Cutting tool insert

[0001] The present invention relates to a polycrystalline diamond abrasive element according to the preamble of claim 1 and known for example from WO2004 / 106003. These elements are used as instrument inserts, and in particular as inserts of cutting tools used for drilling and coring holes in underground formations.

[0002] A commonly used cutting tool insert used in core cutters comprising a polycrystalline diamond (PCD) layer bonded to a cemented carbide substrate. The PCD layer forms the working surface and cutting edge extending around part of the periphery of the working surface.

[0003] Polycrystalline diamond, also called diamond abrasive compacts, is in the form of a mass of diamond particles containing a significant amount of direct diamond diamond bonds. Polycrystalline diamond usually contains a second phase that contains a diamond catalyst / solvent such as cobalt, nickel, iron or an alloy containing one or more such metals.

[0004] During the drilling operation, the cutting tool insert is subjected to high loads and high temperatures, these conditions occur at various stages of its life. In the early stages of drilling, when the sharp edge of the insert contacts the underground formation, the cutting tool is subjected to high contact pressure. This results in the possibility of initiating a number of processes related to cracking, for example fatigue cracking.

[0005] As the cutting edge of the insert wears out, the contact pressure decreases and is usually too low to cause high energy damage. However, this pressure can cause the propagation of cracks initiated under high contact pressure; it can even potentially cause damage to this type of peeling.

[0006] In the drilling industry, the quality of the PCD milling cutter is determined both by the ability to achieve high penetration speeds in increasingly demanding environments, as well as by maintaining good condition after drilling (and therefore reusability). In all drilling operations, the milling cutters can be subject to wear that is a combination of even wear type abrasive and wear type peeling / chipping. An even wear mode is desirable because it provides the greatest benefits associated with the use of highly wear-resistant PCD material, while peel or chipping wear is undesirable. Even a very small crack of this type can have an adverse effect on the durability and performance of the cutter.

[0007] In the case of wear consisting of peeling, the cutting efficiency can be drastically reduced, because the penetration rate of the drill bit in the formation is reduced. After the start of chipping, the damage to the sheets increases continuously, which is the result of an increase in the normal force that is required to obtain a given depth of cut. The occurrence of cutter damage and reduction of the drill bit penetration rate is therefore associated with an increase in drill load, which can quickly lead to further damage and finally to complete destruction of the cracked cutting element.

[0008] When optimizing the performance of a PCD cutter, an increase in wear resistance (to obtain a longer cutter life) is usually achieved by manipulating variables such as average diamond grain size, overall catalyst / solvent content, diamond density and similar values. However, the production of PCD material that is more resistant to wear usually results in an increase in fragility or susceptibility to cracking. PCD components designed for increased wear resistance therefore tend to exhibit low impact strength and reduced peeling resistance. This compromise between impact resistance and wear resistance means that the development of optimized PCD structures is inherently self-limiting, especially for demanding applications. [0009] The possibility of eliminating or controlling the phenomenon of chipping more wear-resistant PCD would allow fuller use of the potentially better performance of this type of PCD cutters.

[0010] Modifying edge geometry by chamfering has previously been seen as a promising approach to reduce the effect of peeling. It has been shown (US 5437343 and US 5016718) that pre-chamfering or rounding of the cutting edge of a PCD sheet causes a significant reduction in the flaking tendency of the diamond cutting sheet. This rounding, by increasing the contact surface, reduces the phenomenon of initial high stresses arising at high load when the insert contacts the ground formation. The chamfered edge, however, is subject to wear when using the PCD cutter, eventually achieving a state where the chamfer no longer occurs. At this point, the cutting edge resistance to peeling wear is reduced to the level of unprotected / non-phased PCD material.

[0011] US 5135061 suggests that the phenomenon of peeling can be controlled by producing a milling cutter having a cutting surface in the form of a layer of PCD material with less wear resistance than the underlying PCD material (s), which reduces the tendency to peeling. . Higher wear of the layer less resistant to wear in the area of ​​the cutting edge ensures obtaining a rounded edge of the cutting element in the place of its contact with the formation. The cutting edge rounding obtained with this invention therefore provides a similar peeling prevention effect to chamfering. The advantages of this approach may be much smaller than the technical difficulties associated with obtaining in situ a satisfactorily thin layer less resistant to wear during the synthesis process. (The permanent and controlled operation of this anti-peeling layer is obviously very dependent on the geometry obtained.) In addition, the reduced wear resistance of the top layer can also begin to affect the overall wear resistance of the milling cutter, resulting in faster blunting of the cutting edge and lower than optimal performance.

[0012] JP 59119500 discloses the improvement of the performance of sintered PCD materials after chemical working surface treatment. During this treatment, the catalyst / solvent matrix is ​​dissolved and removed in the area immediately adjacent to the working surface. The invention discloses an increase in the thermal resistance of the PCD material in the region of matrix removal, which did not reduce the strength of the sintered diamond.

[0013] A cutting element has recently been introduced on the market that supposedly has increased wear resistance without showing reduced impact resistance. The production and behavior of such milling cutters is described in US Patent Nos. 6,544,308 and 6,562,462. The PCD cutting element is characterized, inter alia, by having an area adjacent to the cutting surface in which substantially no catalytic material is present. The increase in performance obtained with these cutters is attributed to the increased wear resistance of the PCD located in this area, while the removal of catalyzing material results in a slower deterioration in quality due to temperatures occurring when the cutter is used.

[0014] Removal of the catalyst / solvent in this area results in a significant reduction in the occurrence of very harmful damage consisting of peeling of the front edge and damage of the type of flaking of the back edge, which is caused by the characteristic lamellar cracking occurring in this area, can also have a significant impact on performance. The stresses in the rear edge area are not as high as those of the front edge, however, cracking in this area may result in significant material losses and hence reduced milling performance.

[0015] US 6562462 discloses a super-hard PCD or diamond-like material that is made using a process involving the use of a binding-catalysing material carried out under high temperature and high pressure (HTHP) conditions. The PCD element contains many partially bound diamonds or diamond-like crystals that form a continuous body in the form of a diamond matrix with a diamond volume density greater than 85%. The spacing between the diamond crystals form a continuous interstitial matrix containing the catalysing material. When the HTTP process is carried out, a diamond matrix pane is created that is inseparably bonded to the substrate containing the catalysing material. The diamond matrix body has a working surface, the portion of the interstitial matrix located in the body adjacent to the working surface essentially free of catalysing material, and the remaining portion of the interstitial matrix containing catalyzing material. Usually, less than about 70% of the body of the diamond matrix pane is substantially free of catalysing material.

SUMMARY OF THE INVENTION [0016] According to the present invention, a polycrystalline diamond abrasive element is provided, in particular a cutting element, comprising a polycrystalline diamond layer, preferably a high quality diamond layer, associated with a substrate, in particular a cemented carbide substrate, along a contact surface, wherein the polycrystalline diamond layer has a working surface on the opposite side from the contact surface and an outer edge surface between the working surface and the contact surface, wherein the polycrystalline diamond abrasive element is characterized by having an annular region adjacent the edge surface extending away from the work surface, the annular region or part thereof is poor in catalysing material.

[0017] The polycrystalline diamond layer preferably comprises an area, usually a layer, adjacent to the working surface and also poor in catalysing material.

[0018] As a result, the preferred polycrystalline diamond layer comprises an annular area forming a full or intermittent ring that extends away from the working surface, and an area adjacent to the working surface that is poor in catalysing material, so that When used, as the signs of wear appear, both the front edge and the rear edge are in an area poor in catalysing material.

[0019] The polycrystalline diamond abrasive is preferably as described in published international patent applications WO 2004/106003 and WO 2004/106004.

[0020] The polycrystalline diamond layer has an area adjacent the edge surface that is poor in catalysing material. This area extends transversely into the polycrystalline diamond from the edge surface generally to a depth of about 30 μm to about 500 μm. This area also extends from the edge of the working surface towards the contact surface to a depth of at least half the total thickness of the polycrystalline diamond layer, but ends at a distance of at least about 500 μm from the contact surface.

[0021] The polycrystalline diamond layer preferably further has an area adjacent the working surface that is poor in catalysing material. There is essentially no catalyst material in this area. This area extends deep into the polycrystalline diamond from the working surface generally to a depth of only about 30 μm to no more than about 500 μm.

[0022] Polycrystalline diamond also has a region rich in catalysing material. The catalysing material is a sintering agent used in the manufacture of the polycrystalline diamond layer. It is possible to use any diamond catalyzing material known in the art. Preferred catalyst materials are transition metals from Group VIII, such as cobalt or nickel. The area rich in catalysing material usually has a contact surface with the area poor in catalysing material and extends to the contact surface with the ground.

[0023] The area rich in catalysing material alone may contain more than one area. These areas may differ in average particle size as well as chemical composition. If such areas are used, they are usually located in planes parallel to the working surface of the polycrystalline diamond layer.

[0024] In a preferred structure of the invention, the areas poor in catalytic material form a structure resembling a cap covering an area rich in catalytic material or part thereof.

[0025] Another aspect of the invention relates to a method for producing the abovementioned PCD abrasive element, comprising the steps of forming an unbound assembly by providing a substrate that may have a non-flat contact surface, placing a mass containing diamond particles on the substrate, wherein the mass comprising diamond particles is preferably selected from in such a way as to ensure that high-grade polycrystalline diamond is obtained, and providing a source of catalysing material for the diamond particles, subjecting the unbound assembly to conditions of elevated temperature and pressure suitable to form a polycrystalline diamond layer from the mass containing the diamond particles, such layer being associated with the substrate, and removing the catalyzing material from the respective areas of the polycrystalline layer of diamond adjacent its working and peripheral surfaces, respectively.

[0026] The catalyst material is preferably removed to a depth of at least half the total thickness of the polycrystalline diamond layer.

[0027] The substrate is usually in the form of a cemented carbide substrate. The source of catalyzing material is usually a cemented carbide substrate. It is possible to mix some amount of additional catalytic material with the diamond particles.

[0028] The catalyzing material is removed from regions of the polycrystalline diamond layer adjacent to its exposed surfaces. These surfaces are generally located on the opposite side of the polycrystalline layer from the substrate, providing a working surface of the polycrystalline diamond layer, and the edge surface extending between the working surface and the substrate. Removal of the catalysing material can be carried out by methods known in the art, for example by electrolytic etching techniques, acid leaching or by evaporation.

[0029] The catalyst material is usually removed by acid washing. In order to obtain a so-called broken ring poor in catalysing material, it is possible to use an acid-resistant agent, which allows washing to be carried out using a mask.

[0030] The conditions of elevated temperature and pressure necessary to form a polycrystalline diamond layer from the mass of diamond particles are well known in the art. Such conditions are usually a pressure in the range of 4 to 8 GPa and a temperature in the range of 1300 ° C to 1700 ° C.

[0031] According to the invention, there is further provided a rotary core bit comprising a plurality of cutting tools, essentially all of which are in the form of the PCD abrasive elements described above.

[0032] The invention also extends to a method of reducing, preferably eliminating, peeling and / or chipping abrasive from a polycrystalline diamond susceptible to such wear, including the step of removing the catalysing material from the areas of the polycrystalline diamond layer adjacent to both exposed surfaces.

[0033] It has been found that the PCD abrasives according to the invention exhibit significantly better wear characteristics than the PCD abrasives known in the art as a result of controlling components of wear by peeling and chipping.

BRIEF DESCRIPTION OF THE DRAWINGS [0034] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a preferred embodiment of a polycrystalline diamond abrasive according to the invention; and

Fig. 2 is a side cross-sectional view taken along line 2-2 of the polycrystalline diamond abrasive element.

DETAILED DESCRIPTION OF THE INVENTION [0035] The polycrystalline diamond abrasive element according to the invention finds use especially as a cutting element in core cutters. It has been found that in this application it exhibits excellent wear resistance and impact resistance, while not showing a tendency to peeling and chipping, either at the front edge or at the rear edge of a typical trace of wear. These properties enable its effective use in drilling and reaming of underground formations with high compressive strength.

[0036] Referring to Figures 1 and 2 in the accompanying drawings, the cutting element 10 has a crystalline diamond layer 12 associated with the substrate 14. The crystalline diamond layer has an upper working surface 16 around which there is an edge cutting edge 18 and an edge surface 20.

[0037] The post-crystalline diamond layer 12 comprises respective areas 22, 24 poor in catalyst material and region 26 rich in catalyst material. The areas 22, 24 poor in catalysing material extend from the working surface 16 and the edge surface 20 into the crystalline diamond layer 12 respectively. The depth of each of the areas in the transverse direction, respectively, from the surface 16, 20 usually does not exceed 500 microns, and preferably is 30 to 400 microns, most preferably 60 to 350 microns. The area 24 further extends from the working surface 16 towards the substrate 14 to a depth of at least half the total thickness of the crystalline diamond layer 12, but it preferably ends at a distance of at least 500 μm from the contact area 28 to avoid unintentional leaching of the area contact 28.

[0038] If the PCD edge is chamfered, the regions 22, 24 poor in catalytic material usually have a shape corresponding to the shape of the chamfer and extend along the length of the phase. The balance of the crystalline diamond layer 12 extending into the cemented carbide substrate 14 provides a region 26 rich in catalytic material. The surfaces 16, 20 of the PCD element may further be mechanically polished to obtain a low friction surface or finish.

[0039] Because during use, the PCD layer 12 contacts the ground in which the drilling is carried out, a wear trail 30 having a front edge 32 and a rear edge 34 is formed. By providing respective areas 22, 24 poor in catalysing material, during the formation of a wear trail 30 both the front edge 32 and the rear edge 34 are in an area poor in catalysing material. The aforementioned advantages associated with the removal of the catalysing material from the working surface of the PCD abrasive element now also apply to the rear edge 34, which provides a further increase in performance obtained during use. In the present embodiment of the invention, the area 24 has the shape of a full ring poor in catalytic material. In practice, only a few segments of a diamond layer 12 are usually used when drilling. If the wear trace becomes too large, the insert can be rotated, for example, by 90 °, which creates a new trace of wear. Repeating this operation may result in, for example, four signs of wear. It is therefore possible to wash only those parts of the area 24 that correspond to the segments where the corresponding signs of wear are formed, which leads to the formation of the so-called intermittent annular region poor in catalysing material.

[0040] Crystalline diamond layer 12 is generally produced and bonded to cemented carbide substrate 14 using methods known in the art. Next, removal of the catalysing material from the working surface 16 and the edge surface 20 of the given embodiment of the invention is carried out by any of many known methods. One such method is to use leaching with hot inorganic acid, for example leaching with hot hydrochloric acid. The acid temperature is usually around 110 ° and the leaching time is between 3 and 60 hours. In the area of ​​the post-crystalline diamond layer that is not intended for leaching, the cemented carbide substrate is appropriately masked using an acid-resistant material. This also applies if the dotted area 24 is used.

[0041] During the manufacture of polycrystalline diamond abrasive elements described above, a layer of diamond particles, optionally mixed with a catalyst material, is placed on a cemented carbide substrate. This unbound assembly is then subjected to conditions including elevated temperature and elevated pressure to form a polycrystalline diamond particle diamond bound to a cemented carbide substrate. The conditions and steps required to achieve this are well known in the art.

[0042] The diamond particles are preferably in the form of a mixture of diamond particles that differ in their average particle size. In one embodiment of the invention, the mixture comprises particles having the following five different average particle sizes:

Average particle size (in micrometres) to 25 (preferably 22) 10 to 15 (preferably 12) 5 to 8 (preferably 6) to 5 (preferably 4) less than 4 (preferably 2)

Percentage (by weight) up to 30 (preferably 28) 40 to 50 (preferably 44) 5 to 10 (preferably 7) 15 to 20 (preferably 16) less than 8 (preferably 5) [0043] In another embodiment of the invention, the crystalline diamond layer contains two layers that differ in the mixture of particles used. The first layer, which is adjacent to the working surface, comprises a mixture of particles of the type described above. The second layer, which is between the first layer and the substrate, is in the form of a layer in which (i) the majority of the particles have an average particle size in the range of 10 to 100 microns, using at least three different average particle sizes, and (ii) at least 4 percent by weight of the particles have an average particle size of less than 10 microns. Both diamond mixtures used in the first and second layers may contain an admixture of catalyzing material.