Patent Publication Number: US-2017362727-A1

Title: Systems and Methods for Forming Metal Matrix Composites

Description:
TECHNICAL FIELD 
     The present disclosure relates in general to forming composites, and more specifically to systems and methods for forming metal matrix composites. 
     BACKGROUND 
     Traditional methods of forming metal matrix composites involve melting the matrix, which exposes the fibers to a reactive metal at 1200 degrees Fahrenheit to 3000 degrees Fahrenheit. Most fibers cannot survive this environment, and many fibers will react to the matrix and form undesirable compounds. Further, cooling the fibers to room temperature can induce thermal strains high enough to destroy the metal matrix composite. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with the present disclosure, disadvantages and problems associated with forming metal matrix composites may be reduced or eliminated. 
     In one embodiment, a method includes placing nonconductive fibers adjacent to a conductive material, immersing the nonconductive fibers and the conductive material in a plating medium, applying a voltage to the conductive material to initiate electroplating, and engulfing, by electroplating, the nonconductive fibers in metal to create a metal matrix composite. 
     In some embodiments, a method includes placing nonconductive fibers adjacent to a conductive material, placing a form in the nonconductive fibers, immersing the nonconductive fibers, the conductive material, and the form in a plating medium, and applying a voltage to the conductive material to initiate electroplating. The method further includes engulfing, by electroplating, the nonconductive fibers in metal to create a metal matrix composite and removing the form from the metal matrix composite. 
     In certain embodiments, a metal matrix composite is formed by placing nonconductive fibers adjacent to a conductive material, immersing the nonconductive fibers and the conductive material in a plating medium, applying a voltage to the conductive material to initiate electroplating, and engulfing, by electroplating, the nonconductive fibers in metal. 
     Technical advantages of embodiments of the disclosure may include electroplating nonconductive fibers at or within a few degrees of room temperature, which creates a metal matrix composite with virtually no internal stresses and no heat-induced damage or interactions with the fibers. Further, the electroplating process requires no touch labor and relatively low cost facilities, which keeps the processing costs low. 
     Another advantage of disclosed embodiments of forming metal matrix composites is that they may have a lower coefficient of thermal expansion and a lower density than most conventional metals. Further, disclosed embodiments of metal matrix composites may have improved high temperature properties and damping properties than most conventional metals. For example, a much higher temperature may be possible with disclosed metal matrix composites than with polymer matrix composites. As another technical advantage, in certain embodiments, fugitive forms may be placed in the nonconductive fibers and removed after electroplating to create one or more voids, wherein the voids may be used to construct cooling passages or integral stiffening of the metal matrix composite part. As still another advantage, stiffened metal matrix composite panels may be formed using the electroplating method. Also, the electroplating method may be used to form radii in metal matrix composite parts. In some embodiments, an advantage of forming metal matrix composites using the disclosed electroplating process is that the metal matrix composite may be formed to any desired shape. For example, a metal matrix composite may be formed in the shape of a turbine blade, a rocket engine, a piston, or an air frame part. 
     A further advantage of some embodiments of forming metal matrix composites with nonconductive fibers is that aerospace parts may be formed that increase performance of the aircraft. For example, embedding fibers (e.g., ceramic fibers) into metal as discussed herein may allow the metal part (e.g., an engine) to operate at higher temperatures than it could without the fibers. The ability of the metal matrix composite to operate at higher temperatures may enable the aircraft to operate at a higher speed without failing in comparison to a part without fibers. For example, an aluminum part without fibers may operate at 350 degrees Fahrenheit, whereas an aluminum metal matrix composite part with fibers, according to certain embodiments, may operate at 700 degrees Fahrenheit. To achieve the 700 degree Fahrenheit temperature without fibers, a titanium or steel part may be required in place of aluminum. Additionally, the metal matrix composite&#39;s ability to operate at higher temperatures may enable an aircraft to operate at the same speed but at a lower weight, which may increase the aircraft&#39;s performance. 
     Another advantage of fiber reinforcement in a metal matrix is the reduction of the large property differential found in organic and ceramic matrix advanced composites between the in-plane and out-of-plane directions. The metallic matrix has a substantial percentage of the composite in-plane properties, greatly reducing the risk of out-of-plane failures in complex parts and loading scenarios. 
     In some embodiments, conductive fibers may be used with a nonconductive coating, which promotes adhesion, producibility, or other properties of the fiber. In certain embodiments, a conductive fiber may be used with electroplating, or any fiber may be used with an electroless plating process, but the preferred process is a nonconductive fiber with an electroplating process. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a method for forming metal matrix composites, according to certain embodiments; 
         FIG. 2  illustrates a metal matrix composite that may be formed by the method of  FIG. 1 , according to certain embodiments; 
         FIG. 3  illustrates a metal matrix composite formed with voids, according to certain embodiments; 
         FIG. 4  illustrates a metal matrix composite formed with radii, according to certain embodiments; 
         FIG. 5  illustrates a metal matrix composite of an assembly, according to certain embodiments; and 
         FIG. 6  illustrates a stiffened metal matrix composite panel, according to certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     To facilitate a better understanding of the present disclosure, the following examples of certain embodiments are given. The following examples are not to be read to limit or define the scope of the disclosure. Embodiments of the present disclosure and its advantages are best understood by referring to  FIGS. 1 through 6 , where like numbers are used to indicate like and corresponding parts. 
     Metal matrix composites exhibit superior characteristics over their polymer or ceramic competitors, such as conductivity, strength, ductility, and fracture toughness. However, processing metal matrix composites presents disadvantages. Current processing methods include melting the metal and infusing the metal into fibers or mixing the fibers with a metal powder and sintering to form a solid composite. 
     Melting the metal and infusing the metal into fibers exposes the fibers to a reactive metal at 1200 degrees Fahrenheit to 3000 degrees Fahrenheit. Most fibers cannot survive this environment, and many fibers will react with the matrix and form undesirable compounds. Further, this process is expensive. Additionally, once a suitable fiber and matrix have been formed in this manner, they must be cooled to or within a few degrees of room temperature. This cooling alone can induce thermal strains high enough to destroy the part. The same general problems also apply to sintering of powders with slightly lower temperatures but much higher pressures. 
     Composites may be formed by electroplating simple composites. A simple composite usually refers to a particulate composite with randomly placed and oriented reinforcements. An example of a simple composite is concrete, wherein aggregate is randomly tossed into cement for reinforcement. An advanced composite, on the other hand, usually refers to a fibrous composite that has a well-defined location and orientation of the reinforcements. An example of an advanced composite is a fighter wing skin with hundreds of plies of graphite fibers in epoxy, wherein the location and orientation of each fiber and each ply is controlled. While advanced composites may cost more than simple composites, advanced composites do not depend on random orientation or variability of flow orientation to ensure strength in a certain location or direction. 
     Another example of a simple composite is NIKASIL®. NIKASIL® may be made by tossing small silicon carbide particles into a nickel plating bath such that a layer of silicon carbide/nickel composite forms. While the volume of silicon carbon particles poured into the plating bath may be controlled, the location and orientation of the particles is uncontrolled. Flat plates may be suitable for simple composites. However, complex shapes may result in ‘clumping’ or ‘dry areas’. 
     To reduce or eliminate these and other problems, some embodiments of the present disclosure include electroplating nonconductive fibers at or within a few degrees of room temperature to create a metal matrix composite with virtually no internal stresses and no heat induced damage or interactions with the fibers. Additionally, the location and orientation of each nonconductive fiber and each ply may be controlled. Nonconductive fibers include, but are not limited to, unidirectional fibers, woven fabrics, and felts. Further, the electroplating process requires no touch labor and relatively low cost facilities, which keeps the processing costs low. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages.  FIGS. 1-6  provide additional details relating to forming metal matrix composites. 
       FIG. 1  illustrates a method  100  for forming metal matrix composites, according to certain embodiments, and  FIG. 2  illustrates a metal matrix composite  270  that may be formed by the method of  FIG. 1 , according to certain embodiments. Method  100  of  FIG. 1  starts at step  110 . At step  120 , nonconductive fibers are placed adjacent to a conductive material. For example, as illustrated in the embodiment of  FIG. 2 , nonconductive fibers  210  may be placed on a conductive material  220 . Nonconductive fibers  210  may be any fibers not capable of conducting electricity and are suitable for forming a metal matrix composite. In certain embodiments, nonconductive fibers  210  are ceramic fibers. In some embodiments, nonconductive fibers  210  may be woven (e.g., a woven piece of cloth.) In other embodiments, nonconductive fibers  210  may be straight fibers laid in a stack. 
     In the illustrated embodiment of  FIG. 2 , nonconductive fibers  210  are placed on conductive material  220 , wherein conductive material  220  is located on a floor  235  of a cell  230 . Cell  230  may be a basic fabrication cell of any size and may include one or more containment walls  240 . Floor  235  of cell  230  may be any desired contour. In certain embodiments, floor  235  of cell  230  is shaped to a compound curve and conductive material  220  is applied to match the compound curve. For example, floor  235  of cell  230  may be shaped to the contour of a desired engine part, similar to a mold. In some embodiments, metal matrix composite  270  may be formed using an inner surface of cell  230 . For example, several metal matrix composites  270  may be simultaneously processed within cell  230 . In certain embodiments, conductive material  220  is paint, wherein the paint is applied to the floor of cell  230 . In some embodiments, conductive material  220  is a conductive mat. 
     As shown in  FIG. 2 , cell  230  may include an electrode  250  in contact with conductive material  220 . Electrode  250  is any conductor of electricity. In some embodiments, electrode  250  may be embedded in cell  230 . In certain embodiments, electrode  250  may not be embedded in cell  230 . For example, electrode  250  may be located adjacent to a surface of cell  230  (e.g., floor  235  of cell  230 ), wherein the surface or a portion of the surface is coated with conductive material  220 . As another example, electrode  250  may be suspended above cell  230 . 
     Returning to  FIG. 1 , method  100  then proceeds to step  130 . At step  130 , nonconductive fibers  210  and conductive material  220  are immersed in a plating medium  260 , as shown in  FIG. 2 . In certain embodiments, plating medium  260  may be any acid-based solution. Plating medium  260  may vary depending on the type of metal to be plated. In certain embodiments, plating medium  260  is poured into cell  230  such that it immerses conductive material  220  and nonconductive fibers  210 . In some embodiments, plating medium may be at or near room temperature at the time it is poured into the cell, wherein room temperature ranges from 68 to 77 degrees Fahrenheit. 
     At step  140  of  FIG. 1 , a voltage is applied to conductive material  220  to initiate electroplating. For example, a voltage may be applied to electrode  250  of  FIG. 2  such that a current is introduced through electrode  250  and into conductive material  220 . In certain embodiments, applying the voltage initiates plating on the surface of conductive material  220 . Applying the voltage to conductive material  220  may increase the temperature of plating medium  260  a few degrees, wherein the temperature increase depends on the amount of current running through plating medium  260 . In certain embodiments, the electroplating process forms a metal on the surface of conductive material  220 . The surface of conductive material  220  may be flat or contoured. 
     Method  100  of  FIG. 1  then moves to step  150 . At step  150 , nonconductive fibers  210  are engulfed, by electroplating, in metal to create a metal matrix composite  270 . In certain embodiments, a metal forms on the surface of conductive material  220  and engulfs nonconductive fibers  210  such that nonconductive fibers  210  are embedded into metal matrix composite  270 . The plating process engulfs nonconductive fibers  210  as the process advances. In certain embodiments, the plating process may proceed at approximately 0.001 inches per hour. 
     In certain embodiments, metal matrix composite  270  is created after plating has engulfed all nonconductive fibers  210 . Metal matrix composite  270  is then removed from the bath of plating medium  260 . In some embodiments, conductive material  220  (e.g., paint) is removed from metal matrix composite  270 . Metal matrix composite  270  may then be trimmed. For example, during the plating process different portions of metal matrix composite  270  may grow laterally from conductive material  220 , and metal matrix composite  270  may be trimmed to square up the edges of the part. Metal matrix composite  270  may be trimmed to any desired shape. Method  100  of  FIG. 1  ends at step  160 . 
       FIG. 3  illustrates a metal matrix composite  310  formed with voids, according to certain embodiments. Similar to metal matrix composite  270 , metal matrix composite  310  of  FIG. 3  is formed by placing nonconductive fibers  210  adjacent to conductive material  220 . Additionally, one or more forms  320  may be placed in nonconductive fibers  210 . Form  320  may be made of wax, sand, plaster, or any other medium capable of forming a void during the electroplating process. Forms  320  may be placed in nonconductive fibers  210  before or after nonconductive fibers  210  are placed adjacent to conductive material  220 . For example, forms  320  may be placed in nonconductive fibers  210  and then nonconductive fibers  210  with forms  320  may be placed on the surface of cell  230 , wherein the surface of cell  230  is painted with conductive material  220 . 
     In the illustrated embodiment of  FIG. 3 , nonconductive fibers  210 , conductive material  220 , and forms  320  are immersed in plating medium  260  and a voltage is applied to conductive material  220  via electrode  250  to initiate electroplating. After engulfing, by electroplating, nonconductive fibers  210  in metal to create metal matrix composite  310 , forms  320  may be removed from metal matrix composite  310 . The removal process may depend on the type of medium used for form  320 . For example, where forms  320  are made of wax, plating may engulf nonconductive fibers  210  and wax forms  320 , and wax forms  320  may then be removed by heating the wax and pouring the wax out of metal matrix composite  310 . Alternatively, a solvent may be used to remove wax forms  320  from metal matrix composite  310 . As another example, where forms  320  are made of sand, water may be used to remove the sand from metal matrix composite  310 . 
     After forms  320  are removed, metal matrix composite  310  includes one or more voids. In some embodiments, the voids may be cleaned. Voids may pass partially or completely through metal matrix composite  310 . In certain embodiments, voids of metal matrix composite  310  form one or more cooling passages. As an example, the voids of metal matrix composite  310  may form one or more cooling passages of a turbine or rocket engine. In certain embodiments, voids of metal matrix composite  310  form one or more integral stiffening members. 
       FIG. 4  illustrates a metal matrix composite  410  formed with radii  420 , according to certain embodiments. In the illustrated embodiment of  FIG. 4 , metal matrix composite  410  includes two radii  420 , a web  430 , and a stiffener  440 . Some embodiments may include more or less radii  420 , webs  430 , and stiffeners  440 . For example, metal matrix composite may include four radii  420 , one web  430 , and two stiffeners  440 . In the embodiment shown in  FIG. 4 , each radius  420  is located between web  430  and stiffener  440 . 
     Metal matrix composite  410  is formed by placing a preform  450  adjacent to conductive material  220  (e.g., paint) in cell  230 . Preform  450  is any preform capable of holding nonconductive fibers  210  in position and may be any shape. In certain embodiments, preform  450  allows for an exact, predetermined placement of nonconductive fibers (e.g., nonconductive fibers  210 ) within a desired shape of metal matrix composite  410 . In the illustrated embodiment of  FIG. 4 , preform  450  is a woven preform of nonconductive fibers (e.g., nonconductive fibers  210 ), wherein preform  450  includes a horizontal portion and a vertical portion that takes the shape of an upside down letter “T”. Preform  450  and conductive material  220  are then immersed in plating medium  260 , and a voltage is applied to conductive material  220  via electrode  250  to initiate electroplating. The plating of preform  450  proceeds until nonconductive fibers  210  of preform  450  reach a desired thickness. In the illustrated embodiment of  FIG. 4 , the electroplating process proceeds until the horizontal portion of preform  450  is plated, creating web  430  of metal matrix composite  410 . 
     After web  430  is created, selected surfaces of web  430  may be masked or potted with fugitive material to prevent electroplating of the masked surfaces. For example, forms  320  may be used to mask selected surfaces of web  430 . In the illustrated embodiment of  FIG. 4 , forms  320  are placed on either side of the vertical portion of preform  450  and on the surface of web  430  to prevent further electroplating of web  430 . Also, forms  320  are shaped to create a desired radius  420  on either side of the vertical portion of preform  450 . Voltage is then applied to conductive material  220  via electrode  250  to initiate electroplating of the vertical portion of preform  450  and continues until nonconductive fibers  210  of preform  450  are engulfed in metal, creating stiffener  440  of metal matrix composite  410 . In certain embodiments, one face of form  320  may be conductive to accelerate the creation of stiffener  440 . 
     Metal matrix composite  410  may then be removed from plating medium  260 , and forms  320  and conductive material  220  (e.g., paint) may be removed from metal matrix composite  410 . In the illustrated embodiment of  FIG. 4 , metal matrix composite  410  is a single member comprising two radii  420 , web  430 , and stiffener  440 . Metal matrix composite may be formed to any desirable shape. As an example, metal matrix composite may be formed in the shape of a wide flange beam. 
       FIG. 5  illustrates a metal matrix composite  510  of an assembly, according to certain embodiments. The assembly of  FIG. 5  includes two parts, a first part  520  and a second part  530 . In certain embodiments, the assembly may include more than two parts. In the illustrated embodiment of  FIG. 5 , first part  520  and second part  530  are each made of one or more conductive materials. A preform  540  may be placed between first part  520  and second part  530  to form a basis of a joint. For example, preform  540  may be a woven Pi preform in the shape of an upside down Greek letter Pi. Some embodiments may include more than one preform  540 . For example, the assembly may include three parts and two preforms  540 . 
     In certain embodiments, the surfaces of first part  520  and second part  530  are masked at selected locations to prevent plating of the selected locations. For example, in the illustrated embodiment of  FIG. 5 , masking  550  is applied to the outer surfaces of first part  520  and second part  530  with the exception of the portions of the surfaces in contact with preform  540 . As shown in  FIG. 5 , masking  550  is applied to preform  540  to form tapers. Masking  550  may be applied to form any desired contour during processing. 
     In some embodiments, the assembly including first part  520 , second part  530 , and woven preform  540  is immersed in a plating medium (e.g., plating medium  260 ) to initiate plating on the exposed surfaces (e.g., the unmasked surfaces) of first part  520  and second part  530 . For example, in the embodiment illustrated in  FIG. 5 , plating may begin on the surfaces in contact with preform  540 . Plating may proceed until nonconductive fibers  210  of preform  540  are engulfed and a desired thickness of metal matrix composite  510  is achieved. The process ends when the final thickness is reached. At any time in the process, selected surfaces of composite  510  may be masked to control the thicknesses of various features. A voltage may likewise be applied to a part (e.g., part  530 ) to control the thicknesses of various features. Once the plating process has formed the final joint thickness, the assembly may be removed from the plating medium bath, and the masking  550  and paint may be removed from the assembly. In the illustrated embodiment of  FIG. 5 , metal matrix composite  510  forms a Pi-shaped joint with tapered ends. 
       FIG. 6  illustrates a stiffened metal matrix composite panel  610 , according to certain embodiments. In the illustrated embodiment of  FIG. 6 , a method of forming metal matrix composite panel  610  includes tooling a surface of cell  230  to a desired contour, wherein cell  230  includes embedded electrode  250 . Conductive material  220  (e.g., paint) is applied to the surface of cell  230 , and preforms or plies of nonconductive fibers (e.g., nonconductive fibers  210 ) are placed on conductive material  220 . Forms  320  are placed within the preforms or plies of the nonconductive fibers, wherein the outer surfaces of forms  320  are conductive. 
     In the illustrated embodiment of  FIG. 6 , a voltage is applied in a plating medium (e.g., plating medium  260 ) to begin the electroplating process. The electroplating process continues until a desired portion of the nonconductive fibers are engulfed in metal. For example, the electroplating process may continue until the nonconductive fibers below forms  320  are engulfed in metal, creating a plate like member. After this first stage of nonconductive fibers  620  is processed, masking  550  may be applied to stop matrix growth in selected regions, as shown in  FIG. 6 . The second stage of nonconductive fibers  630  and forms  320  may be added after the first stage of nonconductive fibers  620  are entirely engulfed in electroplate. A voltage is applied to begin processing the second stage of nonconductive fibers  630  and continues until the second stage of nonconductive fibers  630  are engulfed in metal, creating stiffened metal matrix composite panel  610 . As shown in  FIG. 6 , the second stage plating process thickens portions of the plate-like member created in the first stage and also produces composite over forms  320 . In certain embodiments, forms  320  may be curved or sloped to sufficiently allow the plating media to reach the first stage of nonconductive fibers  620  in cases where all fibers and forms are assembled at once. Stiffened metal matrix composite panel  610  is then removed from the plating medium bath, conductive material  220  and forms  320  are removed from stiffened metal matrix composite panel  610 , and panel  610  is trimmed. 
     Modifications, additions, or omissions may be made to the methods depicted in  FIGS. 1 through 6 . The depicted method may include more, fewer, or other steps. For example, method  100  may include contouring the surface of cell  230  to a desired shape (e.g., an aircraft structure). Further, the steps of the depicted method may be performed in parallel or in any suitable order, and any suitable component may perform one or more steps of the depicted method. 
     Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. 
     The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.