FIELD

This disclosure relates to a method of treating a polycrystalline diamond (PCD) body.

BACKGROUND

Polycrystalline diamond, also known as a diamond abrasive compact, comprises a mass of diamond particles containing a substantial amount of direct diamond- to-diamond bonding. Polycrystalline diamond will generally have a second phase which contains a diamond catalyst/solvent such as cobalt, nickel, iron or an alloy containing one or more such metals.

When diamond particles are combined with a suitable metallic catalyst/solvent, this catalyst/solvent promotes diamond-to-diamond bonding between the diamond grains, resulting in an intergrown or sintered structure. This intergrown diamond structure therefore comprises original diamond grains as well as newly precipitated or re-grown diamond phase, which. bridges these original grains. In the final sintered structure, catalyst/solvent material remains present within the interstices that exist between the sintered diamond grains. The sintered PCD has sufficient wear resistance and hardness for use in aggressive wear, cutting and drilling applications.

A well-known problem experienced with this type of PCD compact, however, is that the residual presence of solvent/catalyst material in the microstructural interstices has a detrimental effect on the performance of the compact at high temperatures.

A potential solution to this problem is to remove, typically by leaching, the catalyst/solvent or binder phase from the PCD material. US 3,745,623 and US 4,636,253 teach the use of heated acid mixtures in the leaching process in which mixtures of HF, HCI, and HN0 ₃ and HN0 ₃ and HF, respectively, are used.

US 4,288,248 and US 4,224,380 describe removal of the catalyst/solvent by leaching the PCD tables in a hot medium comprising HN0 ₃ -HF (nitric acid and hydrofluoric acid), alone or in combination with a second hot medium comprising HCI-HNO ₃ (hydrochloric acid and nitric acid).

US 2007/0169419 describes a method of leaching a portion or all of the catalyst/solvent from a PCD table by shielding the portion of the PCD table not to be leached and immersing the shielded PCD table in corrosive solution to dissolve the catalyst/solvent in water and aqua regia. The leaching process is accelerated by the use of sonic energy, which agitates the interface between the PCD table and the corrosive solution to accelerate the dissolution rate of the catalyst/solvent.

US 4,572,722 discloses a leaching process that is accelerated by forming a hole in the PCD table by laser cutting or spark emission prior to or during the leaching process. The PCD table is then leached by using conventional acid leaching techniques, electrolytic leaching and liquid zinc extraction.

It is typically extremely difficult and time consuming effectively to remove the bulk of a metallic catalyst/solvent from a PCD table, particularly from the thicker PCD tables required by current applications. In general, the current art is focussed on achieving PCD of high diamond density and commensurately PCD that has an extremely fine distribution of metal catalyst/solvent pools. This fine network resists penetration by the leaching agents, such that residual catalyst/solvent often remains behind in the leached compact. Furthermore, achieving appreciable leaching depths can take so long as to be commercially unfeasible or require undesirable interventions such as extreme acid treatment or physical drilling of the PCD tables. SUMMARY

Viewed from a first aspect there is provided a method of treating a polycrystalline diamond body having at least one metal dispersed through its microstructure, comprising the step of treating the polycrystalline diamond body in order to remove some or all of the at least one metal from the polycrystalline diamond body, which treating step includes applying energy directly to the at least one metal, in order to heat the polycrystalline diamond body and/or the at least one metal.

A polycrystalline diamond (PCD) body has a second phase comprising a catalyst/solvent material located within interstices of the PCD microstructure, and may be treated as described above in order to remove some or all of the catalyst/solvent material from the PCD body.

The treating step preferably comprises contacting a surface or region of the polycrystalline diamond body to be treated with a leaching agent, the application of energy to the polycrystalline diamond body or the at least one metal being independent of the leaching agent.

The leaching agent may be an acid, such as hydrochloric acid, nitric acid, hydrofluoric acid, aqua regia, or the like, or may, for instance, be any other appropriate corrosive or leaching solution capable of removing the at least one metal from the diamond containing body.

Important to accelerating the rate of removal or leaching of the at least one metal from the polycrystalline diamond body is the heating of the at least one metal by application of an appropriate energy source, hereinafter termed 'direct heating'. By 'direct heating' is meant that heating of the at least one metal takes place independently of the leaching agent, hence there is no need to provide heated leaching agent in the method.

The energy typically causes heating initially of the metal exposed at or adjacent a surface or region of the polycrystalline diamond body being treated, and subsequently of the metal within the microstructure of the polycrystalline diamond body.

The direct heating may take the form of induction heating, radio frequency heating, laser heating, or any other appropriate electromagnetic or other heating method capable of heating the diamond containing body and/or the at least one metal with minimal direct heating of the leaching agent..

The treating or leaching step can be enhanced using ultrasonics applied to the system, leaching conducted under pressure, either in a pressure vessel or with the leaching step conducted under a higher ambient pressure, or combined in an ultrasonic pressure vessel.

The electromagnetic energy reaching the polycrystalline diamond bodies, leaching container, and leaching agent can also be controlled by use of a susceptor surrounding the system. Typical susceptor systems use graphite. It may be advantageous at times for the leaching process to heat both the leaching agent (indirectly through the susceptor) and the polycrystalline diamond bodies directly.

The leaching agent can also be flowed through the leaching container while direct heating is applied to the polycrystalline diamond bodies. A possible advantage of this is the temperature gradient between a polycrystalline diamond body and the leaching agent can more easily be controlled since the leaching agent temperature can be controlled/changed while away from the leaching process unit. Additional benefits may include the opportunity for removal of any leached metal or catalyst/solvent material from the leaching agent during the process. This controls and enhances the chemical gradient between the polycrystalline diamond body and leaching agent, thereby potentially enhancing the leaching process. The flow of the leaching agent may also allow recycling and removal of the metal or catalyst/solvent during the leaching process continuously instead of the stop-start necessary to replace spent leaching agent otherwise. In the case of PCD bodies, the typical thickness of the PCD bodies to be treated may be in the region of about 1.5mm to about 3.0mm.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of methods of treating a polycrystalline diamond body will now be described in more detail, with reference to the accompanying figures in which:

Figure 1 shows a treatment system for use in accordance with a first embodiment of a method of treating a polycrystalline diamond body;

Figure 2 shows a treatment system for use in accordance with a second embodiment of a method of treating a polycrystalline diamond body;

Figure 3 shows a treatment system for use in accordance with a third embodiment of a method of treating a polycrystalline diamond body;

Figure 4 shows a treatment system for use in accordance with a fourth embodiment of a method of treating a polycrystalline diamond body;

Figure 5 shows a treatment system for use in accordance with a fifth embodiment of a method of treating a polycrystalline diamond body;

Figure 6 shows a treatment system for use in accordance with a sixth embodiment of a method of treating a polycrystalline diamond body;

Figure 7 shows a treatment system for use in accordance with a seventh embodiment of a method of treating a polycrystalline diamond body.

DETAILED DESCRIPTION

Some embodiments concern a method of treating, in particular a method of leaching, a polycrystalline diamond (PCD) body. The method described has particular application to the treatment of PCD bodies, and in what follows reference is made to leaching a PCD body containing a catalyst/solvent material.

Accordingly, viewed in a first aspect, there is provided a sintered PCD body having diamond to diamond bonding and having a second phase comprising catalyst/solvent dispersed through interstices of its microstructure. The PCD body is typically formed in the presence of a conventional diamond catalyst/solvent, such as Co, Ni, Fe or alloys thereof, preferably Co, according to standard methods using HpHT conditions, typically temperatures in the order of 1400°C and pressures in the order of 55 kbar, to produce a sintered PCD body. The PCD bodies to be leached typically have a thickness of about 1.5 mm to about 3.0 mm.

In the method of leaching a polycrystalline diamond (PCD) body, energy is applied directly to the PCD body, preferably directly to the catalyst/solvent material, in order to heat the catalyst/solvent material, whilst exposing the PCD body to a leaching agent.

In accordance with some embodiments, a PCD table including a catalyst/solvent material, such as Co, Ni or Fe, or an alloy thereof, located within the interstices of its microstructure is placed in an acid resistant container, for example a Teflon container, with a liquid or gaseous leaching agent. If there are regions or surfaces of the PCD table that do not require leaching, and particularly where the PCD is supported on a cemented carbide backing that needs to be protected from the leaching agent, these regions or surfaces can be masked by methods known in the art. These would include the use of polymer components made of Telfon, high density polyethylenes, PEEK (poly ether ether ketone), polyimides, and nylon, for example. The Teflon container is then exposed to an energy source, such as a source of radio frequency, induction heating coils, laser heating or other similar electromagnetic energy source.

Without wishing to be bound by theory or to limit the scope in any way, in this embodiment, the energy created by the energy source interacts directly with the catalyst solvent material causing the catalyst/solvent material to be heated. Since the catalyst/solvent materials typically used in PCD synthesis are ferromagnetic metals, and hence conducting, the energy applied to them causes eddy currents to be generated within the metal and the resultant resistance leads to so-called Joule heating. This enhanced energy in the form of heat increases the rate of reaction with the leaching agent without the need for high temperatures and/or high pressures currently being used by microwave and high pressure heating methods. The exothermic chemical reaction along with the temperature gradient from the heated catalyst/solvent towards the leaching agent enhances movement of the leaching agent and catalyst/solvent material into and out of the fine interstices of the PCD body.

Whilst the laser heating interacts directly with the catalyst/solvent material in the fine interstices, it may also interact with the defects in the diamond microstructure or crystal structure. However, the submicron metal is very reactive with the laser energy and will preferentially be heated before reactions of the laser energy with the diamond defects. Accordingly, the fine metal particles, whether as a dispersed metal powder or as a fine network filligree of interconnected catalyst/solvent in the diamond interstices, will react strongly with the laser energy. The laser energy would range from the near infrared, such as that produced by a typical industrial Nd-YAG laser that has a low asorption by the leaching agent, to higher frequencies into visible radiation and higher. The only practical engineering matter would be limiting the loss of the incoming laser radiation during the combined leaching-heating step by controlling the path through the leaching agent between the laser source and the PCD body and adjusting the laser frequency to minimize absorption by the leaching agent.

Several exemplary heating methods have been suggested for directly heating a PCD table and/or the catalyst solvent distributed in the microstructural interstices thereof. This should, however, not be construed as limiting the scope, it being envisaged that any appropriate method of heating the PCD table and/or catalyst/solvent material can be used, provided it does so without significantly heating or otherwise interacting with the leaching agent. A possible advantage of laser heating is the preferential leaching of the catalyst/solvent to change the location of the available metal in the PCD. This effect can then be used to change where metal brazes and other surface wetting agents are able to wet. This may be beneficial in controlling the movement of brazes during manufacture of components from leached or partially leached PCD bodies. This process can also be used in the manufacture of specialized components such as bearing supports where there are locations that metals, even in the interstices of the diamond, are not desired during manufacture and use.

Heating using induction, for example through the use of induction coils placed in a liquid medium, may enable the residual metal from the catalyst/solvent material (eg Cobalt) in the PCD body to be heated rapidly and efficiently. Heat transfer to the liquid is rapid at the point of contact of the liquid and the metal, the metal being oxidised quickly to expose fresh hot metal in the PCD material. This form of heating therefore targets the metal to be leached out of the PCD material enabling localised heating of the metal to be controlled. Once the metal has been leached from the PCD material, the PCD material becomes thermally inert thereby inhibiting damage to the PCD material from continued heating.

When using induction coils, it may be beneficial to coat the coils with a protective film such as Teflon and/or a noble metal, e.g. Platinum, to protect the coils from acid attack when using an acidic leaching agent The coated coils may then be placed directly in the acid whilst introducing the necessary energy to heat the PCD body and/or catalyst/solvent material. In certain cases, for instance where Teflon or the like is used, the film on the coils could also protect a user from electrical burns resulting from touching the coil.

The introduction of a coated coil could also be useful to enhance catalyst/solvent removal by electrochemical methods, as opposed to using an acidic leaching agent, when energy is applied directly to the PCD bodies.

Due to the fine sub-micron size of the islands of catalyst/solvent materials, modest inputs of electromagnetic energy can achieve enhanced reactions of the catalyst/solvent materials with the leaching agents. This has been referred to as the "skin effect" in the literature when using electromagnetic radiation for induction and radio-frequency heating.

Therefore modest increases in temperature of the PCD body due to direct heating can result in increases in leaching rate as compared with using leaching agents conventionally, heated to the same temperature. .

In view thereof, the minimum temperature required for enhancing the leaching of the catalyst/solvent material is believed to be around and slightly above ambient temperature due to the enhancement effect from direct heating, in particular from induction and radio frequency heating.

The maximum temperature is dictated by the reaction of the catalyst/solvent with the diamond leading to graphitization of the diamond. This temperature is dependant on the catalyst/solvent. In the example of a traditional infiltrated cobalt based catalyst/solvent, amorphous or sp2 bonded carbon was found to start to occur at ~600°C with graphitization becoming clear at ~850°C.

Accordingly, the maximum temperature to which the catalyst/solvent can be heated is believed to be related to the time required for leaching versus time required for the graphitization of the diamond by the catalyst/solvent. Shorter times at higher temperatures may be just as satisfactory as longer times at lower temperatures.

Referring to the accompanying schematic drawings, Figures 1 to 7 show various alternative systems that can be used for carrying out the treatment methods. Referring to Figure 1 , a number of PCD bodies (1 ) are located in a leaching container (2) that is surrounded by radio frequency or induction coils (3). The PCD bodies (1) are submerged in a leaching agent (4) that is capable of leaching catalyst/solvent material from the PCD bodies (1) whilst energy is applied to the PCD bodies (1) from the coils (3). Referring to Figure 2, a device (5) for introducing ultrasonic energy into the container (2) and leaching agent (4) can be used to accelerate the process further. Alternatively, or additionally, agitation of the leaching agent can also be used to accelerate the process further. For instance, as depicted in Figure 3, Teflon or similar beaker (2) can be rotated mechanically inside the induction or radio frequency coils (3) at an angle, thereby increasing the mixing of the leaching agent (4) and PCD bodies (1), and thereby increasing the leaching rate. Furthermore, the location of the induction or radio frequency coils (3) can be optimised to allow the introduction of ultrasonic horns into the Teflon container system, enhancing mixing of the leaching agent (4) and the PCD bodies (1), and in turn the leaching rate.

The process can also be accelerated by feeding through leaching agent either continuously or discontinuously while applying energy directly to the PCD bodies and/or catalyst/solvent material. Referring to Figure 4, leaching agent (4) is fed into the container (2), as shown generally by the annotation (5), and exits as pregnant leachate (6). As a further example, not shown, a soxylitic extractor in which a flux of acid vapour evaporates and condenses back down on the PCD bodies can be used.

An alternative system is depicted in Figure 5 in which the radio frequency or induction coils (3) are placed inside the container (2) in contact with the leaching agent (4), and surrounding the PCD bodies (1). In such an arrangement, the coils (3) are advantageously coated by an appropriate coating material in order to avoid corrosion by the leaching agent (4).

In some instances it may be desirable to control the amount of energy being applied to the PCD bodies. As shown in Figure 6, this can be achieved by surrounding the container (2) with a device (5), which could be a tube formed of graphite, for example.

It may also be desirable to control the pressure of the container (2). Referring to Figure 7, a device (5) may be provided for controlling the pressure surrounding the container (2), thus allowing for leaching under increased or reduced pressure. Furthermore, liquid channels (not shown in any of the illustrated systems) can be introduced into the leaching container to provide a direct means of controlling the temperature of the leaching agent without coming into contact with it. The temperature gradient between the cool leaching agent and the heated PCD bodies can provide greater chemical gradients, which accelerates leaching.