Abstract:
A method of forge welding laminates of titanium and titanium alloys includes interleaving first and second pluralities of metal pieces in an enclosure, filling the enclosure with an inert gas, heating the enclosure and the first and second pluralities of metal pieces, and mechanically pressing the enclosure on a first axis with a force sufficient to cause the first and second pluralities of metal pieces to forge-weld together. The first and second pluralities of metal pieces may be metallurgically dissimilar from each other, and may each comprise a percentage of titanium.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/361,070 filed Feb. 27, 2002, where this provisional application is incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention is in the field of metal laminates, and more particularly relates to metal laminate structures of nonferrous, noncorrosive metals.  
           [0004]    2. Description of the Related Art  
           [0005]    A number of conventional techniques exist for the bonding of metals to achieve composite or laminate products. One technique is forge welding, which is used for the manufacturing of compound steel, wherein two types of steel are bonded together in open atmosphere to produce a composite product. In order to achieve such a composite, plates or layers of steel are heated to a high temperature and pressed together, using a pressure sufficient to cause the plates to form a molecular bond. One of the advantages of forge-welding over other methods of joining metals is that the bond is achieved without the use of additional metal. This may be contrasted with arc welding, for example, where an electrode of a metal that is compatible with the metals to be joined is heated by the passage of an electric current, to melt and become part of the welded joint. This alters the chemical makeup of the metal at the joint. Physical characteristics, as well as the appearance of the joined parts are changed. While this may be desirable in some cases, in others it is not acceptable. A properly forge-welded joint is extremely strong while retaining all the physical characteristics of the component parts, as well as presenting an attractive (sometimes invisible) bond.  
           [0006]    This type of forge-welding has been practiced for many years and is also known in the industry as pattern welding. Another common term for this technique is damascened forging, with steel made by this technique being referred to as Damascus steel. Knife blades made from Damascus steel have been used for many years and are valued for the decorative and artistic qualities, as well as for the high quality of the blade.  
           [0007]    One of the benefits of Damascus or forge welded steel is that a blade made using this technique tends to enjoy the advantages of each of the component ingredients. For example, a steel alloy having a high degree of flexibility may be combined in alternating layers with an alloy having superior hardness. The result is a blade of great flexibility that also takes and holds a sharp edge. It is not fully understood how characteristics of individual alloys are imparted to such a composite, when a single alloy composed of the same ingredients and in the same proportions as the combination of the two component alloys does not, generally, capture the combination of characteristics. Nevertheless, the phenomenon has been known and exploited by master smiths for centuries.  
           [0008]    Regrettably, the techniques used to make Damascus steel are only effective on a very limited group of steel products. Only those steels that have a very high workability and low alloy content are able to be worked with this process.  
           [0009]    Currently the knife-making industry is limited to unalloyed or alloyed carbon steels for decorative composite materials. This means that these components or materials are prone to corrosion and can add significant weight to the final product. Forge welding of other metals has been attempted, without good results. For example, efforts to achieve a reliable forge welded laminate of titanium or titanium alloys has been generally unsuccessful.  
           [0010]    In an attempt to forge-weld other steel alloy materials, different techniques have been attempted. See, for example, U.S. Pat. No. 5,815,790. This patent describes a technique in which two stainless steel materials, at least one of which is in powder form, are placed under isostatic pressure while being heated to a high temperature. Working with metals in powdered form is difficult and expensive.  
           [0011]    Hot isostatic compaction, or hot isostatic pressing (HIP) is known in the industry, and used, for example, to form parts from metallic powders, including powders of steel, aluminum, and titanium. HIP requires a cylindrical pressure vessel into which the material to be processed is inserted. The interior of the vessel (and the material) is heated to a high temperature, and the atmosphere of the vessel is pressurized to pressures sufficient to compact a powdered metal into a solid form. The HIP process requires expensive machinery and has limits to the size of the parts that can be made thereby, since a pressure vessel capable of withstanding huge pressures is required for the process. The vessel must be internally insulated from the heat of the process, to prevent the extreme temperatures from weakening the walls of the vessel under pressure. As the size of the vessel increases in a linear manner, the required thickness and strength of the vessel walls increases exponentially. This places a practical limit on the maximum size of parts that can be produced. Currently, the maximum working size is on the order of around four feet in diameter. It will be recognized that, as the size increases, the cost of owning and operating such a device also increases. Additionally, the materials in a pressure vessel cannot be handled or manipulated in any way until the procedure is complete. These issue, individually or in combination, make the use of HIP expensive and complicated for small parts, and impossible for large ones.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    According to one embodiment of the invention, a method is provided, comprising the steps of arranging first and second metal pieces in an enclosure, filling the enclosure with an inert gas, heating the enclosure and the first and second pieces of metal, and mechanically pressing the enclosure on a first axis with a force sufficient to cause the first and second pieces of metal to forge-weld together. The first metal piece may be one of a first plurality of metal pieces and the second metal piece may be one of a second plurality of metal pieces, with the arranging step comprising interleaving the first and second pluralities of metal pieces with each other. The first and second metal pieces, or the first and second pluralities of metal pieces may be metallurgically dissimilar from each other. Additionally, each of the first and second metal pieces, or each of the first and second pluralities of metal pieces may comprise a percentage of titanium.  
           [0013]    Another embodiment of the invention provides a metal laminate, including a first plurality of layers of a first metal containing titanium, a second plurality of layers of a second metal containing titanium, the second metal having a chemical composition different from a chemical composition of the first metal, with the first and second pluralities of layers interleaved with each other, and with each of the layers of the laminate having a forge welded bond with the layers contiguous thereto. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 includes a modified, exploded of an encapsulating chamber.  
         [0015]    [0015]FIG. 2 is an isometric view of various alloys placed within the encapsulating chamber.  
         [0016]    [0016]FIG. 3 is a side elevational view of the encapsulating chamber having an inert gas flow therein in preparation for treatment.  
         [0017]    [0017]FIG. 4A illustrates one embodiment for placing the encapsulation chamber under high pressure.  
         [0018]    [0018]FIG. 4B illustrates a second embodiment for placing the encapsulation chamber under high pressure.  
         [0019]    [0019]FIG. 5A is a side elevational view of the encapsulation chamber being placed under high pressure.  
         [0020]    [0020]FIG. 5B is a side elevational view of the encapsulation chamber rotated 90° and placed under high pressure.  
         [0021]    [0021]FIG. 6 is an isometric view of the final billet of laminate material.  
         [0022]    [0022]FIG. 7 is an isometric view of the elongated billet.  
         [0023]    [0023]FIG. 8 is a side elevational view of an artistic pattern being pressed into the billet.  
         [0024]    [0024]FIG. 9 is a side elevational view of the billet being machined to a desired shape and having a desired artistic pattern.  
         [0025]    [0025]FIG. 10 illustrates, in plan view, a simple design pressed into a portion of the surface of the billet.  
         [0026]    [0026]FIG. 11 is a cross-section of the portion of the billet of FIG. 10.  
         [0027]    [0027]FIG. 12 is a plan view of the portion of the billet of FIG. 10, showing the appearance of the billet after the upper surface has been removed.  
         [0028]    [0028]FIG. 13 is a cross-section of the billet of FIG. 12.  
         [0029]    [0029]FIGS. 14A, 14B and  14 C illustrate some possible arrangements of parts in the chamber of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    As is illustrated in FIG. 1, an encapsulating chamber or enclosure  10  is provided, which initially is open at both ends. The chamber  10  can be made of a mild steel box tube, or steel square or rectangular tubing of another type of metal as starting member. The chamber  10  has any desired height, width, and length. According to one embodiment, the width w is in the range of 1-2 inches, the height h is in the range of 2-4 inches, and the length/in the range of 4-10 inches. In one preferred embodiment, the rectangular tubing to form the chamber  10  has a width w on the inside of 1¼ inches and ? inch thick walls for an overall outside width w of 1½ inches. The inside height is 3 inches and the length is 6 inches.  
         [0031]    Such material may be easily obtained from commercial metal supply companies. The chamber  10  has a front end  14 , a rear end  20 , sides  32 ,  34 , a top surface  28  and a bottom surface  30 . A front cap  12  is connected by any acceptable technique, such as welding, adhesive, strapping, or other attachment method to the front end  14 . A rear cap  18  is coupled to the rear end  20  of the chamber  10  by any acceptable technique, such as welding, brazing, adhesive, strapping, or other known method. The front cap  12  and rear cap  18  have appropriate apertures  13  and  19 , respectively, to permit selected gases to enter and exit. In one preferred embodiment, the front cap  12  has a small aperture to permit gases to escape under exhaust and the rear cap  18  has a larger aperture for input of gases in order to fill the chamber with the appropriate gas content during the treatment. The small hole in the front cap may be in the range of around? −¼ inch in diameter and the rear hole in the range of ½-1 inch in diameter in one acceptable embodiment.  
         [0032]    A handle  22  is connected to the chamber  10 , as shown in FIGS. 2 and 3, preferably by connecting to the rear cap  18 , by any appropriate mechanism. In one embodiment, the handle  22  is a metal pipe that is welded over the rear hole  19 , which provides the dual purpose of serving as a handle for carrying the chamber as well as an inlet pipe for gas to be pumped into the chamber at a later stage in the process.  
         [0033]    In carrying out the invention, the rear cap  18  is connected to the chamber  10  and the handle  22  is then connected to the rear cap  18 , as seen, for example, in FIG. 3. The chamber is now prepared to receive the metal to be laminated into a single thick stock. Thin plates  24 ,  26  of selected alloys are stacked into the chamber  10 . The plates  24 ,  26  stacked into the chamber  10  are of an acceptable size and shape to fit snugly into the chamber and to have a sufficient number within the stack for the desired number in the final laminate. According to one embodiment, the materials used are titanium alloys of various materials and compositions. One of the layers may be a commercial grade pure titanium. One acceptable grade is known in the industry as CP grade 1 titanium. This is a lighter colored metal  24  as indicated in FIG. 2. In between the generally pure titanium layer  24 , an alloy layer  26  of titanium is placed. This alloy can be any acceptable alloy of titanium that is compatible with being bonded to the pure titanium in the process. One example includes an alloy known as titanium 6AL4V, meaning 6% aluminum and 4% vanadium with the remainder being titanium. Other acceptable alloys of titanium include titanium alloy 13AL3Z; titanium 13AL3V, titanium alloy 6AL, 3CR; and various combinations of titanium alloy with aluminum, vanadium, chromium, nickel, zinc, and other metals. Alternatively, another alloy is used in place of the pure titanium, such that two different alloys are bonded. In a further embodiment of the invention, more than two different metals are placed together in the chamber  10  to be bonded.  
         [0034]    According to an embodiment of the invention, the sheets of titanium and titanium alloy may be scrubbed and cleaned, if desired, to remove all surface oxide layers and impurities, prior to loading them into the chamber  10 . The scrubbing can take any acceptable form, such as a mechanical scrub, a wash, or a chemical bath. The scrub is selected to be sufficient to remove any oxide layers, nitride layers, or any other build-up of materials caused by dirt or by a reaction with the atmosphere, the result of which is to expose the pure metal. After being appropriately cleaned and scrubbed, the metal plates  24 ,  26  are placed into the chamber  10  in preparation for the bonding process. After the metal is placed in the chamber  10 , the front cap  12  is bonded to the chamber  10  by any acceptable technique.  
         [0035]    As shown in FIG. 3, an inert gas  38  is then pumped in at a selected rate sufficient to displace all nitrogen and oxygen in the chamber  10 . The inert gas is preferably pumped in at a slow rate so as to evacuate all atmosphere and leave only pure inert gas within the chamber  10 . Pumping at a slow rate ensures that pure inert gas will be present rather than a mixture of inert gas and ambient air, which contains some oxygen and some nitrogen. A preferred inert gas is argon, although other gases besides argon may be used. At this point in the process, the hole  13  may be plugged by any appropriate method. Alternatively, the hole  13  may be left open, in which case the inert gas may be pumped at a very low rate into the chamber  10  during the next steps of the process, to prevent recontamination of the atmosphere in the chamber.  
         [0036]    In one embodiment, oxygen is removed from the chamber during pressing, since titanium oxidizes at high temperatures and oxygen may affect the process. Pumping inert gas into the chamber is one acceptable technique, but other methods that remove oxygen from around the metal pieces may also be used.  
         [0037]    Once the chamber  10  is filled with inert gas, or otherwise evacuated of oxygen, it is then placed into a furnace to heat the capsule  10  and the plates  24 ,  26  therein to a selected temperature. In the case of titanium alloy, the preferred temperature is in the range of 1700-2000 20  F. The temperature is selected to be sufficiently high to permit bonding of the layers into a single laminate and yet is not so high that the pure titanium becomes liquid or too soft to hold firm shape during the lamination process. The temperature is selected to be sufficiently high to facilitate bonding of the titanium layers to each other to form the single laminate piece, without each of the layers losing their individual characteristics, such as color, position, etc.  
         [0038]    When the chamber and its contents have reached a stable temperature inside the forge, the chamber  10  is removed from the forge. A pressure is then applied to cause the plates  24 ,  26  to bond to each other, forming, thereby, a single billet of laminated metal plates. In one acceptable technique, as illustrated in FIG. 4A, a high pressure hydraulic press  39  is used to apply force to the chamber  10 . A die  40  is placed on the anvil of the high-pressure hydraulic press, and a die  42  is placed on the stand  41  and force is applied to the chamber  10  having the metal plates therein. Sufficient force is applied so as to slightly deform the chamber  10 . For example, it may be pressed with sufficient force to reduce the height in the range of around ?-? inch, with ¼ inch being preferred. The hydraulic press may exert in the range of 5 to 15 tons of force in such an example. In an alternative embodiment, the force may be applied by some other acceptable technique. For example, steel rollers, impact hammers, hammering by hand, or some other technique of applying sufficient force to bond the plates  24  and  26  to each other may be employed. This will also cause the sides of the chamber  10  to bulge and some of the metal in the middle portion may become slightly wider than their initial width of 1¼ inches.  
         [0039]    If the hole  13  was not previously closed, the preceding pressure step is usually sufficient to have closed the hole. In any event, the plates  24 ,  26  are now bonded, so the pumped gas is no longer necessary.  
         [0040]    [0040]FIG. 4B illustrates an alternative shape for the dies  40  and  42 . Rather than being a flat die that matches the shape of the top surface  28  of the chamber  10 , it can be a square die having a surface area substantially smaller than the area of the top or bottom surfaces  28 ,  30  of the chamber  10 . In other embodiments, the dies  40  and  42  may be spherical, conical, semi-round, or have other shapes as desired. In those embodiments where the surface area of the dies used to apply pressure is smaller than the surface areas of the respective surface  28 ,  30  of the chamber  10 , the pressure is applied repeatedly to the chamber  10 , progressing over the entire surface of the chamber, such that the entire top and bottom surfaces  28 ,  30  of the chamber  10  are subjected to the requisite pressure to effect the bonding of the plates  24 ,  26 .  
         [0041]    [0041]FIG. 5A illustrates the interior of the chamber  10  while force is being applied by hydraulic press  39 . Under the constant pressure of the hydraulic press, additional heat is generated in the center of the stack. The force that compresses the top  28  and bottom  30  closer to each other by some distance will cause the sides  32  and  34  to bulge outward. Because the center portion of the stack is hotter, it is also softer. As a result, more bulge will generally occur in the softer inner layers  58  as shown in FIG. 5A. Alternative types of application of the force may cause slightly different shapes or bulging to occur in the chamber  10 . For example, impact hammering may cause slightly more bulging at the top and bottom, whereas rolling may cause a more uniform bulge. Different types of machines for applying the force will cause different reactions in the laminate inside the chamber  10 .  
         [0042]    In some embodiments, the chamber  10  is then placed into the forge again and reheated and the pressure steps repeated, once again pressing the chamber  10  on the top surface  28  between dies  40  and  42  while it is hot. As shown in FIG. 5B, the chamber is then rotated 90° about an axis extending through the handle  22  so that the sides  32  and  34  are between the dies  40  and  42 . The chamber  10  is pressed on the sides  32  and  34  so as to return the chamber to rectangular shape, pressing in the bulges that have occurred during the previous pressing steps.  
         [0043]    The laminate is now bonded in the form of a single billet of metal. It is desired to remove the billet from the chamber  10 . This is done by cutting the chamber  10  open by any acceptable method, such as a saw, cutting torch, or other technique. The chamber  10  may then be discarded leaving a billet of a laminate metal structure of titanium layers  58  in a single integral piece.  
         [0044]    One purpose of the chamber  10  and the gas  38  is to prevent any reactive gasses, such as oxygen, from interfering with the bond between the plates  24 ,  26  of the billet, or from reacting with the heat to form oxides on surfaces of the plates. According to one embodiment, the chamber is formed from a titanium tube of a desired profile, into which are stacked additional titanium and titanium alloy plates. Alternatively, the chamber may be formed of individual pieces of titanium joined together to form an enclosure. Thus, this structure can be considered a chamber only in the broadest sense of being a structure that facilitates the removal or displacement of oxygen. The chamber is heated and pressed as described above with reference to FIGS.  4 A- 5 B. An advantage of this embodiment is that the billet need not be removed from the chamber, but rather, the chamber becomes part of the billet. If it is desired, the side surfaces of the billet, corresponding to the sides  32  and  34  of the chamber of FIG. 1, may be removed to reveal the layers of metal. Alternatively, the sides may be left on as part of the billet, or removed at a later stage of manufacturing of the billet into a final product.  
         [0045]    As shown in FIG. 6, a single piece of metal composed of layers  58  has been obtained through the heat and pressure steps. The plates  24 ,  26  are now fully bonded and any further treatment is on the unified metal billet  50  having an upper surface  54 . For purposes of clarity and economy, FIGS.  5 - 13  do not show the billet  50  as comprising dark and light layers representing different metal alloys, but only show lines  51  indicating boundaries between layers  58 . However, it will be understood that each of the layers  58  of metal in the billet  50  will retain the appearance and characteristics of the particular metal or alloy plate from which it was formed.  
         [0046]    As shown in FIG. 7, according to one technique, the billet  50  is further shaped by appropriate rolling, pressing, or other techniques to flatten and shape it as desired. For example, it may be cold rolled or flattened to have a final length of 30-40 inches and a final thickness in the range of ½ to 1½ inches. Other metal working techniques may also be used to achieve a desired final shape for the billet, including pounding with a hammer on an anvil, pressing, hot rolling or other techniques.  
         [0047]    [0047]FIG. 8 shows an image being impressed into the upper surface  54  of the final billet using a die having a desired pattern. In the embodiment illustrated, a triangular profile is pressed into the final billet  50 , after which it is machined to remove the upper surface and expose a decorative surface  55  based on the pattern that has been pressed therein. Other profiles may be pressed into the final billet, including square, round or oval profiles, or the like. Once the appropriate image has been pressed therein, the billet is processed to expose the underlying layers, such as by grinding, cutting, or other machine techniques, as shown in FIG. 9.  
         [0048]    The shape pressed into the billet may have any desired design, such as a symbol or logo. FIG. 10 shows a plan view of a portion of a billet  50  such as the billet  50  pictured in FIG. 7, into the surface  54  of which a box shape  56  has been impressed. FIG. 11 shows, in cross section, the billet  50 , with the impression  56  in the surface  54 , and the effects thereof on the underlying layers  58 . FIG. 12 shows the billet  50  after a selected amount of surface  54  has been removed, as described with reference to FIGS. 7 and 8, exposing the decorative surface  55 , including lines  60  formed by the underlying layers  58 . FIG. 13, shows a cross section of the billet  50  of FIG. 12, illustrating exposure of the surface  55  and the underlying layers  58  caused by the removal of the surface  54  to form lines  60 .  
         [0049]    After the billet has been appropriately shaped and decorated according to a desired aesthetic or artistic treatment, as shown in FIGS.  7 - 13 , it may be treated by other artistic techniques. For example, it may be anodized at different voltages in order to provide a desired color pattern, tint or other effect. Additionally, heating at a medium temperature, for example 1,000° F., causes the titanium to take a rainbow appearance. Treating at higher temperatures causes it to darken somewhat, while treating at lower temperatures results in a lighter somewhat different pattern.  
         [0050]    Heat, in the presence of oxygen will cause titanium to oxidize. Different alloys of titanium will oxidize to a greater or lesser degree at any given temperature, depending upon the presence of other metals, and depending upon the total percentage of titanium in the alloy. Thus, by heating the billet in open air, the exposed portions of the layers of titanium and its various alloys can be made to react to the oxygen in the air to take on contrasting colors and shades, for aesthetic appeal.  
         [0051]    Other treatments, such as heating while applying pressure, twisting with or without heat, elongating, compressing, or other techniques, may be used in order to impart a desired artistic pattern into the billet. These techniques may be used on the billet at various stages in order to create different effects. For example, it may be applied to the billet of FIG. 6, the shaped billet of FIG. 7, or the billets of FIGS.  8 - 13  having a pattern impressed therein. Of course, in many embodiments, the elongated billet  50  of FIG. 7 with the appropriate heat treatments will already have a desired appearance, and additional patterns need not be formed; rather, the machining of the billet  50  to produce a finished product will create the artistic pattern without any further treatment. For example, the tapers and bevels that are part of the shape of a knife handle or a piece of jewelry will naturally expose layers in interesting and appealing patterns.  
         [0052]    The final piece can be made to have an artistic design based on the color and selected patterns of the various alloys as well as the patterns that have been pressed or formed therein. It may be used to produce a wide range of finished products. For example, it may be used for the handle of a knife. It may be used for jewelry, such as rings, necklaces, pendants, pins, or other decorative metal ornaments. It may be used as a functional metal part and also as artwork on motorcycles, such as handles, exhaust pipes, or other decorative metal ware.  
         [0053]    The invention has been described with reference to flat plates or layers  24 ,  26  in the chamber  10 , as illustrated in FIGS.  1 - 13 . It will be recognized that other shapes and patterns of material may be positioned within the chamber. A very simple forge-weld can be created using only two pieces of metal. Complex patterns can be created using different shapes and types of metal. FIGS. 14A, 14B and  14 C illustrate many configurations that are possible. FIG. 14A shows an end view of the chamber  10  in which rectangular bars of two different compositions  62 ,  64  are positioned in a herringbone pattern. It is not necessary for the metals to be the same amount of each other or alternating in position. Rather, the same type of metal may be in greater quantities than other types of metal or two metals of the same type may be adjacent to each other. For example 30% of one type of metal and 70% of another type of metal may be used. FIG. 14B shows the chamber  10  in which round bars of two different compositions  66 ,  68  are alternated, with square bars  70  of a third composition positioned in the interstices between the round bars  66 ,  68 . Other patterns include checkerboard, parquet, and concentric, in which round or square tubing of various dimensions is placed, one tube within another, in the chamber  10 .  
         [0054]    [0054]FIG. 14C illustrates another alternative embodiment of a regular pattern of metals placed in the chamber  10 . In the example of FIG. 14C, numerous types of metals are provided, in a regular arrangement which is non-uniform. First metals  72  and  76  are stacked in the pattern as shown adjacent to which can be the same type of metal or, alternatively a second type of metal  74 . If desired, a rod  78  of the same types of metal of  72  and  76  or alternatively a different type of metal may also be present in the chamber  10 . In some embodiments, a powder  84  may exist around the rod  78  and in other portions of the chamber so as to provide an additional metal. The powder  84  can be the same type of metal as other metals or, alternatively may be of a different alloy or other metal in powder form. Of course, the embodiments of FIGS. 14A and 14B can also have powder metal interspersed between the various layers and solid metal members and still fall within the embodiments of the present invention. As also shown in FIG. 14C, additional metals  82  and  80  may also be present within the chamber  10  so that a plurality of different types of metals are forge welded together as explained herein. In some embodiments, voids may be present, such as void  86  so as to create a desired pattern. Alternatively, no voids are present in the chamber and, to the extent possible the chamber is filled with metallic alloys of a particular type according to a desired end pattern.  
         [0055]    Thus, as shown in FIGS. 14A, 14B and  14 C a plurality of different metals may be arranged in a regular pattern within the chamber in order to achieve a desired final result using the forge welding techniques as explained herein. The number of possible configurations is virtually infinite, with each configuration resulting in a unique pattern in a finished product.  
         [0056]    The invention has the advantage of being composed of a lightweight, hard, and highly useful metal. It may be used in any application for which titanium alone is used since it has similar properties, characteristics, and hardness of titanium or of a titanium alloy. It thus may be the functional metal piece for any application in which a strong, lightweight metal part might be used. This ranges from metal blades for scissors, knives, gun barrels, and plate metal, to the metal parts for motorcycles, bicycles, automobiles, racecars, airplanes, and other products that use titanium as a structure component.  
         [0057]    The invention may also have industrial applications, apart from the decorative and artistic appearance it lends to functional components. It has been observed that forge welded composites often combine the advantageous characteristics of their component layers in a single piece. Similarly, various titanium alloys have different advantages. For example, one alloy may have a greater flexibility than pure titanium or other titanium alloys, while another alloy is harder than pure titanium or other alloys. A third alloy may have superior tensile strength characteristics. Preliminary tests suggest that combinations of titanium alloys in forge welded composites, according to the invention, impart their respective characteristics to the final product. Thus, it is reasonable to expect that titanium parts of hitherto unattainable combined characteristics of strength, hardness, flexibility, or other desirable characteristics may be possible, by practice of the principles of the present invention.  
         [0058]    The invention has been described with reference to a chamber having dimensions of around 2×4×10 inches. It will be understood that the same principles may be applied to manufacture large laminated panels or blocks of titanium. Using industrial equipment commonly available, panels or blocks having dimensions of many feet on a side may be produced in accordance with the principles of the invention, and at relatively low costs. Such panels and blocks may find many industrial applications, such as in the aerospace industry, where their unique and selectable characteristics may provide significant advantages over conventional materials for the manufacture of parts.  
         [0059]    For example, for a particular component in an airplane wing, an alloy having desirable characteristics of flexibility is chosen. However, the same alloy may not have an adequate degree of tensile strength, so the component must be made more massive than is optimal, to impart the necessary strength. In contrast, it may be possible to laminate layers of an alloy having the desirable flexibility with an alloy having superior strength characteristics to manufacture a part that shares both virtues, and thus enable the use of a component having lower mass and weight that still exceeds the functional requirements of the component. Reduction of mass and weight is a constant and endless endeavor in aerospace products.  
         [0060]    In the preferred embodiment, titanium and a titanium alloy are used as two alternating layers in composing the final billet  50 . Alternatively, more than two different materials or alloys may be used. Such a use may include titanium and two or more different alloys, each having different characteristics. In further alternative embodiments, other metals besides titanium are used. Titanium is advantageous because it has the properties of being light in weight, noncorrosive in the elements, and non-magnetic. It may be desired to select a combination of metals that can be anodized to cause contrasting color variations between the metals, or that can otherwise be heat treated or hardened to vary the structural properties, as well as impart various patterns. Other metals that may be used include cobalt-based alloys, as well as other metals that have acceptable properties for the end uses as described herein.  
         [0061]    All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety.  
         [0062]    From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.