Abstract:
An assembly for High-Pressure High-Temperature (HPHT) processing comprising a can, a cap, a meltable sealant and sealant barrier, and a superhard mixture comprising superhard particles. The superhard particles may be positioned adjacent a substrate of cemented metal carbide. The can and cap contain the superhard mixture with the sealant barrier positioned within the assembly so as to be intermediate the sealant and at least a portion of the mixture, thereby preventing the sealant from coming in contact with the mixture during processing. The assembly is placed within a vacuum chamber and heated to a temperature sufficient to cleanse the assembly and then melt the sealant providing a hermetic seal for the assembly in preparation for further HPHT processing.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to superhard products such as diamond, polycrystalline diamond, and cubic boron nitride produced by the high pressure and high temperature (HPHT) method. More particularly this invention relates to the HPHT container or can assembly in which the superhard materials are processed. The assembly comprises a metal can containing the superhard materials, an end cap, a meltable sealant, and a sealant barrier, the improvement being the use of the sealant barrier to prevent contamination of the superhard materials during processing.  
         [0002]     Superhard materials by the HPHT method are produced by encapsulating the materials into a container, variously known in the art as a container, a can, an enclosure, a cup, a shield, and a tube. The applicants prefer the term “can”, and, therefore, all references to a “can” in this application refer to the container as used in the art.  
         [0003]     Examples of some of the methods for producing superhard materials are reported in U.S. Pat. No. 4,954,139, to Cerutti, and U.S. Pat. No. 4,518,659, to Gigl et al., both of which are incorporated herein by this reference for all that they teach and claim.  
         [0004]     Producing superhard materials is somewhat problematic due to the nature of the materials used and of the extreme conditions under which they must be processed. Generally, the raw materials for the production of superhard products are in the form of ceramic and hard metal composites and fine powders. These materials must be cleaned of foreign particles and oxides in preparation for HPHT processing. This may be accomplished by either subjecting the components to high heat, a reducing environment, or to high vacuum, or a combination thereof. Afterwards, the HPHT components must be protected before and during processing from unwanted impurities and contamination by sealing the components in a metal can. The sealed can, then, must be suitable for processing under conditions of elevated pressure and temperature as reported in the art. The can components are usually refractory materials comprising the can and a lid. It is also known to employ a sleeve, disks, and/or a cap, over the lid as additional levels of protection. The can components are either tightly fit together, or are pressed together in assembly to make a tight seal. It may be desirable to seal the can further using a braze procedure, a vacuum braze procedure, or electron-beam welding, which may also be accomplished in a vacuum.  
         [0005]     Examples of the vacuum braze sealing techniques are reported in U.S. Pat. No. 4,333,902, to Hara, and U.S. Pat. No. 4,425,315, to Tsuji et al., both disclosures are incorporated herein by this reference for all that they teach and claim.  
         [0006]     The Hara reference discloses a process for producing a sintered compact by filling a cup with a powdered material mixture and putting on the opening of the cup a covering consisting of a lid and solder so as to permit ventilation between the interior and exterior of the cup assembly. The cup assembly is then placed inside a chamber in a vacuum furnace and taken to a high vacuum. While at the desired level of vacuum, the cup is heated to a sufficient temperature to cleanse the can elements and HPHT materials. Then, the temperature in the chamber is increased to melt the solder. By capillary action the solder melts around the cup and the lid and hermitically seals the container. Afterwards, the oven is cooled and the vacuum released and the sealed container retrieved for further HPHT processing.  
         [0007]     When solder compositions are detrimental to the sintering process, a means must be provided to protect the HPHT materials mixture from contamination during the sealing process. The methods disclosed in Hara position the solder either adjacent the HPHT materials, or provide a capillary path between the HPHT materials and the solder, without providing a means of protecting the HPHT materials mixture from contamination from the solder. As a result, the flow of the solder by capillary action tends to contaminate the sintered materials producing low quality products and low production yields.  
         [0008]     The Tsuji reference, and its related references, all incorporated herein by this reference, disclose a method of producing HPHT sintered bodies using a process similar to that disclosed in the Hara reference and further teaching the use of a container assembly comprising inner and outer refractory sleeves, in addition to the ventilating solder material and lid. Although the inner and outer sleeves are referred to in the disclosure as providing a double seal, a narrow opening is provided between the overlapping sleeves. The opening is necessary for a ventilation path from the HPHT materials mixture to the vacuum chamber. Also, the opening provides the surface energy to drive the capillary flow of the sealant. Once again, no provision is made to protect the HPHT materials mixture from contamination from the solder.  
         [0009]     U.S. Pat. No. 6,596,225, to Pope et al., and its related references, all incorporated herein by this reference, teach sealing of the can by electron beam welding at high temperature and in a vacuum. However, no details are disclosed concerning the method.  
         [0010]     Therefore, it is desirable in the art of HPHT processing of superhard materials that the can assembly provides for a hermetic seal that protects the assembly from contamination and for protecting the HPHT materials mixture from contamination during the sealing process as well as during HPHT processing by the use of a solder/sealant barrier.  
       SUMMARY OF THE INVENTION  
       [0011]     This invention presents a refractory can assembly for High-Pressure High-Temperature (HPHI) processing of superhard materials mixtures such as diamond and cubic boron nitride. The can is used to contain the superhard materials during processing. The assembly&#39;s components comprise a can, a cap, a meltable sealant, a sealant barrier, and a superhard mixture comprising superhard particles. The components of the can assembly are arranged so as to allow for the ventilation of the contaminants from the HPHT materials mixture and simultaneously provide an extended path between the meltable sealant and the HPHT materials mixture. The meltable sealant may be a solder or braze material. The assembly may also include a lid and disks for further containment. The mixture may include a cemented metal carbide substrate positioned adjacent the superhard particles. The can and cap contain the superhard mixture with the sealant barrier positioned within the assembly so as to be intermediate the sealant and at least a portion of the mixture. The sealant barrier keeps the meltable solder or braze sealant from contaminating the superhard mixture. The assembly is placed within a vacuum chamber and heated to a temperature sufficient to cleanse the assembly and then melt the sealant, thus providing a hermetically sealed assembly in preparation for further HPHT processing. The sealant barrier comprises materials that interrupt the capillary flow of the meltable sealant and may be selected from the group consisting of a stop-off compound, a solder/braze stop, a mask, or a sealant flow control, or a combination thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a cross-section diagram of a prior art can assembly of the Hara reference.  
         [0013]      FIG. 2  is a cross-section diagram of a prior art can assembly of the Tsuji reference.  
         [0014]      FIG. 3  is a perspective diagram of a cylindrical embodiment of the present invention.  
         [0015]      FIG. 4  is a perspective diagram of a conical embodiment of the present invention.  
         [0016]      FIG. 5  is a cross-section diagram of an embodiment of the present invention depicting, inter alia, the meltable sealant and sealant barrier.  
         [0017]      FIG. 6  is a cross-section diagram of the embodiment of  FIG. 5  depicting, inter alia, the melted sealant and the barrier.  
         [0018]      FIG. 7  is a cross-section diagram of an embodiment of the present invention depicting, inter alia, the assembly of  FIG. 5  with the addition of the lid or disk as additional protection for the superhard mixture.  
         [0019]      FIG. 8  is a cross-section diagram of an embodiment of the present invention depicting, inter alia, the meltable sealant and more than one sealant barrier.  
         [0020]      FIG. 9  is a cross-section diagram of an embodiment of the present invention depicting, inter alia, a can assembly having sealant and sealant barrier sleeves.  
         [0021]      FIG. 10  is a cross-section diagram of an embodiment of the present invention depicting, inter alia, mechanical crimps in cooperation with the sealant barrier circumscribing the can assembly and HPHT materials mixture. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     The present invention will be further described in reference to the following drawing figure diagrams which teach all that is depicted therein and anticipations thereof. Although, the diagrams are representative embodiments of the present invention, it will be obvious to those skilled in the art that deviations from the figures are also beneficial, and such deviations are also within the scope and spirit of the present invention.  
         [0023]      FIG. 1  is a cross-section diagram of a prior art can assembly. Can assemblies are generally cylinders closed on one end and open on the other. The can assembly  13  is such a cylinder. Inside the can assembly  13  is the superhard materials mixture  14 , comprising a composite of superhard particles for sintering. The can assembly is closed by lid  15 , having a sealant material  16  arranged between the lid  15  and superhard material mixture  14 . Openings  17  and  18  are provided between the superhard mixture and the can assembly to promote ventilation of contaminants and capillary flow of the meltable sealant  16 , in this case copper. The HPHT assembly is heated in a vacuum furnace that produces an environment which cleanses the components of unwanted contaminants and hermetically seals the container in preparation for further HPHT processing.  
         [0024]      FIG. 2  is a cross-section diagram of a prior art can assembly employing an outer can  20  and an inner can  21 . The double can assembly contains the superhard materials mixture comprising a substrate  22  and a layer of superhard particles  23 . The assembly is closed by a lid  24  having a meltable sealant  25 . Once again an opening  26  is provided between the inner and outer can assembly and the superhard materials mixture in order to allow the flow of contaminants from the can assembly and to promote the capillary flow of the sealant, in this case a copper braze, around the mixture  22  and  23 . Although the purpose of the inner and outer can assembly is to provide a better seal from contamination, the figure fails to provide a sealant barrier in the opening  26  to prevent the sealant&#39;s access to the mixture. Contamination from undesirable impurities is the leading cause of low quality products and low production yields in the art of HPHT superhard products such as polycrystalline diamond and cubic boron nitride.  
         [0025]      FIG. 3  is a perspective diagram of an embodiment of the can assembly of the present invention comprising a cylindrical can  30  and a cap  31 . Line AA describes the plane of the cross section in subsequent figures.  
         [0026]      FIG. 4  is a perspective diagram of an embodiment of the can assembly of the present invention comprising a cylindrical can  40  having a convex, or conical, region  42  and an end cap  41 . Those skilled in the art will understand that the conical region produces a superhard element having a similar shape.  
         [0027]      FIG. 5  is a cross-section diagram of an embodiment of the present invention depicting a can assembly comprising a can  50  having an extended side wall length  51 . The can contains a superhard substrate  53  and a layer  54  comprising superhard particles such as diamond or cubic boron nitride. The extended side wall length  51  of the can  50  is formed over the surface of substrate  51  in aid of assembly and compaction of the superhard mixture and to promote sealing of the mixture. The can assembly is closed by end cap  52  which is fitted onto the can. A meltable sealant material  55  is interposed between the end cap and the can with access to narrow opening  57 . Opening  57  is of sufficient width, say between about 0.0005 to 0.050 inches, to promote the outflow of contamination and yet produce the surface energy necessary to drive the capillary flow of the meltable sealant  55 . A sealant barrier  56  is provided around the circumference of the substrate  53  intermediate the meltable sealant  35  and the superhard mixture comprising  53  and  54 . When the can assembly of  FIG. 5  is placed in the vacuum chamber of a high temperature furnace and placed under high vacuum and high temperature sufficient to ventilate contaminates from the assembly, the assembly is cleansed of undesirable contamination. The temperature of the furnace is then increased sufficiently to melt the sealant. By capillary action, the sealant flows into the opening  57  and hermetically seals the can assembly. The flow of the sealant is stopped by the sealant barrier  56 , thereby protecting the cleansed HPHT mixture from further contamination from the sealant itself. The can is then retrieved from the furnace in preparation for further HPHT processing.  
         [0028]     The sealant barrier  56  comprises a material that inhibits the surface tension between mating surfaces and interrupts the flow of the sealant melt under the cleansing environment of the vacuum furnace and under the further conditions of HPHT processing. Such materials are commonly known as: Stop-Off, Stop-Off Compound, Solder/Braze Stop, Solder Mask, and Sealant Flow Control. One such material is marketed under the name of “Green Stop-Off Type 1” by Nicrobraz, Wall Colmondy Corporation, Madison Hts., MI. Such sealant barriers comprise refractory materials of inert oxides, graphite, silica, magnesia, yttria, boron nitride, or alumina and are applied by coating, etching, brushing, dipping, spraying, silk screen painting, plating, baking, and chemical or physical vapor deposition techniques. In the embodiment of  FIG. 5 , the sealant barrier was applied as a paint using a brush. It may be applied to the surface of anyone of the assembly components where it would be desirable to prevent the flow of the liquid sealant.  
         [0029]      FIG. 6  is a cross-section diagram of an embodiment of the present invention similar to that depicted in  FIG. 5  comprising at can  61  containing a substrate  64  and a superhard mixture  67 . The can is closed by end cap  62 . The sealant  65  is depicted as melted filling the opening  66  and stopped by the sealant barrier  63  so that it does not flow into the region of the superhard mixture  64  and  67 .  
         [0030]      FIG. 7  is a cross-section diagram of an embodiment of the present invention similar to that depicted in  FIG. 5  comprising a can  70  and an end cap  71  containing a substrate  72  and superhard particles  73 . The assembly comprises the addition of a lid  75  as a further protection for the superhard mixture comprising a substrate  72  and superhard particles  73 . The sealant  76  and the sealant barrier  77  are contained within the opening  74  so that when the sealant is melted it flows within the opening  74  around the lid  75  and is stopped by the sealant barrier  77 . The can assembly will thereby be hermetically sealed from contamination during further HPHT processing.  
         [0031]      FIG. 8  is a cross-section diagram of a double can assembly embodiment of the present invention. The assembly comprises an inner can  80  and an outer can  81  containing a substrate  82  and a mixture of superhard particles  83 . Within the space  84  are positioned the lid  85 , the sealant  86 , and the sealant barrier  87 . The assembly also comprises an additional sealant barrier  88 . The additional sealant barrier  88  serves to prevent the sealant from escaping the assembly during processing. When the sealant is melted, it flows within the opening  84  to surround the open portion of the can and is confined between the two regions of sealant barrier  87  and  88 .  
         [0032]      FIG. 9  is a cross-section diagram of a sealable assembly comprising a can  90  containing a substrate  91  and superhard particles  92 . The assembly further comprises an opening  95  for positioning a sealant sleeve  94  and a sealant barrier  96 , which may be a sleeve or a coating. The can  90  further comprises a recess  93  for cooperating with the insertion of the sealant sleeve  94 . The assembly may be swaged together so that the components of the assembly are tightly fit together prior to sealing in a vacuum furnace. As noted in the other figures, the sealant barrier is positioned intermediate the sealant and the superhard particles. In this manner, the superhard particles are protected from undesirable contamination during HPHT processing.  
         [0033]      FIG. 10  is a cross-section diagram of a sealed embodiment of the present invention comprising a can  90  and an end cap  93  containing a substrate  91  and superhard particles  92 . Within the space  94  are located the lid  95 , the sealant  96 , and the sealant barrier  97  and  100 . In cooperation with the sealant, the assembly comprises a circumferential groove  101  around the substrate  91  and a cooperating indentation  98  in the wall of the can  90 . The end cap  93  also comprises cooperating indentations  99  and  100  that may be used in connection with the sealant barrier. When the can assembly is assembled, it may be swaged together so that the components are in tight fit with each other. The cooperating indentations, when used in association with the sealant barrier, provide a mechanical and a chemical stop for the flow for the sealant. Surprisingly, the applicants have found that regardless of the fit between the components, the heat and vacuum of the furnace are sufficient to drive off contaminants within the assembly. It is believed that the during high temperature processing the superhard mixture expands less than the metal can components thereby providing sufficient opening for the escape of contaminants during the vacuum cycle. By maintaining a tight fit between the components, the applicants believe that higher surface tension is achieved to drive the capillary action of the melting sealant. The applicants have found, also, that smooth surface finishes between the can and the superhard components is beneficial for achieving a competent seal.