Patent Application
20070169419
The present invention relates to the manufacture of polycrystalline diamond cutting tools, and in particular, cutting tools which have had a portion or all of the binder material leached from the diamond.
In the exploration of oil, gas, and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. These operations normally employ rotary and percussion drilling techniques. In rotary drilling, the borehole is created by rotating a tubular drill string with a drill bit secured to its lower end. As the drill bit deepens the hole, tubular segments are added to the top of the drill string. While drilling, a drilling fluid is continually pumped into the drilling string from surface pumping equipment. The drilling fluid is transported through the center of the hollow drill string and into the drill bit. The drilling fluid exits the drill bit at an increased velocity through one or more nozzles in the drill bit. The drilling fluid then returns to the surface by traveling up the annular space between the borehole and the outside of the drill string. The drilling fluid carries rock cuttings out of the borehole and also serves to cool and lubricate the drill bit.
One type of rotary rock drill is a drag bit or fixed cutter bit. Early designs for fixed cutter bits included hard facing applied to steel cutting edges. Modern designs for drag bits have extremely hard cutting elements, such as natural or synthetic diamonds, mounted to a bit body. The synthetic diamonds are generally known as polycrystalline diamond compact cutters (PDCs). As the drag bit is rotated, the PDC cutters scrape against the bottom and sides of the borehole to cut away rock.
The polycrystalline diamond element portion of the PDC cutters is also available in forms in which some or all of their binder material are leached from between the diamond crystals. These cutters are known as thermally stable polycrystalline diamond cutters (hereinafter collectively referred to as “TSD cutters”). The PDC cutters and TSD cutters may be used in the manufacture of PDC bits.
Polycrystalline diamond elements are most commonly formed by sintering diamond powder with a binder-catalyzing material in a high-pressure, high-temperature press. Typically, in the manufacture of polycrystalline diamond elements, diamond powder is applied to the surface of a preformed tungsten carbide substrate incorporating a cobalt binder-catalyst. The assembly is then subjected to very high temperature and pressure in the press. During the process, the 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. The binder-catalyst also causes the diamond layer to bond to the substrate by bonding, for example, with the cobalt in the tungsten carbide substrate.
The completed polycrystalline diamond element comprises a matrix of connected diamond crystals bonded together with interstices comprised of the binder-catalyzing material. Typically, diamond crystals may constitute 85% to 95% by volume of the PDC, and the binder-catalyzing material may constitute the remaining 5% to 15%. Due to significantly different thermal expansion rates of the binder-catalyzing material and the diamond matrix, the PDC is susceptible to thermal degradation. The binder-catalyst expands at a substantially greater rate. As the binder-catalyst expands, it creates pressure on the diamond-to-diamond bonds, expanding and weakening them. Combined with the external forces acting on the PDC, they begin to break, causing accelerated degradation of the PDC.
In addition to thermal cracking, the diamond may graphitize in the presence of the binder-catalyst as temperature increases, further accelerating degradation and reducing the life of the PDC. The combined causes of thermal degradation greatly accelerate the destruction of the polycrystalline diamond when the temperature of the diamond exceeds 700° centigrade.
As stated, cobalt is the most commonly used binder-catalyzing material. Other materials, including any of Group VIII elements, may be employed.
To reduce thermal degradation, various post-sintering attempts to remove the binder-catalyst from the PDC have been developed. The resulting product is a PDC with all or some of the binder-catalyst removed from the interstices of the bonded diamond crystals. Typically, the binder-catalyst is removed by exposing the PDC to a highly corrosive substance, such as acid, or by an electrolytic process, or a combination thereof. As used herein, “corrosive solution” refers to a solution that is corrosive to the binder-catalyst, and not to diamond.
It is desirable to remove the binder-catalyst only from the working, or “cutting” surface of the PDC. Therefore, it is necessary to shield the remainder of the PDC from exposure to the corrosive substance.
These products are commonly referred to as “thermally stable” polycrystalline diamond compacts or “TSD” elements. A number of prior patents address leaching of polycrystalline diamond.
U.S. Pat. No. 3,745,623, issued to Wentorf, Jr. et al., discloses a cutting tool formed of diamond particles subjected to a superpressure process in which the diamond particles are bonded to a sintered carbide substrate. A fragment of a cutting tool was leached in HF, HCL and HNO3, which resulted in removal of residual metal, although some magnetic metal remained in the compact (Column 8, lines 33-55).
U.S. Pat. Nos. 4,224,380 and 4,288,248, issued to Bovenkerk et al., are related patents disclosing similar inventions with variations in the claims. Both disclose treatment of a diamond compact to remove substantially all infiltrated material in order to improve the thermal stability of the PDC. In Example IV, a carbide substrate was masked with epoxy and leached in 3HCL:1HNO3 until a “substantial portion of the metallic phase” was removed. Other examples use HF, HCL and HNO3 in various combinations and for varying times to leach material from the diamond. The precise degree of removal of the metallic phase is unclear, but seems to vary from 0.2 weight percent to 0.15 weight percent remaining in the diamond.
U.S. Pat. No. 4,572,722, issued to Dyer, discloses a diamond abrasive compact that is leached in HF and HCL (Example I) or Aqua Regia (3HCL:1HNO3, Example II) to remove 99 weight percent of the original cobalt in the diamond material.
U.S. Pat. No. 4,518,659, issued to Gigl et al., discloses the “sweep through” method of making polycrystalline diamond compacts that is improved by “sweeping through” with an intermediate metal having a melting point lower than the catalyst metal. The resulting compacts may be made “thermally stable” by leaching first in 1HF:1HNO3 and second in Aqua Regia in accordance with the '380 patent referenced above.
U.S. Pat. No. 4,636,253, issued to Nakai, et al., discloses a diamond sintered body using cobalt as a catalyst. The body is leached with Aqua Regia so that the pore volume in the sintered body is less than 10%. Only the diamond table or layer is dipped in the Aqua Regia. In Example 9, the body was only “partially” leached, leaving 0.8 volume percent cobalt and 3.06 volume percent pores.
U.S. Pat. No. 4,931,068, issued to Dismukes, et al., discloses a “fully dense” diamond body that is heated to 155° C. for 60 minutes to rearrange and remove dislocations. The resulting body is leached free of cobalt impurities using HCl and water, and 3HCl:1HNO3.
U.S. Pat. No. 4,943,488, issued to Sung et al., discloses a method for securing TSDs to carbide substrates, either singly or in “mosaics.” The process begins with leached TSDs, but no leaching details are supplied.
U.S. Pat. No. 5,068,148, issued to Nakahara et al., discloses a diamond coating on a substrate. The coating is etched for 5 minutes in nitric acid to remove cobalt from outermost portions of the coating.
U.S. Pat. No. 5,127,923, issued to Bunting et al., discloses a sintered diamond compact that is leached with Aqua Regia for 7 days and resintered with a non-catalyst sintering aid material (Ni—Fe, for example).
U.S. Pat. No. 6,344,149, issued to Oles, discloses a polycrystalline diamond member that is etched with nitric acid to produce an exterior region that is essentially free of the catalyst (typically cobalt), while the interior region has catalyst in conventional quantities. The exterior region is covered with a CVD-applied hard material, such as diamond.
U.S. Pat. No. 6,447,560 issued to Jensen et al., discloses a method of forming superhard (PDC or CBN) cutting tools having integral chip-breaking features or surfaces. In the background, it is noted that catalyst may be leached from the superhard material, but no leaching process or step is disclosed. It also states that maintaining a uniform distribution of cobalt throughout the diamond particles improves durability and temperature tolerance.
U.S. Pat. No. 6,601,662, issued to Matthias et al., discloses polycrystalline diamond or diamond-like cutters for rock bits in which one region is leached of catalyst and another region is not. This is consistent in its disclosure with the Griffin patents discussed below.
U.S. Pat. No. 6,410,085, issued to Griffin et al., discloses a superhard polycrystalline diamond or diamond-like element that is leached “by an appropriate treatment of the component to remove the catalyzing material from the interstices located within a volume close to a surface which, in the final product, will be a working surface thereof.” The diamond table then is coated with a metallic or other conductive material to permit electronic discharge machining (EDM) of the element.
U.S. Pat. Nos. 6,562,462, 6,544,308, 6,585,064, 6,589,640, 6,592,985, 6,739,214, 6,749,033, 6,797,326, and U.S. Publication Nos. 2003/0235691, 2004/0105806 and 2004/0115435, issued to Griffin et al., are commonly owned and related as continuations and divisions of one another. The disclosed structure is a diamond or diamond-like structure for a rock bit insert or cutting element in which a portion of the element retains catalyzing material, and the portion adjacent to the cutting surface is substantially free of the catalyzing material. While the leaching process is not detailed, the leached cutting surface is claimed in combination with other features, such as diamond particle size, insert geometry, and the like.
A principal disadvantage of the prior-art methods of leaching binder-catalyst from PDC elements is that they all rely on a slow chemical process in which the binder-catalyst is slowly dissolved by an acidic reagent in a static bath. A second disadvantage of this process is it produces a relatively uneven plane of transition between the binder-catalyst free zone of the diamond structure and the binder-catalyst filled zone of the diamond structure. The uneven and unpredictable transition between these zones can yield areas of the diamond structure that are particularly susceptible to thermal degradation. A third disadvantage of this process is that it generates a substantial quantity of hazardous waste.
Therefore, there is a need to develop an improved method and apparatus for leaching binder-catalyst from sintered PDC elements that is faster, and that produces a more uniform transition between the binder-catalyst free zone of the diamond structure and the binder-catalyst filled zone of the diamond structure.
A primary advantage of the present invention is that it accelerates the known methods of chemical leaching of binder-catalysts from sintered polycrystalline diamonds (PDCs). Another advantage of the present invention is that it produces a more uniform transition between the binder-catalyst free zone of the diamond structure and the binder-catalyst filled zone of the diamond structure. Another advantage of the present invention is that it reduces the generation of hazardous waste.
As referred to hereinabove, the “present invention” refers to one or more embodiments of the present invention which may or may not be claimed, and such references are not intended to limit the language of the claims, or to be used to construe the claims in a limiting manner.
The present invention relates to a method of leaching a portion or all of the binder-catalyst of a PDC from between the bonded diamond crystals by:
1. shielding the portion of the PDC not to be leached;
2. immersing the shielded PDC in corrosive solution; and
3. inducing sonic energy at the interface between the PDC and the corrosive solution.
In another preferred embodiment, the immersed and shielded PDC is substantially isolated from other immersed and shielded PDCs in the corrosive solution.
The objects and features of the invention will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like elements.
The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.
The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
The present invention relates to a method of leaching a portion or all of the binder-catalyst of a PDC from between the bonded diamond crystals. In the preferred embodiment, a method of sonochemically leaching binder-catalyst material from a polycrystalline structure 14 of a PDC 10 includes the steps of:
The first step of the sonochemical leaching process is shielding that portion of the PDC 10 in which exposure to corrosive solution 82 is not desired, including at least the substrate portion 12. In a preferred embodiment, PDC 10 is shielded by placing it in fixture 40. Fixture 40 is an acid-resistant material such as graphite or high-density polyethylene (HDPE). Graphite is the more preferred material since it more readily transmits sonic energy than HDPE. Fixture 40 has a hollow cylindrical center 44 for receiving PDC element 10. In the preferred embodiment, an acid-resistant sealant 70, such as grease, is applied to the surface of center 44. As PDC 10 is pressed into center 44, excess sealant escapes through relief 52. Seal 60 is compressed to provide an interference fit against PDC 10. In a preferred embodiment, cutting surface 18 of PDC 10 is coated with a surfactant, such as acetone, prior to immersion.
The second step of the sonochemical leaching process is immersion of shielded PDC 10 in a corrosive solution 82. Fixture 40, with PDC 10 encased and shielded, is placed in an acid-resistant vessel 80, such as a glass beaker. Vessel 80 is then filled with a corrosive solution 82 for the purpose of dissolving the binder-catalyst in diamond wafer 14 of PDC 10. In the preferred embodiment, corrosive solution 82 is an Aqua Regia solution. Aqua Regia is a chemical industry reference for a mixture of concentrated hydrochloric and nitric acids, containing one part by volume of nitric acid (HNO3) to three parts of hydrochloric acid (HCl). It has been proven to be an effective solvent for dissolving cobalt. Other acids are also well known to be effective.
Sealant 70 blocks relief 52 and prevents corrosive solution 82 from attacking substrate portion 12 of PDC 10. Likewise, seal 60 and sealant 70 prevent corrosive solution 82 from attacking those other portions of PDC 10 for which exposure to corrosive solution 82 is not desired. This leaves PDC 10 properly shielded from corrosive solution 82. Cutting surface 18 of PDC 10 is exposed in direct contact with corrosive solution 82.
In another preferred embodiment, cutting surface 18 of PDC 10 is coated with a surfactant prior to immersion. In the preferred embodiment, the surfactant is acetone. The surfactant acts primarily as a cleaning agent.
The third step of the sonochemical leaching process is inducing sonic energy at the interface between PDC 10 and corrosive solution 82. A sonic vessel 90 is provided having sonic transducers attached to provide the sonic energy. In the preferred embodiment, sonic vessel 90 is an ultrasonic vessel, producing a frequency of less than approximately 20 kilohertz. A stand 92 may be provided within sonic vessel 90. Sonic vessel 90 is partially filled with inert liquid 94, such as water. Beaker 80 containing corrosive solution 82, fixture 40, and PDC 10, is located on stand 92 and the sonic vessel is energized. In the preferred embodiment, ultrasonic energy is thus transmitted to the interface between cutting face 18 and corrosive solution 82.
The sonic energy agitates the interface and greatly accelerates the dissolution rate of the binder-catalyst in corrosive solution 82. This is achieved, in part, by displacing static aeration associated with dissolution of the binder-catalyst at cutting surface 18 and within the polycrystalline diamond structure as leaching progresses. This provides a significant advantage over prior-art methods of leaching binder-catalyst from PDC 10 elements that rely on a chemical process in which the binder-catalyst is slowly dissolved by an acidic reagent in a static bath.
In addition to the accelerated processing rate, the sonochemical process reduces the uncertainty with regards to the depth of the leach into diamond wafer 14. Referring to
In addition to controlling the depth of leach, the disclosed sonochemical process provides a more uniform transitional interface 30 between filled portion 32 and leached portion 34. This uniformity represents a reduction in the quantity and size of stress-risers that may be generated at interface 30 and which can lead to premature failure of PDC 10.
A tray 100 is disclosed as part of a system for efficiently sonochemical leaching a plurality of PDC 10 elements together. Tray 100 has a plurality of spaced-apart reservoirs 106 which are substantially isolated from each other. Isolation of reservoirs 106 enables sonochemical leaching with a predetermined volumetric exposure to corrosive solution 82. By utilizing a metered amount of corrosive solution 82, the leaching process is further controlled, and results are improved. This helps to resolve important process issues which add uncertainty to results related to sonic decomposition of corrosive solution 82, and dilution and pH reduction of corrosive solution 82 as the binder-catalyst dissolves.
In an optional embodiment, equalizing channels 116 interconnect reservoirs 106 to equalize the volume of corrosive solution 82 between reservoirs 106. In a related embodiment, overflow channels 120 provide a limit to the volume of corrosive solution 82 in each reservoir 106. Overflow channels 120 may be directed to an overflow reservoir 122.
In addition to the increased process control that isolated and volume controlled exposure provides, the quantity of hazardous waste generated by the process is reduced.
It will be readily apparent to those skilled in the art that the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention.
Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.
