Abstract:
Cutting elements for earth-boring applications may include a substrate and a polycrystalline diamond material secured to the substrate. A first region of the polycrystalline diamond material may exhibit a first volume percentage of nanoparticles bonded to diamond grains within the first region. A second region of the polycrystalline diamond material adjacent to the first region may exhibit a second, different volume percentage of nanoparticles bonded to diamond grains within the second region. Methods of making cutting elements for earth-boring applications may involve positioning a first mixture of particles having a first volume percentage of nanoparticles and a second mixture of particles having a second, different volume percentage of nanoparticles within a container. The first and second mixtures of particles may be sintered in the presence of a catalyst material to form a polycrystalline diamond material including intergranular bonds among diamond grains and nanoparticles of the polycrystalline diamond material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/208,989, filed Aug. 12, 2011, now U.S. Pat. No. 8,985,248, issued Mar. 24, 2015, which claims the benefit of the filing date of U.S. Provisional Patent App. Ser. No. 61/373,617, which was filed on Aug. 13, 2010, and is titled “CUTTING ELEMENTS INCLUDING NANOPARTICLES IN AT LEAST ONE PORTION THEREOF, EARTH-BORING TOOLS INCLUDING SUCH CUTTING ELEMENTS, AND RELATED METHODS,” the disclosure of each of which is incorporated herein in its entirety by this reference. 
    
    
     FIELD 
     Embodiments of the present invention generally relate to cutting elements that include a table of superabrasive material (e.g., polycrystalline diamond or cubic boron nitride) formed on a substrate, to earth-boring tools including such cutting elements, and to methods of forming such cutting elements and earth-boring tools. 
     BACKGROUND 
     Earth-boring tools for forming wellbores in subterranean earth formations generally include a plurality of cutting elements secured to a body. For example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”) include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit. Similarly, roller cone earth-boring rotary drill bits may include cones that are mounted on bearing pins extending from legs of a bit body such that each cone is capable of rotating about the bearing pin on which it is mounted. A plurality of cutting elements may be mounted to each cone of the drill bit. 
     The cutting elements used in such earth-boring tools often include polycrystalline diamond compact (often referred to as “PDC”) cutting elements, which are cutting elements that include cutting faces of a polycrystalline diamond material. Such polycrystalline diamond cutting elements are formed by sintering and bonding together relatively small diamond grains or crystals with diamond-to-diamond bonds under conditions of high temperature and high pressure in the presence of a catalyst (such as, for example, Group VIIIA metals including, by way of example, cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer or “table” of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) such as, for example, cobalt-cemented tungsten carbide. In such instances, the cobalt (or other catalyst material) in the cutting element substrate may be swept into the diamond crystals during sintering and serve as the catalyst material for forming the diamond table from the diamond crystals. In other methods, powdered catalyst material may be mixed with the diamond crystals prior to sintering the crystals together in an HTHP process. 
     Upon formation of a diamond table using an HTHP process, catalyst material may remain in interstitial spaces between the crystals of diamond in the resulting polycrystalline diamond table. The presence of the catalyst material in the diamond table may contribute to thermal damage in the diamond table when the cutting element is heated during use due to friction at the contact point between the cutting element and the formation. Accordingly, the polycrystalline diamond cutting element may be formed by leaching the catalyst material (e.g., cobalt) out from interstitial spaces between the diamond crystals in the diamond table using, for example, an acid or combination of acids, e.g., aqua regia. Substantially all of the catalyst material may be removed from the diamond table, or catalyst material may be removed from only a portion thereof, for example, from the cutting face, from the side of the diamond table, or both, to a desired depth. 
     PDC cutters are typically cylindrical in shape and have a cutting edge at the periphery of the cutting face for engaging a subterranean formation. Over time, the cutting edge becomes dull. As the cutting edge dulls, the surface area in which the cutting edge of the PDC cutter engages the formation increases due to the formation of a so-called wear flat or wear scar extending into the side wall of the diamond table. As the surface area of the diamond table engaging the formation increases, more friction-induced heat is generated between the formation and the diamond table in the area of the cutting edge. Additionally, as the cutting edge dulls, the downward force or weight on the bit (WOB) must be increased to maintain the same rate of penetration (ROP) as a sharp cutting edge. Consequently, the increase in friction-induced heat and downward force may cause chipping, spalling, cracking, or delamination of the PDC cutter due to a mismatch in coefficient of thermal expansion between the diamond crystals and the catalyst material. In addition, at temperatures of about 750° C. and above, presence of the catalyst material may cause so-called back-graphitization of the diamond crystals into elemental carbon. 
     Accordingly, there remains a need in the art for cutting elements that increase the durability as well as the cutting efficiency of the cutter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the present invention, advantages of the invention may be more readily ascertained from the description of some example embodiments of the invention provided below, when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an enlarged longitudinal cross-sectional view of one embodiment of a cutting element of the present invention; 
         FIG. 2  illustrates an enlarged longitudinal cross-sectional view of one embodiment of a multi-portion polycrystalline material of the present invention; 
         FIG. 3  is a simplified figure illustrating how a microstructure of the multi-portion polycrystalline material of  FIG. 2  may appear under magnification; 
         FIGS. 4-9  illustrate additional embodiments of enlarged longitudinal cross-sectional views of a multi-portion polycrystalline material of the present invention; and 
         FIGS. 10A-10K  are enlarged latitudinal cross-sectional views of embodiments of a multi-portion polycrystalline material of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrations presented herein are not meant to be actual views of any particular material or device, but are merely idealized representations that are employed to describe some examples of embodiments of the present invention. Additionally, elements common between figures may retain the same numerical designation. 
     Embodiments of the present invention include methods for fabricating cutting elements that include multiple portions or regions of relatively hard material, wherein one or more of the multiple portions or regions include nanoparticles (e.g., nanometer sized grains) therein. For example, in some embodiments, the relatively hard material may comprise polycrystalline diamond material. In some embodiments, the methods employ the use of a catalyst material to form a portion of the relatively hard material (e.g., polycrystalline diamond material). 
     As used herein, the term “drill bit” means and includes any type of bit or tool used for drilling during the formation or enlargement of a wellbore in a subterranean formation and includes, for example, rotary drill bits, percussion bits, core bits, eccentric bits, bicenter bits, reamers, mills, drag bits, roller cone bits, hybrid bits and other drilling bits and tools known in the art. 
     As used herein, the term “polycrystalline compact” means and includes any structure comprising a polycrystalline material formed by a process that involves application of pressure (e.g., compaction) to a precursor material or materials used to form the polycrystalline material. 
     As used herein, the term “inter-granular bond” means and includes any direct atomic bond (e.g., covalent, metallic, etc.) between atoms in adjacent grains of material. 
     As used herein the term “nanoparticle” means and includes any particle having an average particle diameter of about 500 nm or less. 
     As used herein, the term “catalyst material” refers to any material that is capable of substantially catalyzing the formation of inter-granular bonds between grains of hard material during an HTHP but at least contributes to the degradation of the inter-granular bonds and granular material under elevated temperatures, pressures, and other conditions that may be encountered in a drilling operation for forming a wellbore in a subterranean formation. For example, catalyst materials for diamond include cobalt, iron, nickel, other elements from Group VIIIA of the Periodic Table of the Elements, and alloys thereof. 
       FIG. 1  is a simplified cross-sectional view of an embodiment of a cutting element  100  of the present invention. The cutting element  100  may be attached to an earth-boring tool such as an earth-boring rotary drill bit (e.g., a fixed-cutter rotary drill bit). The cutting element  100  includes a multi-portion polycrystalline table or layer of hard multi-portion polycrystalline material  102  that is provided on (e.g., formed on or attached to) a supporting substrate  104 . In additional embodiments, the multi-portion polycrystalline material  102  of the present invention may be formed without a supporting substrate  104 , and/or may be employed without a supporting substrate  104 . The multi-portion polycrystalline material  102  may be formed on the supporting substrate  104 , or the multi-portion diamond table  102  and the supporting substrate  104  may be separately formed and subsequently attached together. In yet further embodiments, the multi-portion polycrystalline material  102  may be formed on the supporting substrate  104 , after which the supporting substrate  104  and the multi-portion polycrystalline material  102  may be separated and removed from one another, and the multi-portion polycrystalline material  102  subsequently may be attached to another substrate that is similar to, or different from, the supporting substrate  104 . The multi-portion polycrystalline material  102  includes a cutting face  117  opposite the supporting substrate  104 . The multi-portion polycrystalline material  102  may also, optionally, have a chamfered edge  118  at a periphery of the cutting face  117  (e.g., along at least a portion of a peripheral edge of the cutting face  117 ). The chamfered edge  118  of the cutting element  100  shown in  FIG. 1  has a single chamfer surface, although the chamfered edge  118  also may have additional chamfer surfaces, and such chamfer surfaces may be oriented at chamfer angles that differ from the chamfer angle of the chamfer edge  118 , as known in the art. Further, in lieu of a chamfered edge  118 , the edge may be rounded or comprise a combination of one or more chamfer surfaces and one or more arcuate surfaces. 
     The supporting substrate  104  may have a generally cylindrical shape as shown in  FIG. 1 . The supporting substrate  104  may have a first end surface  110 , a second end surface  112 , and a generally cylindrical lateral side surface  114  extending between the first end surface  110  and the second end surface  112 . 
     Although the first end surface  110  shown in  FIG. 1  is at least substantially planar, it is well known in the art to employ non-planar interface geometries between substrates and diamond tables formed thereon, and additional embodiments of the present invention may employ such non-planar interface geometries at the interface between the supporting substrate  104  and the multi-portion polycrystalline material  102 . Additionally, although cutting element substrates commonly have a cylindrical shape, like the supporting substrate  104 , other shapes of cutting element substrates are also known in the art, and embodiments of the present invention include cutting elements having shapes other than a generally cylindrical shape. 
     The supporting substrate  104  may be formed from a material that is relatively hard and resistant to wear. For example, the supporting substrate  104  may be formed from and include a ceramic-metal composite material (which are often referred to as “cermet” materials). The supporting substrate  104  may include a cemented carbide material, such as a cemented tungsten carbide material, in which tungsten carbide particles are cemented together in a metallic matrix material. The metallic matrix material may include, for example, catalyst metal such as cobalt, nickel, iron, or alloys and mixtures thereof. Furthermore, in some embodiments, the metallic matrix material may comprise a catalyst material capable of catalyzing inter-granular bonds between grains of hard material in the multi-portion polycrystalline material  102 . 
     In some embodiments, the cutting element  100  may be functionally graded between the supporting substrate  104  and the multi-portion polycrystalline material  102 . Thus, an end of the supporting substrate  104  proximate the multi-portion polycrystalline material  102  may include at least some material of the multi-portion polycrystalline material  102  interspersed among the material of the supporting substrate  104 . Likewise, an end of the multi-portion polycrystalline material  102  may include at least some material of the supporting substrate  104  interspersed among the material of the multi-portion polycrystalline material  102 . For example, the end of the supporting substrate  104  proximate the multi-portion polycrystalline material  102  may include at least 1% by volume, at least 5% by volume, or at least 10% by volume of the material of the multi-portion polycrystalline material  102  interspersed among the material of the supporting substrate  104 . As a continuing example, the end of the multi-portion polycrystalline material  102  proximate the supporting substrate  104  may include at least 1% by volume, at least 5% by volume, or at least 10% by volume of the material of the supporting substrate  104  interspersed among the material of the multi-portion polycrystalline material  102 . As a specific, nonlimiting example, the end of a supporting substrate  104  comprising tungsten carbide particles in a cobalt matrix proximate a multi-portion polycrystalline material  102  comprising polycrystalline diamond may include 25% by volume of diamond particles interspersed among the tungsten carbide particles and cobalt matrix and the end of the multi-portion polycrystalline material  102  may include 25% by volume of tungsten carbide particles and cobalt matrix interspersed among the inter-bonded diamond particles. Thus, functionally grading the material of the cutting element  100  may provide a gradual transition from the material of the multi-portion polycrystalline material  102  to the material of the supporting substrate  104 . By functionally grading the material proximate the interface between the multi-portion polycrystalline material  102  and the supporting substrate  104 , the strength of the attachment between the multi-portion polycrystalline material  102  and the supporting substrate  104  may be increased relative to a cutting element  100  that includes no functional grading. 
       FIG. 2  is an enlarged cross-sectional view of one embodiment of the multi-portion polycrystalline material  102  of  FIG. 1 . The multi-portion polycrystalline material  102  may comprise at least two portions. For example, as shown in  FIG. 2 , the multi-portion diamond table  102  includes a first portion  106 , a second portion  108 , and a third portion  109  as discussed in further detail below. The multi-portion polycrystalline material  102  is primarily comprised of a hard or superabrasive material. In other words, hard or superabrasive material may comprise at least about seventy percent (70%) by volume of the multi-portion polycrystalline material  102 . In some embodiments, the multi-portion polycrystalline material  102  includes grains or crystals of diamond that are bonded together (e.g., directly bonded together) to form the multi-portion polycrystalline material  102 . Interstitial regions or spaces between the diamond grains may be void or may be filled with additional material or materials, as discussed below. Other hard materials that may be used to form the multi-portion polycrystalline material  102  include polycrystalline cubic boron nitride, silicon nitride, silicon carbide, titanium carbide, tungsten carbide, tantalum carbide, or another hard material. 
     At least one portion  106 ,  108 ,  109  of the multi-portion polycrystalline material  102  comprises a plurality of grains that are nanoparticles. As previously discussed, the nanoparticles may comprise, for example, at least one of diamond, polycrystalline cubic boron nitride, silicon nitride, silicon carbide, titanium carbide, tungsten carbide, tantalum carbide, or another hard material. The nanoparticles may not be hard particles in some embodiments of the invention. For example, the nanoparticles may comprise one or more of carbides, ceramics, oxides, intermetallics, clays, minerals, glasses, elemental constituents, various forms of carbon, such as carbon nanotubes, fullerenes, adamantanes, graphene, amorphous carbon, etc. Furthermore, in some embodiments, the nanoparticles may comprise a carbon allotrope and may have an average aspect ratio of about one hundred (100) or less. 
     The at least one portion  106 ,  108 ,  109  comprising nanoparticles may comprise about 0.01% to about 99% by volume or weight nanoparticles. More specifically, at least one of the first, second, and third portions  106 ,  108 , and  109  may comprise between about 5% and about 80% by volume nanoparticles. Still more specifically, at least one of the first, second, and third portions  106 ,  108 , and  109  may comprise between about 25% and about 75% by volume nanoparticles. Each portion  106 ,  108 ,  109  of the multi-portion polycrystalline material  102  may have an average grain size differing from an average grain size in another portion of the multi-portion polycrystalline material  102 . In other words, the first portion  106  comprises a plurality of grains of hard material having a first average grain size, the second portion  108  comprises a plurality of grains of hard material having a second average grain size that differs from the first average grain size, and the third portion  109  comprises a plurality of grains of hard material having a third average grain size that differs from the first average grain size and the second average grain size. The one or more portions  106 ,  108 ,  109  that comprise nanoparticles optionally may include additional grains or particles that are not nanoparticles. In other words, such portions may include a first plurality of particles, which may be referred to as primary particles, and the nanoparticles may comprise secondary particles that are disposed in interstitial spaces between the primary particles. The primary particles may comprise grains having an average grain size greater than about 500 nanometers. In some embodiments, each of the first portion  106 , the second portion  108 , and the third portion  109  may comprise a volume of polycrystalline material that includes mixtures of grains or particles as described in provisional U.S. Patent Application Ser. No. 61/252,049, which was filed Oct. 15, 2009, and entitled “Polycrystalline Compacts Including Nanoparticulate Inclusions, Cutting Elements and Earth-Boring Tools Including Such Compacts, and Methods of Forming Such Compacts,” the disclosure of which is incorporated herein in its entirety by this reference, but wherein at least two of the first portion  106 , the second portion  108 , and the third portion  109  differ in one or more characteristics relating to grain size and/or distribution. 
     In one embodiment, as shown in  FIG. 2  the first portion  106  may be formed adjacent the supporting substrate  104  ( FIG. 1 ) along the surface  110 , the second portion  108  may be formed over the first portion  106  on a side thereof opposite the supporting substrate  104 , and the third portion  109  may be formed over the second portion  108  on a side thereof opposite the first portion  106 . In other words, the second portion  108  may be disposed between the first portion  106  and the third portion  109 . The third portion  109 , which includes the cutting face  117  of the multi-portion diamond table  102 , may comprise the nanoparticles of hard material. In one non-limiting embodiment, the first portion  106  may not have any nanoparticles, the second portion  108  may comprise between five and ten volume percent nanoparticles having a 200 nm average cluster size, the third portion  109  may comprise between five and ten volume percent nanoparticles having a 75 nm average cluster size. In another non-limiting embodiment, the first portion  106  may comprise between five and ten volume percent nanoparticles having a 400 nm average cluster size, the second portion  108  may comprise between five and ten volume percent nanoparticles having a 200 nm average cluster size, and the third portion  109  may comprise between five and ten volume percent nanoparticle having a 75 nm average cluster size. 
     In some embodiments, the multi-portion polycrystalline material  102  may include portions comprising nanoparticles adjacent other portions lacking nanoparticles. For example, alternating layers of the multi-portion polycrystalline material  102  may selectively include and exclude nanoparticles from the material thereof. As a specific, nonlimiting example, the third portion  109  including the cutting face  117  of the multi-portion polycrystalline material  102  and the first portion  106  adjacent the supporting substrate  104  (see  FIG. 1 ) may include at least some nanoparticles, while the second portion  108  interposed between the first portion  106  and the third portion  109  may be devoid of nanoparticles. 
     In embodiments where a portion comprising nanoparticles is located adjacent another portion having a comparatively smaller quantity of nanoparticles or being at least substantially free of nanoparticles, the portions may be functionally graded between one another. For example, a region of a portion including nanoparticles (e.g., third portion  109 ) proximate another portion having a comparatively smaller quantity of nanoparticles or being at least substantially free of nanoparticles (e.g., second portion  108 ) may comprise a volume of nanoparticles that is intermediate (i.e., between) the overall volumes of nanoparticles in the portion including nanoparticles (e.g., third portion  109 ) and the other portion having the comparatively smaller quantity of nanoparticles or being at least substantially free of nanoparticles. Alternatively or in addition, a region of a portion having a comparatively smaller quantity of nanoparticles or being at least substantially free of nanoparticles (e.g., second portion  108 ) proximate a portion including nanoparticles (e.g., third portion  109 ) may comprise a volume of nanoparticles that is intermediate (i.e., between) the overall volumes of nanoparticles in the portion having the comparatively smaller quantity of nanoparticles or being at least substantially free of nanoparticles (e.g., second portion  108 ) and the portion including nanoparticles (e.g., third portion  109 ). Thus, an end of a portion (e.g., third portion  109 ) including nanoparticles proximate another portion (e.g., second portion  108 ) generally lacking nanoparticles may include a reduced volume percentage of nanoparticles as compared to an overall volume percentage of nanoparticles in the portion. Likewise, an end of a portion (e.g., second portion  108 ) generally lacking nanoparticles proximate another portion (e.g., third portion  109 ) including nanoparticles may include at least some nanoparticles. For example, the end of a third portion  109  including nanoparticles proximate a second portion  108  generally lacking nanoparticles may include a volume percentage of nanoparticles that is 1% by volume, 5% by volume, or even 10% by volume less than an overall volume percentage of nanoparticles in the third portion  109 . As a continuing example, the end of a second portion  108  generally lacking nanoparticles proximate a first portion  109  including nanoparticles may include at least 1% by volume, at least 5% by volume, or at least 10% by volume nanoparticles, while a remainder of the second portion  108  may be devoid of nanoparticles. As a specific, nonlimiting example, the end of a third portion  109  comprising nanoparticles proximate a second portion  108  generally lacking nanoparticles may include a volume percentage of nanoparticles that is 3% smaller than an overall volume percentage of nanoparticles in the third portion  109  and the end of the second portion  108  proximate the third portion  109  may include 3% by volume nanoparticles, while the remainder of the second portion  108  may be devoid of nanoparticles. 
     In some embodiments, the multi-portion polycrystalline material  102  may be functionally graded between a portion including nanoparticles (e.g., third portion  109 ) and another portion (e.g., second portion  108 ) either having a comparatively smaller quantity of nanoparticles or being at least substantially free of nanoparticles by providing layers that gradually vary the quantity of nanoparticles between the portions (e.g., between the second and third portions  108  and  109 ). For example, the quantity of nanoparticles in layers of a portion including nanoparticles (e.g., third portion  109 ) proximate the interface between the portion (e.g., third portion  109 ) and another portion either having a comparatively smaller quantity of nanoparticles or generally lacking nanoparticles (e.g., second portion  108 ) may gradually decrease as distance from the interface decreases. More specifically, a series of layers having incrementally smaller volume percentages of nanoparticles, for example, may be provided as a region of the portion comprising nanoparticles (e.g., third portion  109 ) proximate the portion either having a comparatively smaller quantity of nanoparticles or being at least substantially free of nanoparticles (e.g., second portion  108 ). As a continuing example, the quantity of nanoparticles in layers of a portion either having a comparatively smaller quantity of nanoparticles or generally lacking nanoparticles (e.g., second portion  108 ) proximate the interface between the portion (e.g., second portion  108 ) and another portion having an higher quantity of nanoparticles (e.g., third portion  109 ) may gradually increase as distance from the interface decreases. More specifically, a series of layers having incrementally larger volume percentages of nanoparticles, for example, may be provided as a region of the portion either having a comparatively smaller quantity of nanoparticles or being generally free of nanoparticles (e.g., second portion  108 ) proximate the portion having a comparatively larger quantity of nanoparticles (e.g., third portion  109 ). 
     In some embodiments, the transition between the quantities of nanoparticles in adjacent portions (e.g., second and third portions  108  and  109 ) may be so gradual that no distinct boundary between the portions is discernible, there being an at least substantially continuous gradient in volume percentage of nanoparticles. Furthermore, the gradient may continue throughout some or all of the multi-portion polycrystalline material  102  in some embodiments such that an at least substantially continuous or gradual change in the quantity of nanoparticles may be observed, there being no distinct boundary between the disparate portions of the multi-portion polycrystalline material  102 . Thus, functionally grading the quantities of nanoparticles may provide a gradual transition between the portions of the multi-portion polycrystalline material  102 . By functionally grading the material proximate the interface between portions of the multi-portion polycrystalline material  102 , the strength of the attachment between the portions may be increased relative to a multi-portion polycrystalline material  102  that includes no functional grading. 
       FIG. 3  is an enlarged simplified view of a microstructure of one embodiment of the multi-portion polycrystalline material  102 . While  FIG. 3  illustrates the plurality of grains  302 ,  304 ,  306  as having differing average grain sizes, the drawing is not drawn to scale and has been simplified for the purposes of illustration. As shown in  FIG. 3 , the third portion  109  comprises a third plurality of grains  302 , which have a smaller average grain size than both an average grain size of a second plurality of grains  304  in the second portion  108  and an average grain size of a first plurality of grains  306  in the first portion  106 . The third plurality of grains  302  may comprise nanoparticles. The second plurality of grains  304  in the second portion  108  may have an average grain size greater than the average grain size of the third plurality of grains  302  in the third portion  109 . Similarly, the first plurality of grains  306  in the first portion  106  may have an average size greater than the average grain size of the second plurality of grains  304  in the second portion  108 . In some embodiments, the average grain size of the second plurality of grains  304  in the second portion  108  may be between about fifty (50) to about one thousand (1000) times greater than the average grain size of the third plurality of grains  302  in the third portion  109 . The average grain size of the first plurality of grains  306  in the first portion  106  may be between about fifty (50) to about one thousand (1000) times greater than the average grain size of the second plurality of grains  304  in the second portion  108 . As a non-limiting example, the second plurality of grains  304  in the second portion  108  may have an average grain size about one hundred (100) times greater than the average grain size of the third plurality of grains  302  in the third portion  109 , and the first plurality of grains  306  in the first portion  106  may have an average grain size about one hundred (100) times greater than the average grain size of the second plurality of grains  304  in the second portion  108 . 
     The plurality of grains  302 ,  304 ,  306  in the first portion  106 , the second portion  108 , and the third portion  109  may be inter-bonded to form the multi-portion polycrystalline material  102 . In other words, in embodiments in which the multi-portion polycrystalline material  102  comprises polycrystalline diamond, the plurality of grains  302 ,  304 ,  306  from the first portion  106 , the second portion  108 , and the third portion  109  may be bonded directly to one another by inter-granular diamond-to-diamond bonds. 
     In some embodiments, the plurality of grains  302 ,  304 ,  306  in each of the portions  106 ,  108 ,  109  of the multi-portion polycrystalline material  102  may have a multi-modal (e.g., bi-modal, tri-modal, etc.) grain size distribution. For example, in some embodiments, the second portion  108  and the first portion  106  of the multi-portion polycrystalline material  102  may also comprise nanoparticles, but in lesser volumes than the third portion  109  such that the average grain size of the plurality of grains  304  in the second portion  108  is larger than the average grain size of the plurality of grains  302  in the third portion  109 , and the average grain size of the plurality of grains  306  in the first portion  106  is larger than the average grain size of the plurality of grains  304  in the second portion  108 . For example, in one embodiment, the third portion  109  may comprise at least about 25% by volume nanoparticles, the second portion  108  may comprise about 5% by volume nanoparticles, and the first portion  106  may comprise about 1% by volume nanoparticles. 
     As known in the art, the average grain size of grains within a microstructure may be determined by measuring grains of the microstructure under magnification. For example, a scanning electron microscope (SEM), a field emission scanning electron microscope (FESEM), or a transmission electron microscope (TEM) may be used to view or image a surface of the multi-portion polycrystalline material  102  (e.g., a polished and etched surface of the multi-portion polycrystalline material  102 ) or a suitably prepared section of the surface in the case of TEM as known in the art. Commercially available vision systems or image analysis software are often used with such microscopy tools, and these vision systems are capable of measuring the average grain size of grains within a microstructure. 
     In some embodiments, one or more regions of the multi-portion polycrystalline material  102  (e.g., the diamond table  102  of  FIG. 1 ), or the entire volume of the multi-portion polycrystalline material  102 , may be processed (e.g., etched) to remove metal material (e.g., such as a metal catalyst used to catalyze the formation of direct inter-granular bonds between grains of hard material in the multi-portion polycrystalline material  102 ) from between the inter-bonded grains of hard material in the multi-portion polycrystalline material  102 . As a particular non-limiting example, in embodiments in which the multi-portion polycrystalline material  102  comprises polycrystalline diamond material, metal catalyst material may be removed from between the inter-bonded grains of diamond within the polycrystalline diamond material, such that the polycrystalline diamond material is relatively more thermally stable. 
     A material  308  may be disposed in interstitial regions or spaces between the plurality of grains  302 ,  304 ,  306  in each portion  106 ,  108 ,  109 . In some embodiments, the material  308  may comprise a catalyst material that catalyzes the formation of the inter-granular bonds directly between grains  302 ,  304 ,  306  of hard material during formation of the multi-portion polycrystalline material  102 . In additional embodiments, the multi-portion polycrystalline material  102  may be processed to remove the material  308  from the interstitial regions or spaces between the plurality of grains  302 ,  304 ,  306  leaving voids therebetween, as mentioned above. Optionally, in such embodiments, such voids may be subsequently filled with another material (e.g., a metal). In embodiments in which the material  308  comprises a catalyst material, the material  308  may also include particulate (e.g., nanoparticles) inclusions of non-catalyst material, which may be used to reduce the amount of catalyst material within the multi-portion polycrystalline material  102 . 
     Referring again to  FIG. 2 , the first portion  106  may be formed to have a region boundary  118 ″ that is substantially parallel to the chamfered edge  118 . The second portion  108  may be formed over the first portion  106  extending along a top surface  202  and sides  204  of the first portion  106 . The second portion  108  may also be formed to include a region boundary  118 ′ that is substantially parallel to the chamfered edge  118 . The third portion  109  may be formed over the second portion  108  extending along a top surface  206  and around sides  208  of the second portion  108 . The third portion  109  forms the cutting face  117  and the chamfered edge  118  of the multi-portion polycrystalline material  102 . 
     In another embodiment, as shown in  FIG. 4 , the first portion  106  and the second portion  108  may be formed without the regional boundaries  118 ″,  118 ′ of  FIG. 2 . The top surface  202  of the first portion  106  and the sides  204  of the first portion  106  may intersect at a right angle to one another. Similarly, the top surface  206  and the sides  208  of the second portion  108 , formed over the first portion  106 , may intersect at a right angle to one another. The third portion  109  may be formed over the second portion  108  and include the chamfered edge  118  and front cutting face  117  of the multi-portion polycrystalline material  102 . 
     In another embodiment, as shown in  FIG. 5 , each of the first portion  106  and the second portion  108  may be substantially planar, and the second portion  108  may not extend down a lateral side of the first portion  106 , as it does in the embodiments of  FIGS. 2 and 4 . As shown in  FIG. 5 , the second portion  108  may be formed over the top surface  202  of the first portion  106  and the third portion  109  may be formed over the top surface  206  of the second portion  108 . The sides  204  of the first portion  106  and the sides  208  of the second portion  108  may be exposed to the exterior of the multi-portion polycrystalline material  102 . The third portion  109  includes the front cutting face  117  and the chamfered edge  118 . 
       FIG. 6  illustrates another embodiment of the multi-portion polycrystalline material  102 . As illustrated in  FIG. 6 , the second portion  108  may be formed over the top surface  202  of the first portion  106  and the third portion  109  may be formed over the top surface  206  of the second portion  108 . The sides  204  of the first portion  106  and the sides  208  of the second portion  108  may be exposed to the exterior of the multi-portion polycrystalline material  102 . The third portion  109  includes the front cutting face  117  and the chamfered edge  118 . The top surface  202  of the first portion  106  and the top surface  206  of the second portion  108  are not planar, and the interfaces between the first portion  106 , the second portion  108 , and the third portion  109  are accordingly non-planar. As shown in  FIG. 6 , the top surface  202  of the first portion  106  and the top surface  206  of the second portion  108  are convexly curved. In additional embodiments, the top surface  202  of the first portion  106  and the top surface  206  of the second portion  108  may be concavely curved. In yet further embodiments, the top surface  202  of the first portion  106  and the top surface  206  of the second portion  108  may include other non-planar shapes. 
     In another embodiment, as shown in  FIG. 7 , the second portion  108  may be formed on the lateral sides  204  of the first portion  106  and the third portion  109  may be formed on the lateral sides  208  of the second portion  108 . The top surface  202  of the first portion  106  and the top surface  206  of the second portion  108  may be exposed to the exterior of the multi-portion polycrystalline material  102  and form portions of the cutting face  117 . In such embodiments, the second portion  108  and the first portion  106  may comprise concentric annular regions. In an additional embodiment, the sides  204  of the first portion  106  may be angled as shown, for example, by dashed line  204 ′. In other words, the lateral side surface of the first portion  106  may have a frustoconical shape. Similarly, the sides  208  of the second portion  108  may be angled as shown, for example, by dashed line  208 ′. In other words, the lateral side surface of the second portion  108  also may have a frustoconical shape. The second portion  108  may be formed on the sides  204 ′ of the first portion  106  and the third portion  109  may be formed on the sides  208 ′ of the second portion  108 . The top surface  202  of the first portion  106  and the top surface  206  of the second portion  108  may be exposed to the exterior of the multi-portion polycrystalline material  102 , and may form at least a portion of the front cutting face  117 . 
     In further embodiments, as shown in  FIG. 8 , the first portion  106 , the second portion  108 , and the third portion  109  may have generally randomly shaped boundaries therebetween. In such embodiments, as shown in  FIG. 8 , the top surface  202  of the first portion  106  and the top surface  206  of the second portion  108  may be uneven. In still further embodiments, as shown in  FIG. 9 , the first portion  106 , the second portion  108 , and the third portion  109  may be intermixed throughout the multi-portion polycrystalline material  102 . In other words, each of the second portion  108  and the third portion  109  may occupy a number of finite, three-dimensional, interspersed volumes of space within the first portion  106 , as shown in  FIG. 9 . 
       FIGS. 10A-10K  are enlarged transverse cross-sectional views of additional embodiments of the multi-portion diamond table  102  of  FIG. 1  taken along the plane illustrated by section line  10 - 10  in  FIG. 1 . As shown in  FIG. 10A , the multi-portion diamond table  102  includes at least two portions, such as a first portion  402  and a second portion  404 . At least one portion of the at least two portions  402  and  404  comprises a plurality of grains that are nanoparticles. In other words, the average grain size of a plurality of grains (but not necessarily all grains) in at least one of the two portions  402  and  404  may be about 500 nanometers or less. The at least one portion  402 ,  404  comprising nanoparticles may comprise about 0.01% to about 99% by volume nanoparticles. The first portion  402  comprises a different concentration of nanoparticles than the second portion  404 . In some embodiments, the first portion  402  may comprise a higher concentration of nanoparticles than the second portion  404 . Alternatively, in additional embodiments, the first portion  402  may comprise a lower concentration of nanoparticles than the second portion  404 . The portion  402 ,  404  having the lower concentration of nanoparticles may not comprise any nanoparticles in some embodiments. Each portion of the at least two portions  402 ,  404  may independently comprise a mono-modal, mixed modal, or random size distribution of grains. 
     The first portion  402  may occupy a volume of space within the multi-portion polycrystalline material  102 , the volume having any of a number of shapes. In some embodiments, the first portion  402  may occupy a plurality of discrete volumes of space within the second portion  404 , and the plurality of discrete volumes of space may be selectively located and oriented at predetermined locations and orientations (e.g., in an ordered array) within the second portion  404 , or they may be randomly located and oriented within the second portion  404 . For example, the first portion  402  may have the shape of one or more of spheres, ellipses, rods, platelets, rings, toroids, stars, n-sided or irregular polygons, snowflake-type shapes, crosses, spirals, etc. As shown in  FIG. 10A , the first portion  402  may include a plurality different sized spheres dispersed throughout the second portion  404 . As shown in  FIG. 10B , the first portion  402  may include a plurality of rods dispersed throughout the second portion  404 . As shown in  FIG. 10C , the first portion may comprise a plurality of different sized rods dispersed throughout the second portion  404 . As shown in  FIG. 10D , the first portion  402  may comprise a plurality of similarly shaped spheres dispersed throughout the second portion  404 . As shown in  FIG. 10E , the first portion  402  may comprise a plurality of rods extending radially outward from a center of the multi-portion polycrystalline material  102 , and dispersed within the second portion  402 . As shown in  FIG. 10F , there may not be a definite, discrete boundary between the first portion  402  and the second portion  404 , but rather the first portion  402  may gradually transform into the second portion  404  along the direction illustrated by the arrow  407 . In other words, a gradual gradient in the concentration of nanoparticles and other grains may exist between the first portion  402  and the second portion  404 . As shown in  FIG. 10G , the first portion  402  may comprise a center region of the multi-portion polycrystalline material  102 , and the second portion  404  may comprise an outer region of the multi-portion polycrystalline material  102 . As shown in  FIG. 10H , the first portion  402  may comprise a star-shaped volume of space surrounded by the second portion  404 . As shown in  FIG. 10I , the first portion  402  may comprise a cross-shaped volume of space surrounded by the second portion  404 . As shown in  FIG. 10J , the first portion  402  may comprise an annular or ring-shaped volume of space having the second portion  404  on an interior of the ring. A third portion  406  may be formed on an exterior portion of the ring. The third portion  406  may have the same or a different concentration of nanoparticles as the second portion  404 . As shown in  FIG. 10K , the first portion  402  may comprise a plurality of parallel rod-shaped volumes of space dispersed throughout the second portion  404 . In embodiments in which the first portion  402  includes more than one region, such as the plurality of spheres shown in  FIG. 10A , the spacing between each region of the first portion  402  may be uniform or stochastic and the first portion  402  may be homogeneous or heterogeneous throughout the second portion  404 . 
     In some embodiments, the multi-portion polycrystalline material  102  may include nanoparticles in at least one layered portion  106 ,  108 ,  109  of the multi-portion polycrystalline material  102  as shown in  FIGS. 2-9  and nanoparticles in at least one discrete portion  402  of the multi-portion polycrystalline material  102  as shown in  FIGS. 10A-10K . Including nanoparticles in at least one portion  106 ,  108 ,  109 ,  402 ,  404  of the multi-portion polycrystalline material  102  may increase the thermal stability and durability of the multi-portion polycrystalline material  102 . For example, the nanoparticles in the at least one portion  106 ,  108 ,  109 ,  402 ,  404  may inhibit large cracks or chips from forming in the multi-portion polycrystalline material  102  during use in cutting formation material using the multi-portion polycrystalline material  102 , such as on a cutting element of an earth-boring tool. 
     The multi-portion polycrystalline material  102  of the cutting element  100  may be formed using a high temperature/high pressure (or “HTHP”) process. Such processes, and systems for carrying out such processes, are generally known in the art. In some embodiments of the present invention, the nanoparticles used to form at least one portion  106 ,  108 ,  109 ,  402 ,  404  of the multi-portion polycrystalline material  102  may be coated, metalized, functionalized, or derivatized to include functional groups. Derivatizing the nanoparticles may hinder or prevent agglomeration of the nanoparticles during formation of the multi-portion polycrystalline material  102 . Such methods of forming derivatized nanoparticles are described in U.S. Provisional Patent Application No. 61/324,142 filed Apr. 14, 2010 and entitled “Method of Preparing Polycrystalline Diamond From Derivatized Nanodiamond,” the disclosure of which provisional patent application is incorporated herein in its entirety by this reference. 
     In some embodiments, the multi-portion polycrystalline material  102  may be formed on a supporting substrate  104  (as shown in  FIG. 1 ) of cemented tungsten carbide or another suitable substrate material in a conventional HTHP process of the type described, by way of non-limiting example, in U.S. Pat. No. 3,745,623 to Wentorf et al. (issued Jul. 17, 1973), or may be formed as a freestanding polycrystalline compact (i.e., without the supporting substrate  104 ) in a similar conventional HTHP process as described, by way of non-limiting example, in U.S. Pat. No. 5,127,923 to Bunting et al. (issued Jul. 7, 1992), the disclosure of each of which patents is incorporated herein in its entirety by this reference. In some embodiments, a catalyst material may be supplied from the supporting substrate  104  during an HTHP process used to form the multi-portion polycrystalline material  102 . For example, the supporting substrate  104  may comprise a cobalt-cemented tungsten carbide material. The cobalt of the cobalt-cemented tungsten carbide may serve as the catalyst material during the HTHP process. 
     To form the multi-portion polycrystalline material  102  in an HTHP process, a particulate mixture comprising grains of hard material, including nanoparticles of the hard material, may be subjected to elevated temperatures (e.g., temperatures greater than about 1,000° C.) and elevated pressures (e.g., pressures greater than about 5.0 gigapascals (GPa)) to form inter-granular bonds between the grains, thereby forming the multi-portion polycrystalline material  102 . A particulate mixture comprising the desired grain size for each portion  106 ,  108 ,  109 ,  402 ,  404  may be provided on the supporting substrate  104  in the desired location of each portion  106 ,  108 ,  109 ,  402 ,  404  prior to the HTHP process. 
     The particulate mixture may comprise the nanoparticles as previously described herein. The particulate mixture may also comprise particles of catalyst material. In some embodiments, the particulate material may comprise a powder-like substance prepared using a wet or a dry process, such as those known in the art. In other embodiments, however, the particulate material may be processed into the form of a tape or film, as described in, for example, U.S. Pat. No. 4,353,958, which issued Oct. 12, 1982 to Kita et al., or as described in U.S. Patent Application Publication No. 2004/0162014 A1, which published Aug. 19, 2004 in the name of Hendrik, the disclosure of each of which is incorporated herein in its entirety by this reference, which tape or film may be shaped, loaded into a die, and subjected to the HTHP process. 
     Conventionally, because nanoparticles may be tightly compacted, the catalyst material may not adequately reach interstitial spaces between all the nanoparticles in a large quantity of nanoparticles. Accordingly, the HTHP sintering process may fail to adequately form the multi-portion polycrystalline material  102 . However, because embodiments of the present invention include portions  106 ,  108 ,  109 ,  402 ,  404  comprising different volumes of nanoparticles, the catalyst material may reach farther depths in the particulate mixture, thereby adequately forming the multi-portion polycrystalline material  102 . 
     Once formed, certain regions of the multi-portion polycrystalline material  102 , or the entire volume of multi-portion polycrystalline material  102 , optionally may be processed (e.g., etched) to remove material (e.g., such as a metal catalyst used to catalyze the formation of inter-granular bonds between the grains of hard material) from between the inter-bonded grains of the multi-portion polycrystalline material  102 , such that the polycrystalline material is relatively more thermally stable. 
     While the present invention has been described herein with respect to certain embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions and modifications to the embodiments described herein may be made without departing from the scope of the invention as hereinafter claimed. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventor. 
     CONCLUSION 
     In some embodiments, cutting elements comprise a multi-portion polycrystalline material. At least one portion of the multi-portion polycrystalline material comprises a higher volume of nanoparticles than at least another portion of the multi-portion polycrystalline material. 
     In other embodiments, earth-boring tools comprise a body and at least one cutting element attached to the body. The at least one cutting element comprises a hard polycrystalline material. The hard polycrystalline material comprises a first portion comprising a first volume of nanoparticles. A second portion of the hard polycrystalline material comprises a second volume of nanoparticles. The first volume of nanoparticles differs from the second volume of nanoparticles.