions are required to produce the desired interlayer chemistry, it may be desirable to use several sets of the two foils to reduce diffusion distances and shorten the bonding cycle, the time required to produce a homogeneous bond, especially if a thick interlayer is desired.
B. Use of an interlayer is described in A above wherein the separate ductile foils have been bonded together, for example by co-rolling, to produce an integral lamellar interlayer material.
C. Use of at least one rolled ductile interlayer foil in combination with at least one directly deposited layer on at least one of the surfaces to be joined.
The layer would usually be metallic but might contain nonmetallic elements such as boron. An example might be one in which the reaction of chromium and carbon was a problem, in which case a layer of chromium could be directly applied to the surfaces to be bonded (plating, vapor ~68453 deposition, etc.) with a wrought ductile interlayer foil containing carbon. Such a directly deposited layer need not be as ductile as the underlying foil, provided that the directly deposited layer were sufficiently adherent. That is to say, if the composite interlayer were deformed, cracking of the surface layer is not deleterious, so long as the surface layer does not spall off the interlayer surface D. Use of one or more ductile rolled interlayers with a directly applied layer on at least one surface of the rolled interlayer. The layer would usually be metallic, but might contain nonmetallic elements such as boron. For example an electroless plating scheme could be used to apply a nickel boron alloy to the two surfaces of the interlayer, and the interlayer could be a (ductile) nickel-chromium-aluminum alloy. The same comments made above with reference to ductility of surface layers also apply to this embodiment.
In the above schemes boron would normally be used as the melting point depressant, although other depressants might be used. The boron could be applied by conventional boron~zing; by vapor deposition, either pure boron or a boron metallic mixture; or by electroless plating, for example of a ~06845.3 nickel boron alloy or nickel-cobalt-boron alloy. Other elements include alumin~lm which is desirable for precipitation strengthening and might be supplied in pure form, as part of a ductile alloy, or by various vapor deposition methods.
Chromium is desirable since it lowers the melting point of some alloy interlayers, and because it increases the oxidation and corrosion resistance of the bond region;
chromium ~ight be applied as part o a ductile alloy or by plating or vapor deposition. Various refractory elements such as W and Mo, and carbide formers, such as Zr and Hf are desirable for high strength and creep resistance; these materials may also be applied as part of a ductile alloy or by plating and/or vapor deposition. In general these elements (except boron) would be desirable in substantially the same concentration as in the base alloy, and sufficient melting point additions would be used to depress the melting point as desired.
Another embodiment of the invention which should be discussed is an embodiment in which not all of the interlayer parts melt. For example the refractory metals such as tungsten are present in many superalloys and would be desirable in the interlayer but for the fact that they act to increase the interlayer melting point. It is desirable that bonding be performed at a low temperature so that minimal metallurgical changes occur in the articles being bonded. If a three part interlayer were utilized with the central alloy interlayer containing tungsten and the outer parts being fabricated from a Ni-15% Cr-3.5% B alloy(melting point 1930F), the transient liquid phase bonding process could be performed at a temperature just slightly in excess of 1930F. The tungsten free portions of the interlayer would melt at this temperature, and, although the tungsten containing layer would not melt it would be partially dissolved by the melted layers and permit satisfactory bonding. If however one unitary interlayer containing all of the tungsten was utilized, the process temperature required would be much greater Another similar embodiment involves the preparation of interlayers for wide gap bonding in which a lamellar interlayer is utilized to provide elements such as aluminum, titanium, carbon and the refractory metals within the bond area so that homogeneous bonds can be developed with only short diffusion times. For example, one of the interlayer components might have a composition close to that of the parent metal.
Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be under-stood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and the scope of the invention.
Claims (10)
1. In an interlayer for bonding metallic articles which are based on a metal chosen from the group consisting of nickel, cobalt, and iron, said interlayer having a composition similar to that of the articles being joined, except for the addition of a quantity of at least one melting point depressant, said inter-layer having a brittle characteristic because of the formation of brittle phases, the improvement which comprises:
providing the interlayer in the form of a plurality of lamellae, each of said lamellae being free from those combinations of elements which form brittle phases, whereby the lamellar interlayer is ductile even though its overall composition is one which would be brittle if produced in a homogeneous form.
providing the interlayer in the form of a plurality of lamellae, each of said lamellae being free from those combinations of elements which form brittle phases, whereby the lamellar interlayer is ductile even though its overall composition is one which would be brittle if produced in a homogeneous form.
2. An interlayer as in claim 1 wherein no single lamella contains amounts of the brittle gamma prime phase sufficient to impair fabricability.
3. An interlayer as in claim 1 wherein no single lamella contains significant amounts of both carbon and a material chosen from the group consisting of hafnium, chromium, tantalum, columbium, titanium, zirconium and tungsten and mixtures thereof.
4. An interlayer as in claim 1 wherein the lamellae are bonded together to form a unitary interlayer.
5. An interlayer as in claim 1 wherein at least one of the lamellae melts at a lower temperature than would a corres-ponding alloy of the overall composition of the lamellar interlayer.
6. A process for producing a ductile lamellar interlayer containing a melt depressant useful in the transient liquid phase bonding of metallic articles which includes the steps of a. providing a plurality of ductile lamellae having an overall composition which is similar to that of the articles being joined (exclusive of the melting point depressant) b. bonding the lamellae together by co-rolling to produce a unitary ductile interlayer.
7. A process for producing a ductile lamellar interlayer, useful in the transient liquid phase bonding of metallic articles, containing a melting point depressant, and containing combinations of elements which form brittle phases, which includes the steps of:
a. providing a ductile lamellar substrate, with each ductile lamella being free from those combinations of elements which form significant amounts of brittle phases, b. depositing at least one adherent coating on the surface of the lamellar substrate.
a. providing a ductile lamellar substrate, with each ductile lamella being free from those combinations of elements which form significant amounts of brittle phases, b. depositing at least one adherent coating on the surface of the lamellar substrate.
8. A process as in claim 7 wherein the deposition process involves electroplating.
9. A process as in claim 7 wherein the deposition process involves electroless plating.
10. A process as in claim 7 wherein the deposition process involves vapor deposition.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA268,544A CA1068453A (en) | 1976-12-22 | 1976-12-22 | Composite interlayer for diffusion bonding |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA268,544A CA1068453A (en) | 1976-12-22 | 1976-12-22 | Composite interlayer for diffusion bonding |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1068453A true CA1068453A (en) | 1979-12-25 |
Family
ID=4107578
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA268,544A Expired CA1068453A (en) | 1976-12-22 | 1976-12-22 | Composite interlayer for diffusion bonding |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1068453A (en) |
-
1976
- 1976-12-22 CA CA268,544A patent/CA1068453A/en not_active Expired
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