Methods and systems for testing a superhard polycrystalline construction

Abstract

A method of testing a superhard polycrystalline construction having a body of polycrystalline superhard material with a work face and a peripheral side surface, incudes contacting one or other of the work face or the peripheral side surface with a body of material forming an applied load until a crack and / or chip forms in the body of polycrystalline superhard material and recording the applied load required to achieve cracking and / or chipping.

Description

[0001] [OFFICIAL]

[0002] PF1633-WO-0-ORD

[0003] METHODS AND SYSTEMS FOR TESTING A SUPERHARD POLYCRYSTALLINE CONSTRUCTION

[0004] Field

[0005] This disclosure relates to methods and systems for testing superhard polycrystalline constructions, particularly but not exclusively to testing constructions comprising polycrystalline diamond (PCD) structures attached to a substrate.

[0006] Background

[0007] Polycrystalline superhard materials, such as polycrystalline diamond (PCD) material 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.

[0008] 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 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 which forms a cutting layer is typically polycrystalline diamond (PCD) material, or a thermally stable product (TSP) material such as thermally stable polycrystalline diamond.

[0009] Polycrystalline diamond (PCD) is an example of a superhard material (also called a superabrasive material or ultra hard material) comprising a mass of[OFFICIAL]

[0010] PF1633-WO-0-ORD

[0011] 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.

[0012] 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 which may typically also be referred to as filler or binder material. Most typically, PCD is 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.

[0013] 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 superhard 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[OFFICIAL]

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[0015] bonding between the diamond grains occurs, forming a super hard polycrystalline diamond layer.

[0016] In some instances, the substrate may be fully cured prior to attachment to the superhard 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 used to sinter the super hard polycrystalline diamond construction. The substrate may be in powder form and may solidify during said sintering process.

[0017] 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.

[0018] Methods used to improve the abrasion resistance of a PCD composite often result in a decrease in impact resistance of the composite.

[0019] 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 as 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.[OFFICIAL]

[0020] PF1633-WO-0-ORD

[0021] 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.

[0022] The industry demands ever-improving rates of penetration (ROP) and footage covered. It is therefore desirable for the super hard construction to retain a sharp cutting edge for the required duration of use. Cutting edge sharpness is lost through material removal at the cutting edge, the modes of which range from controlled wear of the material through to uncontrolled fracture events.

[0023] 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.

[0024] There is therefore a need for a laboratory test of super hard polycrystalline composites such as a PCD composites to assist in identifying the resistance of said PCD composites to crack initiation and propagation in the tangential and axial directions prior to application.

[0025] Summary

[0026] Viewed from a first aspect there is provided a method of testing a superhard polycrystalline construction comprising a body of polycrystalline superhard material bonded to a substrate, the body of polycrystalline superhard material comprising a work face and a peripheral side surface, the method comprising:

[0027] contacting one or other of the work face or the peripheral side surface with a body of material forming an applied load until a crack and / or chip forms in the body of polycrystalline superhard material; and

[0028] recording the applied load required to achieve cracking and / or chipping.[OFFICIAL]

[0029] PF1633-WO-0-ORD

[0030] In some examples, the step of contacting with a load material comprises applying a static load to the one or other of the work face or peripheral side surface.

[0031] The step of contacting one or other of the work face or the peripheral side surface with the body of material forming a load may comprise contacting said face or said surface with a steel ball.

[0032] In some examples, the step of contacting comprises contacting the work face at a location adjacent an edge of the body of superhard polycrystalline with the peripheral side surface.

[0033] The superhard polycrystalline construction may comprise a polycrystalline diamond construction comprising a body of polycrystalline diamond material bonded to a cemented carbide substrate along an interface. Also, the step of contacting may comprise contacting the peripheral side surface at a location closer to the work face than the interface.

[0034] In a further example, the method further comprises detecting crack initiation and / or propagation during the step of contacting using an acoustic emission technique.

[0035] The method may further comprise ranking superhard polycrystalline constructions based on the applied load required to achieve cracking and / or chipping recorded in the step of recording; and selecting a superhard polycrystalline construction for use in a selected application based on said ranking.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Examples will now be described with reference to the accompanying drawings in which:[OFFICIAL]

[0038] PF1633-WO-0-ORD

[0039] Figure 1 is a perspective view of an example PCD cutter element for a drill bit for boring into the earth;

[0040] Figure 2 is a view from above and one side of a super hard polycrystalline construction such as the PCD cutter element of Figure 1 to be tested by the example method, showing the test site on the working face thereof;

[0041] Figure 3 is a view from one side of an example system for testing a super hard polycrystalline construction, such as the PCD cutter element of Figure 1 , to be tested by the example method, showing the test site on the working face of the construction;

[0042] Figure 4 is a view from above and one side of a super hard polycrystalline construction, such as the PCD cutter element of Figure 1 , to be tested by the example method, showing the test site on the peripheral side surface thereof;

[0043] Figure 5 is a view from one side of an example system for testing a super hard polycrystalline construction, such as the PCD cutter element of Figure 1 , to be tested by the example method, showing the test site on the peripheral side surface of the construction; and

[0044] Figure 6 is a schematic flow diagram showing the method stages for testing a superhard polycrystalline construction according to an example method.

[0045] The same references refer to the same general features in all the drawings.

[0046] DESCRIPTION

[0047] As used herein, a “superhard material” is a material having a Vickers hardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN) material are examples of superhard materials.

[0048] As used herein, a “superhard construction” means a construction comprising a body of polycrystalline superhard material. In such a construction, a[OFFICIAL]

[0049] PF1633-WO-0-ORD

[0050] substrate may be attached thereto or alternatively the body of polycrystalline material may be free-standing and unbacked.

[0051] As used herein, polycrystalline diamond (PCD) is a type of polycrystalline superhard (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. In one example of PCD material, interstices between the diamond grains may be at least partly filled with a binder material comprising a catalyst for diamond. As used herein, “interstices” or “interstitial regions” are regions between the diamond grains of PCD material. In 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 accessible catalyst material has been removed from the interstices, leaving interstitial voids between the diamond grains.

[0052] A “catalyst material” for a superhard material is capable of promoting the growth or sintering of the superhard material.

[0053] The term "substrate" as used herein means any substrate over which the superhard material layer is formed. For example, a "substrate" as used herein may be a transition layer formed over another substrate.

[0054] 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.

[0055] As shown in Figure 1 , a cutting element 1 includes a substrate 10 with a layer of superhard material 14 formed on the substrate 10. The substrate 10 may be formed of a hard material such as cemented tungsten carbide. The superhard material 14 may be, for example, polycrystalline diamond (PCD),[OFFICIAL]

[0056] PF1633-WO-0-ORD

[0057] or a thermally stable product such as thermally stable PCD (TSP). The cutting element 1 may be mounted into a bit body such as a drag bit body (not shown) and may be suitable, for example, for use as a cutter insert for a drill bit for boring into the earth.

[0058] The exposed top surface of the superhard material opposite the substrate forms the cutting face 15, which is the surface which, along with its edge 16, performs the cutting in use.

[0059] At one end of the substrate 10 is an interface surface 12 that forms an interface with the superhard material layer 14 which is attached thereto at this interface surface. As shown in Figure 1, the substrate 10 is generally cylindrical and has a peripheral side surface 20. The superhard material layer 14 has a peripheral side surface 17 that is typically flush with the peripheral side surface 20 of the substrate 10.

[0060] Examples shown in Figures 2 to 6 relate to systems and methods for testing a superhard polycrystalline construction , such as a PCD construction in the form, for example, of a cutter element 1 using mechanical loading at selected test sites on the construction to assist in determining the construction’s resistance to crack initiation and crack propagation in the tangential (cutting) or axial (normal) directions.

[0061] Figures 2 and 3 show a super hard polycrystalline construction 1 such as the cutter element 1 of Figure 1 to be tested by the example method, showing the test site 40 on the cutting face (working face) 15 of the construction.

[0062] Figure 3 shows an example system for testing a super hard polycrystalline construction such as the cutter element of Figure 1, to be tested by the example method, the test site 40 being on the working face (cutting surface) 15 of the construction 1. A body of material 42 to form a mechanical load in the system is applied to the body of superhard polycrystalline material 14 at[OFFICIAL]

[0063] PF1633-WO-0-ORD

[0064] the test site 40 on the cutting face 15 of the body of superhard polycrystalline material. Selecting the test site 40 to be on the cutting face 15 enables the testing system to assist in determining the construction’s resistance to crack initiation and propagation in the tangential (cutting) direction.

[0065] In a further example as shown Figures 4 and 5, the test site 40 is selected to be on the peripheral side surface 17 of the body of superhard polycrystalline material 14. Selecting the test site 40 to be on the peripheral side surface 17 of the body of superhard polycrystalline material 14 enables the testing system to assist in determining the construction’s resistance to crack initiation and propagation in the axial direction, that is in a plane parallel to the longitudinal axis of the construction 1 , normal to the plane of the cutting face 15.

[0066] The example test system of Figure 5 differs from that shown in Figure 3 in that the test site 40 is instead selected to be on the peripheral side surface 17 of the body of superhard polycrystalline material 14 and a body of material 42 to form a mechanical load in the system is applied to the body of superhard polycrystalline material at the test site 40 on the peripheral side surface of the body of superhard polycrystalline material.

[0067] The superhard material may be, for example, polycrystalline diamond material, and the diamond grains used to form the polycrystalline diamond material may be natural or synthetic.

[0068] 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.[OFFICIAL]

[0069] PF1633-WO-0-ORD

[0070] The constructions, such as PCD elements, capable of being tested using the systems and methods disclosed herein include PCD bodies of superhard polycrystalline material such as PCD integrally formed and bonded to a cemented carbide substrate. A body of PCD material typically includes directly interbonded diamond grains exhibiting diamond-to-diamond bonding therebetween that define a plurality of interstitial regions. A metal-solvent catalyst (e.g., iron, nickel, cobalt, or alloys thereof) is typically disposed in at least a portion of the interstitial regions.

[0071] The cemented carbide substrate may, for example 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 examples, the metal carbide is tungsten carbide; examples may include tungsten carbide, tantalum carbide, vanadium carbide, niobium carbide, chromium carbide, titanium carbide, or combinations of the foregoing carbides cemented with iron, nickel, cobalt, or alloys of the foregoing metals. For example, the cemented carbide substrate may comprise cobalt-cemented tungsten carbide.

[0072] Generally, a PDC construction may be formed by placing un-bonded diamond particles adjacent to a cemented carbide substrate and subjecting the diamond particles and the cemented carbide substrate to an HPHT process under diamond stable HPHT conditions. During the HPHT process, metalsolvent catalyst from the cemented carbide substrate at least partially melts and sweeps into interstitial regions between the diamond particles to catalyze growth of diamond and formation of diamond-to-diamond bonding between adjacent diamond grains so that a body of PCD material is formed that bonds to the cemented carbide substrate upon cooling from the HPHT process.

[0073] The superhard polycrystalline construction such as a PCD construction may be subjected to a leaching process to remove at least a portion of the residual metal-solvent catalyst or infiltrant from the body of polycrystalline material to[OFFICIAL]

[0074] PF1633-WO-0-ORD

[0075] a selected depth and from one or more exterior surfaces. Removal of the metal-solvent catalyst or infiltrant may help improve thermal stability and / or wear resistance of the construction.

[0076] After sintering, and before or after leaching, the polycrystalline super hard construction may be ground to a desired size and / or shape.

[0077] Figure 6 is a flow diagram of an example method 100 of testing a superhard polycrystalline construction such as a PCD cutter element. The method 100 includes an act 102 of securing the construction in a fixture. The method further includes an act 104 of selecting a test site on the body of superhard polycrystalline material based on which of axial loading or tangential loading is to be tested and positioning the construction in the fixturing accordingly. The method further includes an act 106 of applying the body of loading material to the body of superhard material at the test site until any one or more of cracking or chipping occurs in the body of superhard polycrystalline material. The method further includes recording the load required to crack and / or chip the body of polycrystalline material.

[0078] The results of the loads required to crack and / or chip the bodies of superhard polycrystalline materials being tested may be compared and the constructions ranked according to crack initiation and / or propagation resistance.

[0079] To test a construction’s resistance to crack initiation and propagation in the tangential (cutting) direction, the construction to be tested is placed in a fixture and oriented at an angle comparable to the back rake angle of a construction when it is located in, for example, a drill bit into which it would be brazed in use. The back rake angle may be considered to be the angle between the cutting face of the construction and a line in a plane perpendicular to the load material it is to contact. This may be, for example, an angle of between 10 to 20 degrees.[OFFICIAL]

[0080] PF1633-WO-0-ORD

[0081] The body of load material, which may be, for example a body of steel, such as a steel ball, eg a hardened steel ball bearing, is applied to the cutting face of the construction at the test site until the body of superhard material cracks and / or chip formation occurs, such as a shear type fracture. In some examples, the loading is static rather than dynamic.

[0082] To test a construction’s resistance to crack initiation and propagation in the axial direction, the construction to be tested is placed in a fixture and any movement other than vertical movement is inhibited.

[0083] The body of load material is applied to the peripheral side edge of the body of polycrystalline material at the selected test site until the body of superhard material cracks and / or chip formation occurs.

[0084] Crack initiation may be determined by conventional acoustic emission techniques which identify cracks by capturing the sound waves generated as cracks initiate and propagate through the material. These waves may be detected by sensors which convert them into electrical signals for analysis.

[0085] Crack propagation and / or chipping of the superhard material may be determined by displacement measurement such as a visual inspection or using conventional scanning electron microscope (SEM) or X-ray techniques to analyze images of the material.

[0086] Whilst not wishing to be bound by any theory, it is believed that crack initiation is generally controlled by the strength and / or stiffness of the superhard polycrystalline material such as PCD, and that crack propagation is typically controlled by the toughness of said material. It has been appreciated that the exemplary method and system herein described may assist in selecting constructions having resistance to such failure mechanisms appropriate to a desired end application and application area. Furthermore, having a small contact area may enable the generation of high local stresses close to the[OFFICIAL]

[0087] PF1633-WO-0-ORD

[0088] edge of the construction and, if applied to the point of successful cracking and fracturing of the superhard material, this may provide an efficient method of identifying a particular construction’s resistance to crack initiation and / or propagation. This is extremely useful in assisting a user in the identification and selection of constructions for use in particular end applications and application areas. Different application areas typically have different formations to be drilled that require a different resistance to certain types of failure mechanisms and the exemplary method and system of testing may assist in selecting and ranking constructions and construction performances depending on the application area in which the construction is to be used.

[0089] While various examples have been described, 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 disclosed.

Claims

[OFFICIAL]PF1633-WO-0-ORDClaims:

1. A method of testing a superhard polycrystalline construction comprising a body of polycrystalline superhard material bonded to a substrate, the body of polycrystalline superhard material comprising a work face and a peripheral side surface, the method comprising:contacting one or other of the work face or the peripheral side surface with a body of material forming an applied load until a crack and / or chip forms in the body of polycrystalline superhard material; andrecording the applied load required to achieve cracking and / or chipping.

2. The method of claim 1, wherein the step of contacting with a load material comprises applying a static load to the one or other of the work face or peripheral side surface.

3. The method of any one of the preceding claims, wherein the step of contacting one or other of the work face or the peripheral side surface with the body of material forming a load comprises contacting said face or said surface with a steel ball.

4. The method of any one of the preceding claims, wherein the step of contacting comprises contacting the work face at a location adjacent an edge of the body of superhard polycrystalline with the peripheral side surface.

5. The method of any one of the preceding claims wherein the superhard polycrystalline construction comprises a polycrystalline diamond construction comprising a body of polycrystalline diamond material bonded to a cemented carbide substrate along an interface; the step of contacting comprises[OFFICIAL]PF1633-WO-0-ORDcontacting the peripheral side surface at a location closer to the work face than the interface.

6. The method of any one of the preceding claims further comprising detecting crack initiation and / or propagation during the step of contacting using an acoustic emission technique.

7. The method of any one of the preceding claims further comprising ranking superhard polycrystalline constructions based on the applied load required to achieve cracking and / or chipping recorded in the step of recording; and selecting a superhard polycrystalline construction for use in a selected application based on said ranking.

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