Diamond composites by lithography-based manufacturing

Abstract

A lithography based method for the manufacture of diamond composite materials in which green bodies are prepared by a layer-by-layer construction with resulting green bodies de-bound and sintered to achieve a dense high hardness material.

Claims

1. A method of preparing a diamond composite with a layered structure comprising: preparing a slurry containing a polymerisable binder, an initiator and diamond particles; forming a layered structure green body by stepwise irradiation curing of the slurry containing diamond particles, binder and initiator; forming a white body comprising at least 30 vol % diamond particles by de-binding the layered structure green body; introducing an infiltrant to the white body; and sintering the white body by heating the white body from an initial stage up to a maximum sintering temperature by incremental temperature increases at a rate of 10 to 60° C./min at a first pressure to form a layered microstructure having diamond rich layers with binder matrix rich layers in between, wherein the diamond rich layers are in the range of 25 to 200 microns and the binder matrix rich layers are in the range of 1 to 15 microns, and a content of the diamond particles in the diamond composite article being between 30 and 65 vol %, wherein the binder in the binder matrix rich layers is SiC.

2. The method as claimed in claim 1, wherein the diamond particles have a particle size of less than or equal to 200 μm.

3. The method as claimed in claim 1, wherein the diamond particles have a particle size of less than or equal to 100 μm.

4. The method as claimed in claim 1, wherein the diamond particles have a bi-modular or multi-modular particle size distribution and at least one fraction of diamond particles has a particle size of less than 30 μm and at least one fraction of diamond particles has a particle size of less than 100 μm.

5. The method as claimed in claim 1, wherein the step of de-binding includes heating the green body up to a first de-binding temperature via incremental temperature increases, wherein the de-binding temperature is in a range of from 200° C. to 600° C. and the incremental temperature increases are at increments of 0.1 to 2° C./min.

6. The method as claimed in claim 1, wherein the step of de-binding includes exposing the green body to a supercritical fluid.

7. The method as claimed in claim 1, further comprising continuing to heat the white body in a further stage at a second pressure greater than the first pressure.

8. The method as claimed in claim 7, wherein the maximum sintering temperature during the initial stage is in the range of from 850 to 1750° C.

9. The method as claimed in claim 7, wherein the second pressure at the further stage is at least 50% greater than the first pressure at the initial stage.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) A specific implementation of the present disclosure will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic illustration of the lithography processing apparatus to create green bodies according to one aspect of the present disclosure;

(3) FIG. 2 is an SEM image at 60× magnification of a cubic diamond/silicon carbide composite according to one aspect of the present disclosure;

(4) FIG. 3 is an SEM image at 100× magnification of a cubic diamond/silicon carbide composite according to one aspect of the present disclosure;

(5) FIG. 4 is a CT-image of a lithographic built profiled body according to one aspect of the present disclosure;

(6) FIG. 5 is a CT-image of a lithographic built, supercritical de-bound and sintered cube according to one aspect of the present disclosure;

(7) FIG. 6 is a CT-image of a lithographic built profiled body according to one aspect of the present disclosure;

(8) FIG. 7 is a schematic illustration of a mining insert; and

(9) FIG. 8 is backscattered SEM-image at 95X of a sintered structure of a partly polished cutting edge of the mining insert of FIG. 7 according to a prior art preparation method.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE DISCLOSURE

(10) A diamond composite is manufactured using lithography and in particular stereolithography. The process comprises generally, in a first stage, irradiation, such as LED-radiation curing of a free-flowing slurry to create a geometric three-dimensional article in the form of a compact, alternatively termed a green body. In a second stage, the green body is subjected to a de-binding process to remove the binder to obtain a white (or brown) body. As a final stage, the white body is infiltrated and sintered to create the dense diamond composite. The sintered body may then be finished by grit blasting and/or acid etching to yield a final superhard diamond composite suitable for a variety of applications such as use as a high abrasion resistant body for processing hard materials such as alloys and rock.

(11) With the aim of achieving a superhard diamond composite with low porosity, high density and a uniform distribution of the diamond grains within the sintered composite, bi-modular and multi-modular diamond feeds were prepared. Utilising a lithographic, and in particular a stereolithographic, process require dark raw materials such as silicon and/or dark carbides to be minimised within or excluded from the initial slurry. In particular, the slurry needs to be transparent or semi-transparent to allow transmission of the light radiation during the layer-by-layer stepwise building.

(12) The present disclosure is illustrated by reference to the non-limiting examples 1 to 5 that include selectively the following preparation stages.

(13) Diamond Powder Preparation

(14) Diamond powders were dry blended together to form a uniform mixture. The final diamond mixture was a mixture of 80 wt % 20 to 30 μm and 20 wt % 4 to 8 μm diamonds of grade MBM-ULC and MBM-LC obtained from Diamond Innovations Inc., thus having a weight fraction LD/ESD of 4. This diamond mixture is referred to herein as a PSD1 feed. In addition, a PSD2 feed was prepared as described above using MBM-ULC and MBM-LC grades from Diamond Innovations Inc., but having a multi-modular diamond particle size distribution ranging from 2-80 μm with a weight fraction of LD/ESD of 1.6.

(15) Slurry Preparation

(16) Polycrystalline diamond slurries was prepared by mixing i) PS-m-FlEA (a reaction product of 1 mol phthalic acid anhydride with 1 mol 2-hydroxyethyl acrylate); NK-ester CBX-1N (pentaerythritol triacrylate monophthalate) at 70%, ii) solvents PEG-400 and PPG-400 respectively. A dispersant was introduced and the obtained composition was mixed homogeneously. A photo initiator K-69 (bis(4-methoxybenzoyl)diethylgermanium, Ivoclar Vivadent AG) or Irgacure 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, Ciba SC) was then added and dissolved by simple stirring. As a final stage, the diamond feed PSD1 was added and dispersed to create free-flowing homogeneous slurries. Diamond loading of the PSD1 feed was 80 wt % which corresponds to about 54 vol % and the binder content was approximately 20 wt % which corresponds to 46 vol %.

(17) Lithographic Process and Apparatus—Green Building

(18) The lithographic process and apparatus is described generally with reference to FIG. 1 and comprises a container 100 (or polymerization tank) for the slurry 101. Container 100 has a transparent window 102 through which slurry 101 is selectively irradiated and cured from below. A micro-mirror array 103 is moveably positioned underneath container 100 and is a computer controlled. A radiation source 104 directs irradiating energy (in the form of LED generated light) onto mirror 103. Accordingly an image of the mirror 103 is projected onto the slurry 101 via window 102 using an optical device (not shown). Arranged above container 100 is a substrate carrier 106 having a carrier plate 109 movable in a Z-direction which carries a building platform 109 on which the green body 108 is constructed layer-by-layer. The carrier plate 109 is immersed in slurry 101 until a distance between carrier plate 109 and an inner surface of the container 100 corresponds to the desired layer thickness to be produced. The slurry layer, between carrier plate 109 and the inner surface of container 100, is then selectively irradiated and cured through the transparent window 102 via mirror 103. Cured regions of the slurry 101 adhere to carrier plate 109 and are then raised from the container 100 in the Z-direction. More slurry is then spread across window 102 using a wiper blade 110 and the selective irradiation curing process is repeated to construct the desired three-dimensional article.

(19) Greens were built according to the following stereolithographic parameters settings: lateral resolution 40 μm (635 dpi); number of pixel (X,Y) 1920×1080; building envelope (X,Y,Z) 76 mm×43 mm×150 mm; data format .stl (binary); slice thickness 25-100 μm; building velocity up to 100 slices per hour, 2.5-10 mm per hour; light source LED. After the building process, the greens are washed with organic solutions (washing agents) to remove excess slurry and create a fine surface finish.

(20) De-Binding (Heat Treatment)

(21) The de-binding was performed in air and involved slow temperature ramping at 0.3° C./minute intervals up to 220° C. and/or 320° C. The modest temperature increments were advantageous to avoid cracking of the greens during de-binding particularly as the washing agents tended to cause cracking during de-binding. The mass loss during de-binding differed depending on if the green had been cleaned or not after building and was between 8-11 wt %. Mass loss in wt % was calculated as ((m(built)−m(de-bound))/m(built))*100.

(22) De-Binding (Supercritical Solvent)

(23) De-binding trials using oscillating supercritical CO.sub.2 with pressures of 30 MPa (300) bars and temperatures between 55-65° C. for 4.5 h up to 28.5 h were also undertaken. The resulting greens were crack free. Additionally, the resulting sintered composites exhibited no external cracks with no major defects detected. The supercritical solvent processing was undertaken in accordance with the parameter configuration as detailed in table 1.

(24) TABLE-US-00001 TABLE 1 De-binding processing parameters using supercritical solvent extraction A22 M220 M220 Duration P200 Pressure H2100 H2200 OSC Speed Flow Process Step (min) CO.sub.2 (Kg/h) (MPa) Temperature ° C. Temperature ° C. (Sec) (rpm) Direction 0 Pre- 5 Constant Mode 0 Gradient Mode Constant Mode Constant Mode 0 0 Up Compression 0 to 0.35 52 55 1 Compression 55 Constant Mode Gradient Mode Constant Mode Constant Mode 30 20 Up 40 h 0.35 to 2 52 55 2 Compression 25 Gradient Mode Gradient Mode Constant Mode Constant Mode 30 20 Down 40 to 20 2 to 3 52 55 3 Main 90 Constant Mode Constant Mode 3 Constant Mode Constant Mode 30 20 Down Extraction 20 52 55 4 Main 90 Constant Mode Constant Mode 3 Constant Mode Constant Mode 30 20 Down Extraction 20 58 61 5 Main 90 Constant Mode Constant Mode 3 Constant Mode Constant Mode 30 20 Down Extraction 20 62 65 6 Depressurize 40 Constant Mode 0 Gradient Mode Constant Mode Constant Mode 30 20 Down 3 to 1 62 65 7 Depressurize 100 Constant Mode 0 Gradient Mode Constant Mode Constant Mode 0 0 Down 1 to 0 62 65 8 Depressurize 10 Constant Mode 0 Constant Mode 0 Constant Mode Constant Mode 0 0 Up 52 55 9 End 0 Constant Mode 0 Constant Mode 0 Constant Mode Constant Mode 0 0 Up 50 54 10 End 0 Constant Mode 0 Constant Mode 0 Constant Mode Constant Mode 0 0 Up 50 54
Sintering, Si-Infiltration and Densification

(25) A second de-binding step was applied under flowing hydrogen up to 500° C. with a temperature ramping of about 1° C./min. The Si-infiltration was performed under vacuum using a fast ramping temperature (about 50° C./minute) to a temperature of 1650° C. (1700° C.). After 10 min an Ar-pressure of 9.5 MPa (95 bar) was applied when the body was fully infiltrated which helped in the densification i.e. increased the final density and reduced porosity. The diamond brown bodies were placed in hBN-coated graphite crucibles with silicon lumps in large excess (200% in weight, placed in the bottom of the crucible). The silicon used was Silicon 99 Refined —Si 30 015 from Elkem with a silicon content of 99.4 wt % and oxygen content of 0.004% analyzed by LECO and a with a particle size of 10-100 mm. After an additional 10 min at 1650° C. 9.5 MPa (95 bar) under argon, the samples were allowed to cool down freely.

(26) Sintering and HIP-Infiltration Using a Zr-Capsule

(27) Si-infiltration may optionally be achieved by hot isostatic gas pressure (HIP) processing and/or high pressure high temperature (HPHT) processing to apply high pressure and temperature to the diamond powders to provide melting and Si-infiltration The brown bodies may then be placed in a Zr-capsule with a sealed bottom and with a dense-packed silicon powder blend completely surrounding the brown bodies. The Zirconium capsule may be manufactured from a tube with a commercial grade Zr, a purity of ≥92.2 wt % and with Hf-content of ≤4.5 wt %. The Si-powder blend may be a mixture of 86 wt % Silgrain® coarse from Elkem with a purity of 99.5 wt % and with an oxygen content of 0.119 wt % analyzed by LECO and grain size of 0.2-0.8 mm and Silgrain HQ from Elkem with a purity of 98% and with an oxygen content of 0.059 wt % analyzed by LECO and a grain size between 20-300 microns. The tap density of the Si-blend may be about 1.36 g/cm.sup.3, measured by filling a calibrated volume (Ford cup) with the Si-powder blend during subsequent manual tapping of the cup in the same way as performed during the filling of the capsules and then measuring the weight, which corresponds to about 58% of the theoretical sintered density of silicon. After filling the capsule, it may be sealed by welding. The sealed capsules may then be arranged in a HIP furnace and the temperature increased to 400° C. under vacuum. After a 30 min hold time at 400° C., the argon gas pressure may be rapidly raised to 4.0 MPa (40 bar) and then the temperature may be increased with 16°/min to 1300° C. At 1300° C. the pressure may be increased to 100 MPa (1000 bar) during roughly 55 minutes at constant temperature followed by a concurrent temperature and pressure increment until the maximum sintering temperature 1570° C. and the maximum pressure of 11.25 MPa (1125 bar) is reached after 20 min. The capsules may then be allowed to cool down freely during pressure release.

(28) Blasting and Etching

(29) Green bodies obtained following the Si-infiltration were then be processed to remove excess silicon from the surface and internally. Internal excess Si removal was achieved by introducing the green bodies to a bath containing 2% HF and 20% HNO.sub.3 in an aqueous solution for about 24 hours to remove Si-residuals surrounding the inserts. External excess Si removal was achieved using a grit blaster with SiC grit. The SiC grit removed Si from the sintered body but did not abrade the body itself, indicating that the body was well sintered and had a very high hardness and abrasion resistance.

(30) Quality Control

(31) Density, CT and ocular control was used for all samples and the target density was ≥3.23 g/cm.sup.3, 32 wt % diamond, 64 wt % SiC & 6 wt % Si corresponding to about 30 vol % diamond, 62 vol % SiC & 8 vol % Si, which is regarded as the minimum desired diamond content and maximum allowed residual Si content. It will be appreciated that Si has the lowest density and a decrease of free Si will have a preferred effect to increase the density. During the HIP-process a certain volume shrinkage occurs i.e., linear shrinkage of a few percent. The sintered bodies will also contain zirconium which will increase the sintered density significant compared to the purely Si-infiltrated parts. The density of the bodies were typically about 3.5 g/cm.sup.3.

(32) The sintered bodies were CT-scanned for defect detection. The CT-system used was a v|tome|x s240 from GE Sensing and Inspection Technologies, with the following settings: Magnification 9.1; Voxelsize (Resolution) 22 μm; X-ray voltage 80 kV; X-ray current 270 ρA; X-ray filter (Cu) 0.1 mm; Detector timing 200 ms; Detector averaging 3; Detector skip 1; Detector sensitivity 4; Number of projections 1200.

(33) Sintered Diamond Composites

Example 1 (LCM-Built Cube)

(34) A three dimensional cube green body was built from a slurry containing the PSD1 diamond feed according to the lithographic process described with reference to FIG. 1 and in accordance with the procedures under Slurry Preparation and Green Building. A layer building thickness of 50 μm was employed. The diamond density in the resulting green body was approximately 54% and was calculated as the mass of diamonds in the green body (polymerisable binders and other additions excluded) divided by the volume of the green body obtained divide by the X-ray density of diamonds (3.52 g/cm.sup.3) multiplied by 100. The resulting green bodies were carefully de-bound in air using slow ramping temperature of 0.3° C./minute up to maximum de-binding temperature of 220° C. The de-binding process was purposefully not completed as it was desired to retain residual carbon in the brown body for strength (of the de-bound green). When infiltrating with a carbide forming infiltrant (silicon) the residual carbon will react and form carbides to reduce the amount of diamond consumed. The de-binding process was optimized according to the processing parameters as excessive residual carbon in the brown will impede infiltration resulting in macroporosity/graphitization particularly at the inner region of the brown body.

(35) The brown body was then placed in the graphite cubicle and the sintering/Si-infiltration performed as detailed above, using 99.4% pure Silicon 99 Refined —Si 30 015 from Elkem with a particle size of 10-100 mm. After sintering the cube was treated by SiC grit blasting to remove residual Si on the surface, as detailed above. The cube was weighed and the density was determined using Archimedes' method with the result shown in table 2.

(36) TABLE-US-00002 TABLE 2 Physical characteristics of LCM-built diamond composite cube (Example 1) mass volume sintered density mass green mass brown sintered sintered Archimedes body (g) body (g) body (%) body (cm.sup.3) (g/cm.sup.3) 1.592 1.417 2.105 0.637 3.307

(37) Sintered inserts were prepared by careful mechanical polishing of the insert tip to a depth of ˜2 mm below the top, and a final polishing step was performed with 1 μm diamond paste. FIG. 2 and FIG. 3 are SEM images (of different magnification) of the cubic diamond-silicon carbide composites. It will be noted that the diamond grains are black and the silicon carbide phase is light grey, with residual silicon showing as white regions. It can be seen that the diamond distribution is uniform with no ‘large’ areas of residual silicon present. The images also clearly illustrate the printing layers within the resulting sintered composite body with each layer separated by narrow light lines/bands corresponding to the 50 μm layer thickness.

Example 2 LCM-Built Nozzle

(38) A three-dimensional nozzle green body was constructed from a slurry containing the PSD1 diamond feed at 80 wt % with 20 wt % organic additives as detailed in example 1. A green body nozzle was constructed layerwise to comprise a total height of 12 mm with two negative parts of diameter 9.85 mm separated by an annular groove having a diameter 7.75 mm and a height 2.1 mm. The nozzle comprised an internal bore having a hole size diameter of 1.3 mm to 3 mm. The resulting green was carefully de-bound in air using a slow ramping temperature of 0.5° C./minute with 60 minute holding times at 150° C. and 190° C. before continuing to heat up to a maximum de-binding temperature of 240° C. via a temperature ramping of 0.3° C./minute. The brown body was then placed in the graphite cubicle and the sintering/Si infiltration performed as described above under ‘Sintering—Si infiltration and densification’ using 99.4% pure Silicon 99 Refined —Si 30 015 from Elkem with a particle size of 10-100 mm. After sintering, the nozzle was acid treated followed by SiC grit blasting to remove residual Si internally and on the surface, as detailed above. The nozzle was weighed and the density determined using Archimedes' method with results shown in table 3.

(39) TABLE-US-00003 TABLE 3 Physical characteristics of LCM-built diamond composite nozzle (Example 2) mass volume sintered density mass green mass brown sintered sintered Archimedes body (g) body (g) body (%) body (cm.sup.3) (g/cm.sup.3) 1.785 1.582 2.335 0.709 3.295

(40) Surface roughness analysis was performed using a Wyko NT9100 on a 470.3×627.1 μm.sup.2 surface. The magnification was 10.1 and the field of view 1.0 times. The results are shown in table 4

(41) TABLE-US-00004 TABLE 4 Surface roughness of diamond composite nozzle (Example 2) Place of Stylus X Ra measurement Sa (μm) Sz (μm) (μm) OD (9.88 mm) 2.15 20.62 1.05 OD (7.75 mm) 1.99 16.26 0.76

(42) The outer dimensions of the sintered body in relation to the CAD-drawing were measured on different parts of the nozzle and was performed by scanning the outer surface of the whole body using a Mitutoyo CMM (Cordenat Measuring Machine) equipped with a Nikon laser head and employing Fokus software. The deviation from the CAD-model on the sintered part for the negative part with OD 9.88 mm was −0.076 mm to −0.040 mm and the deviation from the CAD-model for the green part with OD 7.75 mm was −0.031 to −0.016 mm. During the present infiltration and sintering process the size and shape of the de-bound green body is maintained and the dimensions of the sintered bodies are within at least 1.5% when compared to the built greens.

Example 3 LCM-Built Profiled Body

(43) A three-dimensional profile body having a generally curved outer surface was built from slurry containing the PSD1 diamond feed at 80 wt % with 20 wt % organic additives as detailed in example 1. The resulting green were carefully de-bound in air using a slow ramping temperature of 0.5° C./minute with holding times at pre-determined temperatures to avoid cracks. No cracks were found in the brown when examined by LOM and X-ray CT. The brown body was then placed in the graphite cubicle and the sintering/Si infiltration performed as described above using 99.4% pure Silicon 99 Refined —Si 30 015 from Elkem with a particle size of 10-100 mm. After sintering, the profiled body was treated by SiC grit blasting to remove residual Si on the surface, as detailed above. The body was weighed and the density determined using Archimedes' method with results shown in table 5.

(44) TABLE-US-00005 TABLE 5 Physical characteristics of LCM-built diamond profiled body (Example 3) mass volume sintered density mass green mass brown sintered sintered Archimedes body (g) body (g) body (%) body (cm.sup.3) (g/cm.sup.3) 2.344 2.109 3.109 0.941 3.304

(45) Surface roughness analysis was performed using a Wyko NT9100 on a 470.3×627.1 μm2 surface. The magnification was 10.1 and the field of view 1.0 times.

(46) TABLE-US-00006 TABLE 6 Surface roughness of diamond composite profiled body (Example 3) Place of measurement Sa (μm) Sz (μm) Stylus X Ra (μm) Cutting edge 1.76 14.72 1.01 Plane surface 1 1.84 15.93 0.92 Plane surface 2 1.86 19.73 0.87

(47) The outer dimensions of the sintered body in relation to the CAD-drawing were measured on different parts of the profiled body and were performed by scanning the outer surface of the whole body using a Mitutoyo CMM (Cordenat Measuring Machine) equipped with a Nikon laser head and employing Fokus software. When comparing the dimension of the built greens with the dimensions of the sintered bodies the deviation from the CAD-model for the green body compared with the final obtained body when viewing the the outer dimensions of the radial part was −0.023 mm to −0.014 mm.

(48) FIG. 4 is a CT-image of the LCM built profiled body according to example 3 which shows that the sintered body is free from internal defects as cracks and macroporosity.

Example 4 LCM-Built Cube De-Bound in Supercritical Solvent

(49) A three dimensional cube green body was built from a slurry containing the PSD1 diamond feed according to Example 1. As a departure from Example 1, de-binding was performed by extracting the LCM-binders using supercritical CO.sub.2 for 24 hours at a temperature of 60° C. and a pressure of 30 MPa (300 bar) according to table 1 and the de-binding process under De-binding (supercritical solvent). No cracks or internal defects were found in the brown or in the sintered part when examined by LOM and X-ray CT. The body was weighed and the density determined using Archimedes' method with results shown in table 7.

(50) TABLE-US-00007 TABLE 7 Physical characteristics of LCM-built diamond composite (Example 4) mass volume sintered density mass green mass brown sintered sintered Archimedes body (g) body (g) body (%) body (cm.sup.3) (g/cm.sup.3) 1.113 1.029 1.459 0.443 3.291

(51) FIG. 5 is a CT-image of the LCM-built supercritical de-bound and sintered cube according to example 4.

Example 5 LCM-Built Profiled Body

(52) A three-dimensional profile body having a generally curved outer surface was built from slurry containing the PSD2 diamond feed at 80 wt % with 20 wt % organic additives as detailed in example 1. As a departure from Example 1, de-binding was performed by extracting the LCM-binders using supercritical CO.sub.2 for 24 hours at a temperature of 60° C. and a pressure of 30 MPa (300 bar) according to table 1 and the de-binding process under De-binding (supercritical solvent). No cracks or internal defects were found in the brown body when examined by LOM and X-ray CT. The brown body was then placed in the graphite cubicle and the sintering/Si infiltration performed as described above using >99% pure CZ-Silicon wafers from Okmetic. After sintering, the profiled body was treated by SiC grit blasting to remove residual Si on the surface, as detailed above. The body was weighed and the density determined using Archimedes' method with results shown in table 8.

(53) TABLE-US-00008 TABLE 8 Physical characteristics of LCM-built diamond profiled body (Example 5) mass volume sintered density mass green mass brown sintered sintered Archimedes body (g) body (g) body (%) body (cm.sup.3) (g/cm.sup.3) 2.439 2.241 3.073 2.126 3.236

(54) FIG. 6 is a CT-image of the LCM-built supercritical de-bound and sintered profiled body according to example 5 which shows that the sintered body is free from internal defects such as cracks and macro porosity.

(55) Low Pressure Sintering—Infiltration in Vacuum at 1650° C. (Comparative Study)

Example 6 Surface Roughness of Prior Art Manufactured Parts

(56) A Homogenous slurry was prepared using the PSD1 diamond mixture described Diamond Powder Preparation 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 tool tips (buttons) typically used in mining operations (rock drilling) 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 30-50 kN and the press tool was made from a high wear resistance cemented carbide grade. 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 de-bound as described in De-binding (heat treatment) to create a brown body (white body) of enough strength for further handling.

(57) The diamond brown bodies were placed in hBN-coated graphite crucibles with silicon lumps in large excess (200% in weight, placed in the bottom of the crucible). The silicon used was Silicon 99 Refined —Si 30 015 from Elkem with a silicon content of 99.4 wt % and oxygen content of 0.004% analyzed by LECO and a with a particle size of 10-100 mm. The brown body was then placed in the graphite cubicle and the sintering/Si-infiltration performed as detailed above, using 99.4% pure Silicon 99 Refined —Si 30 015 from Elkem with a particle size of 10-100 mm. After sintering the cube was treated by SiC grit blasting to remove residual Si on the surface, as detailed above. The bodies was weighed and the density was determined using Archimedes' method with the result shown in table 9.

(58) Surface roughness analysis were carried and found in table 10. The top of the dome of the insert was than polished by diamond grits and the microstructure was investigated using SEM.

(59) TABLE-US-00009 TABLE 9 Physical characteristics of uni-axial pressed diamond profiled body (Example 6) mass volume sintered density mass green mass brown sintered sintered Archimedes body (g) body (g) body (%) body (cm.sup.3) (g/cm.sup.3) 7.707 7.016 11.126 3.365 3.303

(60) TABLE-US-00010 TABLE 10 Surface roughness of diamond composite mining insert (Example 6) Place of Stylus X Ra measurement Sa (μm) Sz (μm) (μm) OD (16 mm) 1.56 14.39 0.79 Cutting edge, 5.19 36.92 2.36 top of dome

(61) FIG. 7 is a drawing of a mining insert as described in example 6 where the cutting edge (tope of dome) (TD, and the outer diameter (OD) and height (h) are indicated. FIG. 8 is a backscattered SEM-image 95 X of the sintered structure of the partly polished cutting edge (top of dome) of the mining insert in Example 6. In the image large white Si-lakes as well as un-crushed granules are clearly visible. (Diamond=black, SiC=light grey, residual Si=white).