Patent Document

BACKGROUND OF THE INVENTION 
     The invention relates to a metal-infiltrated polycrystalline diamond composite tool. More particularly, the invention relates to diamond particles that are used to form such a tool. Even more particularly, the invention relates to diamond particles having an activated surface layer. Finally, the invention relates to a method of forming a metal-infiltrated polycrystalline diamond composite tool from diamond particles having such an activated surface layer. 
     Polycrystalline diamond tools are often manufactured from dense blanks that are formed by infiltrating a matrix of diamond particles with a molten metal, such as cobalt. The molten metal acts as a liquid-state sintering aid, partially dissolving the diamonds and producing diamond-to-diamond bonding within the composite. One problem encountered with infiltrating the bed of diamond particles is that the metal does not wet the surface of the diamonds well. As a result, the matrix is not completely infiltrated and the diamond-to-diamond bonds are not formed in some locations, thus preventing the optimization of the overall strength and abrasion resistance of the cutting tool. 
     To improve wetting of the diamonds by the molten metal, the diamonds in such tools may be initially coated with the same—or similar—metal that is used as an infiltrant metal to facilitate infiltration and formation of the diamond-to-diamond bonds. An electroless plating technique, in which the diamonds are exposed to a solution containing the coating material, has been used to coat diamond particles with a metal. Electroless plating of a substrate, however, requires a catalytic reduction of metal ions in the presence of a reducing agent. For non-conducting materials such as diamond, the substrate surface must therefore be activated prior to plating. In contrast, many metal substrates do not require such activation, as the surface is already catalytic. 
     Palladium (Pd) is frequently used to activate substrate materials prior to coating. The most common procedure is to first sensitize the substrate surface with tin dichloride (SnCl 2 ), followed by activation using a solution of Pd and hydrochloric acid (HCl). Alternatively, a colloidal Pd solution, which also frequently contains Sn, can be used to activate the substrate surface. One of these two methods is commonly used in the electroless plating of diamond. Kanada et al. (U.S. Pat. No. 5,759,216), for example, have used an activation solution comprised substantially of palladium to obtain metal-coated diamonds, which were subsequently used to form polycrystalline diamond (PCD) under high pressure and high temperature conditions. 
     One drawback to the use of palladium as an activating metal is its expense. It is therefore desirable to identify a less expensive alternative procedure for producing metallic coatings that are applied to the diamond particles. Therefore, what is needed is a diamond particle having a palladium-free coating that enhances wetting by the molten metal infiltrant. What is also needed is a diamond particle coated with an activation layer formed from a relatively inexpensive metal, the activation layer being capable of catalytically reducing metallic coatings that are applied to the diamond particles by electroless deposition. What is further needed is a method of applying such an activation layer to the diamond particles. In addition, what is needed is a metal-infiltrated polycrystalline diamond composite tool that comprises a number of diamond particles having;,such an activation layer. Finally, what is needed is a method of forming such a tool. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention satisfies these needs and others by providing a metal-infiltrated polycrystalline diamond composite tool having a plurality of diamond grains forming a continuous polycrystalline diamond matrix, the polycrystalline diamond matrix being interpenetrated by a substantially palladium-free metallic phase. The present invention also provides a preform for such metal-infiltrated polycrystalline diamond composite tools, in which diamond particles having a substantially palladium-free wetting enhancement layer contact a metallic infiltrant source. The present invention also provides methods of making a metal-infiltrated polycrystalline diamond composite tool, a preform, and a coated diamond particle for such a tool, all of which are substantially palladium-free. 
     Accordingly, one aspect of the present invention is to provide a metal-infiltrated polycrystalline diamond composite tool. The metal-infiltrated polycrystalline diamond composite tool comprises: a plurality of diamond grains, the plurality of diamond grains forming a continuous polycrystalline diamond matrix; 
     a substantially palladium-free metallic phase, the metallic phase being substantially palladium-free and contiguous to the continuous polycrystalline diamond matrix, wherein the metallic phase interpenetrates the continuous polycrystalline diamond matrix and substantially wets an outer surface of the continuous polycrystalline diamond matrix; and a working surface. 
     A second aspect of the invention is to provide a preform for a metal-infiltrated polycrystalline diamond composite tool. The preform comprises: a container formed from a refractory material; a plurality of coated diamond particles disposed in the container and forming a bed therein, each of the plurality of coated diamond particles comprising a diamond having an outer surface and a wetting-enhancement coating disposed thereon, the wetting-enhancement coating being substantially palladium-free and comprising at least one metal selected from the group consisting of cobalt, iron, and nickel, wherein the wetting-enhancement coating substantially covers the outer surface; and a metallic infiltrant source disposed in the container and contacting the bed of the plurality of: coated diamond particles. The metallic infiltrant source comprises at least one metal selected from the group consisting of cobalt, iron, and nickel. 
     A third aspect of the invention is to provide a metal-infiltrated polycrystalline diamond composite tool formed from a preform. The preform comprises: a container formed from a refractory material; a plurality of coated diamond particles disposed in the container and forming a bed therein, each of the plurality of coated diamond particles comprising a diamond having an outer surface and a wetting-enhancement coating disposed thereon, the wetting-enhancement coating being substantially palladium-free and comprising a metal selected from the group consisting of cobalt, iron, and nickel, wherein the wetting-enhancement coating substantially covers the outer surface; and a metallic infiltrant source contacting the bed of the plurality of coated diamond particles. The metal-infiltrated polycrystalline diamond composite tool comprises: a plurality of diamond grains, the plurality of diamond grains forming a continuous polycrystalline diamond matrix; a metallic phase, the metallic phase being substantially palladium-free and contiguous to the continuous polycrystalline diamond matrix, wherein the metallic phase interpenetrates the continuous polycrystalline diamond: matrix and substantially wets an outer surface of the continuous polycrystalline diamond matrix, and wherein the metallic phase comprises at least one metal selected from the group consisting of cobalt, iron, and nickel; and an abrasive working surface;. 
     A fourth aspect of the invention is to provide a method of making a metal-infiltrated polycrystalline diamond composite tool. The method comprises the steps of: providing a preform, the preform comprising: a container containing a metallic infiltrant, the metallic infiltrant being substantially palladium-free, and a plurality of coated diamond particles, wherein each of the coated diamond particles comprises a diamond having an outer surface and a substantially palladium-free wetting-enhancement coating disposed thereon; infiltrating the plurality of coated diamond particles with the metallic infiltrant and producing diamond-to-diamond bonding, thereby forming a metal-infiltrated polycrystalline diamond composite blank; and forming a working surface on at least one surface of the metal-infiltrated polycrystalline diamond composite blank, thereby forming the metal-infiltrated polycrystalline diamond composite tool. 
     A fifth aspect of the invention is to provide a method of making a coated diamond particle for use in a metal-infiltrated polycrystalline diamond composite tool. The method comprises the steps of: providing a diamond; and coating an outer surface of the diamond with a substantially palladium-free wetting-enhancement coating comprising a metal selected form the group consisting of cobalt, iron, and nickel, such that the substantially palladium-free wetting-enhancement coating substantially covers the outer surface, thereby forming a coated diamond particle. 
     Finally, a sixth aspect of the invention is to provide a method of making a preform for a metal-infiltrated polycrystalline diamond composite tool. The method comprising the steps of: providing a container formed from a refractory material; providing a plurality of coated diamond particles to the container, each of the coated diamond particles comprising a diamond having an outer surface and a substantially palladium-free wetting-enhancement coating disposed thereon; and providing a substantially palladium-free metallic infiltrant source to the container such that the substantially palladium-free metallic infiltrant source contacts the plurality of coated diamond particles. 
    
    
     These and other aspects, advantages, and salient features of the invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of an infiltrated polycrystalline diamond composite tool of the prior-art; 
     FIG. 2 is a schematic view of a diamond having a wetting-enhancement coating of the present invention; 
     FIG. 3 is a schematic view of a diamond having a wetting-enhancement coating, activation coating, and sensitized surface; 
     FIG. 4 is a schematic view of a preform for an infiltrated polycrystalline diamond composite tool of the present invention; 
     FIG. 5 is a schematic view of an infiltrated polycrystalline diamond composite tool of the present invention; 
     FIG. 6 is a SEM micrograph of a palladium-activated Co—B coated diamond particle; 
     FIG. 7 is an Auger spectroscopy cobalt scan of a palladium-activated Co—B coated diamond particle; 
     FIG. 8 is a SEM micrograph of a silver-activated Co—B coated diamond particle; and 
     FIG. 9 is an Auger spectroscopy cobalt scan of a silver-activated Co—B coated diamond particle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that terms such as “top,” “bottom,” “outward,” “inward,” and the like are words of convenience and are not to be construed as limiting terms. 
     Referring to the drawings in general and FIG. 1 in particular, it will be understood that the illustrations are for the purpose of describing the preferred embodiment of the invention and are not intended to limit the invention thereto. 
     An infiltrated polycrystalline diamond composite tool  10  of the prior art is shown in FIG.  1 . The infiltrated polycrystalline diamond composite tool  10  includes a plurality of uncoated diamonds  2  with an infiltrant  4  disposed between the diamonds  2 . Free space  16  may exist between the uncoated diamond particles  2 . The infiltrated polycrystalline diamond composite tool  10  has a working surface  18 . Depending on the intended application of the infiltrated polycrystalline diamond composite tool  10 , the working surface may be a cutting edge, an abrasive surface, or the like. The infiltrated polycrystalline diamond composite tool  10  may also include a support  6 , which generally comprises the infiltrant material. The support  6  may also include a hard material  8 , such as a carbide. The support  6  serves as a backing layer and ultimately provides a degree of support and rigidity to the infiltrated polycrystalline diamond composite tool  10 . 
     In the prior-art infiltrated polycrystalline diamond composite tool  10 , the infiltrant  4  has partially in,filtrated most of the free space  16  between the diamonds  2 . During the formation of the infiltrated polycrystalline diamond composite tool  10 , the diamonds  2  are partially dissolved by the infiltrant  8  and subsequently precipitated, resulting in diamond-to-diamond bonding  12  and grain growth, which in turn forms a continuous polycrystalline diamond matrix  13 . Because the matrix material  4  does not wet the surface of the diamonds  2  well, infiltration of the pre-form is incomplete. As a result, diamond-to-diamond bonding  12  within the infiltrated polycrystalline diamond composite tool  10  is incomplete and the polycrystalline diamond matrix  13  does not completely form. In addition, some free space  16  remains within the infiltrated polycrystalline diamond composite tool  10 . Consequently, the durability of the infiltrated polycrystalline diamond composite tool  10  is limited. 
     FIG. 2 is a schematic representation of a coated diamond particle  20  of the present invention. The coated diamond particle  20  comprises a diamond  22  having a palladium-free wetting-enhancement coating  24  disposed on and substantially covering the outer surface of the diamond  22 . The wetting enhancement coating  24  may comprise the same material as that is later used as the infiltrant in the tool. The wetting enhancement coating  24  is preferably formed from either nickel, cobalt, iron, or combinations thereof, with cobalt being the most preferred material. The palladium-free wetting-enhancement coating  24  can be deposited directly onto the surface of the diamond  22  using vapor deposition techniques such as, but not limited to, chemical vapor deposition, physical vapor deposition, plasma assisted chemical vapor deposition, and combinations thereof. 
     A schematic view of another coated diamond particle  30  of the present invention is shown in FIG.  3 . The diamond  22  is coated with a palladium-free activation layer  34  and a palladium-free wetting-enhancement coating  24  to form the coated diamond particle  30 . The surface of the diamond  22  is a sensitized surface  32 , formed by treating the diamond  22  with a sensitizing agent. The sensitizing agent typically has two stable valence states, is capable of reacting with the activation layer  34 , and is stable in water. In the present invention, the surface of the diamond  22  is preferably sensitized by immersing the diamond  22  in a solution of tin dichloride (SnCl 2 ) and hydrochloric acid (HCl) at room temperature for approximately five minutes. Other metals having two stable valence states, including manganese, iron, cobalt, nickel, copper, and cadmium, may be used as sensitizing agents as well. During sensitization, SnCl 2  is physically absorbed onto the surface of the diamond  22 . Following immersion, the diamond is then washed with distilled water and dried. 
     Following sensitization, the palladium-free activation layer  24  is deposited onto the sensitized surface  32  of the diamond  22 . The palladium-free activation layer  34  is preferably formed from silver, although other metals, such as copper, gold, cobalt, and platinum, may be used to form the palladium-free activation layer  34 . When silver is used to form the palladium-free activation layer  34 , the sensitized diamond  22  is immersed in a silver nitrate (AgNO 3 ) solution at room temperature for approximately five minutes. Tin dichloride (SnCl 2 ), which is the preferred sensitizer of the present invention, forms the species Sn(IV) on the sensitized surface  32  of the diamond  22 , thereby preventing the oxidation of the metal activator species in the palladium-free activation layer  34 . The palladium-free activation layer  34  comprising silver is precipitated onto the diamond surface according to the reaction. 
     
       
         Sn 2+ +2Ag + →Sn 4+ +2Ag o   
       
     
     to form elemental silver on the sensitized surface  32  of the diamond  22 . The palladium-free activation layer  34  comprising silver may be alternatively deposited from a colloidal suspension of silver. Following precipitation of the palladium-free activation layer  34 , the diamond  22  is again washed with distilled water and dried. The palladium-free activation layer  34  formed from silver may comprise between about 0.01 and about 10 weight percent of the diamond particle. 
     Following deposition of the palladium-free activation layer  34  on the diamond  22 , the palladium-free wetting-enhancement coating  24  is deposited over the palladium-free activation layer  34 . The palladium-free wetting-enhancement coating  24  is preferably deposited by an electroless plating process. As described above, the palladium-free wetting-enhancement coating  24  may be comprised of the same material as the metallic infiltrant that will ultimately be used to form an infiltrated tool. The palladium-free wetting-enhancement coating  24  may be formed from either nickel, cobalt, iron, or combinations thereof, with cobalt being the preferred material. The electroless plating procedure is a simple reduction reaction, in which the cobalt (II) ion from cobalt (II) sulfate is reduced to elemental cobalt while dimethylamineborane (DMAB) is oxidized to (CH 3 ) 2 NH 2   + and B(OH) 3 : 
      3Co 2+ +3(CH 3 ) 2 NHBH 3  +6H 2 O →3Co o +B +3(CH 3 ) 2 NH 2   + +2B(OH) 3  +9/2H 2  +3H +   
     The reduction of cobalt continues in the presence of the reducing agent as long as the catalytic reduction of the metal is possible. In the present invention, the catalytic sites at which the electroless plating takes place are provided by first depositing the palladium-free activation layer  34 . In the absence of such catalytic sites, little if any coverage of the diamond  22  by the palladium-free wetting-enhancement coating  24  could be achieved by electroless plating. 
     The palladium-free wetting-enhancement coating  24  may further include either phosphorus or boron. In the present invention, the palladium-free wetting-enhancement coating  24  preferably comprises cobalt and boron. Boron, which is produced by the reduction of Co(II) by DMAB, may comprise up to 30 weight percent of the palladium-free wetting-enhancement coating  24 . To achieve the optimum abrasion resistance, a palladium-free wetting-enhancement coating  24  comprising up to about 5 weight percent boron is preferred. The palladium-free wetting-enhancement coating  24  preferably has a thickness of between about 0.01 microns and about 5 microns. 
     The coated diamond particles  20 ,  30  of the present invention have an average diameter in the range of between about 0.0001 and about 1 millimeter. For use in a cutting tool, the average diameter of the coated diamond particles  20 ,  30  is preferably greater than about 10 microns and less than about 100 microns, as coated diamond particles  20 ,  30  in this size range provide optimal abrasion resistance for the tool. In addition to use in a cutting tool application, the coated diamond particles  20 ,  30  of the present invention may be used for mesh products, such as grit for abrasives, which utilize diamond particles having an average diameter between about 10 microns and about 1 millimeter. 
     Infiltrated polycrystalline diamond composite tools of the present invention include cutting tool blanks, wire dies, drill blanks, and the like. These infiltrated polycrystalline diamond composite tools are formed from a preform that is prepared using the coated diamond particles  20 ,  30  described above and a metallic infiltrant source that infiltrates the: free space  16  between the coated diamond particles  20 ,  30  under the application of; high temperature and pressure. FIG. 4 is a schematic representation of a preform  40  of the present invention. A plurality of coated diamond particles  20  are placed in a refractory container  52  to form a bed  53 . Coated diamond particles  30 , having a sensitized surface  32 , palladium-free activation layer  34 , and palladium-free wetting-enhancement coating  24  can be substituted for part or all of the coated diamond particles  20 . The refractory container  52  is formed from a refractory material, such as a ceramic or metal, having a melting temperature above that of the metallic infiltrant  44  and the temperatures used in the infiltration process. A metallic infiltrant source  54 , comprising the metallic infiltrant  44 , is placed in the refractory container  52 , such that the metallic infiltrant source  54  contacts the bed  53  of coated diamond particles  20 . Preferably, the metallic infiltrant source  54 , is placed in the refractory container  52  such that the metallic infiltrant source  54  is positioned on top of and in contact with the bed  53  of coated diamond particles  20 . The metallic infiltrant  44  is substantially palladium-free and preferably comprises cobalt, although iron, nickel, and combinations of iron, nickel, and cobalt may also be used. The pre-form  40  is then heated to a temperature above the melting point of the metallic infiltrant  44  and pressure is applied to the metallic infiltrant source  54 , thereby forcing the molten metallic infiltrant  44  into the free space  16  between the coated diamond particles  20 . The preform  40  is preferably heated to a temperature between about 1300° C. and about 1700° C. Pressures in the range of between about 40 kbar to about 70 kbar are applied to the preform  40  in order to achieve infiltration by the metallic infiltrant  44 . 
     During the infiltration process, the palladium-free wetting-enhancement coating  24  melts and combines with the molten metallic infiltrant  44 . The presence of the palladium-free wetting-enhancement coating  24  on the diamonds  22  permits the molten metallic infiltrant  44  to completely wet the diamonds  22 . At the same time, the combination of molten metallic  44  and palladium-free wetting-enhancement coating  24  acts as a liquid-state sintering aid, dissolving some of the diamonds  22 . The diamonds  22  then ;re-crystallize to form a continuous polycrystalline diamond matrix  56  in which diamond-to-diamond bonding  58  between individual diamonds  22  is present. Upon cooling, the combined molten metallic infiltrant  44  and palladium-free wetting-enhancement coating  24  materials resolidify to form a contiguous, fully dense metallic phase  62 !that interpenetrates the continuous polycrystalline diamond matrix  56 , as shown in FIG. 5, to form a fully infiltrated polycrystalline diamond composite tool blank  59 . A working surface  68 , such as a cutting edge or an abrasive surface, can then be provided to form the infiltrated polycrystalline diamond composite tool  60 . The continuous polycrystalline diamond matrix  56  formed from the diamonds  22  comprises between about  85  and about  95  volume percent of the infiltrated polycrystalline diamond composite tool  60 . 
     The infiltrated polycrystalline diamond composite tool  60  is preferably a supported infiltrated polycrystalline diamond composite tool  60 , having an infiltrated support layer  46 , as shown in FIG.  5 . The infiltrated support layer  46  comprises a continuous matrix formed by a plurality of hard particles  48  that is interpenetrated by the metallic infiltrant  44 . The hard material  48  is preferably tungsten carbide, although other carbides, such as silicon carbide, titanium carbide, zirconium carbide, niobium carbide, combinations thereof, and the like may be used. The supported infiltrated polycrystalline diamond composite tool  60  is formed by including particles of the hard material  48  in the metallic infiltrant source  54  that is used to assemble the preform  40 . During the infiltration process, the infiltrated support layer  46  fuses to the remainder of the infiltrated polycrystalline diamond composite tool  60 . 
     The features of the present invention are illustrated by the following example. 
     EXAMPLE 1 
     An activated layer of palladium was precipitated onto a first group of diamond particles. A second group of diamond particles was provided with a silver activation layer precipitated from solution. Both the first and second groups of diamond particles were then electrolessly plated with a cobalt/boron coating. Scanning electron microscopy (SEM) was used to study the integrity of the cobalt/boron coatings on the two groups of particles. Similarly, auger spectroscopy scans were used to investigate the continuity of the cobalt/boron coatings. A representative SEM micrograph and Auger spectroscopy scan obtained for the palladium-activated diamond particles are shown in FIGS. 5 and 6, respectively. FIGS. 7 and 8 are a SEM micrograph and Auger spectroscopy scan, respectively, obtained for silver-activated diamond particles. There was no discernible difference in the contiguity of the cobalt/boron coatings deposited on the silver-activated particles and the contiguity of the cobalt/boron coatings deposited on the,palladium-activated particles. The integrity of the coating appears to be the same, or perhaps superior for the silver activated material. The experiment also showed no distinct difference in the apparent continuity of the coatings. 
     Polycrystalline diamond composite tools were also produced using these coated diamond particles, with no adverse sintering affects noted. Abrasion tests were then conducted on these polycrystalline diamond composite tools. The tests indicated that the polycrystalline diamond composite tools of the present invention had abrasion resistances that were at least as good as those of tools made using uncoated diamond particles. 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention.

Technology Category: 4