Abstract:
To produce at least two bonded-together layers ( 11, 13; 11′, 13 ), it is proposed that the material of at least one of the layers ( 13 ) is melted and subsequently, by spray compacting with a spray cone ( 10, 10 ′), is applied to the other layer, which is moved in relation to the spray cone ( 10, 10 ′), in such a way that the material composite is thereby produced.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for producing at least two layers bonded together. 
     In addition, the invention relates to a functional component that is produced by the method. 
     BACKGROUND 
     Numerous methods for producing a functional component where a material composite is produced from a substrate material and a functional layer are known. Such functional components are, for example, bearing components that consist of a stable substrate material, preferably of a ferrous metal, in particular steel, with a functional layer that is made of a non-ferrous metal acting as the bearing layer. 
     Known from DE 10 2004 044 519 A1 is a method of forming the sliding object of the non-ferrous metal by spray compacting. Spray compacting is a primary shaping method in which the material is melted and via a nozzle arrangement is divided into fine droplets using pressurized gas such that it is formed into a spray cone made up of the droplets. Spraying is carried out in a manner by which the droplets of the spray cone are distributed into a uniform layer on the surface of the form by strong cooling and create a solid layer. The sliding object produced by spray compacting is bonded to a substrate material of the functional component either superficially or punctually by capacitor discharge welding. The production of such a functional component is elaborate, in particular if the functional component is to assume high pressure or load gradients. In such cases, the bond between the sliding object and the substrate must be produced carefully and elaborately by welding. It is the objective of the present invention to simplify the producibility of such a functional component of the aforementioned kind. 
     SUMMARY 
     To solve this objective, a production method for such a functional component subject to the invention provides that the material of at least one of the layers is melted and then applied by spray compacting with a spray cone to the other layer that is moved relative to the spray cone such that a material composite is produced thereby. 
     Thus, according to the invention, two metallic layers can be combined superficially and in a material composite in a positive manner such that the one layer is applied to the other layer by spray compacting. The other layer can, itself, be produced by spray compacting as well. It may not even be necessary for it to be hardened. 
     The present invention is particularly preferred for a functional component that is made of a metallic substrate material, in particular of a ferrous metal, preferably steel, and of a metallic functional layer made of a non-ferrous metal that is bonded to the substrate. The terms “ferrous metal” and “non-ferrous metal” as well as “metallic material” always include alloys as well. 
     The invention is based on the awareness that when producing the layer by spray compacting a material composite between the sprayed layer and the other layer can be achieved by a suitable selection of the processing parameters essential for spray compacting, even if, for example, the other layer consists of a ferrous metal and the sprayed layer of a non-ferrous metal. The processing parameters that are relevant for the production of a material composite between the layers are in particular the temperature of the melt that is shaped into a spray cone, the temperatures of the pressurized gas and the environment that cause the temperature drop of the spray droplets until they strike the other layer, the pressure of the spray gas and the temperature of the substrate material. According to the invention, it is possible to select these parameters such that a positive material composite between the layers is created. Thus, the spray compacting method subject to the invention is not utilized as a primary shaping method but as a coating method. 
     Although the suitable selection of the processing parameters consistently allows for the production of an effective material composite, it may be prudent to apply an interim layer prior to spray compacting, where said interim layer creates a bond to both the substrate material and the material of the functional layer upon impact of the spray droplets of the spray cone. The bond is made possible by the transferred heat increase when the spray droplets of the spray cone impact the interim layer. As is essentially known for primary shaping using spray compacting, non-metallic solid particles can be added to the melt in order to control the performance characteristics of the sprayed-on functional layer through the consistently uniform distribution of the solid particles in the functional layer. 
     In one particularly advantageous embodiment of the invention, the functional layer is produced in one pass of at least two materials that are provided as a melt and are sprayed onto the substrate. The melts can be sprayed on in the direction of movement of a carrier that may be the substrate. The melts can be sprayed onto the carrier in succession in the direction of the movement of the carrier. Depending on the purpose of the application, it may be useful to spray the layer that is subsequently sprayed on in the direction of the movement of the carrier onto the previously sprayed-on and already hardened layer, such that a functional layer is formed of two layers that are arranged on top of each other on the substrate and are combined with each other in a material composite. In this arrangement it is also possible that the functional layer that is formed of the two layers that are arranged on top of each other is also bonded to the carrier as the substrate or that the carrier receives no bond to the two layers and is removed after the production of the two interconnected layers as is typical for the primary shaping of a component made of a uniform material using a spray compacting method. 
     However, it is also possible to set the temperature of the substrate and/or of the melts such that the materials in the form of fine blended droplets form a functional layer. In this manner it is possible to produce a functional layer with an alloy of materials that cannot be alloyed with each other when using conventional methods. 
     In a modified embodiment of the method subject to the invention, the temperatures of the substrate or the carrier, respectively, and or of the melts of the different materials can be set such that the layers blend only partially prior to solidifying and in this manner form a gradient functional layer. If the two materials are sprayed on in succession in the direction of the movement, such a partial blend is produced across the thickness of the functional layer, thus forming a gradual transition from the primarily first material to the primarily second material, in other words, the layers transitioning from one to the other. 
     The invention can be utilized particularly advantageously for friction bearing layers. Essentially conflicting demands are made on friction bearing layers. For one, such layers are to have a good embedding capacity for foreign particles that may be transported into the bearing by lubricants, for example, in order for the bearing not to be destroyed by the foreign particles, and for another, the friction bearing is to exhibit a long service life and in particular good emergency operation properties for cases when the friction bearing layer exhibiting the high capacity for embedding is worn. 
     By designing a friction bearing layer consisting of two or more different layers the different requirements, in particular the high embedding capacity of one layer and good emergency operation properties of the layer located underneath can be accommodated. The friction bearing layers are in this case layers made of non-ferrous metals. 
     The layers produced according to the invention and arranged on top of each other can exhibit the same matrix structure yet different compositions or can be made of different matrix structures—and thus different compositions. 
     Examples for such layer combinations with the same matrix are CuSn6/CuSn15. According to the invention such a layer combination can be applied on a ferrous substrate. 
     Layer combinations consisting of alloys with different matrixes are for example CuSn/SnSbCu, AlSn/SnSbCu. 
     Solid particles inserted into the layer during spray compacting may be, for example, solid particles made of diamond, carbides, silicates and ceramic-type particles, while the soft particles may be particles with lubricating characteristics such as MoS 2 , PTFE, silicones, barium sulfate, etc. Melting of the solid particles in the melt is typically prevented by mixing in the solid particles via the spray gas, i.e., typically not by adding them to the melt. This results in a short contact time between the spray droplets and the solid particles during which the transferred heat is not sufficient to bring the solid particles to a melting point. As an alternative, solid particles can be used that have a melting temperature that is higher than the temperature of the melt of the material for the functional layer. 
     The method subject to the invention does not exclude that the substrate is produced by spray compacting in an essentially known primary shaping process as well. 
     The method subject to the invention is suited for the production of material composites with plane substrates as well as with three-dimensional substrates such as, for example, tubes, spheres, etc. The relative movement between the substrate and the spray cone can be linear, however, is preferably in the shape of a scanning process with a preferably sinusoidal course of movement. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Below, the invention shall be described in greater detail using exemplary embodiments presented in a drawing, of which: 
         FIG. 1  shows a schematic section of device suitable for carrying out the method subject to the invention for producing a material composite by spray compacting; 
         FIG. 2  shows a schematic presentation of the application of a functional layer of a material composite with a substrate; 
         FIG. 3  shows a schematic presentation of the application of a functional layer consisting of two partial layers using two spray cones. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a tank  1  containing a crucible  2  that is filled with the melt of a material  3 . The material is melted using a heating coil  4  is kept at a desired melt temperature of, for example, 1,150° C. if the material is a CuSn 6  alloy. The melted material prepared in this manner enters a distribution vessel  5  that is kept inside a distribution oven  6  at the desired melt temperature. By opening the floor of the distribution vessel  5 , a melt stream exits and passes through a primary gas nozzle  7  and an atomizer gas nozzle  8  in the form of a melt stream  9 . The atomized gas is reshaped into a spray cone  10  in the atomizer gas nozzle  8  using a positive pressure of, for example, 3.5 bar. The droplets of the material  3  contained in the spray cone  10  arrive on a substrate  11 , which in  FIG. 1  is shaped in the form of a tube. The substrate  11  is preheated using a substrate heater  12  in the form of a conductor coil until a temperature of approximately 1,000° C. (for a St-37 steel substrate) is reached. In the exemplary embodiment shown in  FIG. 1 , the substrate  11  is rotated around an axis that is located in the tube axis of the substrate  11  such that a functional layer  13  is built on the substrate  11 . 
     The entire spray system is located in a chamber  14  that exhibits an outlet  15  for discharging the atomizing gas. 
     An inert gas such as nitrogen in particular is preferably suitable as an atomizer gas. A corresponding inert atmosphere is also useful within the tank  1  or may even be required for many materials. 
     In one exemplary embodiment, the rotational frequency for the rotation of the tube-shaped substrate  11  is 1.2 Hz, the distance Z between the evaporator gas nozzle  8  and the substrate  11  is 330 mm and the coating time is about 130 s. During this time a mass of about 32 kg has been applied as a functional layer  13  onto the substrate  11 . For a diameter of the substrate of 380 mm and a length of 140 mm. 
     The atomizing pressure was between 2.5 and 3.5 bar and it was demonstrated that an increased atomizing pressure of 3.5 bar can be reduced to a pressure of less than 3 bar during the spraying process. Advantageously, after the coating procedure, the substrate  11  with the functional layer  13  can be cooled in air. If required in individual cases, mechanical secondary compacting may be carried out.  FIG. 2  clarifies schematically a plane substrate  11 ′ to which the functional layer  13  is applied using the spray cone  10 . Here too a substrate heater  12  is provided in order to set the optimal conditions for the production of the material composite. 
     However, it shall be pointed out that heating of the substrate for producing a material composite is not required in every case. The potential heating depends on the material used for the substrate  11 ,  11 ′. With the embodiment shown in  FIG. 3 , the functional layer  13  consists of two partial layers  13 ′,  13 ″ that are applied using two spray cones  10 ,  10 ′ arranged in succession in the direction of the substrate movement P. The spray cones  10 ,  10 ′ overlap somewhat at the level of the substrate  11 ′, such that a transitional zone (not shown) occurs between the two partial layers  13 ′ and  13 ″, which is conducive for the bond of the two partial zones  13 ′,  13 ″ to each other. 
     The material composite achieved according to the invention between the substrate  11 ,  11 ′ and the functional layer  13  can be achieved for the various material combinations through the selections of suitable processing parameters as has been explained for the exemplary embodiment presented above. 
     Considered in particular as processing parameters are the temperature of the melt  3  or of the melt stream  9 , respectively, the pressure of the atomizing gas for generating the spray cone  10 , the temperature of the substrate  11 ,  11 ′ as well as the speed of the relative movement of the substrate  11 ,  11 ′ relative to the spray cone  10 ,  10 ′, whereby it is possible that the relative movement is formed by a combined movement of one component in the conveyer direction P and a second component perpendicular to it (for example, a rotational movement for the tube-shaped substrate  11  according to  FIG. 1 ). 
     For some applications it may be prudent to pre-treat the substrate  11 ,  11 ′ by applying a thin interim layer with the interim layer potentially functioning as bond-enhancing interim layer. Such an interim layer can improve the material composite between problematic material pairs of a substrate  11 ,  11 ′ and a functional layer  13  by, for example, creating an inter-metallic bond between the substrate  11 ,  11 ′ and the interim layer on the one hand, and the interim layer and the functional layer  13  on the other hand, while a direct bond between the substrate  11 ,  11 ′ and the functional layer  13  would be problematic. 
     An interim layer can also be useful when the material composite between the functional layer  13  and the substrate  11 ,  11 ′ may be at risk under certain conditions, for example due to very different coefficients of thermal expansion. An interim layer with a coefficient of thermal expansion that is between that of the substrate  11 ,  11 ′ and the functional layer  13  can increase the resultant material composite&#39;s resistance to greater temperature fluctuations. 
     In a similar fashion, the interim layer can also be advantageous for an improved take-up of shear forces, for example for a required secondary compacting of the spray layer if the material of the interim layer is capable of taking up such shear forces and therefore allows only a reduced transfer of these forces to the substrate  11 ,  11 ′. This function of the interim layer can also be utilized advantageously for subsequent processing steps such as pressing, rolling or forging. 
     Conventional weld, solder or diffusion layers are possibilities for bond-enhancing interim layers. In addition, fusions can be used that lead to intermediary bonds and/or to the formation of mixed crystals. 
     The interim layers can be applied to ferrous or non-ferrous substrates using conventional methods such as, for example, electroplating, dipping, roll cladding, friction welding and sputtering. 
     Suitable interim layers may be made, for example solely or primarily, of copper, tin, zinc, nickel, bismuth, silver, nickel-tin, chrome, aluminum, aluminum-tin, aluminum-zinc, nickel-chrome, etc. Zinc or tin interim layers, for example, are bond-enhancing for iron, copper or iron-aluminum material composites. 
     The drawing shows that the two spray cones  10 ,  10 ′ 3 ,  4  exhibit the same height Z above the substrate surface  11 ′, which is defined by the arrangement of the respective (not shown) spray nozzles. It is, of course, also possible to vary the design of the layers  13 ′,  13 ″ by selecting a greater height Z for one spray cone than for the other. Correspondingly, it is also possible to vary the thickness of the applied layers  13 ′,  13 ″ by designing the material throughput through the nozzles of the spray cones  10 ,  10 ′ differently, possibly in connection with different heights Z of the spray cones  10 ,  10 ′. The formation of the functional layer  13  or of the partial layers  13 ′,  13 ″ can also be affected by varying the pressure of the spray gas. 
     The method subject to the invention enables the direct production of functional components in a simple manner by applying the functional layer  13  of the material composite through spray compacting. Thus, all processing steps required thus far for bonding substrates  11 ,  11 ′ and the functional layer  13  can be omitted. 
     One preferred embodiment of the invention is the production of friction or roller bearing components using the described layer structures. 
     EXAMPLES 
     
         
         1. A spray layer of bronze (CuSn, CuMeX) is sprayed onto a steel substrate  11 ,  11 ′, such that a material composite is created. In this case, the spray layer constitutes the functional layer  13 . 
         2. A spray layer of SnAl30 is sprayed onto a steel substrate  11 ,  11 ′ and acts as the functional layer  13 . Prior to that, the substrate  11 ,  11 ′ has been provided with an interim layer with a thickness of less than 10 μm acting as a bond-enhancing or diffusion-preventing layer. Possible materials for the interim layer are Cu, Sn/Zn, Sn, etc. 
         3. Two layers  13 ,  13 ′ consisting of different alloys are sprayed onto a steel substrate  11 ,  11 ′ that consist of differing alloys. In the process, a direct bond with the steel substrate is created. The two layers ( 13 ,  13 ″) can be applied in such a manner that no significant blending areas are formed. Thus, one layer of material is present.
       The two layers  13 ,  13 ″ can also be deposited with a significant blending zone to form a gradient material. The realized layer thicknesses of the layers  13 ′,  13 ″ are freely selectable.   
     
         4. A first functional layer  13 ′ (for example CuSn x ) is sprayed onto a steel substrate  11 ,  11 ′ producing a material composite. An interim layer with a layer thickness of &lt;10 μM is then applied to the first layer  13 ′. The interim layer materials may be, for example Ag, Sn, Ni, etc. Thereafter, a second layer  13 ″ is applied as a spray layer, for example one made of AlSn.
       Without the interim layer, the two layers  13 ′,  13 ″ would form inter-metallic bonds with undesirable characteristics, in particular a high brittleness. Thus, the interim layer prevents diffusion between the layers  13 ′,  13 ″ and the formation of the undesired inter-metallic phase between the layers  13 ′,  13 ″. The interim layer may be sprayed on as well, however, a conventional application is preferred.   
     
         5. A first spray layer  13  acting as the functional layer is applied on a carrier without producing a material composite with the carrier. The spray layer may be designed in the form of a half cylinder. When the functional layer  13  is produced, the substrate  11 ,  11 ′ of steel can then also be produced by spraying and applied to the inner wall of the cylindrical functional layer  13 . If desired, an interim layer can be provided here as well, which will then be applied prior to spraying the substrate  11 ,  11 ′ onto the inside wall of the functional layer  13 .