Abstract:
A system and method for joining materials. The system includes a sealed chamber having a window. A laser is disposed external to the sealed chamber and heats objects in the sealed chamber through the window. The method includes sealing objects to be joined in the sealed chamber with a controlled environment and heating the objects with a laser disposed external to the sealed chamber.

Description:
RELATED APPLICATIONS 
       [0001]    The present patent document claims the benefit of the filing date under 35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No. 62/269,782, filed Dec. 18, 2015, which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to the joining of materials and more particularly to joining materials such as ceramic matrix composites and refractory metals. 
         [0004]    2. Background Information 
         [0005]    Ceramic matrix composites are a type (CMC) of composite material and include ceramic fibers embedded in a ceramic matrix. While ceramics on their own are brittle, cracking easily, ceramic matrix composites are durable and have a high crack resistance. They are useful in situation in fields requiring high-temperature durability and resistance to corrosion. Refractory metals are a class of metals that are resistant to heat and wear. Like ceramic matrix composites, they are durable at high-temperatures. 
         [0006]    Because ceramic matrix composites and refractory metals melt at high temperature, pieces are often joined using brazing. In brazing, a joining material is melted and flows between pieces, where it hardens, joining the pieces. Such joining procedures are typically carried out in either a large furnace, or in an open environment. In a furnace, the entire piece may be heated in a vacuum or inert atmosphere to melt the brazing material. In an open environment, the piece may be heated locally at the spot to be joined. This local heating allows the piece to be heated and cooled quickly, and allows brazing of pieces that are too large for a furnace or may be damaged by furnace heating of the entire piece. While local heating is effective, many joining materials react with oxygen and/or nitrogen, so it is beneficial if the piece is heated and cooled as quickly as possible to deter the joining materials from reacting with oxygen and/or nitrogen. In some instances, the local heating of a piece may be done through the use of a laser. The laser is able to direct a precise beam to heat the piece at a precise location. 
         [0007]    To inhibit the either the piece or the filler material from reacting with oxygen or nitrogen, ambient gas may be shielded from the piece. For example, a shielding gas may be directed to the piece as it is heated to inhibit reaction with the ambient air. Or the piece and the heat source may be placed in a sealed environment where the piece may be heated in a controlled environment. 
         [0008]    Each of these techniques for joining materials have potential downsides. Heating and cooling the piece quickly allows the joint to react with the ambient air, even if only momentarily. Similarly, while shielding gas may inhibit reaction of the ambient air with the piece or the filler, some reaction may still take place. Heating the piece in a controlled environment may suitably inhibit the reaction with ambient air, but a sealed environment large enough to house the pieces being joined and the heat source is typically very expensive. 
       BRIEF SUMMARY 
       [0009]    It would be beneficial to develop a low cost system for joining materials in a low oxygen/nitrogen environment. 
         [0010]    In one aspect, a system for joining materials is disclosed. The system includes a vessel having an inner chamber sealed from an environment external to the vessel, a laser disposed external to the vessel and configured to heat material through electromagnetic radiation, and a window transparent to the electromagnetic radiation of the laser and providing a line of sight between the laser and the material in the chamber. 
         [0011]    In some embodiments, the system includes a reactive metal disposed in the inner chamber with the reactive metal in a line of sight of the laser. In some embodiments, the system further includes a substrate material in the inner chamber. In some embodiments, the laser has a first configuration aimed at the reactive metal and a second configuration that is not aimed at the reactive metal. 
         [0012]    In some embodiments, the window is configured to be removable from the vessel. In some embodiments, the vessel has an upper portion and a lower portion removable from the upper portion and the system further comprises a clamp securing the lower portion to the upper portion. In some embodiments, the system includes an inlet in fluid communication with the inner chamber and configured to receive a purge gas source. In some embodiments, the system includes an outlet in fluid communication with the inner chamber and configured to remove a gas from the inner chamber. 
         [0013]    In another aspect, a method for joining materials is disclosed. The method includes placing a substrate material in a chamber of a sealable vessel having a transparent window, placing a joining material in the chamber proximate the substrate material, sealing the vessel with the substrate material and the joining material in the chamber, directing a laser light source through the transparent window to heat the joining material. 
         [0014]    In some embodiments, the method further includes introducing a purge gas into the chamber after sealing the vessel and removing existing gas within the vessel. 
         [0015]    In some embodiments, the method includes placing a reactive metal in the inner chamber prior to sealing the chamber and directing the laser light source through the transparent window to heat the reactive metal prior to heating the joining material. 
         [0016]    In some embodiments, the vessel is placed in a controlled environment prior to sealing the vessel. 
         [0017]    In some embodiments, the method further includes evacuating the chamber prior to heating the joining material. 
         [0018]    In another aspect, a vessel for joining materials with an external laser is disclosed. The vessel includes a lower portion having a first cavity with a base configured to hold a substrate material, an upper portion having a second cavity, the first cavity and second cavity together forming an inner chamber sealed from an ambient environment when the upper portion is secured to the lower portion, a clamping mechanism for securing the upper portion to the lower portion, and a window disposed in the upper portion, the window providing a line of sight to the base. 
         [0019]    In some embodiments, the window is removable. In some embodiments, the vessel further includes an inlet configured to receive a purge gas and an outlet configured to exhaust gas from within the inner chamber. 
         [0020]    In some embodiments, the upper portion and the lower portion each have a ring extending laterally and wherein the clamping mechanism is a ring clamp. 
         [0021]    In some embodiments, the base is further configured to hold a reactive metal. In some embodiments, a gasket is disposed between the upper portion and the lower portion. In some embodiments, the window is disposed opposite the base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  illustrates an example of a vessel for joining materials. 
           [0023]      FIG. 2  illustrates a schematic of a cross-section of a vessel for joining materials. 
           [0024]      FIG. 3  illustrates a schematic cross-section of the vessel of  FIG. 2  with a laser for heating materials within the vessel. 
           [0025]      FIG. 4  illustrates a flowchart of a method for joining materials. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  illustrates a vessel  10  for joining a substrate material using a joining material while isolating the substrate material and joining material from an ambient environment during localized heating. For example, the substrate material may be a ceramic matrix composite or a refractory metal and the joining material may be a powdered metal or other reactant.  FIG. 2  illustrates a schematic cross section of the vessel  10  of  FIG. 1 . The following description will be in reference to  FIG. 1  and  FIG. 2  together. The vessel  10  encloses a sample chamber  12 , which is isolated from the ambient environment  14 . The vessel  10  has a window  16  providing optical access into the chamber  12 . The window  16  is a material that is transparent to light at a frequency used by a laser for heating components within the chamber  12 . 
         [0027]    The vessel  10  includes a lower portion  18  and an upper portion  20 . The lower portion  18  has a lower cavity  22  that forms a first portion of the chamber  12  and the upper portion has an upper cavity  24  that forms a second portion of the chamber  12 . The upper portion  20  and the lower portion  18  may each have a ring  28  protruding from a cylindrical surface  17  of the vessel  10 . The upper portion  20  and the lower portion  18  are separated by a gasket  26  that forms a seal between the two rings  28 . A ring clamp (not shown for clarity) may encompass a perimeter of the vessel  10  about the rings  18  and force the upper portion  20  and lower portion  18  together, compressing the gasket  26 . The chamber  12  is accessible by removing the ring clamp, freeing the upper portion  20  from the lower portion  18 . 
         [0028]    The window  16  is secured to the upper portion  20  opposite a base  30  of the lower portion  18 . The window  16  is sized and shaped to fit in a recess  32  of the upper portion  20  and is held in place by a cap  34 . The cap  34  is secured to the upper portion  20  through cap screws  35  extending through the cap  34  and into a threaded recess  37  of the upper portion  20 . The cap screws  35  contact the cap  34  and press it towards the upper portion  20 , causing the cap  34  to contact the window  16 . The contact presses the window  16  towards the upper portion  20  where the window  16  contacts a gasket  36  between the upper portion  20  and the window  16 . The gasket  36  provides an air tight seal between the window  16  and the interior chamber  12 . 
         [0029]    While the vessel  10  has been described with regard to the particular structure shown in  FIG. 2 , one of ordinary skill in the art will recognize that other structures and techniques are possible and embodiments are not limited to this particular structure. For example, in one embodiment the upper and lower portion of the vessel  10  may be a single unitary piece with access to the chamber  12  provided through the removable window  16 . In other embodiments, the window  16  may be permanently fixed to the upper portion  20  of the vessel  10  with access to the chamber  12  provided by separating the upper portion  20  and the lower portion  18  of the vessel  10 . In still other embodiments, the upper portion  20  and the lower portion  18  may be secured to one another through cap screws passing through the ring  28  of the upper portion  20  and threaded into the ring  28  of the lower portion. 
         [0030]    In use, a substrate material  38  is disposed in the chamber  12 . The substrate material  38  may rest on the base  30  of the lower portion  18 . The substrate  38  may be a ceramic matrix composite or a refractory metal. The joining material is placed in the chamber  12  proximate the substrate material  38 . A known environment is introduced into the chamber  12  using various techniques. In one embodiment, the vessel  10  may be assembled within a known environment. For example, the vessel  10  may be assembled within a large, environmentally controlled chamber. Thus the environment within the chamber  12  would be known at the time of assembly and the known environment would be maintained in the chamber  12  after removal of the vessel  10  from the environmentally controlled chamber. In other embodiments, the chamber  12  may be purged with a purge gas to introduce a known environment to the chamber  12 . For example, an inlet  19  may be configured to receive a purge gas from a gas source and an outlet  21  may be configured to vent the existing environment of the chamber  12 . As the purge gas is introduced through the inlet  19 , the existing environment in the chamber  12  would vent through the outlet  21  until the environment of the chamber  12  comprised substantially only the purge gas. In other embodiments, the chamber  12  may be evacuated by either assembling the vessel  10  in a vacuum environment, or by applying a vacuum to the chamber  12  after assembly, such as through the inlet  19  or outlet  21 . 
         [0031]      FIG. 3  illustrates the vessel  10  of  FIG. 2  in use with a laser  42  configured to heat components within the chamber  12 . In some embodiments, the controlled environment of the chamber  12  may be further purified by including a reactive material  40  in the chamber  12  at the time the vessel  10  is assembled. The reactive material  40  is then reacted in the controlled environment within the chamber  12  to bond with any unwanted gases. For example, in some embodiments it is desirable for nitrogen and oxygen levels to be minimized within the controlled environment of the chamber  12 . A reactive material  40 , such as titanium or zirconium, is positioned within the chamber  12  in view of the window  16 . The laser  42  is aimed at the reactive material  40  through the window  16 , as shown by laser  44 , to heat the reactive material  40 , causing it to react and bond with any residual oxygen and/or nitrogen within the chamber  12 . The use of the reactive material  40  may result in a controlled environment within the chamber  12  that is more highly purified than otherwise possible. 
         [0032]    In use, the substrate material  38  and the joining material  46  are placed within the chamber  12  in view of the window  16 . The vessel  10  is then assembled and the controlled environment is introduced into the chamber  12 . Once the vessel  10  is sealed with the controlled environment in the chamber  12 , the reactive material  40  may then be reacted to further purify the controlled environment. Once a suitable controlled environment is established in the chamber  12 , a laser  48  is aimed through the window  16  at the substrate material  38  and the joining material  46 . The laser  48  may be the same laser  44  used to heat the reactive material  40 , or it may be a separate laser in some embodiments. The energy of the laser  48  passes through the transparent window  16  and is directed on the substrate material  38  and the joining material  46 , heating them to a desired temperature for joining. 
         [0033]    After the substrate material  38  and the joining material  46  have cooled, they may be removed from the chamber  12 . In embodiments having a ring clamp holding the upper portion  20  and the lower portion  18  together, the ring clamp is released allowing the upper portion  20  to be removed from the lower portion  18  exposing the chamber  12 . In embodiments in which the vessel  10  is a unitary design, the cap screws  35  may be loosened freeing the cap  34 . With the cap  34  free, the window  16  is removed providing access to the chamber  12 . One of ordinary skill in the art will recognize that access to the chamber  12  is dependent upon the structure of the vessel  10  and may vary. 
         [0034]      FIG. 4  illustrates a flowchart of a method  50  for joining materials. The method will be described in relation the vessel  10  described previously, but one of skill in the art will recognize that the method may be applied to any vessel having a controlled environment and a window for passing a laser heat source. In block  52 , a substrate material  38  is placed in the chamber  12 . One of skill in the art will recognize that the substrate material  38  may comprise more than one piece of material to be joined using the joining material  46 . For example, the substrate material  38  may comprise two pieces of ceramic matrix composite being joined together, a piece of ceramic matrix composite and a refractory metal, or two refractory metals, among other combinations. In block  54 , a joining material  46  is placed in the chamber  12  proximate the substrate material  38 . The substrate material  38  and the joining material  46  may be placed in the chamber at the same time, or the order may vary. In embodiments in which further refinement of the controlled environment within the chamber is desired, in block  56 , a reactive material is placed in the chamber. In block  58 , the chamber is sealed with the substrate material and sample material inside. If the vessel was not assembled in environmentally controlled enclosure, at block  60  a controlled environment is introduced into the chamber, either by purging it with a gas or evacuating the chamber through an outlet. If the vessel was assembled within an environmentally controlled chamber, then it may be removed once the chamber is sealed. 
         [0035]    In block  62 , the laser is optionally directed through the window of the vessel and directed on the reactive material to further refine the environment within the chamber. Once the reactive material is suitably reacted, the laser is directed through the window at the substrate material  38  and the joining material  46  for heating. The joining material  46  is then heated to a joining temperature and the substrate material  38  is joined. Once joined, the substrate material  38  may be removed from the chamber in block  64 . 
         [0036]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. For example, instead of the vessel described previously, a different vessel being sealed with a transparent window may be utilized in the method. Additionally, while not described in detail, one of ordinary skill in the art will recognize that the different embodiments may be used in combination with one another. Furthermore, while the embodiments are described in relation to brazing a high temperature substrate material such as a ceramic matrix composite or a refractory metal, one of skill in the art will recognize that embodiments may be used to locally heat materials in a controlled environment. For example, embodiments may be used to heat a reactive powder to a melting temperature for joining in a low oxygen environment.