Patent Application
20110212303
The invention relates to superhard polycrystalline diamond (PCD) elements for wear and cutting applications and particularly as cutting elements for earth boring drill bits where engineered superhard surfaces are needed. The invention particularly relates to PCD elements with working surfaces partially depleted of catalyzing material that have greatly improved impact resistance while maintaining excellent wear resistance.
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, suitable for applications such as hollow dies, heat sinks, friction bearings, valve surfaces, indentors, tool mandrels, etc. 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 PCD's used as cutting elements, for example in fixed cutter or rolling cutter earth boring bits when received in a socket of the drill bit, or when fixed to a post in a machine tool for machining. These PCD elements are typically called polycrystalline diamond cutters (PDC), and the surfaces of the PCD that contact the material to be modified are called working surfaces.
It has become well known that the cutting properties of these PCD materials are greatly. enhanced when a relatively thin layer of the diamond material adjacent to the working surface is treated to remove the catalyzing material that remains there from the manufacturing process. This has been a relatively thin layer, generally from about 0.05 mm to about 0.4 mm thick, and the depth from the working surface tends to be generally uniform. This type of PDC cutting element has now become nearly universally used as cutting elements in earth boring drill bits and has caused a very significant improvement in drill bit performance.
Because these surfaces tend to be planar, however, it has been observed that fracture adjacent to the treated layer may occur. It has been speculated that the often lenticular type of fracture may be related to stresses that form in the area between the depleted and non-depleted regions. It is believed that stress concentrations in this ‘transition’ region may lead to these fractures.
A plurality of stress disruption features are formed in PDC cutting elements for use in earth boring drill bits. These cutting elements for drilling earthen formations, have a plurality of partially bonded diamond crystals with interstices disposed therebetween and are formed with a substrate of less hard material. The cutting element also has a generally planar end formed adjacent a generally cylindrical periphery, and a formation engaging working surface on the end and the periphery.
The interstices remote from the working surface are filled with a catalyzing material, and the interstices adjacent to the working surface are substantially free of the catalyzing material. An intermediate region between the substantially free portion and filled portion has a plurality of generally conically sectioned catalyst-free projections which taper down, extending to a second depth from the planar working surface at least about 0.5 times the first depth.
The invention will further be described, by way of example, with reference to the accompanying drawings, in which:
A typical polycrystalline diamond or diamond-like material (PCD) element 2 is generally shown in
The working surface 4 is any portion of the PCD body 8 which, in operation, may contact the object to be worked. In this specification, when the working surface 4 is discussed, it is understood that it applies to any portion of the body 8 which may be exposed and/or used as a working surface. Furthermore, any portion of any of the working surface 4 is, in and of itself, a working surface.
PCD's of both the prior art and the present invention are made under conditions of high-temperature and high-pressure (HTHP). During this process the interstices 62 among the crystals 60 fill with the catalyzing material 64 followed by bonds forming among the crystals 60. In a further step of the manufacture, some of the catalyzing material 64 is selectively depleted from some of the interstices 62. The result is that a first volume of the body 8 of the PCD element 2 remote from the working surface 4 contains the catalyzing material 64, and a second volume of the body 8 adjacent to the working surface 4 is substantially free of the catalyzing material 64 to a depth ‘D’. The interstices 62 which are substantially free of the catalyzing material 64 to the depth ‘D’ are indicated by numeral 66.
In this specification, when the term ‘substantially free’ is used referring to catalyzing material 64 in the interstices 62, the interstitial matrix 68, or in a volume of the body 8, it should be understood that many, if not all, the surfaces of the adjacent diamond crystals 60 may still have a coating of the catalyzing material 64. Likewise, when the term ‘substantially free’ is used referring to catalyzing material 64 on the surfaces of the diamond crystals 60, there may still be catalyzing material 64 present in the adjacent interstices 62.
Because the body adjacent to the working surface 4 is substantially free of the catalyzing material 64, the deleterious effects of the binder-catalyzing material 64 are substantially decreased, and thermal degradation of the working surface 4 due to the presence of the catalyzing material 64 is effectively eliminated, as is now well known in the art.
The PCD cutting element 10 may be a preform cutting element 10 of a fixed cutter rotary drill bit 12 (as shown in
Typically, the PCD cutting element 10 has a body in the form of a circular tablet having a thin front facing table 30 of diamond or diamond-like (PCD) material, bonded in a high-pressure high-temperature press to a substrate 32 of less hard material such as cemented tungsten carbide or other metallic material. The cutting element 10 is preformed and then typically bonded on a generally cylindrical carrier 34 which is also formed from cemented tungsten carbide, or may alternatively be attached directly to the blade. The PCD cutting element 10 has working surfaces 70 and 72.
The cylindrical carrier 34 is received within a correspondingly shaped socket or recess in the blade 16. The carrier 34 will usually be brazed or shrink fit in the socket. In operation the fixed cutter drill bit 12 is rotated and weight is applied. This forces the cutting elements 10 into the earth being drilled, effecting a cutting and/or drilling action.
In the process of bonding the crystals 60 in a high-temperature, high-pressure press, the interstices 62 among the crystals 60 become filled with a binder-catalyzing material 64, typically cobalt or other group VIII element. It is this catalyzing material 64 that allows the bonds to be formed between adjacent diamond crystals 60 at the relatively low pressures and temperatures present in the press.
Referring now to
There are many methods for removing or depleting the catalyzing material 64 from the interstices 62. In one method, the catalyzing material 64 is cobalt or other iron group material, and the method of removing the catalyzing material 64 is to leach it from the interstices 62 near the working surface 104 of the PDC cutting element 100 in an acid etching process. It is also possible that the method of removing the catalyzing material 64 from near the surface may be by electrical discharge or other electrical or galvanic process or by evaporation. Many other methods and apparatus are well known or have been contemplated by those skilled in the art. Further explanation and details of these prior art cutters and cutting elements may be found in the published International Patent Application No. PCT/GB01/03986 and also in U.S. Pat. No. 6,544,308 which is incorporated by reference herein for all it discloses.
In prior art cutters, however, it has been found that fractures adjacent to this layer may occur. It is believed that these lenticular types of fractures may be related to stresses that form in the area between the depleted and non-depleted regions and that stress concentrations in this ‘transition’ region may lead to these fractures.
In the present invention the working surface 104 is treated to a first depth 102 from about 0.05 mm to about 0.5 mm from the planar portion 106 of the working surface 104, as described above. However, beneath this first depth are a plurality of projections 108 depleted of catalyzing material in the PDC material which help prevent the above described fractures. In
There are numerous ways to form these projections 108. In one embodiment, the PDC cutter may be masked in a manner such that the working surface exposed to the acid bath (described above) is ‘windowed’ through a plurality of openings in the mask. These openings may be of any convenient shape or size, and function so as to allow the acid to leach only the selected areas. The leaching may progress for hours or days, as may be required, for the desired geometry of the projections 108.
Once the projections 108 have been formed, a second leaching operation may be performed which removes substantially all of the catalyzing material from the surface to the required first depth 102 and causes further growth of the projections 108 to the second depth 110 below the first depth 102.
It is believed that these projections reduce stress induced fractures in the region depleted of catalyzing material to the first depth 102 because they provide a far more gradual transition from the depleted to non-depleted regions in the PDC, and therefore remove the abrupt transition from the catalyst free zone to the catalyst filled zone. Therefore, the stresses that form in the area between the depleted and non-depleted regions during operation of the PDC in operation are substantially mitigated.
Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0716268.8 | Aug 2007 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB08/02739 | 8/14/2008 | WO | 00 | 5/6/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60956519 | Aug 2007 | US |
