Patent Application
20180021924
This disclosure relates to super hard constructions and methods of making such constructions, particularly but not exclusively to constructions comprising polycrystalline diamond (PCD) structures which may or may not be attached to a substrate, and tools comprising the same, particularly but not exclusively for use in rock degradation or drilling, or for boring into the earth.
Polycrystalline super hard materials, such as polycrystalline diamond (PCD) may be used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. In particular, tool inserts in the form of cutting elements comprising PCD material are widely used in drill bits for boring into the earth to extract oil or gas. The working life of super hard tool inserts may be limited by fracture of the super hard material, including by spalling and chipping, or by wear of the tool insert.
Cutting elements such as those for use in rock drill bits or other cutting tools typically have a body in the form of a substrate which has an interface end/surface and a super hard material which forms a cutting layer bonded to the interface surface of the substrate by, for example, a sintering process. The substrate is generally formed of a tungsten carbide-cobalt alloy, sometimes referred to as cemented tungsten carbide and the super hard material layer is typically polycrystalline diamond (PCD), or a thermally stable product TSP material such as thermally stable polycrystalline diamond.
Polycrystalline diamond (PCD) is an example of a super hard material (also called a super abrasive material or ultra hard material) comprising a mass of substantially inter-grown diamond grains, forming a skeletal mass defining interstices between the diamond grains. PCD material typically comprises at least about 80 volume % of diamond and is conventionally made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa, and temperature of at least about 1,200° C., for example. A material wholly or partly filling the interstices may be referred to as filler or binder material.
PCD is typically formed in the presence of a sintering aid such as cobalt, which promotes the inter-growth of diamond grains. Suitable sintering aids for PCD are also commonly referred to as a solvent-catalyst material for diamond, owing to their function of dissolving, to some extent, the diamond and catalysing its re-precipitation. A solvent-catalyst for diamond is understood be a material that is capable of promoting the growth of diamond or the direct diamond-to-diamond inter-growth between diamond grains at a pressure and temperature condition at which diamond is thermodynamically stable. Consequently the interstices within the sintered PCD product may be wholly or partially filled with residual solvent-catalyst material. Most typically, PCD is often formed on a cobalt-cemented tungsten carbide substrate, which provides a source of cobalt solvent-catalyst for the PCD. Materials that do not promote substantial coherent intergrowth between the diamond grains may themselves form strong bonds with diamond grains, but are not suitable solvent—catalysts for PCD sintering.
Cemented tungsten carbide, which may be used to form a suitable substrate, is formed from carbide particles being dispersed in a cobalt matrix by mixing tungsten carbide particles/grains and cobalt together then heating to solidify. To form the cutting element with a super hard material layer such as PCD, diamond particles or grains are placed adjacent the cemented tungsten carbide body in a refractory metal enclosure such as a niobium enclosure and are subjected to high pressure and high temperature so that inter-grain bonding between the diamond grains occurs, forming a polycrystalline super hard diamond layer.
In some instances, the substrate may be fully cured prior to attachment to the super hard material layer whereas in other cases, the substrate may be green, that is, not fully cured. In the latter case, the substrate may fully cure during the HTHP sintering process. The substrate may be in powder form and may solidify during the sintering process used to sinter the super hard material layer.
Ever increasing drives for improved productivity in the earth boring field place ever increasing demands on the materials used for cutting rock. Specifically, PCD materials with improved abrasion and impact resistance are required to achieve faster cut rates and longer tool life.
Cutting elements or tool inserts comprising PCD material are widely used in drill bits for boring into the earth in the oil and gas drilling industry. Rock drilling and other operations require high abrasion resistance and impact resistance. One of the factors limiting the success of the polycrystalline diamond (PCD) abrasive cutters is the generation of heat due to friction between the PCD and the work material. This heat causes the thermal degradation of the diamond layer. The thermal degradation increases the wear rate of the cutter through increased cracking and spalling of the PCD layer as well as back conversion of the diamond to graphite causing increased abrasive wear.
Methods used to improve the abrasion resistance of a PCD composite often result in a decrease in impact resistance of the composite.
The most wear resistant grades of PCD usually suffer from a catastrophic fracture of the cutter before it has worn out. During the use of these cutters, cracks grow until they reach a critical length at which catastrophic failure occurs, namely, when a large portion of the PCD breaks away in a brittle manner. These long, fast growing cracks encountered during use of conventionally sintered PCD, result in short tool life.
Furthermore, despite their high strength, polycrystalline diamond (PCD) materials are usually susceptible to impact fracture due to their low fracture toughness. Improving fracture toughness without adversely affecting the material's high strength and abrasion resistance is a challenging task.
There is therefore a need for a super hard composite such as a PCD composite that has good or improved abrasion, fracture and impact resistance and a method of forming such composites.
Viewed from a first aspect there is provided a method of forming a super hard polycrystalline construction, comprising:
Viewed from a second aspect there is provided a super hard polycrystalline construction comprising:
Versions will now be described by way of example and with reference to the accompanying drawings in which:
The same references refer to the same general features in all the drawings.
As used herein, a “super hard material” is a material having a Vickers hardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN) material are examples of super hard materials.
As used herein, a “super hard construction” means a construction comprising a body of polycrystalline super hard material. In such a construction, a substrate may be attached thereto or alternatively the body of polycrystalline material may be free-standing and unbacked.
As used herein, polycrystalline diamond (PCD) is a type of polycrystalline super hard (PCS) material comprising a mass of diamond grains, a substantial portion of which are directly inter-bonded with each other and in which the content of diamond is at least about 80 volume percent of the material. As used herein, “interstices” or “interstitial regions” are regions between the diamond grains of PCD material. In some examples of PCD material, interstices between the diamond grains may be at least partly filled with a binder material comprising a catalyst for diamond. In some examples of PCD material, interstices or interstitial regions may be substantially or partially filled with a material other than diamond, or they may be substantially empty. PCD material may comprise at least a region from which catalyst material has been removed from the interstices, leaving interstitial voids between the diamond grains.
A “catalyst material” for a super hard material is capable of promoting the growth or sintering of the super hard material.
The term “substrate” as used herein means any substrate over which the super hard material layer is formed. For example, a “substrate” as used herein may be a transition layer formed over another substrate.
As used herein, the term “integrally formed” regions or parts are produced contiguous with each other and are not separated by a different kind of material.
An example of a super hard construction is shown in
The exposed top surface of the super hard material opposite the substrate forms the cutting face 4, also known as the working surface, which is the surface which, along with its edge 6, performs the cutting in use.
At one end of the substrate 3 is an interface surface 8 that forms an interface with the super hard material layer 2 which is attached thereto at this interface surface. As shown in the example of
The super hard material may be, for example, polycrystalline diamond (PCD) and the super hard particles or grains may be of natural and/or synthetic origin.
The substrate 3 may be formed of a hard material such as a cemented carbide material and may be, for example, cemented tungsten carbide, cemented tantalum carbide, cemented titanium carbide, cemented molybdenum carbide or mixtures thereof. The binder metal for such carbides suitable for forming the substrate 3 may be, for example, nickel, cobalt, iron or an alloy containing one or more of these metals. Typically, this binder will be present in an amount of 10 to 20 mass %, but this may be as low as 6 mass % or less. Some of the binder metal may infiltrate the body of polycrystalline super hard material 2 during formation of the compact 1.
As shown in
The working surface or “rake face” 4 of the polycrystalline composite construction 1 is the surface or surfaces over which the chips of material being cut flow when the cutter is used to cut material from a body, the rake face 4 directing the flow of newly formed chips. This face 4 is commonly also referred to as the top face or working surface of the cutting element as the working surface 4 is the surface which, along with its edge 6, is intended to perform the cutting of a body in use. It is understood that the term “cutting edge”, as used herein, refers to the actual cutting edge, defined functionally as above, at any particular stage or at more than one stage of the cutter wear progression up to failure of the cutter, including but not limited to the cutter in a substantially unworn or unused state.
As used herein, “chips” are the pieces of a body removed from the work surface of the body being cut by the polycrystalline composite construction 1 in use.
As used herein, a “wear scar” is a surface of a cutter formed in use by the removal of a volume of cutter material due to wear of the cutter. A flank face may comprise a wear scar. As a cutter wears in use, material may progressively be removed from proximate the cutting edge, thereby continually redefining the position and shape of the cutting edge, rake face and flank as the wear scar forms.
As shown in
In some examples, the average grain size of the third fraction 34 may be around 60 nm to around 1 micron.
Non-super hard phase material 24 such as residual catalyst/binder may remain in a number of the interstices between adjacent super hard grains 32, 34, 36, and the average binder pool size of these interstices may be smaller than in conventional PCD such as that shown in
As used herein, a PCD grade is a PCD material characterised in terms of the volume content and size of diamond grains, the volume content of interstitial regions between the diamond grains and composition of material that may be present within the interstitial regions. A grade of PCD material may be made by a process including providing an aggregate mass of diamond grains having a size distribution suitable for the grade, optionally introducing catalyst material or additive material into the aggregate mass, and subjecting the aggregated mass in the presence of a source of catalyst material for diamond to a pressure and temperature at which diamond is more thermodynamically stable than graphite and at which the catalyst material is molten. Under these conditions, molten catalyst material may infiltrate from the source into the aggregated mass and is likely to promote direct intergrowth between the diamond grains in a process of sintering, to form a PCD structure. The aggregate mass may comprise loose diamond grains or diamond grains held together by a binder material and said diamond grains may be natural or synthesised diamond grains.
Different PCD grades may have different microstructures and different mechanical properties, such as elastic (or Young's) modulus E, modulus of elasticity, transverse rupture strength (TRS), toughness (such as so-called K1C toughness), hardness, density and coefficient of thermal expansion (CTE). Different PCD grades may also perform differently in use. For example, the wear rate and fracture resistance of different PCD grades may be different.
All of the PCD grades may comprise interstitial regions filled with material comprising cobalt metal, which is an example of catalyst material for diamond.
The PCD structure 2′ of examples may comprise two or more PCD grades.
The grains of super hard material may be, for example, diamond grains or particles. In the starting mixture prior to sintering they may be, for example, bimodal, that is, the feed comprises a mixture of a coarse fraction of diamond grains and a fine fraction of diamond grains having a smaller average grain size than the coarser fraction. By “average particle or grain size” it is meant that the individual particles/grains have a range of sizes with the mean particle/grain size representing the “average”. The average particle/grain size of the fine fraction is less than the size of the coarse fraction.
Some examples may comprise a wide bi-modal size distribution between the coarse and fine fractions of super hard material, and some examples may include three or even four or more size modes which may, for example, be separated in size by an order of magnitude.
Sizing of diamond particles/grains into fine fraction, coarse fraction, or other sizes in between, may be through known processes such as jet-milling of larger diamond grains and the like.
In some examples, the binder catalyst/solvent may comprise cobalt or some other iron group elements, such as iron or nickel, or an alloy thereof. Carbides, nitrides, borides, and oxides of the metals of Groups IV-VI in the periodic table are other examples of non-diamond material that might be added to the sinter mix. In some examples, the binder/catalyst/sintering aid may be Co.
The cemented metal carbide substrate may be conventional in composition and, thus, may be include any of the Group IVB, VB, or VIB metals, which are pressed and sintered in the presence of a binder of cobalt, nickel or iron, or alloys thereof. In some embodiments, the metal carbide is tungsten carbide.
The cutter of
Graphenes with various x-y dimensions and z dimensions are thoroughly dispersed in a liquid, such as deionized water or an organic solvent, for example ethanol, with or without a surfactant, using a sonication process by inserting an ultrasonic probe into the liquid. The dispersions may be pH adjusted to render the mixture slightly acidic which may assist in inhibiting agglomeration or aggregation of the graphenes. Diamond grits are added to the mixture and a sintering agent such as cobalt may also be added at this stage. The mixture is then subjected to a further sonication process by applying the ultrasonic probe into the mixture for a further period of time to form a homogeneous mixture. The resulting mixture is then dried using a fast drying process to maintain the homogeneity. An example of a suitable drying process to form graphene/diamond clusters, in which the graphenes are either coated on the surface of the diamond grits or the diamond grits are incorporated between graphene layers may be freeze drying using, for example, liquid nitrogen, or spray drying, or spray granulation. The clusters in the form of an admix powder are then sintered under conventional diamond sintering conditions, for example at a pressure of around 6.8 GPa, and temperature of around 1300 degrees C., in some examples with a preformed WC substrate, and the graphene is at least partially converted into diamond to form a PCD structure such as that shown in
Whilst not wishing to be bound by a particular theory, it is believed that the thorough dispersion of the graphene and diamond grits in the initial dispersion mixture prior to drying may assist in achieving the desired microstructure in which the grains of the first fraction 30 are bonded along a portion of their peripheral outer surface to plurality of grains of a fraction 34 formed by the conversion during sintering of the graphenes into diamond having an average grain size of between around 60 nm to around 1 micron, the graphene. Various techniques may be used to achieve this dispersion and homogenous mixture, such as ultrasonic dispersing, ball milling, homogenization, and jet milling techniques.
Also, a fast drying process to dry the graphene/diamond suspension without agglomeration may assist in achieving the desired microstructure in the sintered product. Suitable drying techniques to assist in inhibiting agglomeration of the graphene materials during drying may include, for example, freeze drying, spray freeze drying, spray drying, and spray granulation or spray freeze granulation techniques.
In the example in which a spray drying technique is used, a suitable inlet temperature may be, for example, around 120 deg C., and an outlet temperature of around 50-56 deg C., and a feeding rate of around 5.8 ml/min may be used.
In the example in which a freeze drying technique is used, the admix may be in the form of a homogeneous paste which is frozen using liquid nitrogen, and is then placed into a freeze dryer for several days until the paste is thoroughly dried. The freeze drying conditions may be optimized for different solvents, for example, for deionized water, the preferred operation temperature is −55 deg C. plus/minus 5 deg C., and the preferred pressure is between around 50 to 500 microbar.
In some examples, other nanomaterials, such as nanodiamond may be introduced together with the graphene materials into the admix.
In some examples, a surfactant may be added to the suspension mixture such as a non-ionic or cationic surfactant. In some examples, a polymeric stabiliser having, for example, a viscosity close to the viscosity of water may be added to the suspension mixture.
In some examples, the admix material comprising the graphene and diamond admix, and the carbide material for forming the substrate plus any additional sintering aid/binder/catalyst are applied as powders and sintered simultaneously in a single UHP/HT process. The admix of graphene and diamond grains, and mass of carbide powder material are placed in an HP/HT reaction cell assembly and subjected to HP/HT processing. The HP/HT processing conditions selected are sufficient to effect intercrystalline bonding between the diamond grains and to at least partially convert the graphene into diamond grains as well as, optionally, the joining of sintered particles to the cemented metal carbide support. In one example, the processing conditions generally involve the imposition for about 3 to 120 minutes of a temperature of at least about 1200 degrees C. and an ultra-high pressure of greater than about 5 GPa.
In another example, the substrate may be pre-sintered in a separate process before being bonded to the super hard material in the HP/HT press during sintering of the ultrahard polycrystalline material.
In a further example, both the substrate and a body of polycrystalline super hard material are pre-formed. The preformed body of polycrystalline super hard material is then placed in the appropriate position on the upper surface of the preform carbide substrate (incorporating a binder catalyst), and the assembly is located in a suitably shaped canister. The assembly is then subjected to high temperature and pressure in a press, the order of temperature and pressure being again, at least around 1200 degrees C. and 5 GPa respectively. During this process the graphene is at least partially converted into diamond and solvent/catalyst may migrate from the substrate into the body of super hard material and acts as a binder-catalyst to effect intergrowth in the layer and also serves to bond the layer of polycrystalline super hard material to the substrate.
In some examples, the cemented carbide substrate may be formed of tungsten carbide particles bonded together by the binder material, the binder material comprising an alloy of Co, Ni and Cr. The tungsten carbide particles may form at least 70 weight percent and at most 95 weight percent of the substrate. The binder material may comprise between about 10 to 50 wt. % Ni, between about 0.1 to 10 wt. % Cr, and the remainder weight percent comprises Co.
The PCD construction 1 described with reference to
Furthermore, the PCD body in the structure of
In addition, after sintering, the polycrystalline super hard constructions may be ground to size and may include, if desired, a chamfer, for example of around 45 degrees and of approximately 0.4 mm height measured parallel to the longitudinal axis of the construction.
Some versions are discussed in more detail below with reference to the following example, which is not intended to be limiting.
As used herein, graphene and exfoliated graphene materials will be referred to as ‘graphene materials’, and these are two dimensional soft materials which may at least partially convert into fine grain sized diamond materials under conventional diamond sintering pressures.
5 g of C500 graphene (Xscience) was dispersed in 50 ml of deionised water together with 1 g of a surfactant (such as polyvinyl alcohol) to form a suspension. The suspension was then treated with an ultrasonic probe for at least around 15 minutes until the graphene materials were thoroughly dispersed, and then 2 g of SP cobalt was added into the suspension with a further sonication process applied for around 5 minutes, using the ultrasonic probe to disperse the materials.
66.5 g of diamond grains having an average grain size of around 22 microns (Grade 22) and 28.5 g of diamond grains having an average grain size of around 2 microns (Grade 2) were then introduced into the suspension and the mixture was subjected to around 5 minutes further sonication treatment, as above.
The resulting suspension was then passed through an atomized nozzle (having a pressure of around 3 Bar), with a feed rate of around 6 ml/min, and sprayed into a container of liquid nitrogen to freeze the mixture immediately and form frozen granulates. After completion of the atomization, the frozen granulates were collected and placed into a freeze dryer for at least around 2 days to remove water content and form an admix powder. The graphene addition comprised around 5 wt % of the mixture. 2.1 g of the admix powder was then placed into a canister with a pre-formed cemented WC substrate to form a pre-sinter assembly, which was then loaded into a press and subjected to an ultra-high pressure and a temperature at which the super hard material is thermodynamically stable to sinter the super hard grains. The pressure to which the assembly was subjected was about 6.8 GPa and the temperature was at least about 1,200 degrees centigrade. The sintered PCD construction was then removed from the canister.
A conventional PCD cutter construction formed of the same mixture of diamond grain sizes (grades) as set out in the above example, but without adding the C500 type graphene was prepared in a conventional manner for forming PCD by mixing using conventional milling and mixing techniques and the mixture was sintered under the same conditions as above for the example containing the C500 type graphene, with a pre-formed cemented carbide substrate.
Two further example cutters were formed by the above described method used for the C500 type graphene but replacing the C500 type graphene with, in one example, C300 type graphene and, in another example, H15 type graphene.
The prepared PCD constructions formed according to the above methods were compared in a vertical boring mill test. The results are shown in
The first PCD construction tested was that formed of the conventional diamond grain mixture (without any graphene additions) and the results are shown in
The results provide an indication of the total wear scar area plotted against cutting length. It will be seen that the PCD constructions formed according to the second and third examples (lines 300 and 400) were able to achieve a significantly greater cutting length than that occurring in the conventional PCD compact (shown by line 100 in
Thus it will be seen from
An additional sample according to the above example containing 5 wt % of the C500 type graphene was produced as was an additional reference cutter which was formed of the same mixture of diamond grain sizes (grades) as set out in the above example, but without adding the graphene, and it was prepared in a conventional manner for forming PCD by mixing using conventional milling and mixing techniques and the mixture was sintered with a pre-formed cemented carbide substrate under the same conditions as above for the example containing the graphene addition. Polished sections of the constructions were then analysed using conventional SEM techniques to determine the respective diamond densities in the constructions. The results are shown in
It will be seen from
Whilst not wishing to be bound by a particular theory, it is believed that the benefits of adding graphene to improve the abrasion resistance and working life of the PCD construction in use may be influenced by both the surface area of the graphene used in the starting material and the diamond grain size. In some examples, the BET surface area of the graphene may be larger than around 50 m2/g, for example larger than around 100 m2/g, or larger than around 300 m2/g, and even around 500 m2/g or more. In addition, in some examples, the average grain size of at least one of the diamond fractions in the admix may be around 6 microns or less, or around 4 microns or less, or around 2 microns or less.
Thus, examples of a PCD material may be formed having that a combination of high abrasion and fracture performance which is surprising considering the reduction in diamond contiguity in those PCD constructions which is shown schematically in
Diamond contiguity is an important performance indicator, as it indicates the degree of intergrowth or bonding between the diamond particles, and all else being equal the higher the diamond contiguity the better the cutter performance. Higher diamond contiguity is normally associated with high diamond content which in turn results in lower binder content, as the high diamond content translates into low porosity and therefore low binder content, as the binder occupies the pores.
According to classic materials science of composite materials, low binder content results in low fracture toughness, as it is normally the hard grains (in this case diamond) that imparts hardness to the composite material, and the more ductile binder (in PCD, normally Co-WC) that imparts toughness to the composite material.
Therefore, high diamond content and low binder content are expected to be associated with increased hardness and decreased toughness, so that failure due to fracture or spalling of the PCD is expected to increase.
It was therefore surprising to find that PCD with improved wear performance may be obtained by adding graphene in the starting mixture which at least in part converts to form nanodiamond sized diamond grains during sintering at HPHT bridging the surfaces of at least some of the adjacent larger diamond grains, as is evidenced by the results of an analysis of the wear performance of the PCD material shown in
It is further believed that these nanodiamond bridges between the larger diamond grains may assist in arresting cracks which may attempt to propagate through the material in use.
The microstructure of the PCD constructions formed according to one or more of the above described example methods may be determined using conventional image analysis techniques such as scanning electron micrographs (SEM) taken using a backscattered electron signal.
The homogeneity or uniformity of the PCD structure may be quantified by conducting a statistical evaluation using a large number of micrographs of polished sections, as may the diamond density, the latter of which is shown in
While various versions have been described with reference to a number of examples, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof and that these examples are not intended to limit the particular examples or versions disclosed.
For example, in some embodiments of the method, the PCD material may be sintered for a period in the range from about 1 minute to about 30 minutes, in the range from about 2 minutes to about 15 minutes, or in the range from about 2 minutes to about 10 minutes.
In some examples of the method, the sintering temperature may be in the range from about 1,200 degrees centigrade to about 2,300 degrees centigrade, in the range from about 1,400 degrees centigrade to about 2,000 degrees centigrade, in the range from about 1,450 degrees centigrade to about 1,700 degrees centigrade, or in the range from about 1,450 degrees centigrade to about 1,650 degrees centigrade.
In one example, the method may include removing residual metallic catalyst/binder material for diamond from interstices between the diamond grains of the PCD material. In some examples, the PCD structure may have a region adjacent a surface comprising at most about 2 volume percent of catalyst material for diamond.
In further examples, the PCD structure may additionally have a region remote from the surface comprising greater than about 2 volume percent of catalyst material for diamond. In some such examples, the region adjacent the surface may extend to a depth of at least about 20 microns, at least about 80 microns, at least about 100 microns or even at least about 400 microns from the surface, or greater.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1423405.8 | Dec 2014 | GB | national |
| 1508726.5 | May 2015 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/081462 | 12/30/2015 | WO | 00 |
