DUAL SWEEP DESIGN FOR MANUFACTURING POLYCRYSTALLINE DIAMOND COMPACT

Abstract

A method for forming a polycrystalline diamond compact (PDC) includes steps of disposing a first catalyst source on a top of a plurality of diamond crystals; disposing a second catalyst source at a bottom of the plurality of diamond crystals; and applying high temperature and high pressure to the plurality of diamond crystals, the first catalyst source and the second catalyst source such that the plurality of diamond crystals are sintered into a polycrystalline diamond compact.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claiming priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 13/755,589, filed on Jan. 31, 2013.

FIELD OF THE DISCLOSURE

The present application relates to a polycrystalline diamond compact (PDC), and more particularly, to a PDC having a polycrystalline diamond sintered on a carbide substrate using a sweep-through process.

BACKGROUND

In the discussion that follows, reference will be made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.

Twist drills and other tools used in the drilling industry often use a polycrystalline diamond compact (PDC). Commonly, a PDC is made using a high pressure and high temperature (HPHT) sweep-through process. FIG. 1 is a cross-sectional view showing formation of a PDC in accordance with a related art HPHT sweep-through process. As shown in FIG. 1, in the sweep-through process for forming a PDC, a mass of diamond crystals is placed into a refractory metal container. The diamond mass may contain some binder material or additives blended in to promote sintering. Cemented carbide (WC—Co composite hard metal) substrate is placed in the container such that a surface of the substrate touches the mass of diamond crystals. The assembly is then subjected to HPHT conditions. Typically, the binder material present in the substrate melts and sweeps into the mass of diamond crystals. In the presence of the liquid binder material, diamond crystals bond to each other by a dissolution-precipitation process to form a polycrystalline diamond mass attached to the cemented carbide substrate.

The carbide substrate usually includes small amounts of a binder material, such as cobalt, nickel, iron or their alloys, to improve integrity and strength. The binder material is generally selected to function as a catalyst for melting and sintering the diamond crystals. That is, as shown in FIG. 1, in existing processes for forming a PDC, the cobalt or other binder material from the substrate will melt under HPHT conditions from the carbide substrate and “sweep” across the diamond powder to create the PDC. Here, the sweep occurs as a front that moves from an interface between the carbide substrate and the diamond crystals toward a distal surface of the diamond. If the interface between the carbide substrate and the diamond is planar, the sweep may be uniform.

However, in many PDC arrangements, such as those for twist drills, the carbide substrate may define a non planar interface with the diamond crystals. For example, deep valleys may be defined in the carbide substrate with the diamond crystal disposed therein. Because of the geometry of such interfaces, the sweep pattern is irregular. Accordingly, the irregular sweep front may result in areas of poorly sintered diamond (a defect zone), especially in area near the cutting edge of the PDC. Moreover, metal filled cracks or fingers may form in the sintered diamond near the carbide substrate due to the irregular sweep pattern when the related art sweep-through process is applied.

Accordingly, there is a need to provide a controlled and uniform sweep pattern to prevent irregularities even with non planar carbide substrates. In addition, there is a need to control the substrate properties and diamond properties without affecting each other possibly by providing an alternate binder material chemistry than that in the cemented carbide substrate.

SUMMARY

Accordingly, the present invention is directed to an arrangement for forming a polycrystalline diamond compact (PDC) that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An embodiment of a polycrystalline diamond compact (PDC) is provided in which defects and irregularities are minimized or prevented. Another embodiment controls a sweep pattern in forming a polycrystalline diamond compact (PDC). In a further embodiment, a polycrystalline diamond compact (PDC) is provided with an improved cutting edge and reduced costs.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for forming a polycrystalline diamond compact (PDC) includes disposing a first catalyst source on a first side of a plurality of diamond crystals; disposing a second catalyst source at a second side of the plurality of diamond crystals; and applying high temperature and high pressure to the plurality of diamond crystals, the first catalyst source and the second catalyst source such that the plurality of diamond crystals are sintered into a polycrystalline diamond compact.

In another embodiment, a method for forming a polycrystalline diamond compact (PDC) may comprise steps of disposing a first catalyst source and a second catalyst source near a plurality of diamond crystals; and sweeping the plurality of diamond crystals with the first catalyst source and the second catalyst source at high temperature and high pressure to form polycrystalline diamond.

In further another embodiment, a polycrystalline diamond compact may comprise a plurality of sub-micron diamonds; and a sintered catalyst, wherein a thickness of the polycrystalline diamond compact is more than 1.5 mm, wherein the polycrystalline diamond compact does not have a defect zone.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a cross-sectional view showing formation of a polycrystalline diamond compact (PDC) in accordance with a related art sweep-through process;

FIG. 2 is a cross-sectional view showing an polycrystalline diamond compact (PDC);

FIG. 3 is a flowchart showing a method of making polycrystalline diamond compact;

FIG. 4 is schematic diagram showing cross-sectional views to illustrate the arrangement used in a sweep-through process according to an embodiment;

FIGS. 5 and 6 are schematic views showing different arrangements of carbide substrates having non-planar surfaces in accordance with embodiments;

FIGS. 7-11 are SEM images showing the depth of the leach layers as a function of leach time using an aqua regia solution;

FIG. 12 is a graph summarizing the relationship between leach depth and leach time for the SEM images of FIGS. 7-11;

FIG. 13 is a flowchart showing a method of making polycrystalline diamond compact according to an embodiment;

FIG. 14 is a schematic diagram illustrating a dual sweep design according to one embodiment;

FIG. 15 is a flowchart showing a method of making polycrystalline diamond compact according to another embodiment;

FIG. 16 is a graph illustrating a wear rate comparison between the standard solid core and dual sweep solid core polycrystalline diamond; and

FIG. 17 is a schematic diagram illustrating a dual sweep design according to another embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to preferred embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. The detailed description of preferred embodiments can be read in connection with the accompanying drawings in which like numerals designate like elements.

FIG. 2 is a cross-sectional view showing a polycrystalline diamond compact (PDC) in accordance with one embodiment of the present invention. As shown in FIG. 2, the PDC includes a substrate 201, such as cemented carbide substrate, with a polycrystalline diamond table 203 bonded onto a top surface of the substrate 201. The polycrystalline diamond table 203 may initially not have a sweep material from the substrate 201. The sweep material may be cobalt, for example. The carbide substrate 201 may include tungsten carbide (WC) or other material and has a binder metal doped therein to improve integrity and strength of the carbide substrate 201. The binder metal may be cobalt or other iron-group element. A PDC is cylindrical shaped tungsten carbide substrate with from about 6% to about 15% cobalt therein having a diameter of 10-25 mm and a height of 5-20 mm where the polycrystalline diamond crystal is about 1-4 mm thick, for example. In one embodiment, the sweep material may be mixed with a plurality of diamonds before the plurality of diamonds are sintered onto the polycrystalline carbide substrate. In another embodiment, the sweep material may be from a cobalt source on the plurality of diamond crystals on a surface of the diamond crystals at a distance from the cemented carbide substrate.

FIG. 3 is a flowchart showing a method of forming a PDC in accordance with an embodiment of the present invention. FIG. 4 is a schematic diagram showing cross-sectional views to illustrate an arrangement according to a sweep-through process according to the flowchart of FIG. 3.

As shown in step 301 of FIG. 3, a carbide substrate is treated with an aqua regia solution to remove the binder metal from a surface portion of the carbide substrate. For example, 400 ml of aqua regia including HCl and HNO₃ in a 1:3 ratio may be used. The carbide may be completely immersed in the aqua regia acid to leach all exposed surfaces of the carbide substrate. Alternatively, a single surface or a portion of one or more surfaces may be leached by protecting the rest of the surfaces using gaskets such as Viton® gaskets or acid-resistant paste, for example. The leach depth and leach time depends on the acid composition in the aqua regia, temperature, amount of cobalt being leached and quantity of acid. After a certain time (depending on the parameters mentioned above), the aqua regia solution may get saturated with the leaching byproducts, the tungsten carbide on the surface may separate and go into the solution and the leach depth may stay constant. However, it is desired that a sufficient amount of leaching occurs so that there is insufficient cobalt or other materials in the surface portion of the carbide substrate to function as a sweep catalyst during the sintering process. A leaching depth of 20 microns may be sufficient to prevent the remaining binder material in the substrate from melting and sweeping into the mass of diamond powder during sintering, but more desirably, a leaching depth of 40 microns substantially eliminates the carbide substrate as source of sweep material during the sintering process.

After removing the carbide substrate from the aqua regia and cleaning the carbide substrate, a bed of diamond crystals are packed on the top of the treated carbide substrate as shown in step 303. The diamond crystals may be generally synthetic diamond in the form of a powder or grit.

As shown in step 305, a sweep material is disposed on an upper surface of the diamond crystal bed. That is, the sweep material is on a surface of the diamond bed opposite the carbide substrate. The sweep material may be cobalt, nickel, iron or their alloys or other suitable sweep materials. The sweep material may contain additives such as chromium or other metals such as cobalt, nickel and iron. Also, the binder metal in the carbide substrate need not be the same material as the sweep material. By contrast with the related art method, the aqua regia treatment of step 301 may have leached out any cobalt in the surface portion of the carbide substrate. Therefore, a separate sweep material is provided. The interface between the diamond bed and the sweep material may be planar to facilitate a uniform sweep front during the sintering process. A cup, such as a tantalum cup, or other refractory metal, may be disposed over the sweep material, diamond crystals, and carbide substrate to hold the materials in place, as shown for example in FIGS. 5 and 6. In addition, because the high pressure may be applied using a press with salt as the pressure transmitting medium, the cup also serves to prevent contamination.

Alternative to step 305, the plurality of diamond crystals may be mixed with a sweep material, such as cobalt. Additive materials, such as chromium, nickel and iron may be added to the mixture of the plurality of diamond crystals with the sweep material. The mixture of the plurality of diamond crystals with the sweep material and optional additive materials may be disposed on the treated cemented carbide substrate.

In step 307, the carbide substrate, the diamond crystals and the sweep material may be disposed in a press system so that high temperature and pressure may be applied. The particular parameters may vary by equipment, but parameters for pressure, temperature and time are: pressure may be greater than 50-55 Kbar for diamond to be stable and may be typically at 70-75 Kbar, 1400-1600° C., 5-10 min; another example at a lower pressure may be 60-65 Kbar, 1400° C.-1600° C., 20-30 min. In this manner, the diamond crystals are sintered into a polycrystalline diamond attached to the carbide substrate to form the polycrystalline diamond compact. Of course, additional materials as known in the art may be included in the sweep materials.

Because the interface between the sweep material and the diamond crystals is planar, a planar sweep front may be achieved. Thus, problems associated with the related art, such as the metal filled cracks/fingers and areas of poorly sintered diamond, may be prevented. Also, the sweep direction during the sintering process is toward the carbide substrate rather than away from the carbide substrate. Therefore, the described arrangement has the additional advantage of sweeping any contaminants away from the upper surface, i.e., the cutting edge. Here, the contaminants may be present due to a variety of sources, such as calcium from processing of the diamond crystals, contaminants within the diamond crystals that are exposed due to fracturing of the crystals at high pressure. Thus, the sweep direction improves the quality of the cutting edge. Moreover, a near net (final) shape is obtained, thereby reducing finishing costs. For example, in the disclosed process, contaminants are swept away from the cutting edge and into a region which does not take part in the cutting action. So the cutting edge contains well sintered diamond. In contrast, in prior art, the contaminants end up at the cutting edge, and hence additional finishing steps are necessary such as lapping, grinding etc to remove a portion of the diamond and expose a well sintered cutting edge.

FIGS. 5 and 6 are schematic views showing different arrangements of carbide substrates having non-planar surfaces in accordance with embodiments of the present invention. In FIG. 5, the carbide substrate has a raised central portion, and, in FIG. 6, the carbide substrate has a deep valley. Despite having non-planar interfaces between the carbide substrate and the diamond crystals, regular sweep patterns may be achieved using the arrangement of the sweep material and the HPHT processing as disclosed herein. FIGS. 5 and 6 also illustrate the use of a cup, such as a tantalum cup, as described above. Embodiments may have various surfaces other than those shown in FIGS. 5 and 6.

FIGS. 7-11 are SEM images showing the depth of the leach layers as a function of leach time using an aqua regia solution. For each image, 400 mL of aqua regia (300 mL HCl and 100 mL HNO₃) was applied at 24° C. to a tungsten carbide (WC) substrate having 11.5% cobalt (Co) therein and an exposed surface area of 0.3 in². For each leach time, two carbide substrates were used to check consistency. That is, ten carbide substrates were put in the aqua regia at the beginning and two substrates were taken out at each of the respective times.

FIG. 12 is a graph summarizing the relationship between leach depth and leach time for the SEM images of FIGS. 7-11. As shown in FIG. 12, the leach depth levels off after about 60 minutes of leach time under the conditions described above. It has been found that the sweep-through process resultant from cobalt in the carbide substrates is reduced but not eliminated when carbide substrates were leached for 20 minutes to achieve a leach depth of 28 microns. In this case, it was found that the sweep from the carbide substrate was sufficiently reduced so that the sweep from the cobalt disk on the diamond achieved before the sweep from the carbide substrate, thereby providing improved results as compared with the related art. It has also been found that the sweep-through process resultant from cobalt in the carbide substrates was substantially eliminated when the carbide substrates were leached for 60 minutes or more. Thus, under the specified conditions, it may be desired to leach the carbide substrates for at least 60 minutes. Moreover, it may be desired to achieve a leach depth of at least 40 microns.

By removing the cobalt in the layer of the carbide substrate closest to the diamond and by providing a different sweep source, the arrangement described in this application provides a way of altering and controlling the sweep pattern in the sweep-through process. As a result, PDCs may be obtained with improved cutting edges and reduced costs while also preventing defects and irregularities.

In one embodiment, as shown in FIG. 13, a method 1300 of forming a polycrystalline diamond compact (PDC) may comprise steps of disposing a first catalyst source on a first side of a plurality of diamond crystals in a step 1302; disposing a second catalyst source at a second side of the plurality of diamond crystals in a step 1304, wherein the first side may be an opposite side of the second side of the plurality of diamond crystals; and applying high temperature and high pressure, such as at least 45 Kbar and 1400° C. respectively, to the plurality of diamond crystals, the first catalyst source and the second catalyst source such that the plurality of diamond crystals are sintered into a polycrystalline diamond compact in a step 1306. The method 1300 may further include steps of melting the first catalyst source firstly, melting the second catalyst source secondly; sweeping the plurality of diamond crystals with the first catalyst source and the second catalyst source to form polycrystalline diamond.

In one embodiment, the first catalyst source and the second catalyst source may have different compositions. In another embodiment, the first catalyst source and the second catalyst source may have same composition, such as a transition metal catalyst. The transition metal catalyst may be iron group metal, such as cobalt. In one embodiment, the second catalyst may be a cobalt disk. In another embodiment, the second catalyst may be cobalt ring, such as 0.05″ thick, 0.99″ OD, 0.716″ ID. In one embodiment, the first catalyst source may have a plurality of perforated holes. The plurality of perforated holes may be formed after cemented tungsten carbide is leached by acid. The acid may leach cobalt catalyst out and leave unfilled pores where the cobalt catalyst used to occupy. In another embodiment, the second catalyst source may be an unleached cemented tungsten carbide. Because the cobalt solubilizes tungsten carbide, the melting point for the cobalt inside the cemented tungsten carbide may have a lower melting point than a pure cobalt disk or ring. So when temperature increases under pressure, the cobalt inside the tungsten carbide may melt first at lower temperature than cobalt disk or ring.

To further illustrate the dual sweep method 1300, FIG. 14 shows a schematic diagram of a dual sweep design of polycrystalline diamond compact 1400 according to one embodiment. During high temperature high pressure period, cobalt disks 1412 on a top 1402 of the plurality of diamonds (forming diamond bed 1410 in a tantalum cup 1408) melt and sweep through the diamond bed 1410 under high pressure and temperature. The cobalt ring 1414 at a bottom 1404 of the diamond bed 1410 in the cup 1408 may melt and sweep upward on the side of the diamond bed 1410 and toward a bottom center 1416 of cobalt ring 1414 under high pressure while the cobalt disk 1412 from the top 1402 sweeps down through the whole bed. The cobalt from the top of the diamond bed helps to sweep impurities of the diamond bed down to the bottom center 1416 and a nose area 1406, for example. The dual sweep action helps to improve the uniform distribution of Co with the Co ring helping distribution in the bottom zone while the main sweep of Co overlaps dead zone or insufficiently sintered diamond zone. Any cobalt source with different size and geometry may be used as the first or second cobalt source.

In another embodiment, as shown in FIG. 15, a method 1500 of forming a polycrystalline diamond compact (PDC) may comprise steps of disposing a first catalyst source and a second catalyst source near a plurality of diamond crystals, such as the first catalyst source and the second catalyst source being at an opposite side of the plurality of diamond crystals, in a step 1502; and sweeping the plurality of diamond crystals with the first catalyst source and the second catalyst source at high temperature and high pressure, such as at least 45 Kbar and 1400° C., respectively, to form polycrystalline diamond in a step 1504. The method 1500 may further include steps of melting the first catalyst source firstly, then the second catalyst secondly; sweeping the plurality of diamond crystals with the first catalyst source firstly, then with the second catalyst secondly. In one embodiment, the first catalyst source is cobalt cemented tungsten carbide and the second catalyst source may be a cobalt ring. The plurality of diamonds may be any size of diamonds, from 0.1 nm to 1000 microns. In one embodiment, the plurality of diamond is sub-micron diamonds.

A polycrystalline diamond compact may comprise a plurality of sub-micron diamonds and a sintered catalyst, wherein a thickness of the polycrystalline diamond compact is more than 1.5 mm, wherein the polycrystalline diamond compact does not have a defect zone. The defect zone, used herein, may refer to areas of poorly sintered diamond. The defect zone may normally be seen at the far end of the part from the cobalt source. Allowance for this defect zone may lead to additional finishing process and waste volume in the HPHT cell. Tight tolerance parts may be designed that reduces the cost of the finishing processes. The sub-micron diamonds may have sizes less than 0.9 microns, for example. In one embodiment, the sub-micron diamonds may have sizes from about 0.2 microns to about 0.8 microns.

Example 1

Referring again to FIG. 14, the cobalt ring 1414 such as 0.05″ thick, 0.99″ OD, 0.716″ ID was dropped into the tantalum cup 1408. The diamond feeds were poured into the tantalum cup 1408 to form a diamond bed 1410. A cobalt disk 1412 was put on the top of the diamond bed 1410.

This assembly was subjected to HP/HT processing at about 65 Kbar at temperature of about 1400° C. for 10 minutes to form the sintered submicron PCD tool blank 1400. The PCD tool blank 1400 was finished to produce a diamond layer about 20 mm.

A standard solid core PCD tool blank was made according to above procedure except without the cobalt ring under the diamond bed.

A blast wear test was employed to test the quality of PCD. In the blast wear test, submicron diamond media (average grain size 30 microns) was carried through a nozzle (having a diameter of 0.5 mm) by air pressure (about 75 psi) to impact the cross-section of a 20 mm thick sample of PCD at a distance of 1 cm. The sample was held at a 90 degree angle to the nozzle. The sample was then subjected to the high pressure stream of the media for 20 seconds. Weight loss was then measured and converted into a wear rate (mg/min). PCD bodies of the present disclosure exhibited similar wear rate as the standard solid core at the distance between about 2 mm to about 14 mm from the top cobalt disk 1412 (as shown in FIG. 14). But from about 14 mm to about 18 mm distance from the top cobalt disk, the dual sweep solid core PCD showed much lower wear rate than the standard solid core product. This indicated that PCD body of the present embodiment had better sintered diamonds than the standard solid core PCD.

Although not harder than polycrystalline diamond, the loose diamond media impacts the PCD, introducing defects until pieces can break away. This was directly linked to the quality and degree of sintering of the PCD part. Analysis of the samples is shown in FIG. 16 which compares wear rate and PCD thickness. Dual sweep solid core, prepared according the present disclosed method, shows an improved abrasive wear rate compared the standard solid core sample.

Example 2

Referring to FIG. 17, similarly to example 1, an assembly of carbide (containing sweep material 1, such as Cobalt), sub-micron diamonds and a second sweep material (Co with about 3 wt % Fe) contained by a tantalum cup was assembled and subjected to HPHT conditions (about 65 Kbar, about 1400° C.) for about 16 minutes.

The sub-micron diamond was swept first by the Co from the carbide (lower melting point) and secondly by the purer Co (higher melting point) from the top. The sweep zones between sweep 1 and sweep 2 overlapped and the defect zone carbon (from sweep 1) was solubilized by the sweep 2 Cobalt. This rendered a defect free, near net dimension body of sub-micron PCD diamond of thickness about 5 mm. This thickness might not be achievable by a one-sided sweep for the same materials. Also, the defect zone could not be eliminated if the melting points are the same.

To test whether the thicker sub-micron had good quality, the blast test (see description in Example 1) was applied to both sides of the sub-micron part as well as a sub-micron reference standard. Results were shown in Table 1.

TABLE 1
Sample	Wear Rate (mg/min.)	Standard Deviation
SM Std Side 1	10.6	0.05
SM Std Side 2	9.3	1.10
SM Thick Side 1	9.2	0.67
SM Thick Side 2	6.9	0.21

In Table 1 it could be seen that the wear rate of the thick sub-micron PCD was not negatively affected by the dual sweep process and, in fact, on average, the wear rate was improved.

Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method of forming a polycrystalline diamond compact (PDC), comprising:

disposing a first catalyst source on a first side of a plurality of diamond crystals;

disposing a second catalyst source at a second side of the plurality of diamond crystals; and

applying high temperature and high pressure to the plurality of diamond crystals, the first catalyst source and the second catalyst source such that the plurality of diamond crystals are sintered into a polycrystalline diamond compact.

2. The method of claim 1, wherein the first catalyst source and the second catalyst source have different compositions.

3. The method of claim 1, wherein the first catalyst source and the second catalyst source have same composition.

4. The method of claim 1, wherein both the first catalyst source and the second catalyst source are cobalt.

5. The method of claim 1, further comprising melting the first catalyst source firstly, melting the second catalyst source secondly.

6. The method of claim 1, wherein the first side is an opposite side of the second side of the plurality of diamond crystals.

7. The method of claim 1, wherein the second catalyst source is a cobalt ring.

8. The method of claim 1, wherein the second catalyst is a cobalt disk.

9. The method of claim 1, wherein the first catalyst source has a plurality of perforated holes.

10. The method of claim 1, wherein high pressure and high temperature are at least 45 Kbar and 1400° C., respectively.

11. The method of claim 1, further comprising sweeping the plurality of diamond crystals with the first catalyst source and the second catalyst source to form polycrystalline diamond.

12. A method of forming a polycrystalline diamond compact (PDC), comprising:

disposing a first catalyst source and a second catalyst source near a plurality of diamond crystals; and

sweeping the plurality of diamond crystals with the first catalyst source and the second catalyst source at high temperature and high pressure to form the polycrystalline diamond compact.

13. The method of claim 12, wherein the first catalyst source and the second catalyst source are at an opposite side of the plurality of diamond crystals.

14. The method of claim 12, wherein high pressure and high temperature are at least 45 Kbar and 1400° C., respectively.

15. The method of claim 12, wherein the first catalyst source is cobalt cemented tungsten carbide.

16. The method of claim 12, wherein the second catalyst source is a cobalt ring.

17. The method of claim 12, further comprising sweeping the plurality of diamond crystals with the first catalyst source firstly, then with the second catalyst secondly.

18. The method of claim 16, further comprising melting the first catalyst source firstly, then the second catalyst secondly.

19. The method of claim 16, wherein the plurality of diamonds is sub-micron diamonds.

20. A polycrystalline diamond compact, comprising:

a plurality of sub-micron diamonds; and

a sintered catalyst, wherein a thickness of the polycrystalline diamond compact is more than 1.5 mm, wherein the polycrystalline diamond compact does not have a defect zone.

21. The polycrystalline diamond compact of claim 20, wherein the sub-micron diamonds have particle sizes less than 0.9 microns.

22. The polycrystalline diamond compact of claim 20, wherein the sub-micron diamonds have particle sizes from about 0.2 microns to about 0.8 microns.