Patent Publication Number: US-2019184499-A1

Title: Self brazing material and a method of making the material

Description:
CLAIM OF PRIORITY 
     The present application claims priority from U.S. patent application Ser. No. 15/137,361, filed Apr. 25, 2016, which claims priority to U.S. Provisional Patent Application No. 62/152,636, filed on Apr. 24, 2015, the disclosures of which are relied upon and incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to processes of forming self-brazing materials. Specifically, the present invention relates to self-brazing materials where different metals, such as titanium, are used as a base material in the constituent composition (e.g. Ti-Based material). 
     BACKGROUND OF THE INVENTION 
     Generally, brazing (including titanium brazing) involves expensive braze components where the cost is driven by the type of metal used, part complexity and end use requirements. 
     Traditionally titanium has been brazed either with clad TiCuNi foils or TiCuNi in the powder form. Both processes involve stacking layers of titanium (base metal) with intermittent braze foil/powder and brazing in a highly controlled atmosphere. Such processes have a complicated assembly operation, long assembly time and high yield losses combined with use of expensive vacuum furnaces. The additional actions required in individual stacking the base material and filler metal renders the overall brazing process difficult to automate. Further, individually stacking the base material and filler metal is significantly time consuming and often results in a poor intimate contact between the base metal and the filler material, producing poor braze quality and failed parts. Poor contact between a braze filler and base material can also cause oxidation of surface material which degrades the overall braze quality. Such issues often cause a significant loss in the overall yield of the brazed material. Therefore, there is a need to address the described challenges. 
     SUMMARY OF THE INVENTION 
     The present invention is directed at a method for producing a titanium alloy self-brazing strip or other applications that contain filler metal-base metal combinations which allow extracting desired braze constituent elements from the base metal to perform an in-situ braze alloy during brazing. In an aspect, other braze filler metal combinations can be used. 
     These and other aspects of the invention can be realized from reading and understanding of the detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic representation of a cross-sectional view of a cladded product according to an aspect of the current invention. 
         FIG. 2  illustrates a schematic representation of a cross-sectional view of a cladded product according to another aspect of the current invention. 
         FIG. 3  illustrates a cladding process according to an aspect of the current invention. 
         FIG. 4  illustrates a flow diagram of a process according to an aspect of the current invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The new process for creating a self-brazing product is described herein. More specifically, a self-brazing alloy strip is created from the process. In effect, a base is joined with another or multiple layer(s) of different materials that can be later brazed, as shown in  FIGS. 1-2 . Each strip/foil of the self-brazing product includes discrete layers. When the self-brazing product is brazed, then the alloy is formed. 
     In an aspect, the multi-layer product comprises at least one metal base layer that is joined with at least another layer of metal. In an exemplary aspect, the multi-layer product comprises at least one base layer of titanium (Ti) or titanium alloy that is joined with at least another layer of metal that, when both layers (i.e., the base and other layer) are brazed, form a titanium alloy. In reference to the Ti base layer product, each strip/foil of the self-brazing product comprises discrete layers. In an exemplary aspect, the other metal can include copper (Cu), nickel (Ni) or Zirconium (Zr). The layers are selected according, but not limited, to: (a) brazing temperature (e.g. Zr can be added as an extra layer as melting point depressant)—for lower preferred brazing temperature; and (b) ease of bonding—just one layer can be used to braze. In an aspect, the multi-layer titanium alloy strip can include at least one base layer of titanium (or titanium alloy) along with multiple layers of other metals. The combination of the base layer of titanium and at least one other layer of metal creates a multi-layer titanium alloy self-brazing strip, as shown in  FIGS. 1-2 . 
     While the exemplary aspect above focuses on a self-brazing product that has a base material of titanium/titanium alloy to form a titanium alloy when brazed, other base materials, as well as other materials in the other layers, can be used. However, it should be noted that the plurality of layers and base material can include any desired metal or metal alloy sufficient for achieving end product goals. Table 1 details some ideal braze filler metals according to possible base material (e.g. metal) combinations. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Braze filler metal by base metal combination 
               
            
           
           
               
               
               
            
               
                 Braze Filler Metal 
                 Chemical Composition 
                 Base Material 
               
               
                   
               
               
                 BAlSi 
                 Silicon (6 to 13%) 
                 Aluminum and 
               
               
                   
                 remainder Aluminum 
                 aluminum alloys 
               
               
                 BCu 
                 Phosphorus, Silver and 
                 Copper and copper alloys 
               
               
                   
                 remainder Copper 
               
               
                 BTi 
                 See above 
                 Titanium Base alloys 
               
               
                   
               
            
           
         
       
     
     The additional layers are bonded to the base layer through various means, as discussed below. In an aspect, the other materials can be found on either one side (see  FIG. 1 ) or both sides (see  FIG. 2 ) of the base layer. In an aspect, a decision to include a metal on either side of the base layer of the product is based on the end use of the product. In the case of layers on only one side, care needs to be taken to avoid oxidation of the exposed base metal, which can be accomplished by good control of the atmosphere in the brazing furnace. 
       FIGS. 1-2  provide example of the resulting strip/foil according to aspects of the present invention. As shown in  FIG. 1 , the base layer can have another at least one other layer (layer  1  and  2 ) joined to one side. As shown in  FIG. 2 , the base layer can have at least one other layer (layer  1 ,  2 ,  3 , and  4 ) joined to either of its sides. Specifically, the other layers (layers  1 ,  2 ,  3 , and  4 ) can sandwich/surround the base layer, with layers  1  and  2  being oriented on the upper surface of the base layer and layers  3  and  4  being oriented on the lower surface of the base layer. While  FIGS. 1-2  show only combinations of two layers being added to a respective side, other various combination of number of other layers can added to the base layer. 
     In an aspect, when the self-brazing product is configured to produce a titanium alloy, the strip/foil can include, but are not limited to, the following combination of materials in layered order: Cu/Ti/Cu, Ni/Ti/Ni, Ni/Ti/Cu, Cu/Ti/Ni, Cu/Ni/Ti/Ni/Cu, Ni/Cu/Ti/Cu/Ni, Ni/Cu/Ti/Cu/Ni, Cu/Ni/Ti/Cu/Ni, Zr/Cu/Ti/Cu/Zr, Zr/Ni/Ti/Ni/Zr, Zr/Ni/Ti/Cu/Zr, Zr/Cu/Ti/Ni/Zr, Zr/Ni/Ti/Ni/Cu, Zr/Cu/Ti/Cu/Ni, Ni/Cu/Ti/Cu/Zr, and Cu/Ni/Ti/Cu/Zr among other combinations. 
     The bonding of the material can be done through a clad approach, such as a roll bonding application, as shown in  FIG. 3 . In an aspect, other bonding/cladding techniques may be used to produce a clad/bond of different metals, such as, but not limited to, hot roll bonding, cold roll bonding, explosion bonding, vacuum bonding, and laser cladding. Although various techniques of cladding can be used to produce the multilayer self-brazing product, a cold roll bonding is the preferred method for metals (e.g., titanium, aluminum, etc.) that oxidize quickly at high temperatures and form stable oxides that are detrimental to achieving a good bond between the layers. A good bond is desired because a weak bond will result in a weak braze. By cladding the multiple layers together, the addition of the layers or powders need not be done as a separate step in the manufacturing process. 
       FIG. 3  illustrates a roll bonding operation to form the self-brazing alloy product. In an aspect, the roll bonding operation joins a base layer with a plurality of other layers of material. In an aspect, the plurality of other layers can comprise just one additional layer. In other aspects, the plurality of other layers can comprise two layers, one layer to be joined to each side of the base layer. In an exemplary aspect, as shown in  FIG. 3 , the process can include a base layer and four other layers (first layer, second layer, third layer, and fourth layer) that surround the base layer. However, as discussed above, various numbers of layers can be used. The layers are selected according, but not limited, to: (a) brazing temperature (e.g. Zr can be added as an extra layer as melting point depressant)—for lower preferred brazing temperature; and (b) ease of bonding—just one layer can be used to braze. 
       FIG. 4  illustrates the process of producing the self-brazing material for manufacturing purposes. First, the multiple layer self-brazing product is formed by bonding/cladding the layers (step  100 ). Next, the cladded multi-layer product can be cut or formed into the parts needed for the ultimate manufactured purpose (step  200 ). Lastly, the parts are then brazed with one another (step  300 ). 
       FIG. 3  illustrates a manner in which step  100  (bonding/cladding the layers via cold rolling) is carried out. However, as discussed above, various other bonding/cladding methods can be employed. In an aspect, the self-brazing multi-layered product can be formed into strips or foils, depending on the end application. In an exemplary aspect for creating a self-brazing titanium alloy product containing copper and/or nickel, the multi-layer product is readily rollable to foil gauges (0.002 inches) with no intermediate heat treating or annealing. In an aspect, if an intermediate anneal is desired/necessary before forming the parts that need to be brazed, the process needs to be carefully controlled to avoid the formation of Kirkendall (i.e. because copper and nickel mix readily to form Kirkendall voids). Kirkendall voids can prove detrimental to subsequent forming operations. 
     Kirkendall voids form at temperatures above 1200 F (650 C) for the Copper-Nickel binary phase system. As such, the post heat treatment should ideally be set at 1200 F or lower. In an aspect, although the titanium will not be completely annealed at temperatures of 1200 F or lower, it should be sufficiently stress relived to enable further forming operations. It should be noted that, during heat treatment (i.e., the treatment of the multi-layer product before brazing), copper and nickel will mix and alter the chemistry of the product during brazing. 
     Once the multi-layer product is formed (See  FIGS. 1-2  for example), the multi-layer alloy strip can then be cut and/or formed into the various pieces needed for manufacturing purposes (step  200 ). Various methods of cutting and forming can be used for the desired pieces to be formed with the limitations mentioned above for the operating temperature. 
     After the needed pieces/components/parts have been made from the self-brazing alloy strip, the components can then be placed together in the desired orientation and brazed to join the components together (step  300 ). When the brazing occurs, a small amount of the base material can be drawn into the other layers of materials, producing an in-situ braze. Such a process of drawing the base material into a braze joint avoids stacking layers of brazing fillers which contains the base material necessary for brazing, thus producing a more intimate contact and better braze quality. For example, when the base includes titanium and the other layers include nickel or copper alloys, a small amount of the titanium from the base can be drawn into and mixed with the copper and nickel layers. 
     After carefully selecting the composition and brazing temperature, a braze joint can be achieved, drawing a small amount of titanium from the base metal, by mixing the base metal with the filler metals such as Ni and Cu. The result is an in-situ braze product. For example, to produce a brazed 0.050 inch titanium product with a ratio 15 wt % Cu, 15 wt % Ni and 70 wt % Ti (which is a commercially available braze composition) available at the interface, the bonded layers will have thickness measurements of 0.00075 inches Ni and 0.00075 inches Cu on both sides of a 0.057 inch layer of titanium. During the brazing process, 0.007″ inches of titanium will go into the brazing, resulting in a 0.050 inch layer of titanium. The brazing temperature is between 1785 F (975 C)—1922 F (1050 C). As previously mentioned, the brazing temperature must be carefully controlled because a change in brazing temperature can result in a change in the in-situ braze alloy which can in turn change the amount of titanium extracted from the base metal. 
     While U.S. Pat. No. 7,527,187 discloses a brazing of a foil to the base material (Ti), the process described above utilizes the base material (e.g., Ti) in the brazing process. In other words, instead of adding a brazing alloy to the base material, the base material is used to form the brazing alloy. 
     Metals like titanium are reactive and combine with oxygen, carbon, hydrogen and nitrogen readily. As such, it is imperative that highly controlled vacuum furnaces are used to braze exposed titanium products. In an aspect, results from the present invention indicate that the carbon in the graphite elements react with the titanium and form barriers for an ideal braze. Cladding multilayers on both sides of the base titanium avoids exposure to atmosphere which in turn enables the use of furnaces that are less expensive and have less controlled atmospheres. 
     The products made after the brazing can be used in a variety of operations, including, but not limited to, high volume manufacturing operations, such as the production of heat exchangers, brazed bellows and honeycomb structures. By creating the self-brazing alloy product, there is no need for brazing foils, fluxes and powdered products in the joining phase. 
     Having thus described exemplary embodiments of a method to produce metallic composite material, it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives, adaptations, and modifications may be made within the scope of this disclosure. Accordingly, the invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims.