Patent Grant
9488011
This application is a U.S. National Stage Application of International Application No. PCT/US2012/034381 filed Apr. 20, 2012, which designates the United States and claims the benefit of British Patent Application Serial No. 1106765.9, filed on Apr. 20, 2011, the entire disclosures of which are hereby incorporated by reference.
The present invention relates to polycrystalline diamond cutting elements, and to methods for leaching and methods for manufacturing the same.
Polycrystalline diamond and polycrystalline diamond-like elements are known, for the purposes of this specification, as PCD elements. PCD elements are formed from carbon based materials with exceptionally short inter-atomic distances between neighbouring atoms. One type of diamond-like material similar to PCD is known as carbonitride (CN) described in U.S. Pat. No. 5,776,615. In general, PCD elements are formed from a mix of materials processed under high-temperature and high-pressure into a polycrystalline matrix of inter-bonded superhard carbon based crystals. A common trait of PCD elements is the use of catalyzing materials during their formation, the residue from which often imposes a limit upon the maximum useful operating temperature of the element while in service.
A well known, manufactured form of PCD element is a two-layer or multi-layer PCD element where a facing table of polycrystalline diamond is integrally bonded to a substrate of less hard material, such as tungsten carbide. The PCD element may be in the form of a circular or part-circular tablet, or may be formed into other shapes. PCD elements of this type may be used in almost any application where a hard, wear- and erosion-resistant material is required. The substrate of the PCD element may be brazed to a carrier, often also of cemented tungsten carbide. This is a common configuration for PCDs used as cutting elements, for example in fixed cutter or rolling cutter earth boring bits when, received in a socket of the drill bit. These PCD elements are typically called polycrystalline diamond cutters (PDC).
Typically, higher diamond volume densities in the diamond table increases wear resistance at the expense of impact strength. However, modern PDCs typically utilize complex geometrical interfaces between the diamond table and the substrate as well as other physical design configurations to improve the impact strength. Although this allows wear resistance and impact strength to be simultaneously maximized, the trade-off still exists.
Another form of PCD element is a unitary PCD element without an integral substrate, where a table of polycrystalline diamond is fixed to a tool or wear surface by mechanical means or a bonding process. These PCD elements differ from those above in that diamond particles are present throughout the element. These PCD elements may be held in place mechanically, they may be embedded within a larger PCD element that has a substrate, or, alternately, they may be fabricated with a metallic layer which may be bonded by a brazing or welding process. A plurality of these PCD elements may be made from a single PCD, as shown, for example, in U.S. Pat. Nos. 4,481,016 and 4,525,179 herein incorporated by reference for all they disclose.
PCD elements are most often formed by sintering diamond powder with a suitable binder-catalyzing material in a high-pressure, high-temperature (HPHT) press. One particular method of forming polycrystalline diamond in this way is disclosed in U.S. Pat. No. 3,141,746 herein incorporated by reference for all it discloses. In one common process for manufacturing PCD elements, diamond powder is applied to the surface of a preformed tungsten carbide substrate incorporating cobalt. The assembly is then subjected to very high temperature and pressure in a press. During this process, cobalt migrates from the substrate into the diamond layer and acts as a binder-catalyzing material, causing the diamond particles to bond to one another with diamond-to-diamond bonding, and also causing the diamond layer to bond to the substrate.
The completed PCD element has at least one body with a matrix of diamond crystals bonded to each other with intercrystalline bonds and defining many interstices between the crystals which contain a binder-catalyzing material as described above. The diamond crystals comprise a first continuous matrix of diamond, and the interstices form a second continuous interstitial matrix of the binder-catalyzing material. In addition, there are necessarily a relatively few areas where the diamond to diamond growth has encapsulated some of the binder-catalyzing material. These ‘islands’ are not part of the continuous interstitial matrix of binder-catalyzing material.
Such PCD elements may be subject to thermal degradation due to differential thermal expansion between the interstitial cobalt binder-catalyzing material and the diamond matrix, beginning at temperatures of about 400 degrees C. Upon sufficient thermal expansion, the diamond-to-diamond bonding may be ruptured and cracks and chips may occur. The differential of thermal expansion may also be referred to as the differential of co-efficient of thermal expansion.
Also in polycrystalline diamond, the presence of the binder-catalyzing material in the interstitial regions adhering to the diamond crystals of the diamond matrix leads to another form of thermal degradation. Due to the presence of the binder-catalyzing material, the diamond is caused to graphitize as temperature increases, typically limiting the operation temperature to about 750 degrees C.
Although cobalt is most commonly used as the binder-catalyzing material, any group VIII element, including cobalt, nickel, iron, and alloys thereof, may be employed.
To reduce thermal degradation, so-called “thermally stable” polycrystalline diamond components have been produced as preform PCD elements for cutting- and/or wear-resistant elements, as disclosed in U.S. Pat. No. 4,224,380 herein incorporated by reference for all it discloses. In one type of thermally stable PCD element the cobalt or other binder-catalyzing material found in a conventional polycrystalline diamond element is leached out from the continuous interstitial matrix after formation. Numerous methods for leaching the binder-catalyzing material are known. Some leaching methods are disclosed, for example, in U.S. Pat. Nos. 4,572,722 and 4,797,241 both herein incorporated by reference for all they disclose.
Leaching the binder-catalyzing material may increase the temperature resistance of the diamond to about 1200 degrees C. However, the leaching process also has a tendency to remove the cemented carbide substrate. In addition, where there is no integral substrate or other bondable surface, there are severe difficulties in mounting such material for use in operation. There is some belief that it is advisable to not leach closer to the substrate than 500 microns.
The fabrication methods for such ‘thermally stable’ PCD elements typically produce relatively low diamond volume densities, typically of the order of 80 volume % or less. This low diamond volume density enables a thorough leaching process, but the resulting furnished part is typically relatively weak in impact strength. The low volume density is typically achieved by using an admixtures process and using relatively small diamond crystals with average particle sizes of about 15 microns or less. These small particles are typically coated with a catalyzing material prior to processing. The admixtures process causes the diamond particles to be widely spaced in the finished product and relatively small percentages of their outer surface areas dedicated to diamond-to-diamond bonding, often less than 50%, contributing to the low impact strengths.
In these so-called “thermally stable” polycrystalline diamond components, the lack of a suitable bondable substrate for later attachment to a work tool has been addressed by several methods. One such method to attach a bondable substrate to a “thermally stable” polycrystalline diamond preform is shown in U.S. Pat. No. 4,944,772 herein incorporated by reference for all it discloses. In this process, a porous polycrystalline diamond preform is first manufactured, and then it is re-sintered in the presence of a catalyzing material at high-temperatures and pressures with a barrier layer of another material which, in theory, prevents the catalyzing material from re-infiltrating the porous polycrystalline diamond preform. The resulting product typically has an abrupt transition between the preform and the barrier layer, causing problematic stress concentrations in service. This product is considered to be more like a joined composite than an integral body.
Other, similar processes to attach a bondable substrate to “thermally stable” polycrystalline diamond components are shown in U.S. Pat. Nos. 4,871,377 and 5,127,923 herein incorporated by reference for all they disclose. It is believed that the weakness of all these processes is the degradation of the diamond-to-diamond bonds in the polycrystalline diamond preform from the high temperature and pressure re-sintering process. It is felt that this degradation generally further reduces the impact strength of the finished product to an unacceptably low level below that of the preform.
In an alternative form of thermally stable polycrystalline diamond, silicon is used as the catalyzing material. The process for making polycrystalline diamond with a silicon catalyzing material is quite similar to that described above, except that, at synthesis temperatures and pressures, most of the silicon is reacted to form silicon carbide, which is not an effective catalyzing material. The thermal resistance is somewhat improved, but thermal degradation still occurs due to some residual silicon remaining, generally uniformly distributed in the interstices of the interstitial matrix. Again, there are mounting problems with this type of PCD element because there is no bondable surface.
More recently, a further type of PCD has become available in which carbonates, such as powdery carbonates of Mg, Ca, Sr, and Ba are used as the binder-catalyzing material when sintering the diamond powder. PCD of this type typically has greater wear-resistance and hardness than the previous types of PCD elements. However, the material is difficult to produce on a commercial scale since much higher pressures are required for sintering than is the case with conventional and thermally stable polycrystalline diamond. One result of this is that the bodies of polycrystalline diamond produced by this method are smaller than conventional polycrystalline diamond elements. Again, thermal degradation may still occur due to the residual binder-catalyzing material remaining in the interstices. Again, because there is no integral substrate or other bondable surface, there are difficulties in mounting this material to a working surface.
In some known techniques, physical vapor deposition (PVD) and/or chemical vapor deposition (CVD) processes are used to apply the diamond or diamond-like coating. PVD and CVD diamond coating processes are well known and are described, for example, in U.S. Pat. Nos. 5,439,492; 4,707,384; 4,645,977; 4,504,519; 4,486,286 all herein incorporated by reference.
PVD and/or CVD processes to coat surfaces with diamond or diamond like coatings may be used, for example, to provide a closely packed set of epitaxially oriented crystals of diamond or other superhard crystals on a surface. Although these materials have very high diamond densities because they are so closely packed, there is no significant amount of diamond to diamond bonding between adjacent crystals, making them quite weak overall, and subject to fracture when high shear loads are applied. The result is that although these coatings have very high diamond densities, they tend to be mechanically weak, causing very poor impact toughness and abrasion resistance when, used in highly loaded applications, such as when used as drill bit cutting elements.
Some attempts have been made to improve the toughness and wear resistance of these diamond or diamond-like coatings by applying them to a tungsten carbide substrate and subsequently processing them in a high-pressure, high-temperature environment, as described in U.S. Pat. Nos. 5,264,283; 5,496,638; 5,624,068, which are herein incorporated by reference for all they disclose. Although this type of processing may improve the wear resistance of the diamond layer, the abrupt transition between the high-density diamond layer and the substrate make the diamond layer susceptible to wholesale fracture at the interface at very low strains, similar to the above described problems encountered with composite structures having barrier layers. This again translates to very poor toughness and impact resistance in service.
U.S. Pat. No. 6,601,662 discloses PCD cutting elements which are adapted to control the wear profile of the cutting or working faces to increase the operating life of the cutting elements, primarily by making the elements self-sharpening so that a greater proportion of the cutter body can be worn away and used in effectively cutting material.
The cutting elements have one portion of the working surface which is treated to leach substantially all catalyst material from the interstices near the working surface of the PCD element in an acid etching process to a depth of greater than about 0.2 mm, in order to increase the wear resistance of the cutting elements. In particular, this provides a superhard polycrystalline diamond or diamond-like element with greatly improved wear resistance without loss of impact strength.
Each cutting element also has another surface which is not treated, such that some catalyzing material remains in the interstices, or, alternatively, the another surface is only partially treated, or at least less treated than the one portion of the working surface. In one embodiment, a gradual (continuous) change in the treatment is indicated. In this way, the treated, more wear-resistant portions cause the element to be self-sharpening.
Further disclosed arrangements include a treated surface and a surface which is not treated such that some catalyzing material remains in the interstices, and further include another surface which is only partially treated, or at least less treated than the treated surface.
Different arrangements of varied wear resistance on the front and side working surfaces of PCD cutting elements are also disclosed. Again, each has a treated surface and a surface which is not treated such that some catalyzing material remains in the interstices. The disclosed elements have two working surfaces (e.g. the PCD body end face and side wall) such that the varied wear resistance may be applied to either or both surfaces. Another surface which is only partially treated, or at least less treated than the treated surface, may also be included in place of portions of the untreated surface.
U.S. Pat. Nos. 5,517,589; 7,608,333; 7,740,673; and 7,754,333, and U.S. patent application Ser. Nos. 11/776,389 and 12/820,518, disclose various thermally stable diamond polycrystalline diamond constructions.
U.S. Pat. No. 5,120,327, issued to Diamant-Boart Stratabit (USA), Inc. and assigned to Halliburton Energy Services, Inc., discloses an carbide substrate and a diamond layer adhered to a surface of the substrate. That surface includes a plurality of spaced apart ridges forming grooves therebetween.
According to a first aspect of the present invention, there is provided a method of manufacturing a polycrystalline diamond (PCD) cutting element comprising: leaching a PCD body formed from diamond particles using a binder-catalyzing material so as to remove substantially all of the binder-catalyzing material from portions of a cutting surface of the PCD body, wherein the method involves identifying a portion of the cutting surface as a cutting area which, in use of the cutting element to cut material, is heated by the cutting action of the cutting element, and wherein leaching the PCD body includes performing a relatively deep leach in the portion of the cutting surface identified as the cutting area and performing a relatively shallow leach in at least the portion of the cutting surface surrounding the identified cutting area.
In embodiments of the invention, the portion of the cutting surface surrounding the identified cutting area is masked whilst performing the relatively deep leach.
In these or other embodiments of the invention, the relatively deep leach is performed before performing the relatively shallow leach.
In these or other embodiments of the invention, the relatively shallow leach is applied to substantially all of the cutting surface of the PCD body.
In these or other embodiments of the invention, substantially no leaching is performed at a central portion of the cutting surface.
In these or other embodiments of the invention, performing the relatively shallow leach includes performing the relatively shallow leach on a side surface of the PCD body which extends from the cutting surface.
In these or other embodiments of the invention, the PCD body is substantially cylindrical and the cutting surface is one of the end faces of the cylinder, and wherein the identified cutting area includes at least a portion of a cutting edge that extends around the cutting surface, between the cutting surface and the cylindrical side wall. Here, the cutting edge may be a chamfered edge between the cutting surface and the side wall.
In these or other embodiments of the invention, identifying a cutting area which, in use of the cutting element to cut material, is heated by the cutting action of the cutting element, includes identifying multiple areas which independently act as the cutting area in dependence on the orientation of the PCD cutting element in use; and leaching the PCD body includes performing a relatively deep leach in each of the multiple areas of the cutting surface identified as the cutting areas and performing a relatively shallow leach in at least the portions of the cutting surface surrounding each identified cutting area. Here, performing a relatively deep leach may include simultaneously leaching all of the multiple portions of the cutting surface identified as the cutting areas. Also, two or three or more of the multiple areas may be substantially identical and disposed with rotational symmetry about an axis of the PCD body, such that, in use of the cutting element held in a cutting tool, the PCD body can be rotated about the axis after a first of the two or three or more areas has independently acted as a cutting area and become worn down, so as to bring the worn first cutting area out of cutting orientation and to bring another of the two or three or more areas into the cutting orientation.
In these or other embodiments of the invention, the cutting element includes one or more indicia to indicate the position of the identified cutting area.
In these or other embodiments of the invention, the identified cutting area includes substantially all of the cutting edge, which extends substantially entirely around the cutting surface.
In these or other embodiments of the invention, leaching further involves performing leaching to different depths in a transition region between the portions being relatively deep-leached and the portions being relatively shallow-leached, to obtain a desired leaching-depth profile.
According to a second aspect of the present invention, there is provided a method of manufacturing a polycrystalline diamond (PCD) cutting element from a PCD body comprising a diamond matrix of intercrystalline bonded diamond particles, defining interstitial regions containing a binder-catalyzing material therein, the method comprising: removing substantially all binder-catalyzing material from a first surface region of the diamond matrix to a depth of not less than about 0.15 mm; and removing substantially all binder-catalyzing material from a second surface region of the diamond matrix that surrounds the first surface region to a depth of not less than about 0.01 mm and not more than about 0.12 mm, wherein the first surface region includes at least a portion of a cutting edge that extends around at least a portion of a cutting face of the PCD body.
In embodiments of the invention, removing substantially all binder-catalyzing material from the first surface region of the diamond matrix includes removing substantially all binder-catalyzing material to a depth of not less than about 0.18 mm, or not less than about 0.2 mm, or not less than about 0.22 mm.
In these or other embodiments of the invention, removing substantially all binder-catalyzing material from the second surface region of the diamond matrix includes removing substantially all binder-catalyzing material to a depth of not less than about 0.02 mm or not less than about 0.03 mm.
In these or other embodiments of the invention, removing substantially all binder-catalyzing material from the second surface region of the diamond matrix includes removing substantially all binder-catalyzing material to a depth of not more than about 0.1 mm, or not more than about 0.08 mm, or not more than about 0.05 mm.
In these or other embodiments of the invention, the binder-catalyzing material is removed by leaching, and wherein the second surface region of the diamond matrix is masked at a time when the first surface region is being leached.
In these or other embodiments of the invention, the second surface region includes at least a portion of a side surface of the PCD body, which side surface extends from the cutting face and meets the cutting face at the cutting edge. Here, the first surface region may include a portion of the side surface of the PCD body.
In these or other embodiments of the invention, the cutting edge is chamfered.
In these or other embodiments of the invention, the first surface region includes at least two or at least three separate regions which include respective portions of cutting edges extending respectively around at least two or at least three separate portions of the cutting face. Here, the cutting element may include one or more indicia to indicate the positions of the separate regions. Also, the separate regions may be substantially identical and disposed with rotational symmetry about an axis of the PCD body.
In these or other embodiments of the invention, the first surface region includes a cutting edge which extends substantially entirely around the cutting face.
In these or other embodiments of the invention, the PCD body is substantially cylindrical and the cutting face is one of the end faces of the cylinder.
In these or other embodiments of the invention, the second surface region includes substantially all of the cutting face apart from the first surface region.
In these or other embodiments of the invention, the second surface region does not include a central area of the cutting face.
According to a third aspect of the present invention, there is provided a drill bit comprising a cutting element manufactured in accordance with the first and/or second aspect of the invention.
According to a fourth aspect of the present invention, there is provided a polycrystalline diamond (PCD) cutting element comprising: a PCD body exhibiting a cutting face and defining a cutting edge around at least a portion of the cutting face, wherein the PCD body comprises a diamond matrix of intercrystalline bonded diamond particles defining interstitial regions containing a binder-catalyzing material, wherein a first region at the surface of the diamond matrix comprises substantially no binder-catalyzing material to a depth of not less than about 0.15 mm, said first region including at least a portion of said cutting edge, and wherein a second region at the surface of the diamond matrix surrounding said first region contains substantially no binder-catalyzing material to a depth of not less than about 0.01 mm and not more than about 0.12 mm.
In an embodiment of the invention, the first region at the surface of the diamond matrix comprises substantially no binder-catalyzing material to a depth of not less than about 0.18 mm, or not less than about 0.2 mm, or not less than about 0.22 mm.
In these or other embodiments of the invention, the second region at the surface of the diamond matrix contains substantially no binder-catalyzing material to a depth of not less than about 0.02 mm, or not less than about 0.03 mm.
In these or other embodiments of the invention, the second region at the surface of the diamond matrix contains substantially no binder-catalyzing material to a depth of not more than about 0.1 mm, or not more than about 0.08 mm, or not more than about 0.05 mm.
In these or other embodiments of the invention, the second region at the surface of the diamond matrix includes at least a portion of a side surface of the PCD body, which side surface extends from the cutting face and meets the cutting face at the cutting edge. Here, the first region at the surface of the diamond matrix includes a portion of the side surface of the PCD body.
In these or other embodiments of the invention, the cutting edge is chamfered.
In these or other embodiments of the invention, the first region at the surface of the diamond matrix includes at least two or at least three separate regions which include respective portions of cutting edges extending respectively around at least two or at least three separate portions of the cutting face. Here, the cutting element may include one or more indicia to indicate the positions of the separate regions. Also, the separate regions may be substantially identical and disposed with rotational symmetry about an axis of the PCD body.
In these or other embodiments of the invention, the first surface region includes a cutting edge which extends substantially entirely around the cutting face.
In these or other embodiments of the invention, the PCD body is substantially cylindrical and the cutting face is one of the end faces of the cylinder.
In these or other embodiments of the invention, the second region at the surface of the diamond matrix includes substantially all of the cutting face apart from the first region at the surface of the diamond matrix.
In these or other embodiments of the invention, the second region at the surface of the diamond matrix does not include a central area of the cutting face.
In these or other embodiments of the invention, a transition region exists between the first region at the surface of the diamond matrix and the second region at the surface of the diamond matrix, in which the depth to which substantially no binder-catalyzing material is contained substantially continuously varies according to a thermal stability depth profile.
According to a fifth aspect of the present invention, there is provided a method of leaching a polycrystalline diamond (PCD) body comprising: determining an operating temperature expected to be encountered at a working portion of a working surface of the PCD body; determining an isotherm for the temperature experienced in the PCD body if unleached and under application of the operating temperature at the working portion, wherein the isotherm is indicative of the depth to which a temperature will persist at which an unleached PCD body will experience thermal degradation; and setting a leaching profile for the PCD body which substantially corresponds to the isotherm in the region of the working portion.
An embodiment of the present invention further comprises: determining an updated isotherm for the temperature experienced in the PCD body if leached according to the set leaching profile and under application of the operating temperature at the working portion, wherein the isotherm is indicative of the depth to which the temperature, will persist at which unleached portions of the PCD body will experience thermal degradation; and adjusting the leaching profile by identifying differences between the updated isotherm and the set leaching profile, and adjusting the set leaching profile to reduce the leached depth in portions of the leaching profile deeper than the isotherm, whilst eliminating regions where the isotherm indicates that thermal degradation is likely to occur.
In these or other embodiments of the invention, adjusting the leaching profile includes adjusting the leaching depth in portions of the working surface other than the working portion so as to adjust the thermal conduction of heat through the PCD body and away from the working portion.
In these or other embodiments of the invention, the steps of determining an updated isotherm and adjusting the leaching profile are iteratively repeated for the adjusted leaching profile in place of the set leaching profile to minimise the leaching depth throughout the leaching profile whilst eliminating regions where thermal degradation is likely to occur.
In these or other embodiments of the invention, determining an operating temperature expected to be encountered at the working portion of the working surface of the PCD body includes simulating a drilling operation using a drill bit in which the PCD body is employed as a cutting element of the drill bit.
In alternative such embodiments according to the invention, determining an isotherm for the temperature experienced in the PCD body if unleached and under application of the operating temperature at the working portion further includes determining the isotherm for the PCD body in a partially-worn state in which material has been worn away at the working portion of the working surface of the PCD body relative to an unworn PCD body; and setting a leaching profile for the PCD body which substantially corresponds to the isotherm in the region of the working portion includes setting a leaching profile for the unworn PCD body based on the isotherm determined for a PCD body in the partially-worn state.
In these or other embodiments of the invention, the leaching profile for the PCD body is further set in dependence on the rake angle of the cutting element on the drill bit.
According to a sixth aspect of the present invention, there is provided a drill bit comprising a PCD body leached in accordance with the fifth aspect of the present invention.
According to a seventh aspect of the present invention, there is provided a polycrystalline diamond (PCD) cutting element having distinct leached cutting areas at two or three or more separate locations provided offset from an axis of the cutting element so as to be rotationally displaced from one another around said axis such that, by adjusting the rotational orientation of the cutting element about the axis when fixing the cutting element to a cutting tool, each of the two or three or more cutting areas can independently be brought into a cutting position in which they perform cutting during use of the cutting tool.
An embodiment of the present invention further comprises one or more indicia indicative of the positions of the two or three or more cutting areas.
In these or other embodiments of the invention, the cutting areas can be used successively in turn for cutting by adjusting the rotational orientation of the cutting element in the cutter after use, so as to replace a worn cutting area of the cutting element by an unworn cutting area at the cutting position.
In these or other embodiments of the invention, the leached cutting areas each include a portion of an edge of a cutting face of the PCD cutting element. Here, the respective portions are portions of edges or the edge of the same cutting face.
According to an eighth aspect of the present invention, there is provided a polycrystalline diamond (PCD) cutting element having a cutting face at an end thereof, the cutting face defining an edge extending substantially entirely around the cutting face, wherein one or more portions of the edge are leached to form a cutting edge and wherein the centre of the cutting face is unleached.
In an embodiment of the present invention, substantially the entire edge around the cutting face is leached to form a cutting edge.
In these or other embodiments of the invention, the edge is chamfered.
In these or other embodiments of the invention, the leaching extends onto at least a portion of a side wall of the cutting element.
In these or other embodiments of the invention, the cutting element is substantially cylindrical. Here, the cutting element is substantially circular in cross-section.
In these or other embodiments of the invention, the PCD element includes a matrix of intercrystalline bonded diamond particles defining interstitial regions containing a binder-catalyzing material therein, and wherein substantially all binder-catalyzing material has been removed to a predetermined depth from leached parts of the matrix.
According to a ninth aspect of the present invention, there is provided a method of manufacturing a polycrystalline diamond (PCD) cutting element comprising: masking substantially all of the cutting element except for cutting areas at two or three or more separate locations provided offset form an axis of the cutting element so as to be rotationally displaced from one another around said axis; and leaching the masked cutting element to leach the cutting areas.
According to a tenth aspect of the present invention, there is provided a method of manufacturing a polycrystalline diamond (PCD) cutting element having a cutting face at an end thereof, the cutting face defining an edge extending substantially entirely around the cutting face, the method comprising: masking at least a central portion of the cutting face; and leaching the masked cutting element to leach one or more portions of the edge to form a cutting edge or cutting edges, with the centre of the cutting face masked from being leached.
In embodiments of the ninth or tenth aspect of the invention, the PCD cutting element is unleached prior to masking.
These or other embodiments of the ninth and tenth aspects of the invention further comprise removing the mask and again leaching the PCD cutting element. Here, the method may further include, after the mask is removed and prior to again leaching the PCD cutting element, masking the PCD cutting element again with a different masking pattern.
In these or other embodiments of the ninth and tenth aspects of the invention, the method includes leaching the PCD cutting element a total of 3 or more times, with a different masking pattern being applied to mask or expose one or more different portions of the PCD cutting element each time, wherein one of the masking patterns may comprise applying substantially no masking to the surface of the diamond matrix of the PCD cutting element.
To enable a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:—
Before referring specifically to the drawings, some general characteristics of PCD elements and PCD cutting elements (also called polycrystalline diamond cutters, or PDCs) should be noted.
Polycrystalline diamond and polycrystalline diamond-like elements are collectively called PCD elements for the purposes of this specification. These elements are formed with a binder-catalyzing material in a high-temperature, high-pressure (HTHP) process. The PCD element has a plurality of partially bonded diamond or diamond-like crystals forming a continuous diamond matrix table or body. It is the binder-catalyzing material that allows the intercrystalline bonds to be formed between adjacent diamond crystals at the relatively low pressures and temperatures obtainable in a press suitable for commercial production.
The diamond matrix body may have a diamond volume density greater than 85%. During the process, interstices among the diamond crystals form into a continuous interstitial matrix containing the binder-catalyzing material. The diamond matrix body has a working surface, which for polycrystalline diamond cutting elements (also known as polycrystalline diamond cutters, or PDCs) is also known as the cutting surface. One or more portions of the interstitial matrix in the PCD body adjacent to and extending from the working surface are substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.
Because the portion of the PCD body adjacent to the working surface is substantially free of the binder-catalyzing material, the deleterious effects of the binder-catalyzing material are substantially decreased, and thermal degradation of the working surface due to the presence of the catalyzing material can be effectively eliminated. The result is a PCD element that is resistive to thermal degradation for surface generated temperatures above 750 degrees C., up to about 1200 degrees C., while maintaining the toughness, convenience of manufacture, and bonding ability of PDC elements containing the binder-catalyzing material throughout the interstitial matrix. This translates to higher wear resistance in cutting applications. These benefits can be gained without loss of impact strength in the elements.
The diamond matrix table (PCD body) is preferably integrally bonded to a substrate containing the binder-catalyzing material during the HTHP process. Preferably, the layer of interstitial regions where the PCD body contacts the substrate contains binder-catalyzing material and has an average thickness greater than 0.15 mm, in order to secure the diamond matrix table to the substrate.
The substrate is preferably of less hard material than the PCD body, usually cemented tungsten carbide or another metallic material, but use of a substrate is not required.
Typically, a PCD cutting element has a body in the form of a circular tablet having a thin front facing table presenting a cutting face of diamond or diamond-like (PCD) material, bonded in a high-pressure high-temperature press to a substrate of less hard material such as cemented tungsten carbide or other metallic material. The PCD cutting element is typically preformed and then bonded onto a generally cylindrical carrier which is also formed from cemented tungsten carbide.
In application to a fixed blade rotary drill bit, the cylindrical carrier is received within a correspondingly shaped socket or recess in the blade. The carrier will usually be brazed or shrink-fitted into the socket.
In general, the average diamond volume density in the body of the PCD element should range from about 85% to about 99%. Average diamond volume density may also be referred to as the diamond fraction by volume. The high diamond volume density can be achieved by using diamond crystals with a range of particle sizes, with an average particle size ranging from about 15 to about 60 microns, with the preferred range on the order of 15-25 microns. Typically, the diamond mixture may comprise 1% to 60% diamond crystals in the about 1-15 micron range, 20% to 40% diamond crystals in the 25-40 micron range, and 20% to 40% diamond crystals in the 50-80 micron diameter range, although numerous other size ranges and percentages may be use. A mixture of large and small diamond crystals may allow the diamond crystals to have relatively high percentages of their outer surface areas dedicated to diamond-to-diamond bonding, often approaching 95%, contributing to a relatively high apparent abrasion resistance.
There are many methods for removing or depleting the catalyzing material from the interstices. In one common example, the catalyzing material is cobalt or another iron group material (Group VIII metal), and the method of removing the catalyzing material is to leach it from the interstices near the working surface of the PCD element in an acid etching process. It is also possible that the method of removing the catalyzing material from near the surface may be by electrical discharge, or another electrical or galvanic process, or by evaporation.
As previously described, there are two modes of thermal degradation of the PCD today known to be caused by the catalyzing material. The first mode of thermal degradation begins at temperatures as low as about 400 degrees C. and is due to differential thermal expansion between the binder-catalyzing material in the interstitial matrix and the crystals in the intercrystalline bonded diamond matrix. Upon sufficient heating, the attendant differential expansion may cause the diamond-to-diamond bonding to rupture, such that cracks and chips may occur.
The second mode of thermal degradation begins at temperatures of about 750 degrees C. This mode is caused by the catalyzing ability of the binder-catalyzing material contacting the diamond crystals causing the crystals to graphitize as the temperature exceeds about 750 degrees C. As the crystals graphitize, they undergo a phase change accompanied by a large volume increase, which may result in the PCD body cracking and dis-bonding from the substrate. Even a coating of a few microns of the catalyzing material on the surfaces of the diamond crystals can cause this mode of thermal degradation to occur.
It will therefore be appreciated that, for maximum benefit, the catalyzing material must be removed both from the interstices among the diamond crystals and from the surfaces of the diamond crystals as well. If the catalyzing material is removed from both the surfaces of the diamond crystals and from the interstices between them, the onset of thermal degradation for the diamond crystals in that region should not occur until approaching 1200 degrees C.
It should be apparent that it is more difficult to remove the catalyzing material from the surfaces of the diamond crystals than from the interstice. For this reason, depending upon the manner in which the catalyzing material is depleted, to be effective in reducing thermal degradation, the depth of depletion of the catalyzing material from the working surface may vary depending upon the method used for depleting the catalyzing material.
Indeed, in some applications, improvement of the thermal threshold to above 400 degrees C. but less than 750 degrees C. is adequate, and therefore a less intense catalyzing material depletion process is permissible. As a consequence, it will be appreciated that there are numerous combinations of catalyzing material depletion methods which could be applied to achieve the level of catalyzing material depletion required for a specific application.
In this specification, when the term “substantially free” is used to refer to binder-catalyzing material having been removed from the interstices, the interstitial matrix, or a volume of the PCD body, it should be understood that many, if not all, the surfaces of the adjacent crystals in the intercrystalline bonded diamond matrix may still have a coating of the binder-catalyzing material.
To be effective, the binder-catalyzing material has to be removed at the point of heat generation at the working surface to a depth sufficient to allow the temperature in the regions of the PCD body where the catalyzing material is present to be kept below the local thermal degradation temperature. Improved thermal degradation resistance improves wear rates because the thermally stable intercrystalline bonded diamond matrix is able to retain its structural integrity and so its mechanical strength.
Diamond is known as a thermal conductor. If a friction event at the working surface causes a sudden, extreme heat input, the bonded diamond crystals will conduct the heat in all directions away from the event. This can permit an extremely high temperature gradient to be obtained through the intercrystalline bonded diamond material, for example of up to 1000 degrees C. per mm, or higher. Of course, the actual temperature gradient experienced will vary depending upon the diamond crystal size and the amount of inter-crystal bonding. However, it is unclear if such a large thermal gradient actually exists.
One particularly useful application for the PCD elements herein disclosed is as cutting elements, or PDCs (polycrystalline diamond cutters). The working surface of the PCD cutting elements may be a top working surface (endface) and/or a peripheral working surface. The PCD cutting elements shown in the accompanying drawings are ones that may typically be used in fixed cutter type rotary drill bits. Although not illustrated, another type of PCD cutting element is shaped as a dome. This type of PCD cutting element can have an extended base for insertion into sockets in a rolling cutter drill bit or in the bodies of either fixed-cutter or rolling-cone types of rotary drill bits.
Taking into account the foregoing general technical considerations and details relating to PCD elements, a more specific description will now be made, in particular with reference to the accompanying drawings, in which embodiments of the present invention are shown, as well as examples useful for understanding the invention.
It should be appreciated that the drawings are principally schematic in nature, intended to convey the underlying technology of the invention without necessarily expressing the relative sizes, shapes and dimensions of the components illustrated. In particular, certain features may be shown enlarged or exaggerated relative to other features, merely for illustrative purposes.
Where reference is made herein to the depth to which a PCD element has been leached in any portion, region or area, the depth shall be taken to be the distance from the boundary between the leached and unleached portions within the PCD element to the nearest surface of the PCD element from which the leaching took place. In the majority of cases, this will correspond to the perpendicular depth as measured from the surface from which leaching took place.
As explained above, the process of leaching can lead to the leached portion of the intercrystalline bonded diamond matrix becoming brittle, and so less impact resistant. There therefore remains a trade off between the gains in thermal stability achieved by, leaching to a greater depth, and the attendant loss of toughness and impact resistance associated with this.
At the same time, the time, effort and attendant cost associated with the manufacture of the PCD cutting elements has to be weighed against any obtainable effective increase in performance, not only in terms of the performance of the PCD cutting element itself in terms of wear resistance and impact strength but also in terms of the performance of the drilling bit in which the PCD cutting element is contained.
To date, commercially available PCD cutting elements are manufactured almost exclusively by performing a uniform leaching process to the entire outer surface of the PCD body of the cutting element. As such, the existing technology still struggles with the act of balancing between the impact strength and wear resistance or thermal integrity of the PCD cutting element.
A driving factor has therefore been to reduce any trade off in impact strength by minimizing the amount of depletion of the binder-catalyzing material from the interstitial regions in the intercrystalline bonded diamond matrix of the PCD bodies, whilst at the same time maintaining the resistance to thermal degradation achievable with existing leached PCD cutters. This is primarily to be achieved by restricting the application of the leaching process to areas of the PCD cutting elements where heat is known to be generated through use of the cutting elements in the cutting operation. In particular, by eliminating leaching from areas of the cutting elements where there is little or no contact between the cutting element and the material being cut, the toughness and impact strength of the PCD cutting element as a whole can be improved.
Furthermore, by appropriately designing the leaching profile at the areas where cutting and wear is known to take place, the leaching profile can be adapted to accommodate a greater degree of wear, so as to allow the cutting element to be used for longer periods in effectively cutting through material, thereby dramatically increasing the drilling performance of drill bits incorporating the cutting element. Drill bits containing cutting elements of this character are able to drill continuously for longer periods of time, and for further distances, before the cutting elements become blunted and the drill bit has to be tripped out and exchanged. Cutting elements formed in, this manner are also more resistant to cracking or fracture and so are less susceptible to failure during a drilling operation, improving the reliability of a drill bit incorporating the cutting elements.
Referring to
Turning to
The crystal microstructure of the PCD body is illustrated schematically in
In the example shown in
As seen in
Turning to
In known leaching processes, the PCD cutting element 10 is essentially submerged in a bath of leaching acid, i.e. in an etching process, which serves to deplete the binder-catalyzing material 214 from the surface regions of the PCD cutting element. The depth to which depletion of the binder-catalyzing material 214 is achieved is substantially dependent on both the strength and type of acid being used and the length of time for which the leaching process is carried out.
In order to prevent unwanted areas of the PCD cutting element 10 from being leached by the acid, a masking material 40 is applied to those areas of the PCD cutting element where leaching is to be prevented. However, since applying the masking material 40 is a time-consuming, labour-intensive and, at least partially, manual task, existing commercial processes tend to simply mask sidewall areas of the PCD cutting elements according to a simple and substantially uniform masking pattern.
Turning to
In this way, a significant proportion of the cutting surface 22, and the PCD body 20 as a whole, remains unleached, increasing the impact resistance of the PCD cutting body 20.
Additionally, it is believed that the leached portion 24 will have a higher impact resistance than leached surfaces of an equivalent depth in prior art PCD cutting elements, as the unleached portions of the PCD cutting body 20 serve to add structural strength, toughness and integrity to the smaller leached portion 24.
It should be noted that the masking pattern shown in
In this connection, it is noted that for fixed blade rotary drill bits 1, such as shown in
Once the area of impact and frictional contact of the cutting element 10 with the formation material being cut is known, the temperatures likely to be generated at the surface of the cutting element 10 in use of the drill bit 1 can be determined, and the extent and depth of the portion 24 to be leached can be calculated.
The designer of such a selectively leached cutting element 10 has the option to tailor the leaching pattern to a single mounting position of the cutter 10 on the drill bit 1, in which case a different leaching pattern may, in principle, be provided for each cutter location of the drill bit 1 and a specifically tailored PCD cutting element 10 produced for each cutter position of the drill bit 1. Alternatively, the designer may select a more robust design, in which the leached area 24 is not entirely minimised for a single position of the cutting element 10 on the drill bit 1, but is expanded so as to be robust and suited to use at different cutter positions, although with the leached portion 24 of the PCD cutting element 10 suitably rotated to be orientated into a cutting orientation when mounted in any of the respective cutting positions on the drill bit 1. In either case, the leaching profile determined for the PCD cutting element 10 may be adjusted according to the rake angle at which the PCD cutting element 10 may be used, and the associated wear pattern experienced by the PCD cutting element 10 in operation, as discussed further below.
Turning to
As another way to avoid orientation errors when mounting the PCD cutting elements 10 disclosed herein, which is applicable to any of the embodiments of the present invention, an alignment mark or suitable alignment feature may be provided on the PCD cutting element, for example at a position on, or at various position around, the circumference of the substrate 30, in order to indicate the orientation of the leached cutting portion(s) 24 of the PCD body 20 when mounting the PCD cutting element 10 a drill bit. Suitable alignment features may, in fact, prevent mounting of the PCD cutting element 10 at an incorrect orientation, for example by providing a groove on the cutting element 10 and an inter-engaging ridge or notch projecting in the socket of the drill bit, such that the PCD cutting element 10 may only be installed in the socket at the correct orientation by engaging the ridge in the groove. In other cases, a simple mark, such as a line, a colored dot or an alphanumeric character, for example, may provide a visual indicator by which the person installing the PCD cutting element 10 into the socket of the drill bit 1 can correctly orient the cutting element 10.
It is additionally contemplated that, in the embodiment of
It is also noted that, once one edge portion 24 of the PCD cutting element of
As mentioned above, for PCD cutting elements 10 used in fixed blade rotary drill bits with the cutting face 22 facing substantially in the direction of rotation of the blade 5 of the drill bit 1 to which the cutting element 10 is mounted, the face 22 may be designated as the cutting face yet a substantial portion of the cutting action may be achieved at the edge 23. Nevertheless, as far as the terminology in the present specification is concerned, the cutting face 22 is taken to be the end face 22 of the PCD cutting element 10, and the chamfered edge is merely designated as an edge 23.
The chamfered edge 23 can provide improved structural integrity and impact resistance at the edge of the cutting face 22, thus improving the robustness of the PCD cutting element 10 and its resistance to brittle fracture. In particular, the generation of stress concentrations at the edge corner is mitigated.
It will be appreciated that the size and extent of the chamfer applied to the edge 23 is exaggerated in
Turning to
In the embodiment of
Turning to
In the embodiment of
As explained above, in order to obtain thermal stability in the PCD cutting elements, the leached area 24 must be made sufficiently deep so that heat generated by the cutting action as the cutting element 10 scrapes and gouges the formation being drilled during use of the drill bit 1 does not cause the temperature to exceed the degradation temperature for the PCD body 20 in the regions 28 of the polycrystalline bonded diamond matrix 200 which contain the binder-catalyzing material 214.
With the embodiment of
However, with the embodiment of
An additional, coincidental benefit is that, as the cutting area is worn down by use of the PCD cutting element 10 to drill a subterranean formation, the erosion and wear of the leached portion 24 of the PCD cutting element 10 will merely bring a further leached portion of the PCD body 20 into contact with the formation, such that the desired wear resistance and hardness is maintained for a longer period of time, enabling the PCD cutting element 10 to continue to provide a cutting function even after substantial wear has occurred.
In this regard, it is also noted that, due to the relatively small surface area allocated for each of the cutting areas of the embodiments disclosed in the present specification, the deep leached portions 24 may necessarily have to be leached to a greater depth than was necessary for the uniformly leached cutters known in the past. This is not necessarily an entirely detrimental requirement, since, once again, the deeper leaching of the areas 24 means that a leached portion of the PCD cutting element remains in contact with the material being cut even after substantial wear. Furthermore, it is believed that, due to the deeply leached portion 24 extending into a non-leached portion 28 of the PCD body 20, the surrounding non leached portion 28 immediately adjacent to the deeply leached portion 24 helps to provide structural integrity and support; thereby maintaining the impact strength of the PCD cutting element, even when the deep leached area 24 is leached to a depth at which, in the prior art, brittle fracture or impact failure would have been expected to occur. By combining the deeply leached portion 24 of
In regard to both the embodiments of
Turning to
Referring back to
In general, in the foregoing, and in the present specification throughout, leaching may be classified as deep leaching if the leached depth is greater than 100 microns, and as shallow leaching if the leached depth is less than 100 microns. It is contemplated that the leaching depth D for a uniform leaching profile would be of the order of about 100 to 500 microns. For embodiments having relatively deep-leached areas and relatively shallow-leached areas, it is contemplated that the leaching depth D in a shallow-leached area would be about 120 microns or less, but not less than 10 microns; and the leaching depth D in a deep-leached area would be 150 microns or more. As may be appropriate to the particular embodiment, the leaching depth in deep-leached areas may be 100 microns or more, 150 microns or more, 180 microns or more, or 200 microns or more, or 220 microns or more, but typically less than 500 microns. The leaching depth in shallow-leached areas may be 120 microns or less, 100 microns or less, 80 microns or less, or 50 microns or less. The leaching depth in shallow leached areas may be 10 microns or more, 20 microns or more, or 30 microns or more.
It is, additionally, contemplated that, in order to obtain the desired hardness and corrosion resistance at the extreme surfaces of the PCD body 20, a shallow leach would in many cases be desirable across substantially the entire surface of the PCD body 20. In the process of
In general, it may be preferable to perform the leaching steps needed on the largest, surrounding areas 26 of the PCD body 20 first, as this obviates the need to remove the masking material 40 prior to a subsequent leaching step. This not only potentially reduces the labour involved in masking the relevant areas of the PCD body 20, but also ensures that there is no chance for unremoved masking material 40 to remain, for example, in interstices 212 of the diamond matrix 200, which could interfere with a subsequent leaching process in that area of the PCD body 20.
In the process shown in
It will be appreciated that, although the processes presented in
Of course, more or fewer steps of masking and/or leaching may be performed according to the leaching profile sought to be obtained.
As briefly discussed above, the desired leaching profile may be determined based on a number of different considerations, for example depending on whether a very application-specific PCD cutting element is desired or one which is more robust and useful for installation at different cutting positions on the drill bit.
One factor to consider is the thermal profile resulting from heat generated at the surface of the PCD cutting element 10 during use in drilling a subterranean formation. This heat generation can be modelled, or measured, as a thermal event. The temperature profile resulting from that thermal event can then be determined, to identify the depth and extent to which temperatures at or exceeding the degradation temperature (the temperature at which thermal degradation of the PCD body takes place) is experienced. In one method for setting the leaching profile, the depth of the leaching profile may be set to substantially correspond to the depth of an isotherm of the temperature profile, such as the degradation temperature isotherm, at least in the region surrounding the point of heat generation at the surface. Of course, a safety margin may be allowed by incrementally increasing the leaching depth or by using an isotherm with a somewhat lower temperature than the degradation temperature.
Referring to
According to another similar method, account is also to be taken of the effect of wear during use of the PCD cutting element 10. Such a method is shown in
The depth Dmin is typically set as a matter of judgement by the designer, but should be a minimum depth to allow the surface of the diamond matrix to effectively conduct heat laterally away from the point of heat generation and discharge that heat out of the PCD cutting element. This makes use of the beneficial thermal conductivity properties of the intercrystalline bonded diamond matrix.
In
Of course, PCD cutting elements designed in this way are then specifically configured for use at a given rake angle. A more robust design can be obtained by superimposing a series of overlapping leaching profiles, to accommodate wear at different rake angles.
Although the examples here show the wear, thermal and leaching profiles in two-dimensional form, three-dimensional profiles will normally be of greater interest. These may be computed using existing CAD programmes and modelling techniques, such as finite element analysis.
Indeed, it will be clear that the thermal materials properties of the PCD body change in dependence of whether binder-catalyzing material is contained within the interstices of the diamond matrix or not. Once an initial leaching profile has been specified, that profile can then be tested to see whether the thermal profile of a PCD cutting element exhibiting that leaching profile is substantially different from the thermal profile determined for the unleached PCD cutting element, and differences may be reduced by adjusting the leaching profile to move it closer to the Td line of modified thermal profile. If differences persist, an iterative optimisation routine may be run to converge to a design where the thermal profile and leaching profile agree.
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| Publishing Document | Publishing Date | Country | Kind |
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| WO2012/145586 | 10/26/2012 | WO | A |
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