Note: Descriptions are shown in the official language in which they were submitted.
?1015'20âCA 02265399 2005-03-0177680-11METAL-MATRIX DIAMOND OR CUBIC BORON0 NITRIDE COMPOSITESField of InventionThe invention relates to wear resistant materials and moreparticularly to diamond-based materials for manufacturing cutting elements for use incutting and drilling applications.BackgroundSuper-hard materials, such as diamond or cubic boron nitride (CBN), havesuperior wear resistance and are commonly used as cutting elements for cutting ordrilling applications. In these applications, a compact of polycrystalline diamond orCBN is commonly bonded to a substrate material (e.g., cemented metal carbide) to formâ a cutting structure. A compact is a polycrystalline mass of super-hard particles, such asdiamond or CBN, that are bonded together to form an integral, tough, coherent, and high-strength mass. The substrate material generally is selected from the group consisting oftungsten carbide, titanium carbide, tantalum carbide, and mixtures thereof. The substratematerial further contains a metalâbonding material selected from the group consisting ofcobalt, nickel, iron, and mixtures thereof. The metal bonding material is normally 6 to 25percent of the material by weight. Such compacts and other super-hard structures have?101520CA 02265399 l999-03- 17been used as blanks for cutting tools, drill bits, dressing tools, wear parts, and rock bits.Additionally, compacts made in a cylindrical con?guration have been used to make wiredrawing dies.Various methods have been developed to make polycrystalline diamond orCBN compacts. One such method involves subjecting a mass of separate crystals of thesuperâhard abrasive material and a catalyst metal to a high pressure and high temperature(HPHT) process which results in inter-crystal bonding between adjacent crystal grains.The diamond or CBN materials are thermodynamically stable under the pressure andtemperature conditions used in HPHT. The catalyst metal may be a cemented metalcarbide or carbide-molding powder. A cementing agent also may be used that acts as acatalyst or solvent for diamond or CBN crystal growth. The cementing agent generallyhas been selected from cobalt, nickel, and iron when diamonds are used as the superâhardabrasive material. Aluminum or an aluminum alloy generally is used as a cementingagent when CBN is used as the superâhard material. The catalyst metal preferably ismixed with the superâhard crystals (e. g., in powder form).Although the catalyst may be mixed in powder form with the superâhardcrystals, no attempt is made to minimize the formation of clusters of superâhard crystals.As a result, the compacts produced by this method commonly are characterized bydiamond-toâdiamond or CBN-to-CBN bonding (i.e., inter-crystal bonding betweenadjacent grains). This maximization of inter-crystal bonding between adjacent grains isan objective in making superâhard compacts. Typically, a diamond compact formed inthe presence of cobalt contains multiple clusters of diamond grains with each clustercontaining more than one (e. g., 3 to 6) diamond grains. These clusters connect with each?l01520CA 02265399 l999-03- 17other and form a network of diamond grains. In a typical diamond compact, diamondgrain-to-grain contiguity is greater than 40%. The diamond grain-to-grain contiguityrefers to the percentage of continuous diamond phase in a given direction within adiamond compact, and is indicative of the extent of diamondâdiamond contact in thediamond compact. The cobalt phase typically is not a continuous matrix. Instead, poolsof cobalt are distributed in the spaces formed by the diamond clusters. The average sizeof the cobalt pools typically is larger than the average size of the diamond grains.With this microstructure, the compacts are extremely wear resistant, butrelatively brittle. Once a crack starts, it can propagate through the compact andeventually result in failure of the part. This is particularly true in the case of petroleumor rock drill bits, in which a massive failure of the diamond layer of an insert made of apolycrystalline diamond compact can lead to damage of the other cutters on the bit or thebit body.Additionally, diamond or CBN compacts are relatively expensive tomanufacture with the high pressure/high temperature process. Further, the size of thediamond or CBN compacts is limited by the dimensions of the press cell. Typically, onlya few pieces, each having a cross-section of less than 1 inch, can be processed in a presscell, while the largest piece that presently can be processed has a cross-section of lessthan 2 inches.For the foregoing reasons, there exists a need for a wear-resistant materialthat utilizes the wear resistance of diamond or CBN materials while possessing a highertoughness than previously typical of diamond or CBN compacts. Further, it is desirable....-_,,............._..~._._,-.,......, ..-, ..,.,,.,.._..,......z_.....n......................._....â_..._..._...... ...,_.a. . ..?101520CA 02265399 l999-03- 17that the method of manufacturing such a composite material be capable of producingparts that are larger than 2 inches in cross-section.Summary of InventionIn some aspects the invention relates to a superâhard composite materialcomprising: a super-hard component representing about 40% - 85% of the volume of thesuperâhard material; a metal matrix component representing about 15% â 60% of thevolume of the super-hard material; and wherein the super-hard component and the metalmatrix component are combined in a uniform composite mixture with an actual density atleast 95% of the theoretical maximum density of the composite mixture.In an alternative embodiment, the invention relates to a method formanufacturing a superâhard composite material comprising: providing a superâhardcomponent representing about 40% â 85% of the volume of the super-hard compositematerial; providing a metal matrix component representing about 15% - 60% of thevolume of the super-hard composite material; milling the super-hard component with themetal matrix component to achieve a uniform mixture; and compacting the uniformmixture to an actual density at least 95% of the theoretical maximum density of themixture.Brief Description of DrawingsFigure 1a shows a schematic of a typical rapid omniâdirectionalcompaction process before compaction.?l01520CA 02265399 l999-03- 17Figure lb shows a schematic of a typical rapid omni-directionalcompaction process before compaction.Figure 2 is a rock bit manufactured in accordance with an embodiment ofthe invention.Detailed DescriptionExemplary embodiments of the invention will be described with referenceto the accompanying drawings. Like items in the drawings are shown with the samereference numbers.Embodiments of the invention provide a metal-matrix/super-hardcomposite that exhibits a higher toughness than currently available diamond or CBNcompacts while maintaining superior wear resistance. Such metal-matrix/super-hardcomposites contain super-hard grains that are dispersed uniformly in a metal matrix suchas cobalt, nickel, iron, or alloys thereof. Suitable super-hard materials include diamondand cubic boron nitride. The microstructure of the composites is such that the compositeis substantially free of large clusters of grains of the super-hard material. The grain-toâgrain contiguity of the super-hard material is less than 40%, and the average size of thematrix metal pools in the composite is smaller than the average size of the grains of thesuper-hard material.Although embodiments of the invention include both diamond and boronnitride as the super-hard material, metal-matrix/diamond composites are exemplified andexplained in more detail than metal-matrix/CBN composites. However, it should beunderstood that any such descriptions are similarly applicable to metal-matrix/CBNcomposites.?101520CA 02265399 l999-03- 17In preferred embodiments, each diamond grain is surrounded by cobalt,which acts as a matrix. The superâhard, brittle diamond grains thus are embedded in amatrix of a relatively ductile metal. The ductile metal matrix provides the necessarytoughness, while the grains of superâhard material in the matrix furnish the necessarywear resistance. The grains of superâhard material perform the cutting function whilebeing held in place by the relatively ductile metal matrix. The ductile metal matrix alsoreduces crack formation and suppresses crack propagation through the compositematerial once a crack has been initiated. As a result of this combination of super-hardmaterial grains surrounded by a metal matrix, these composites possess higher toughnessbut still maintain superior wear resistance as compared to conventional diamond or CBNcompacts.The metalâmatrix/diamond or metal-matrix/CBN composites of thepresent invention may be manufactured by the following method: (1) milling a mixture ofdiamond or CBN grains and one or more metal powders to form a uniform mixture; and(2) hot-compacting the mixture to an actual density that is at least 95% of the theoreticalmaximum density of the mixture. It should be understood that, in a powder mixture,there typically is a certain degree of porosity. The theoretical maximum density of amixture refers to the density of such a mixture with zero porosity.In some embodiments, the mixture includes between 40% to 85% byvolume of diamond grains and correspondingly between 15% to 60% by volume of metalmatrix material. It should be recognized that it is possible to obtain a mixture thatcontains between 1°/o to 99% by volume of diamond or CBN grains according toembodiments of the invention.?101520CA 02265399 l999-03- 17The diamond grains used in the embodiments may either be natural orsynthetic diamond grit. Although it is possible to use diamond grains of any size, it ispreferred that the average grain size of diamond falls in the range of between 1 pm and30 pm.In some embodiments, the super-hard grains are coated with a metal layerbefore milling to prevent surface oxidation of the super-hard material during the hot-compaction process. While copper is a suitable material for such a coating, othermaterials, such as titanium nitride, titanium carbonitride, zirconium nitride, cobalt,tungsten, and nickel, also may be used.Sometimes it is desirable to heatâtreat the diamond grains in a hydrogenatmosphere at an elevated temperature. Typically, the temperature range is from 600 ° Cto l200° C. It is believed that the hydrogen treatment step facilitates the removal ofoxygen-containing species on the surface of the diamond grains. This tends to reduce theextent of oxidation of the diamond grains in the subsequent hot-compaction process.This step may be done either before or after the milling of the grains and the powder.Suitable metal powders that may be mixed with diamond grains includenickel, iron, cobalt, and mixtures or alloys thereof. Suitable metals also may include Mo,W, Ti, Nb, Ta, V, other transitional metals, and their alloys. In a preferred embodiment,cobalt powder is used to form the metal matrix. Although the particle size of the cobaltpowder may be in any range, it is preferred that the average cobalt powder particle sizefalls within a range between 1 pm and 30 pm.The cobalt powder and diamond grains are milled together to form amixture where the diamond grains are uniformly distributed in the cobalt powder. Such?101520CA 02265399 l999-03- l7uniformity may be indicated by diamond grainâto-grain contiguity, although otherparameters also are acceptable. Any powder milling technique that renders a uniformmixing can be used. In a preferred embodiment, attritor-milling was employed at300 rpm for two hours to obtain a uniform mixture.After a uniform mixture of diamond grains and cobalt powder is obtained,a cold-compacted "greenâ piece of a desired shape is made from the mixture. The greenpiece then is subjected to a hot-compaction process to achieve an actual density that is atleast 95% of the theoretical maximum density. Suitable methods of hot compaction mayinclude hot isostatic pressing, hot pressing, rapid omni-directional compaction, and a highpressure/high temperature process. Although it is preferred that a hot-compactionprocess be used to obtain the desired density, it should be understood that anycompaction process, including cold-compaction, may be utilized. Further, it should berecognized that compaction to an actual density to less than 95% of the theoreticalmaximum density may be acceptable for some applications.In a preferred embodiment, the rapid omni-directional compaction processis used to make the composites because it operates at a lower pressure than the HPHTprocess. Additionally, it provides excellent dimensional control. This makes it an idealnear-net shape production method with mechanical properties at least equal to or betterthan those produced by hot isostatic pressing. Another advantage is higher productionoutput and lower production cost than other processes. Also, when compared to theHPHT process, the rapid omni-directional compaction process can produce substantiallylarger work pieces.Finally, the relatively short thermal exposure given to the powdersduring rapid omni-directional compaction results in retention of a very fine?10IS20CA 02265399 2005-03-0177680-11microstructure with excellent mechanical properties. The rapid omni-directionalcompaction process has been described in U.S. Patents No. 4,428,906 and No. 4,656,002.Figure I illustrates a typical rapid omni-directional compaction apparatusthat is used in some embodiments. A forging press 20 commonly is employed in a rapidomni-directional compaction process. It includes a ram 10, a pot die 12, and a ?uid die22. There is a close ?t betweenthe ram 10 and the ?uid die 22. Inside the ?uid die 22there is a pressure-transmitting medium 16. The pressure-transmitting medium may bemade from various materials that melt at a lower temperature than the temperatures usedduring compaction. In some embodiments, the pre-pressed diamond/metal powdermixture 14 is surrounded by a non-reactive insulation layer 15 to prevent contact betweenthe molten medium 16 and the powder mixture 14.As the ram 10 travels downward, the powder mixture 14 is pressed fromall directions, resulting in a metal-matrix/diamond composite 18. Complete consolidationin the inter-particle bonding is accomplished, without pressure dwell, in a single ramstroke that produces pressures in the range of approximately 345 to 895 MPa (50 to 130ksi). A typical consolidation temperature is between about 800° C and lS00° C, althoughother temperature ranges also are acceptable. In a preferred embodiment, thediamond/metal powder mixtureis compressed to 120 ksi at l200° C for about twominutes.In addition to the rapid omni-directional compaction process, the HPHTprocess for sintering diamond or cubic boron nitride may be used. Such a process hasbeen described in U.S. Patents No. 5,676,496 and No. 5,598,621,?101520CA 02265399 2005-03-0177680-11Another suitable method for hot-compacting pre-pressed diamond/metal powder mixtures is hot isostatic pressing, which is known in theart. See Peter E. Price and âSteven P. Kohler, "Hot Isostatic Pressing of MetalPowders", Metals Handbook. Vol. 7, pp. 419-443 (9th ed. 1984).The metal-matrix diamond or cubic boron nitride composites made inaccordance with embodiments of the invention may be used as blanks for cutting tools,drill bits, dressing tools, and wear parts. Further, the metal-matrix diamond or cubicboron nitride composites that are made in a cylindrical configuration may also be used tomake wire drawing dies. An example of a rock bit for downhole drilling constructed inaccordance with embodiments of the invention is illustrated in Figure 2. An rock bit 30includes a bit body 40 with a threaded section 34 on its upper end for securing the bit to adrill string (not shown). The bit 30 generally has three roller cones 36 rotatably mountedon hearing shafts (hidden) that depend from the bit body 40. The bit body 40 comprisesthree sections or legs 42 (two legs are shown) that are welded together to form the bitbody 40. The bit 30 further includes a plurality of nozzles 45 that are provided fordirecting drilling ?uid toward the bottom of a borehole and around the roller cones 36.In addition, the bit 30 also may include lubricant reservoirs 44 that supply lubricant to thebearings of each of the roller cones.Generally, each roller cone 36 includes a frustoconical surface 37 that isadapted to retain inserts that scrape or ream the sidewalls of a borehole as the roller cones36 rotate about the borehole bottom. The frustoconical surface 37 will be referred toherein as the "heel" surface of the roller cones 36, although the same surface may besometimes referred to in the art as the "gage" surface of the roller cone.10?l01520CA 02265399 2005-03-0177680-11M The roller cone 36 includes a plurality of heel row inserts 50 that aresecured in a circumferential row in the frustoconical heel surface 37. The roller cone 36further includes a circumferential row of gage inserts 35 secured in locations along ornear the circumferential shoulder 39. Also, the roller cone 36 includes a plurality of innerrow inserts 38 that are secured to the roller cone surface and arranged in respective rows.Although various geometric shapes of the inserts are acceptable, it is preferred that theyhave a semi-round top, a conical top, or a chiseled top.The inserts include generally cylindrical base portions that are secured byan interference ?t into mating sockets drilled into the lands of the cone cutter and cuttingportions that are connected to the base portions. The cutting portion includes a cuttingsurface that extends from the surface of the roller cone for cutting or crushing the rockformation being drilled.In accordance with embodiments of the invention, the metal-matrix/diarnond or metalâmatrix/CBN composites may be manufactured in the form ofinserts for use in rock bits. Rock bits incorporating inserts made of these compositeshave a longer bit life and a higher rate of penetration. Preferably, the composites are usalfor making gage row inserts and heel row inserts, although it is conceivable that they alsomay be used to make inner row inserts. In addition to forming an insert, the compositesalso may be used to replace the diamond layer in diamond-enhanced inserts. Examples ofsuch diamond-enhanced inserts. are described in U.S. Patents No. 4,006,788 andNo. 4,972,912.As described above, embodiments of the invention provide a metal-matrix/diamond or metal-matrix/CBN composite that is tougher than polycrystallinell?101520CA 02265399 l999-03- l7diamond or CBN compacts manufactured by the high pressure/high temperature sinteringprocess. The metal-matrix/diamond or metal-matrix/CBN composite has a very finemicrostructure in which grains of diamond or CBN generally are unifonnly distributed ina metal matrix. Such a fine microstructure results in a higher fracture toughness thanconventional polycrystalline diamond or CBN compacts. In addition, the hot-compaction process may be carried out at a lower pressure than the traditional HPHTsintering process, thereby reducing production costs. Moreover, it is possible tomanufacture parts made of the metalâmatrix/diamond or metal-matrix/CBN compositehaving dimensions larger than those currently available using the traditional HPHTsintering process.While the invention has been disclosed with respect to a limited number ofembodiments, numerous modifications and variations therefrom are possible. Forexample, suitable super~hard grains are not limited to diamond, CBN, and mixturesthereof. Other super-hard materials, such as ceramics, cerrnets, nitrides, and carbides,also may be used. Particles of diamond-like carbon also may be used. With respect tosuitable metals for the metal matrix, any suitable metal or alloys may be used. It isintended that the appended claims cover all such modifications and variations as fallwithin the true spirit and scope of the invention.While the invention has been disclosed with reference to speci?cexamples of embodiments, numerous variations and modi?cations are possible.Therefore, it is intended that the invention not be limited by the description in thespecification, but rather the claims that follow.12
