METHOD OF MAKING A DIAMOND COMPOSITE

Abstract

In a method of making a diamond composite a diamond green body, together with an infiltrant, is placed onto a graphite crucible and the graphite crucible is placed onto a carbon source, such that during infiltration, excess infiltrant is leaked down to the carbon source and excess infiltrant is thus avoided on the diamond composites.

Claims

1. A method of preparing a diamond composite comprising the steps of: providing at least one diamond green body including at least 25 vol % of diamond particles and an organic binder; providing an infiltrant; placing the at least one diamond green body together with the infiltrant onto a graphite crucible; subjecting the at least one diamond green body to at least one debinding step before and/or after placing the at least one diamond green body together with the infiltrant onto the graphite crucible, thus forming at least one debound diamond green body; and subjecting the at least one debound diamond green body to an infiltration step at a temperature of between 1500 and 1680 C., in a vacuum or in a presence of a protective gas at a pressure of below 50 mBar, for a time between 5 and 60 minutes, wherein, during the infiltration step, the graphite crucible, together with the at least one debound diamond green body and the infiltrant, is placed onto an underlying carbon source.

2. The method according to claim 1, wherein the at least one diamond green body during the at least one debinding step is subjected to a temperature of between 180 and 550 C., for a time between 1 and 15 hours.

3. The method according to claim 1, wherein the graphite crucible is a graphite foil or sheet.

4. The method according to claim 3, wherein the graphite foil has a thickness of between 0.05 and 3 mm.

5. The method according to claim 1, wherein the infiltrant is Si.

6. The method according to claim 1, wherein the infiltrant is added in excess of 200 wt % of the at least one diamond green body.

7. The method according to claim 1, wherein carbon source is a carbon powder.

8. The method according to claim 7, wherein the carbon powder is provided as a powder bed with a height of at least 5 mm.

9. The method according to claim 1, wherein at an end of the infiltration step, a pressure of below 200 Bar is applied using an inert gas for at least 3 minutes before the temperature starts to decrease.

10. The method according to claim 1, wherein the diamond green body is prepared by 3D printing.

11. The method according to any claim 10, wherein the diamond green body is prepared by stereolithography.

12. The method according to any of claims claim 1, wherein the diamond green body is prepared by compaction.

Description

DRAWINGS

[0050] FIG. 1 shows a schematic image of the set up prior to infiltration where A is the diamond green body, B is the infiltrant, C is the graphite crucible, D is the carbon source and E is the compact graphite sintering tray.

[0051] FIG. 2 shows a diamond green body in the shape of a test cube printed with stereolithography according to Example 1.

[0052] FIG. 3 shows a diamond composite body in the shape of a test cube after infiltration according to the present invention from Example 1.

[0053] FIG. 4 shows a diamond green body from Example 2 in a graphite crucible together with Si lumps prior to infiltration.

[0054] FIG. 5 shows a diamond composite body from Example 2 in the graphite crucible after infiltration.

[0055] FIG. 6 shows a CT scan of the diamond composite body from Example 2.

EXAMPLE 1

[0056] Diamond green bodies were prepared using the 3D printing technique called stereolithography (SLA).

[0057] A feed for the printing step was prepared from diamond powders and an organic binder. Diamond powder from Hyperion, MBM-ULC, was used which contained 80 wt % of diamonds grains having a grain size of 20-30 m, and 20 wt % of diamonds grains having a grain size of 4-8 m.

[0058] 53 vol % of the diamond powder was mixed with 47 vol % of an organic binder being a photo reactive resin provided by Incus GmbH.

[0059] The 3D printing processes were performed in a 3D printer from Incus named Hammer HD35 using the following settings: 40 m layer height, 100 mW exposure intensity, 4.5 seconds exposure time, 82 C. blade temperature, 18 C. chamber temperature.

[0060] The printed pieces were test cubes comprising different patterns on the surface as well as holes, see FIG. 2.

[0061] After printing, the pieces were removed and cleaned using IncuSol followed by pre-conditioning at 120 C. for 72 hours in vacuum.

[0062] The diamond containing green bodies were then placed together with a Si infiltrant onto a graphite foil having a thickness of 0.2 mm (Mersen Papyex N98). The Si infiltrant was provided in large excess, >200 wt % of the green bodies, and was crushed Si pieces approximately 4-8 mm from ReSiTech.

[0063] When the samples were placed in the furnace, some of the graphite foils were then placed on top of a bed of carbon powder, ultrafine carbon black from IMCD Nordic AB, with a height of approximately 10 to 20 mm and for comparison, some graphite foils were placed directly onto the compact graphite sintering tray.

[0064] Debinding and infiltration were then performed in the same furnace, a GPS Furnace. The debinding was performed by, during about 7 hours, stepwise heating the diamond green bodies up to 500 C. in H.sub.2. After that, the temperature was increased up to 575 C. where the temperature was kept for 1 hour. Then vacuum was applied, and the temperature was increased further. From 700 C. to 1350 C. the temperature was increased by 43 C./min. At 1350 C. the temperature was kept for 2 minutes, after which the temperature was further increased by 37 C./min up to 1630 C. At 1630 C. the temperature was kept for 5 minutes after which Ar was introduced into the furnace during 10 minutes until the pressure was 100 Bar. After that, the temperature 1630 C. was kept for an additional 10 minutes. The temperature was then decreased in a controlled manner, 7.8 C./min, to 1000 C. After that it was free cooling.

[0065] When the samples were investigated after the infiltration, the samples according to the invention (i.e. where a bed of carbon black powder has been used) were easily removed and did not contain any excess Si after a visual inspection. The small holes in the printed bodies according to the present invention were not filled with Si, samples for which no carbon powder had been used under the graphite foil was stuck to the graphite foil and had to be removed by force. The small holes were filled with Si.

[0066] FIG. 3 shows one of the test cubes after infiltration according to the present invention.

[0067] All pieces, both according to the invention (with bed of carbon powder) and comparative (without the bed of carbon powder) were infiltrated to full density.

EXAMPLE 2

[0068] Pressed diamond green bodies were manufactured using the following raw materials.

Sample A

[0069] Diamond powders were dry blended together with a well de-agglomerated TiC powder to form a uniform mixture. The powder mixture was a multi-modal mixture of MBM-diamonds from Diamond Innovation with particle sizes in the range of 6 to 80 m, which gives a high density during compaction. In addition to the diamond blend, also 2 wt % of TiC was added to the slurry.

[0070] A homogenous slurry was prepared using this mixture and then adding PEG1500 and PEG4000 as temporary organic binders and Acusol 460 NK as a dispersant agent, with de-ionized water as the fluid. The slurry was freeze spray granulated and dried to produce granules for pressing and the amount of organic binders in the powder was 7.92 wt % corresponding to 20 vol %. Granules were used in uni-axial pressing of green bodies in the shape of tool tips typically used in mining operations to a green density as high as possible with the used compaction technique. The pressing pressures were about 20 kN and the relative diamond density in the green bodies was around 66%. The green bodies were slowly heated up to 220 C. in the presence of air to partially remove the PEG to create a partly de-bound diamond green body of enough strength for further handling.

Samples B and C

[0071] Diamond powders were dry blended together to form a uniform mixture. The diamond was a mixture of 80 wt % 20 to 30 micron and 20 wt % 4 to 8 micron diamond of grade MBM from Diamond Innovations Inc,. Homogenous slurry was prepared using this mixture and then adding PEG1500 and PEG4000 as temporary organic binders, with de-ionized water as the fluid. The slurry was spray granulated to produce granules for pressing and the amount of organic binders in the powder was 9.26 wt % which corresponds to 23 vol %. Granules were used in uni-axial pressing of green bodies in the shape of a cylinder (RNGN), 2 mm diameter for Sample B and 5 mm diameter for sample C, typically used in metal cutting operations to a green density as high as possible with the used compaction technique. The force applied for the compaction of the green bodies was typically 40-50 kN. The relative diamond density in the green bodies was around 60%. The relative diamond density in percentage was calculated as the mass of diamonds in the green body (temporary organic binders and other additions excluded) divided by the volume of the green body obtained from the press tool drawing divided by the X-ray density of diamonds (3.52 g/cm.sup.3), multiplied by 100. Depending on the compaction technique and the shape of the body the density can vary slightly between different parts of the green body. The green bodies were slowly heated up to 220 C. in the presence of air to partially remove the PEG to create partially de-bound diamond green body of enough strength for further handling.

[0072] The diamond green bodies, Samples A-C, were then subjected to the same infiltration step as described in Example 1 where the graphite foils were placed on top of a bed of carbon powder, ultrafine carbon black from IMCD Nordic AB, with a height of approximately 10 to 20 mm and for comparison one graphite foil containing diamond green bodies (Sample A), were placed directly onto the compact graphite sintering tray.

[0073] All diamond composites that were infiltrated according to the invention (i.e. where a bed of carbon black powder has been used) were easily removed and did not contain any excess Si after a visual inspection.

[0074] The different weights of the diamond green bodies/diamond composites at different stages are shown in Table 1.

TABLE-US-00001 TABLE 1 Weight Weight Relative Diamond Green debound density Sintered Density Green body Green after weight sintered body (g) body (g) pressing (%) (g) body (g/cm.sup.3) Invention 1 A 8.96 8.31 66 11.99 3.357 Invention 2 B 1.15 1.07 60 1.290 3.350 Invention 3 C 3.14 2.91 60 4.516 3.326 Comparison 1 A 9.10 8.47 66 11.99 3.360

[0075] In FIG. 4 the graphite foil with the Si infiltrant and the pressed bit (Sample A) is shown before infiltration and the infiltrated diamond composite after infiltration is shown in FIG. 5. In FIG. 6, an image of Invention 1 using X-ray computer tomography (CT) is shown.

[0076] The samples (Comparison 1) for which no carbon powder had been used under the graphite foil was stuck to the graphite foil and to each other and had to be removed by force.

[0077] All pieces, both according to the invention (with bed of carbon black powder) and comparative (without the bed of carbon powder) were infiltrated to full density as can be seen in Table 1.