Method for manufacturing diamond composite

Abstract

The present invention relates to a method for producing a diamond composite, in which a diamond green body together with a infiltrant is placed on a graphite crucible, which is placed on a carbon source, whereby excess infiltrant leaks down into the carbon source during infiltration, thus avoiding excess infiltrant on the diamond composite.

Description

[Technical field]

[0001] The present invention relates to a method for producing a diamond composite in which residual infiltrating agent has already been removed during the infiltration step. [Background technology]

[0002] Diamond composites are known in the art and can be used in many applications such as cutting tools, mining bits, etc.

[0003] Diamond composites can be produced in a variety of ways, for example by forming a green body containing diamond particles and then reacting an infiltrant, usually silicon, with some of the diamond particles at high temperature to form a carbide binder, usually SiC, in which the diamond particles are embedded. This process can be carried out at both high temperatures and pressures, although diamond composites can also be produced by infiltration at lower pressures or even in a vacuum, depending on the type of composite required.

[0004] For diamond composites that are infiltrated at more moderate pressures, residual penetrant remaining in the diamond composite becomes an issue. If the final composite has holes or cavities, these are often filled with residual penetrant and must then be removed. If thin and / or hollow details are being printed, the residual solidified silicon can also cause cracks and breakage due to tensile forces that develop in the sintered body during solidification as the silicon expands. Residual penetrant can also react with the graphite sintering trays in the sintering furnace, and therefore they must be replaced more frequently.

[0005] Excess penetrant can be removed mechanically, for example by efficient blasting if the diamond composite does not contain internal holes or channels. If the diamond composite does contain internal holes or channels, blasting is not sufficient and the residual penetrant must be removed, for example by dissolving in a strong acid such as HF. Both of these processes are complex and time consuming, and the use of strong acids in particular is dangerous.

[0006] Residual penetrant can also lead to the infiltrated pieces adhering to the underlying material during infiltration, requiring additional steps to release the pieces.

[0007] Residual penetrant is a problem in all shapes of diamond composites, but especially in shapes that contain holes and cavities.

[0008] Additive manufacturing or 3D printing is known to be particularly well suited to creating complex geometric shapes with cavities, internal holes and channels that would otherwise be difficult and / or very expensive to achieve.

[0009] One object of the present invention is to achieve a method for producing a diamond composite that can reduce residual penetrant to a minimum in order to avoid the above-mentioned problems. [Brief description of the drawings]

[0010] [Figure 1] A schematic image of the setup before infiltration is shown, where A is the diamond green body, B is the infiltrant, C is the graphite crucible, D is the carbon source, and E is a small graphite sintering tray. [Diagram 2] 1 shows a stereolithographically printed diamond green body in the shape of a test cube according to Example 1. [Diagram 3] 3 shows a diamond composite in the shape of a test cube after infiltration according to the present invention from Example 1. [Figure 4] 1 shows the diamond green body from Example 2 in a graphite crucible along with the Si chunks before infiltration. [Diagram 5] 4 shows the diamond composite from Example 2 in the graphite crucible after infiltration. [Figure 6] 1 shows a CT scan of the diamond composite of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention relates to a method for preparing a diamond composite, the method comprising: - providing at least one diamond green body comprising at least 25% by volume of diamond particles and an organic binder; providing a penetrant; - placing at least one diamond green body on a graphite crucible together with an infiltrant; - 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 on the graphite crucible with the infiltrating agent, thereby forming at least one debinding diamond green body. - subjecting at least one debindered diamond green body to an infiltration step at a temperature between 1500 and 1680 °C for a time period between 5 and 60 minutes in vacuum or in the presence of a protective gas at a pressure below 50 mBar; Including, During the infiltration step, a graphite crucible is placed onto an underlying carbon source together with at least one debound diamond green body and an infiltrant. It concerns the method.

[0012] By diamond green body is meant herein a body comprising diamond particles and an organic binder, the amount of diamond particles being at least 25% by volume of the green body, preferably 30-75% by volume, more preferably 35-70% by volume.

[0013] By debindered diamond green bodies it is meant herein diamond green bodies from which at least 60% of the organic binder has been removed.

[0014] The debound diamond green body is placed on a graphite crucible together with the infiltrant. The diamond green body can be placed directly on the graphite crucible, next to the infiltrant, or on top of the infiltrant. The distance between the debound diamond green body and the infiltrant is preferably small enough that they are in direct contact with each other when the infiltrant becomes molten during infiltration.

[0015] The graphite crucible (also called a sip) can be any type of foil, sheet, sip, or crucible suitable for infiltration in a furnace. The graphite crucible should be thin and / or porous enough to allow residual infiltrant to pass through to the underlying carbon source. After infiltration, the graphite crucible reacts with the infiltrant and is composed mostly of carbide of the infiltrant, i.e., if the infiltrant is Si, the crucible is converted to SiC during infiltration.

[0016] Preferably, graphite foil or sheet is used. Foil or sheet is suitable for several reasons. The appropriate thickness is easily obtained and the foil or sheet is cost-effective since the graphite crucible is used only once. The thickness of the graphite foil or sheet is preferably 0.05-3 mm, more preferably 0.1-2 mm, and most preferably 0.1-0.5 mm.

[0017] In one embodiment of the present invention, a graphite crucible is formed to surround the diamond green body. For example, when using graphite foil, the foil is usually soft and can be wrapped around the diamond green body. This can be beneficial to avoid contamination on the surface of the diamond green body from the carbon source.

[0018] Optionally, the infiltrant may be selected from silicon, silicon compositions, aluminum and aluminum alloys.Preferably, the infiltrant is Si.The infiltrant can be provided as chunks, coarse powder, wafers, etc., preferably chunks or wafers.The amount of infiltrant is preferably present in large excess relative to the diamond green body, preferably more than 200% by weight excess of the amount of infiltrant theoretically required to completely infiltrate the diamond body.If the amount of infiltrant is too small, the diamond composite is not completely infiltrated and diamond graphitization occurs.

[0019] In one embodiment of the invention, the infiltrant is silicon. Suitably, the infiltrant may comprise silicon having a purity of greater than 99% by weight and may be present in large excess (greater than 200% by weight excess).

[0020] The infiltrant is placed on the graphite crucible with the debound diamond green bodies. The infiltrant should preferably be placed close to the debound diamond green bodies such that when the infiltrant melts it will come into contact with the diamond green bodies.

[0021] The graphite crucible is then placed on the carbon source so that the graphite crucible, together with the debindered diamond green body and the infiltrant on the graphite crucible, is in contact with the carbon source. The carbon source can be any material that contains mainly carbon, preferably at least 95% by weight of carbon. The carbon source should preferably be added in excess of the infiltrant used. This means that there must be enough carbon source to react with the total amount of infiltrant. The amount of carbon source used also depends on the size and number of diamond green bodies to be infiltrated. If the amount of carbon source is too small, there will still be excess infiltrant on the infiltrated diamond composite, which may cause the infiltrated diamond composite to stick to the graphite crucible.

[0022] As the carbon source, a powder containing carbon is preferred. It can be provided as an agglomerated powder or carbon particles. Preferably, the carbon source is a carbon or graphite powder, more preferably a carbon powder in the form of soot or carbon black. Preferably, the powder is not too compact so that the penetrant reacts easily with the powder. The powder is usually placed on a tray in the furnace, and the powder bed should preferably have a height of at least 5 mm, preferably at least 10 mm, but must be lower than the height of the tray to avoid leakage of the penetrant through the tray below on which the carbon source is placed.

[0023] Prior to infiltration, the green diamond body is subjected to at least one debinding step to form a debinding green body. Since the diamond green body contains a large amount of organic binder, at least a significant amount of the organic binder must be removed from the body in a controlled manner prior to infiltration to avoid cracking. Significant amount means herein that at least 60%, preferably at least 70% of the organic binder is removed. Some residual organic binder may remain in the debinding diamond green body in some cases. If the debinding step is performed as a separate step and the diamond green body has to be moved, some residual organic binder is beneficial to the strength of the diamond green body, which may otherwise easily break during handling. The residual organic binder may be removed in a second debinding step included at the beginning of the infiltration step in these cases, or may remain in the diamond green body. If the debinding diamond green body contains residual organic binder during infiltration, the carbon in the organic binder reacts with the infiltrant during infiltration, thus limiting the amount of diamond lost by reaction with the infiltrant.

[0024] The diamond green bodies are subjected to at least one debinding step before and / or after placing the at least one diamond green body on the graphite crucible with the infiltrating agent. Thus, the debinding step may be performed as a separate step or may be incorporated as a first step of the infiltration step.

[0025] For larger pieces, it may be advantageous to carry out the debinding step in a separate furnace, which makes it possible to remove the binder slowly and thus avoid cracks.

[0026] Preferably, the debinding step is integrated into the infiltration step and takes place in the same furnace.

[0027] The debinding step may include heating the diamond green body to a first maximum temperature by an incremental temperature increase. Optionally, the incremental temperature increase includes an increment of 0.1-5°C / min, preferably 0.1-2°C / min. Optionally, the debinding is performed in an environment selected from nitrogen, argon, hydrogen and mixtures thereof. Air can also be used as the environment. Optionally, the maximum debinding temperature ranges from 180°C to 550°C, preferably 200°C to 500°C. The debinding temperature depends on the type of organic binder used as well as the environment (gas used) in which the debinding step is performed. The duration of the debinding step can vary widely depending on the size of the diamond green body, the type of binder, the amount of binder and the atmosphere. If the debinding step is performed too quickly, cracks will occur in the diamond green body. The debinding step typically lasts for 1-50 hours, preferably 1-24 hours.

[0028] The infiltration is suitably carried out at a temperature between 1500 and 1680° C., preferably between 1550 and 1660° C. The infiltration is carried out in vacuum or in the presence of a protective gas, at a pressure of less than 50 mBar, preferably for a period of 5 to 60 minutes, preferably for a period of 10 to 45 minutes. In this specification, a vacuum means a pressure in the furnace of less than 5×10 -1 Less than mbar, preferably 5x10 -2 It is understood that the pressure is less than 50 mbar. An inert gas can be used to protect the furnace, preferably the gas is argon, the argon pressure then being preferably less than 50 mbar.

[0029] In one embodiment of the present invention, the temperature is increased from the debinding temperature at 30-60°C / min, preferably 30-55°C / min, until the desired infiltration temperature is reached. If the temperature is increased too slowly, graphitization of the diamond particles may occur before the infiltrant melts. A rapid increase in temperature also causes the infiltrant to melt quickly, thus achieving a low viscosity beneficial for efficient infiltration.

[0030] Cooling is then carried out in a controlled manner at a rate of 2-30°C / min until the temperature is at least below 1300°C.

[0031] In one embodiment of the present invention, at the end of the infiltration step, the inert gas, e.g., Ar or N, is added for at least 3 minutes, e.g., 3 to 45 minutes, before the temperature starts to decrease. 2 A pressure of less than 200 Bar is applied, preferably using Ar. This is done to further densify the composite and allow the infiltrant to fully react and form carbides.

[0032] During the infiltration process, some of the diamond particles will be consumed by reaction with the infiltrating agent, but it is preferred that the diamond composite contain at least 50% of the diamond particles present within the diamond greens.

[0033] The diamond green body can be formed using any method known in the art. As used herein, diamond green body refers to a green body that includes diamond particles and an organic binder. Examples of suitable manufacturing methods for diamond green bodies are 3D printing techniques or compression.

[0034] Any additive manufacturing or 3D printing technique known in the art can be used, such as binder jetting, stereolithography, etc. Preferably, stereolithography is used. The exact printing parameters applied will depend on the particular device used.

[0035] To form a print, typically a feedstock is first formed that includes diamond particles and an organic binder. The composition and properties, such as viscosity, of the feedstock depend on the type of composite being printed, the type of organic binder, and the printing equipment being used.

[0036] After printing, the printed green body is removed from the printing apparatus and preferably cleaned to remove excess powder and binder.

[0037] Depending on the type of printing technique used, the print may be subjected to a curing step after the printing step.

[0038] For example, in the case of diamond green bodies produced by stereolithography, curing occurs during printing and the green body is directly formed.

[0039] Diamond green bodies can also be made by more conventional methods such as compaction. A slurry is then prepared containing diamond particles and an organic binder, typically PEG (polyethylene glycol). The slurry is then dried, preferably using spray drying or freeze drying, to form granules, which are then pressed into green bodies, for example using a uniaxial press. The diamond green bodies obtained by compaction preferably have an organic binder content of 10-30% by volume, preferably 15-25% by volume.

[0040] The diamond particles used in the preparation of the diamond green body optionally have an average particle size of less than 200 μm, preferably less than 150 μm, more preferably less than 100 μm. Optionally, the diamond particles may comprise an average particle size in the range of 0.5 μm to 100 μm, preferably 1 μm to 100 μm, more preferably 2 μm to 80 μm. In particular, the diamond particles may comprise a bimodular or multimodular particle size distribution. Optionally, at least one fraction of the diamond particles comprises an average particle size of less than 30, 20 or 10 μm, and at least one fraction of the diamond particles comprises a particle size of less than 100, 80, 70, 60 or 50 μm. Such a configuration is advantageous for optimizing the diamond loading in the resulting green body and the final infiltrated article.

[0041] As used herein, organic binder means any binder common in the art of producing diamond green bodies. Depending on how the diamond green body is produced, the composition of the organic binder will vary.

[0042] The organic binder used in diamond green bodies produced by conventional compaction techniques is usually PEG (polyethylene glycol). Preferably, the organic binder is added in an amount of 10-30% by volume of the green diamond body, preferably 15-25% by volume.

[0043] Binders used in 3D printing have a more diverse composition. The type of binder depends on the type of printing technology used. The amount of organic binder is usually 5-60% by volume of the green diamond body, preferably 5-58% by volume. The organic binder preferably has one or more organic compounds selected from the group consisting of resins, polysaccharides, polyvinyl alcohol, cellulose and cellulose derivatives, lignin sulfonates, polyethylene glycols, polyvinyl derivatives, polyacrylates and mixtures thereof.

[0044] In one embodiment of the present invention where stereolithography (SLA) is used, the binder content is preferably 40-60% by volume, preferably 50-58% by volume. Organic binders used in stereolithography are usually photopolymers. This means that when exposed to light, for example from a UV lamp, the polymer reacts and hardens. Organic binders for stereolithography are also called photocurable resins.

[0045] Other additives common to diamond composites, such as TiC, B 4 C and ZrC may also be added to the feedstock. The amount of additive is usually very small, preferably less than 10% by weight, more preferably 0.1 to 5% by weight of the total diamond green body. EXAMPLES

[0046] Example 1 The diamond green bodies were prepared using a 3D printing technique called stereolithography (SLA).

[0047] The feed for the printing process was prepared from diamond powder and an organic binder. Diamond powder from Hyperion (MBM-ULC) was used, containing 80% by weight of diamond particles with a particle size of 20-30 μm and 20% by weight of diamond particles with a particle size of 4-8 μm.

[0048] 53% by volume of diamond powder was mixed with 47% by volume of an organic binder, a photoreactive resin from Incus GmbH.

[0049] The 3D printing process was carried out on an Incus 3D printer called Hammer HD35, using the following settings: layer height of 40 μm, exposure intensity of 100 mW, exposure time of 4.5 s, blade temperature of 82 °C, and chamber temperature of 18 °C.

[0050] The printed pieces were test cubes containing different patterns on the surface and in the holes (see Figure 2).

[0051] After printing, the pieces were removed, cleaned with IncuSol, and then preconditioned in vacuum at 120° C. for 72 hours.

[0052] The diamond-containing green bodies were then placed on a 0.2 mm thick graphite foil (Mersen Papyex N98) along with a Si infiltrant, which was provided in large excess (>200 wt%) of the green bodies and approximately 4–8 mm crushed Si pieces from ReSiTech.

[0053] 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, at a height of approximately 10-20 mm, and for comparison, some graphite foils were placed directly on a small graphite sintering tray.

[0054] The diamond green bodies were then debindered and infiltrated in the same furnace (GPS furnace). Debindering was performed by subjecting the diamond green bodies to H 2The temperature was then increased stepwise to 500°C in a vacuum. The temperature was then increased to 575°C and held for 1 hour. Vacuum was then applied and the temperature was increased further. From 700°C to 1350°C the temperature was increased at 43°C / min. At 1350°C the temperature was maintained for 2 minutes and then the temperature was increased further to 1630°C at 37°C / min. The temperature was maintained at 1630°C for 5 minutes after which Ar was introduced into the furnace for 10 minutes until the pressure was 100 Bar. The temperature at 1630°C was then maintained for another 10 minutes. The temperature was then decreased in a controlled manner to 1000°C at 7.8°C / min. It was then allowed to cool freely.

[0055] When the samples were examined after infiltration, the samples according to the invention (i.e. where a bed of carbon black powder was used) were easily removed and did not contain excess Si after visual inspection. The small holes in the prints of the invention were not filled with Si, and the samples not using carbon powder under the graphite foil stuck to the graphite foil and had to be removed by force. The small holes were filled with Si.

[0056] FIG. 3 shows one of the test cubes after infiltration according to the invention.

[0057] All pieces, both according to the invention (with a bed of carbon powder) and comparative (without a bed of carbon powder), were infiltrated to full density.

[0058] Example 2 The following raw materials were used to produce pressed compact diamond green bodies:

[0059] Sample A Diamond powder was dry blended together with fully deagglomerated TiC powder to form a homogenous mixture. The powder mixture was a multimodal mixture of MBM diamond from Diamond Innovation with particle sizes in the range of 6-80 μm that imparted high density during compaction. In addition to the diamond blend, 2 wt% TiC was also added to the slurry.

[0060] Using this mixture, a homogeneous slurry was then prepared with the addition of PEG1500 and PEG4000 as temporary organic binders and Acusol 460 NK as dispersant, and deionized water as fluid. The slurry was freeze-spray granulated and dried to produce granules for pressing, the amount of organic binder in the powder was 7.92% by weight, corresponding to 20% by volume. The granules were used for uniaxial pressing of green bodies in the shape of tool tips typically used in mining operations, to the highest possible green density, with the compression technique used. The pressing pressure was about 20 kN, and the relative diamond density in the green bodies was about 66%. The green bodies were slowly heated to 220°C in the presence of air to partially remove the PEG, producing partially debindered treated diamond green bodies of sufficient strength for further handling.

[0061] Samples B and C The diamond powders were dry blended together to form a homogenous mixture. The diamonds were a mixture of 80% by weight 20-30 micron and 20% by weight 4-8 micron diamonds of grade MBM from Diamond Innovations Inc. This mixture was then used to prepare a homogenous slurry with PEG1500 and PEG4000 added as temporary organic binders and deionized water as the fluid. The slurry was spray granulated to produce the granules for pressing, the amount of organic binder in the powder was 9.26% by weight, which corresponds to 23% by volume. The granules were used for uniaxial pressing of green bodies in the shape of cylinders (RNGN), 2 mm in diameter for sample B and 5 mm in diameter for sample C, typically used in metal cutting operations to the highest possible green density with the compression technique used. The force applied for compression of the green bodies was typically 40-50 kN. The relative diamond density in the green bodies was about 60%. Relative diamond density (percentage) is calculated by dividing the mass of diamond in the green body (excluding temporary organic binders and other additives) by the volume of the green body obtained from the press drawing of the press tool to obtain the X-ray density of diamond (3.52 g / cm 3) and multiplied by 100. Depending on the compaction technique and the shape of the body, the density may vary slightly between different parts of the green body. The green bodies were slowly heated to 220°C in the presence of air to partially remove the PEG and produce partially debindered treated diamond green bodies of sufficient strength for further handling.

[0062] The diamond green bodies (samples A-C) were then subjected to the same infiltration process as described in Example 1, the graphite foils were placed on a bed of carbon powder, ultrafine carbon black from IMCD Nordic AB, at a height of approximately 10-20 mm, and for comparison, one graphite foil containing the diamond green body (sample A) was placed directly on a small graphite sintering tray.

[0063] All diamond composites infiltrated according to the present invention (ie, where a bed of carbon black powder was used) were easily removed and did not contain excess Si after visual inspection.

[0064] The different weights of diamond green body / diamond composite at different stages are shown in Table 1. TIFF2024544783000001.tif56170

[0065] In Figure 4 the graphite foil with Si infiltrant and press bit (Sample A) is shown (before infiltration) and the infiltrated diamond composite after infiltration is shown in Figure 5. In Figure 6 an image of invention 1 using X-ray computed tomography (CT) is shown.

[0066] The samples that did not use carbon powder under the graphite foil (Comparative 1) adhered to the graphite foil and to each other and had to be removed by force.

[0067] As can be seen in Table 1, all pieces, both according to the invention (with a bed of carbon black powder) and comparative (without a bed of carbon powder), were infiltrated to full density.

Claims

1. 1. A method for preparing a diamond composite, comprising: - providing at least one diamond green body comprising at least 25% by volume of diamond particles and an organic binder; - providing a penetrant; - placing at least one diamond green body together with an infiltrant on 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 on the graphite crucible together with the infiltrant, thereby forming at least one debound diamond green body; - subjecting at least one debindered diamond green body to an infiltration step at a temperature between 1500 and 1680°C for a time period between 5 and 60 minutes in vacuum or in the presence of a protective gas at a pressure of less than 50 mBar; Including, During the infiltration step, a graphite crucible is placed over an underlying carbon source together with at least one debindered diamond green body and an infiltrant; method.

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

3. 3. The method of claim 1 or 2, wherein the graphite crucible is a graphite foil or sheet.

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

5. 3. The method of claim 1 or 2, wherein the penetrant is Si.

6. 3. The method of claim 1 or 2, wherein the infiltrating agent is added in an amount greater than 200% by weight of the at least one diamond green body.

7. 3. The method of claim 1, wherein the carbon source is carbon powder.

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

9. 3. The method according to claim 1 or 2, wherein at the end of the infiltration step, a pressure of less than 200 Bar is applied using inert gas for at least 3 minutes before the temperature starts to decrease.

10. 3. The method of claim 1 or 2, wherein the diamond green body is prepared by 3D printing.

11. The method of claim 10, wherein the diamond green body is prepared by stereolithography (SLA).

12. 3. The method of claim 1 or 2, wherein the diamond green body is prepared by compaction.

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