DE2342774A1 - Bonding titanium - by combined diffusion and brazing process - Google Patents

Abstract

A Ti honey-comb structure consists of a cove and facing sheet bonded by grain growth as a result of diffusion and transport across the joint, and of dissolution in the joint region of brazing material consisting of 38% Cu, 38% Ni, balance Ag, the brazing adding 1-5 gm per aq. st. of the bonded structure and being confined to the joint region.

Description

DIPL.-ING. KLAUS NEUBECKER ^L ° * ^ '

Patent attorney
4 Düsseldorf 1 Schadowplatz 9

Düsseldorf, 23 August 1973 73127

Rohr Industries, Inc.

Chula Vista, California, V.St.A.

Process for joining titanium and alloys based on titanium with titanium and alloys based on titanium by diffusion at a liquid interface

The present invention relates generally to interconnection of titanium and alloys based on titanium through diffusion at a liquid interface and in particular on sandwich panels with a honeycomb core, with a liquid / solid state diffusion Use is made to establish a physical connection between those facing or corresponding to one another Create surfaces of joined materials.

Methods have become known for making sandwich panel assemblies to connect with honeycomb structure by brazing and diffusion, separately with a certain degree of success could be used, but are not completely satisfactory in practical operation for reasons given below proven.

When brazing, the fusing of a filler metal or a filler alloy is required, which occurs after melting Capillary action in the cavities that are always present along the corresponding surfaces of the base metal parts, that are to be connected to each other flows. There is no fusion of the base metal itself.

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Telephone (Ο211) 32Ο8 58 telegrams Custopat

During the process, another filler metal (or more filler metals) is added to the base metal system in order to establish a connection between them. Not only does this added metal often flow to surface areas outside of those needed to make the braze joint, it also adds significantly to the weight of the joint assembly. For example, an additional weight of 50 to 120 g / 0.093 m ^{2 is common} for sandwich panels with a viaben structure, for which a 50 mil thick brazing alloy foil is used.

Filler metals that do not quickly diffuse into the base metal, are considered non-reactive, while those filler metals that rapidly diffuse into the base metal are considered reactive will. The filler metal or alloy has a melting point that is much lower than the melting point of the base metal of the parts to be joined together, and these lower-melting filler materials often react with the base metal, with a corresponding impairment of its properties. For example, titanium is difficult to braze because it is in highly reactive with most filler metals. In many cases, those that have the base metal or filler metals Base metal properties do not significantly affect, do not the characteristics that are necessary to take full advantage of the construction properties such as corrosion resistance, strength to be able to use against high temperatures and toughness, these properties usually due to the Base metals are obtained.

A diffusion bond is generally about a solid state joining process in which no fusion occurs, no harmful foreign matter is added, and the connection only through self-diffusion or solid-state reactions the material components are manufactured in compliance with the appropriate conditions in terms of purity, temperature and pressure

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will. The metal / metal contact under very high pressure is for the process is essential and is obtained by plastic deformation of the components, which is generally due to material migration is effected. After contact is made under ultrapure conditions, the solid state diffusion takes place instead of. The problem of making the metal / metal contact under the ultra-pure conditions is significant. A However, it takes time to maintain contact by material migration, with purity deteriorating over time. The production metal / metal contact by flow distortion or plastic flow is often impractical, especially when applied to Sandwich panel arrangements with honeycomb structure.

The object of the present invention is to create a new method to create a stabilized diffusion connection between to obtain two parts, each made of titanium or an alloy based on titanium. The connection should thereby combine desirable properties of both liquid state and solid state diffusion bonding processes.

To solve this problem, a method for connecting core material with a honeycomb structure with boundary layers is through Diffusion at a liquid interface, with the core material and the boundary layers made of titanium or an alloy based on it Titanium consist, according to the invention, characterized in that two consecutive to the edge surface of the core material Layers of nickel and copper of substantially equal weight are applied to form a diffusion bridge material to form that thereupon the mutually corresponding to be connected by the bridging material in between Faces must be brought together and subjected to sufficient positive pressure to permit location and orientation for the joint to maintain, and that then, while the mutually corresponding surfaces so in a protective atmosphere are maintained, the temperature of the protective atmosphere is increased,

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-A-

so that initially an atomic diffusion in the metal layers of the bridge material and between the bridge material and the Titanium takes place, then the eutectic alloy formed by the diffusion is brought to melt and finally the temperature for a certain time after the solidification of the eutectic melt at a certain level above of the melting level is maintained so as to keep the bridge material and the titanium in the area of the joint by solid state diffusion to mix in between.

According to the invention, a combined liquid-state and solid-state diffusion process is used to produce titanium and titanium alloys to each other, the problems of diffusion bonding processes of the prior art essentially can be avoided while maintaining their benefits. Specifically, a small amount of nickel, copper and Silver brought between the mutually corresponding edges of the materials to be united to a To form diffusion bridge. The metals in between are made up of layers of nickel, copper, silver, copper and nickel - in this order - or as alloys of these metals upset. According to a second embodiment of the invention are the metals to be inserted as layers of copper, nickel and copper - in this order - or as alloys these metals applied. The materials are then in a protective atmosphere from ambient temperatures to a higher temperature heated, with the solid state diffusion that When heating occurs, a eutectic compound forms which for a short period of time at a temperature lower than that than the melting point, into the liquidus area and the beta-transus area of one of the metals involved in the process got. The temperature is increased at a controlled rate up to a predetermined value and for a sufficiently long time held so that the eutectic melt solidifies again and the bridge metals and titanium by solid state diffusion

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are further blended, doing the formation of a given alloy to allow at the junction. The heat source is then disabled, and the temperature is over a The specified cooling period is reduced to the ambient temperature, whereby the protective atmosphere is maintained.

The bridging materials are inserted between the corresponding surfaces to be connected to one another preferably by applying a thin layer of the selected metals or alloys to the edges of the honeycomb-like core Structure in laminar form. This application can be carried out using any suitable means such as a brush (Dalic) or dip electroplating, Vapor deposition and powder flame spraying are carried out, preference being given to immersion electroplating and this method enables control of the volume and application of the clad materials.

The main purpose of the bridge is to make a metal / metal contact and to form a resulting diffusion bridge between the mutually corresponding surfaces, so that a atomic transport causes and accelerates the post-solid state diffufon and thus a stabilized diffusion bond is achieved quickly, and small fillets are also formed in order to improve the properties of the assembled structure Improve fatigue, shear and tangential tensile stress.

To determine the component structure before connecting it the combined liquid interface diffusion process according to the In the present invention, various known auxiliaries can be used. Various known tools can also be used can be used for heating, heating in a pronounced vacuum being preferred.

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Effective cleaning of the titanium is an important phase in the overall process of plating and liquid interface diffusion connection of the sandwich panel structure with honeycomb-like Core to prevent contamination of the titanium.

The creation of a liquid interface on the corresponding surfaces of the titanium or titanium alloy parts, which are to be united by diffusion, serves to form the diffusion bridge and to accelerate atomic diffusion between the parts to be connected without affecting the properties of the base materials impaired or the weight would increase significantly. As a result, compared to known methods, the overall increase in weight when connecting a titanium core material with associated boundary layers can be reduced.

In the diffusion bonding process according to the invention, the structure finally obtained can have grain formation of the base materials across the connection, while the brazing metals in the connection area are mixed with one another.

The invention is explained below using an exemplary embodiment explained in more detail in connection with the accompanying drawing. In the drawing show:

1 shows a micrograph of the true surface condition of the actual parts;

2 shows a micrographic representation of the liquid interface and the diffusion bridge on the mutually corresponding surfaces of the parts to be united, in accordance with the method according to the present invention;

3 shows a diagram of the atomic transport of the basic materials,

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as it is effected by the diffusion bridge, this diagram additionally showing the confusion who reveals bridge materials;

4 shows, on a greatly enlarged scale, a partial micrograph of an edge region of a core element with a honeycomb structure, that the successive plating with different metals in a preferred Sequence for the formation of the liquid interface on at least one of the with each other shows corresponding surfaces that are connected to one another by means of the present invention should be; and

Fig. 5 is a diagram of a typical connection cycle;

as it turns out in the realization of the combined liquid interface diffusion bonding process according to the present invention.

Fig. 1 shows the parts A and B to be joined together, which are neither completely flat nor clean. The micrographic Areas of parts A undiö are magnified many times over reproduced. In order to obtain a diffusion connection, as it is indicated at the interface between A and B, must the parts are brought into an ultra-clean state, and there must then be high pressure and temperature for a prolonged period of time be exercised without causing permanent deformation or a deterioration in mechanical properties, such as that could result from excessive stress, an impermissibly high temperature or an impermissibly high pressure.

According to the prior art method, a connection by intrinsic diffusion either with controlled flow stress, d. H. using bridges that support the Exceed material strength at the connection temperature,

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or with controlled material migration, where an extended period of time is required, around a metal / metal contact to create between the interfacial voids before atomic diffusion can begin. The flow method with plastic flow requires ultra-pure surface conditions, but because of the relatively short exposure times and the high pressure load on the parts, there is less risk of that the interconnected parts have a deterioration in their physical properties due to the presence suffer from atmospheric pollution. In contrast, those with slow, controlled material migration are occurring Process critical in terms of surface cleanliness, and besides, they require a protective atmosphere or a strong one Vacuum to prevent contamination and deterioration in properties. In both cases, one plastic flow of the components to be combined made use of. The one that works with controlled flow stress Processes require relatively short times at the elevated temperature and are therefore preferred, but are high Pressures and the observance of very pure conditions at temperatures in the range of 77 ° C are necessary. That with controlled Flow stress working method requires a great expense for the necessary machines, with the help of which the high Pressures must be applied to the parts to be joined while they are at a high temperature. Therefore these machines must also be free from contamination. The process, which works with controlled material migration, requires extremely long times to get to the plastic flow in which an atomic contact of the components is maintained will. During the long-term treatment at high temperature, the titanium absorbs oxygen and other impurities, which make this process relatively unsuitable.

Figures 2 and 3 graphically depict features and consequential effects associated with the liquid interface diffusion bonding process according to the present invention and that obtained thereby

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Connection are typical.

In Fig. 2, the area L represents the bridge material that at first liquid and shortly afterwards it has become solid, which happens because a small amount of bridge material is on the attack surface at least one of the two parts A or B to be joined together is brought and then the parts and that in between Bred bridge material are heated to at least the eutectic temperature. It should be noted that the cavities of Fig. 1 have been filled when the bridge material has become liquid.

The temperature is increased to a value above about 870 ° C., preferably 930 ° to 950 ° C., but in any case kept below the beta-transus range of the titanium alloy for a period of time sufficient to restore the eutectic alloy to solidify and to continue the solid state diffusion, as indicated in FIG. 3 at D.

A preferred sequence in the application of the bridge materials for realizing the invention is shown with FIG. 4, which shows, on a greatly enlarged scale, a micrograph of the edge area of the titanium core material with the platings applied one after the other. These platings contain, in sequence, a layer of nickel 83, a layer of copper 84, a layer of silver 85, a layer of copper 86 and a layer of nickel 87. The proportional total amounts of the plating metals are 38 to 45% nickel, 38 to 45% Copper and 10 to 24% silver. Preferred percentages for the nickel layer 83, the copper layer 84, the silver layer 85, the copper layer 86 and the nickel layer 87 are 21%, 21%, 16% _f 21 * and 21%, respectively.

The total thickness of the interface plating should preferably be not be larger than is necessary for sufficient diffusion with the base material in order to achieve a good connection composition between 88 to 100% titanium or an alloy on the

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Liaison to get '. In order to connect a material with a honeycomb structure to a sheet-like layer, 1 to 5 g of bridge material are required required for each 0.093 m of the honeycomb core material To connect a sheet-like layer with a sheet-like layer,

0 2

are 6 to 12 g of bridge material per 0.93 m of the corresponding Space necessary.

After the panel components have been joined and fixed, these parts are heated in a protective atmosphere. The heating cycle depends on the structure of the parts. The rate of heating depends on the thermal gradients within the system. Conventionally, the thermal gradients are kept at a relatively low value. As shown in Figure 5, the temperature in the furnace is increased to about 76O ° C at a rate of about 55 ° C (100 ° F) / min, at which point the thermal gradients should have been brought to about 28 ° C or less . The heating rate is therefore now reduced until the thermal gradients are less than 12 ° C when the parts reach the temperature of 870 ° C. A temperature rise rate including increase in the temperature of 76o C to 87O ⁰ ° C and 12 ° C / min has been found to be acceptable. During this period of time, the copper and silver components of the bridge material react with one another, so that they form a "mush" of liquid and solid components, which accelerates the diffusivity of the bridge materials and the titanium at higher temperatures.

At the temperature of 870 ° C, the heating rate lowered to about 1.1 ° C / min in order to keep the thermal gradients under control and the bridge materials time for to let the diffusion. The temperature is increased at this rate in the range of 927 ° C to 954 ° C. While this time the eutectic composition for titanium, copper and nickel is achieved by diffusion and the eutectic Liquid material formed so that the liquid material or the

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Melt the cavities that are always present between the surfaces to be connected and completely fill one forms small packing. The time it takes for liquid material to form is so short because of the continuous diffusion of titanium the composition of the melt changes rapidly from the eutectic composition to an enriched titanium compound. That causes isothermal solidification. The connected or "bonded" structure is held at the elevated temperature / to allow maximum diffusion of the bridge material away from the junction. As can be seen from Fig. 5, the Time for the diffusion of the bridge material away from the connection point depends on the temperature. Preferably with a Temperature of 927 ° C worked for 90 minutes, whereby it is understands that longer treatment times will provide even more diffusion of the bridge material away from the junction. It is also evident that higher temperatures provide more rapid diffusion, but such higher temperatures increase the risk of exceeding the beta transus range of the titanium compound.

The cooling cycle is now run through, this process depending on the thermal gradients, which can lead to undesirable residual stresses in a part. It is therefore common practice to cool as quickly as possible without allowing significant thermal gradients to occur which could lead to warping and thermal stresses. A cooling rate of less than 28 ° C / min to a temperature of 65 ° C is necessary, after which the cooling rate can be increased up to 55 ° C per minute. At the beginning of the cycle, the strong vacuum used has a value in the order of 10 ^-5 Torr, and this vacuum then increases during the secondary diffusion phase and the phase in the controlled cooling down to a value of about 10 ^-6 Torr, which is also retained . After reaching 538 ° C or less, the system can be vented with an inert atmosphere if desired to expedite the cooling process. The part becomes the

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Exposure to the ambient air before it is not is at a temperature below 150 ° C.

A second preferred sequence for applying the bridge materials in practicing the invention is with 4 shows a drawing of a greatly enlarged micrograph of the edge area of the titanium core material with the successive claddings applied, the two outer layers being considered absent are. These platings contain, in sequence, the copper layer 84, the nickel layer 85 and the copper layer 86. The proportional total proportions of the plating metals are 40 to 60% nickel and 60 to 40% copper, with a composition of 50 to 50 being preferred. Half the copper is in each of the two layers 84 and 86 applied.

The total thickness of the interfacial plating should preferably not be greater than that required for sufficient diffusion with the base material so that a good joint composition of 88% to 100% of the base alloy composition is formed at the joint. In order to connect honeycomb material with a sheet-like layer, 1 to 5 g of the bridge ^{material are required for O / 93m 2 of} the honeycomb structure material. In order to connect a sheet-like with a sheet-like layer, 6 to 12 g of bridge material are required for each 93 m of the corresponding surfaces.

After assembling the components of the plate structure and their mutual determination, the structure is brought into a school atmosphere to warm up. The heating cycle depends on the Structure of the parts and the mass distribution. The heating rate depends on the thermal gradient within the Systems. Conventionally, the thermal gradients are kept at a relatively low value. As with Fig. shown, the temperature in the oven is at a rate

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(100 ⁰ F) / raised to about 76o ° C of about 55 ° C min, and then the thermal gradient should be brought to about 28 ° C or less. The heating rate is therefore now reduced until the thermal gradients are less than 12 ° C when the parts reach the temperature of 870 ° C. A rate of temperature increase as the temperature rises from 76O ° C to 870 ° C at 12 ° C / min has been found to be acceptable.

The connection is then further heated and cooled in the same way as previously in connection with FIG. 5 with regard to FIG. 4 for the case of the five-layer coating with layers 83 to 87.

The invention thus provides a method for diffusion bonding of titanium, which eliminates the need to replace the base material either by material migration or by flow stress to be forgiven and that can be achieved at lower cost and in a shorter time than was previously possible was.

Patent claims :

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Claims (17)

- 14 claims; Γ1. / Method for joining core material with a honeycomb structure with web-like boundary layers through diffusion liquid interface, the core material and the boundary layers being made of titanium or an alloy based on titanium, characterized in that two layers of nickel and successively on the edge surface of the core material Copper of substantially equal weight can be applied to form a diffusion bridge material, then with each other corresponding surfaces to be connected by the bridge material located in between and brought together Apply sufficient pressure to maintain the position and alignment for the connection and then, while the mutually corresponding surfaces are kept in a protective atmosphere, the temperature the protective atmosphere is increased, so that initially a atomic diffusion takes place in the metal layers of the bridge material and between the bridge material and the titanium, then the eutectic alloy formed by the diffusion is brought to melt and finally the temperature for a certain time after the solidification of the eutectic melt at a certain level above the Melting levels are maintained so that the bridge material and the titanium in the area of the connection through a solid state diffusion to mix in between. 2. The method according to claim 1, characterized in that the Layers are formed successively as copper, nickel and copper layers. 3. The method according to claim 2, characterized in that substantially half of the total amount of copper in each of the both copper layers. 509815/0464 4, method according to one of the claims 1-3, characterized in that that the weight of the layers is about 1] honeycomb core material. 2 that the weight of the layers is about 1 to 5 g per 0.093 m of the 5. The method according to claim 3 or 4, characterized in that the nickel layer and the copper layers each make up 40 to 60% of the total weight of the layers. 6. The method according to any one of claims 1-5, characterized in that that the bridge material at the interface of the mutually corresponding surfaces is less than 12% by weight of the Material at the interface. 7. Method for connecting web-like boundary layers by diffusion at a liquid interface, with the web-like boundary layers made of titanium or an alloy Based on titanium, characterized in that a sheet-like delimitation layer follows one another on one surface two metals as a coating to form a diffusion bridge material applied, then the corresponding surfaces to be connected to one another with the bridging material located in between are brought together and subjected to sufficient positive pressure to prevent the Maintain location and orientation for the connection and that then, while the mutually corresponding surfaces are kept in a protective atmosphere, the temperature the protective atmosphere is increased, so that initially an atomic diffusion in the metal layers of the bridge material and takes place between the bridge material and the titanium, then the eutectic alloy formed by the diffusion is brought to melt and finally the temperature for a certain time after the solidification of the eutectic melt is kept at a certain level above the melt level, so as to remove the bridge material and the Titanium in the area of the connection by a solid state 509815/0464 Mix diffusion in between, the two metal layers Nickel and copper are. 8. The method according to claim 7, characterized in that the layers successively as a copper, nickel and copper layer are trained. 9. The method according to claim 7 or 8, characterized in that essentially half of the total amount of copper is in each of the two copper layers. 10. The method according to any one of claims 7-9, characterized in that that the weight of the coating is about 6 to 12 g per 0.093 m which makes up corresponding surfaces. 11. A method according to any one of claims 1 - 10, characterized in that the protective atmosphere is in the range of about 10 ^-5 to 10 ^-6 Torr, the temperature at a rate of about 55 ° C / min to about 76o ° C and then increasing at a rate of about 12 ° C / min to about 870 ° C and finally at a rate of about 1.1 ° C / min to about 927 to 954 ° C. 12. Diffusion connection produced by a method according to one of claims 1-11, with a honeycomb structure made of titanium or an alloy based on titanium as well as an associated sheet-like boundary layer made of titanium or an alloy based on titanium, characterized in that the area of the connection between the honeycomb-like structure and the web-like boundary layer grain growth of the base titanium as a result of atomic diffusion and atomic transport of the base titanium through the connection area and an amalgamation within the junction area with a liquid interface diffusion bridge material with copper in the order of 50% and nickel in the order of 50% 509815/0464 having between about 1 to 5 g per 0.093 m des "bonded" structure are added and the web-like boundary layer outside the connection area essentially is free from the bridge materials. 13. Produced by a method according to any one of claims 1-11 Diffusion connection, with a honeycomb structure made of titanium or an alloy based on titanium and a associated web-like boundary layer made of titanium or an alloy based on titanium, characterized in that the area of the connection between the honeycomb-like structure and the web-like boundary layer grain growth of the base titanium as a result of atomic diffusion and transport of the base titanium through the junction area and commingling within the junction area with a liquid interface diffusion bridge material with copper on the order of 38 to 45%, nickel on the order of magnitude & u £ wg d. s t from 38 to 45% and silver in the order of 24 to 10%, with between about 1 to 5 g per 0.093 m of the "bonded" Structure are added and the web-like boundary layer outside the connection area is essentially free of the Bridge materials is. 14. Aufbau according to claim 12 or 13, characterized in that the compound contains between about 88 to 100% titanium or a titanium-based alloy. 15.Verfahren according to any one of claims 1-4, 6, 7, 11, characterized characterized in that the coating additionally has a silver layer. 16.Verfahren according to claim 15, characterized in that the Silver makes up 10 to 24% of the total weight of the coating and the nickel and copper layers are essentially the same Weight and 76 to 90% of the total weight of the coating 509815/0464 - 18 turn off. 17. The method according to claim 16, characterized in that the Coating successively a nickel layer, a copper layer, a silver layer, a copper layer and a nickel layer having. KN / aw 5 509815/0464 Blank page