Polycrystalline chemical vapour deposited diamond tool parts and methods of fabricating, mounting, and using the same
09981317 ยท 2018-05-29
Assignee
Inventors
Cpc classification
C23C16/01
CHEMISTRY; METALLURGY
B23B2228/04
PERFORMING OPERATIONS; TRANSPORTING
International classification
B23B27/00
PERFORMING OPERATIONS; TRANSPORTING
B23B27/20
PERFORMING OPERATIONS; TRANSPORTING
Abstract
A polycrystalline CVD synthetic diamond work piece for use in a polycrystalline CVD synthetic diamond tool, the polycrystalline CVD synthetic diamond work piece comprising: a working surface; and a rear mounting surface; wherein an average lateral grain size of the rear mounting surface is no less than 10 m, and wherein the working surface comprises: (a) smaller diamond grains than the rear mounting surface; (b) an average lateral grain size in a range 10 nm to 15 m; and (c) a Raman signal generated by a laser focused on the working surface which exhibits one or more of the following characteristics: (1) an sp3 carbon peak at 1332 cm.sup.1 having a full width half-maximum of no more than 8.0 cm.sup.1, (2) an sp2 carbon peak at 1550 cm.sup.1 having a height which is no more than 20% of a height of an sp3 carbon peak at 1332 cm.sup.1 after background subtraction when using a Raman excitation source at 633 nm; and (3) an sp3 carbon peak at 1332 cm.sup.1 is no less than 10% of local background intensity in a Raman spectrum using a Raman excitation source at 785 nm.
Claims
1. A polycrystalline CVD synthetic diamond work piece for use in a polycrystalline CVD synthetic diamond tool, the polycrystalline CVD synthetic diamond work piece comprising: a working surface; and a rear mounting surface; wherein an average lateral grain size of the rear mounting surface is no less than 10 m, and wherein the working surface comprises: (a) smaller diamond grains than the rear mounting surface; (b) an average lateral grain size in a range 10 nm to 15 m; and (c) a Raman signal generated by a laser focused on the working surface which exhibits both of the following characteristics: (1) an sp3 carbon peak at 1332 cm.sup.1 having a full width half-maximum of no more than 8.0 cm.sup.1; and (2) an sp2 carbon peak at 1550 cm.sup.1 having a height which is no more than 20% of a height of an sp3 carbon peak at 1332 cm.sup.1 after background subtraction when using a Raman excitation source at 633 nm.
2. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the average lateral grain size of the working surface is no less than 20 nm.
3. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the average lateral grain size of the working surface is no more than 12 m.
4. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the average lateral grain size of the rear mounting surface is no less than 12 m.
5. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the full width half-maximum of the sp3 carbon peak at 1332 cm.sup.1 for the working surface is no more than 7.0 cm.sup.1.
6. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the sp2 carbon peak at 1550 cm.sup.1 for the working surface is no more than 10% of the height of the sp3 carbon peak at 1332 cm.sup.1 after background subtraction when using the Raman excitation source at 633 nm.
7. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein a thickness from the working surface to the rear mounting surface is no less than 200 m.
8. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the working surface has at least one linear dimension of at least 6 mm.
9. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the polycrystalline CVD synthetic diamond work piece is in the form of: a wear part; a dresser; a wire drawing die; a gauge stone; or a cutter.
10. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the polycrystalline CVD synthetic diamond work piece comprises a cutting edge and the working surface extends from the cutting edge.
11. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the working surface has a surface flatness 5 m.
12. A polycrystalline CVD synthetic diamond work piece according to claim 1, wherein the working surface has a surface roughness R.sub.a20 nm.
13. A polycrystalline CVD synthetic diamond tool comprising: a polycrystalline CVD synthetic diamond work piece according to claim 1; and a holder to which the polycrystalline CVD synthetic diamond work piece is mounted, wherein the polycrystalline CVD synthetic diamond work piece is oriented such that the working surface of the polycrystalline CVD synthetic diamond work piece is exposed to form a working surface of the polycrystalline CVD synthetic diamond tool.
14. A method of processing a material using a polycrystalline CVD synthetic diamond tool according to claim 13, the method comprising: orienting the polycrystalline CVD synthetic diamond tool such that the working surface thereof is in contact with the material to be processed; and processing the material by providing relative movement of the material and the working surface of the polycrystalline CVD synthetic diamond tool while the working surface of the polycrystalline CVD synthetic diamond tool is in contact with the material being processed.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) For a better understanding of the present invention and to show how the same may be carried into effect, embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
(2)
(3)
(4)
(5)
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
(6)
(7) The working surface 4 comprises smaller diamond grain than the rear mounting surface 6. This is indicative of the working surface 4 having been formed from a processed nucleation face of the as-grown polycrystalline CVD synthetic diamond material with the rear mounting surface 6 having been formed of a processed growth face of the polycrystalline CVD synthetic diamond as described later. An average lateral grain size of the working surface 4 is in a range 10 nm to 15 m while an average lateral grain size of the rear mounting surface 6 is no less than 10 m.
(8) In this regard, the working surface 4 has a small, controlled, and well defined grain size which is suitable for achieving a fine surface finish in use. In contrast, the rear mounting surface 6 has a large, well inter-grown diamond grain structure providing mechanical support for the working surface 4.
(9) The exact average lateral grain size for the working surface 4 and the rear mounting surface 6 will depending on the particular application including the type of material to be processed and the desired surface finish required. For example, the average lateral grain size of the working surface 4 may be no less than 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 500 nm, 1 m, 2 m, or 5 m, and/or no more than 12 m, 10 m, 8 m, 6 m, 4 m, or 2 m, and/or any combination of the aforementioned upper and lower limits. Furthermore, the average lateral grain size of the rear mounting surface may be no less than 12 m, 14 m, 16 m, 18 m, 20 m, 30 m, 40 m, or 50 m.
(10) In relation to the above, an average lateral grain size of a polycrystalline CVD diamond surface can be measured using scanning electron microscopy (SEM). SEM images of a surface of a polycrystalline CVD diamond material indicate boundaries between grains such that individual grains can be identified and counted. Accordingly, an area of the polycrystalline CVD diamond surface can be imaged using SEM, the total number of diamond grains along a line across the image can then be counted, and then the line length can be divided by the number of grains along the line to obtain and an average lateral grain size. A number of lines across the SEM image can be analysed in this manner, optionally in perpendicular directions, and an average value calculated for the lateral grain size across the imaged area.
(11) In addition to selecting a suitable grain size structure for the working surface 4 and the rear mounting surface 6 as describe above, it is also important to ensure that the working surface 4 is formed of good quality diamond material with a low sp2 carbon content. As described in the summary of invention section of this specification, the quality of the diamond material at the nucleation face of a polycrystalline CVD diamond material is poor and generally has significant quantities of sp2 carbon and a low wear resistance which is insufficient for industrial applications which require long tool operating lifetimes, particularly given the high cost of diamond materials and tool parts. In addition, the high wear rate of the poor quality nucleation face of the polycrystalline CVD diamond material can lead to a relatively rapid change in the quality of surface finishing which is achieved during use. As such, if the nucleation face of polycrystalline CVD diamond material is to be used as the working surface 4 then it is important to ensure that poor quality nucleation material having a high sp2 carbon and a low wear resistance is removed during fabrication of the polycrystalline CVD synthetic diamond work piece 2.
(12) Raman spectroscopy has been found to be a particularly useful technique for measuring sp2 carbon content in localized regions. Raman spectroscopy will typically use a 500 nm-1000 nm light wavelength which, when focused on a surface of diamond, will sample a surface volume of approximately 1 m.sup.3. Non-diamond carbon peaks include: 1580 cm.sup.1graphite; 1350-1580 cm.sup.1nanocrystallite graphite; and 1550-1500 cm.sup.1amorphous carbon and graphitic phases. It has been found that if non-sp3 bonded carbon is evident to any significant extent in a Raman spectrum of a synthetic diamond material then the material will have poorer wear resistance. Accordingly, preferably the sp2 carbon content is sufficiently low as to not exhibit any significant non-diamond carbon peaks in a Raman spectrum of the material.
(13) The sp3 diamond Raman peak resides at approximately 1332 cm.sup.1. The width of the sp3 diamond Raman peak is known to be indicative of the crystal quality of the diamond material. According to certain embodiments, a Raman signal generated by a laser focused on a region of the working surface 4 exhibits an sp3 carbon peak at 1332 cm.sup.1 having a full width half-maximum of no more than 8.0 cm.sup.1, 7.0 cm.sup.1, 6.0 cm.sup.1, 5.0 cm.sup.1, 4.0 cm.sup.1, 3.0 cm.sup.1, 2.5 cm.sup.1, or 2.0 cm.sup.1. While such Raman signal parameters have previously been achieved in working surfaces formed from the growth face of polycrystalline CVD diamond material, embodiments of the present invention provide such parameters in a working surface formed from a processed nucleation surface of polycrystalline CVD diamond material comprising a small granular structure better suited to achieving very high quality machined surface finishes.
(14) According to certain embodiments, using a helium-neon laser (633 nm) as the Raman excitation source focused on a region of the working surface 4 produces a diamond Raman spectrum with an sp2 carbon peak at around 1550 cm.sup.1 which is no more than 20%, 10%, 5%, 1%, 0.1%, 0.01%, or 0.001% of the height of the sp3 diamond Raman peak residing at around 1332 cm.sup.1 after background subtraction. The amount of sp2 carbon may alternatively be assessed by measuring the height of the sp3 diamond Raman peak residing at approximately 1332 cm.sup.1 relative to the height of the local background to that peak which is due to impurities such as sp2 carbon. According to certain embodiments, using a Raman excitation source at 785 nm focused on a region of the working surface 4 produces a diamond Raman spectrum with an sp3 carbon peak at approximately 1332 cm.sup.1 which is no less than 10%, 20%, 30%, 40%, 50%, 60%, or 70% of the local background intensity in the Raman spectrum. Again, while such Raman signal parameters have previously been achieved in working surfaces formed from the growth face of polycrystalline CVD diamond material, embodiments of the present invention provide such parameters in a working surface formed from a processed nucleation surface of polycrystalline CVD diamond material comprising a small granular structure better suited to achieving very high quality machined surface finishes. Certain embodiments may meet all three of the Raman measurement parameters as outlined above.
(15) In addition to the characteristics of the working surface as described above, the polycrystalline CVD synthetic diamond work piece may be fabricated to have relatively large dimensions, both in terms of thickness and length.
(16) A relatively high thickness from working surface to the rear mounting surface is useful for a number of reasons: (i) it provides bulk polycrystalline CVD diamond material to support the working surface; (ii) it allows for significant wear of the working surface while still maintaining a geometry and integrity for further use extending lifetime; (iii) it allows the work piece to be fabricated into a larger range of geometries; and (iv) growth of thicker polycrystalline CVD diamond material can results in better inter-growth of larger micron scale diamond grains having an average lateral size of no less than 10 m providing further mechanical support for the working surface. For example, a thickness from the working surface to the rear mounting surface may be no less than 200 m, 400 m, 600 m, 800 m, 1 mm, 1.5 mm, or 2 mm. The precise thickness will depend on the specific application and its requirements in terms of tool geometry, mechanical strength, and lifetime.
(17) By providing a well inter-grown micron scale polycrystalline CVD synthetic diamond work piece as described above, it is possible to achieve a robust work piece with a relatively high tensile rupture strength. For example, the work piece may have a tensile rupture strength with the working surface in tension of: 760 MPan for a thickness of 200 to 500 m; 700 MPan for a thickness of 500 to 750 m; 650 MPan for a thickness of 750 to 1000 m; 600 MPan for a thickness of 1000 to 1250 m; 550 MPan for a thickness of 1250 to 1500 m; 500 MPan for a thickness of 1500 to 1750 m; 450 MPan for a thickness of 1750 to 2000 m; or 400 MPan for a thickness of 2000 m, wherein multiplying factor n is 1.0, 1.1, 1.2, 1.4, 1.6, 1.8, or 2. Furthermore, the work piece may have a tensile rupture strength with the rear mounting surface in tension of: 330 MPan for a thickness of 200 to 500 m; 300 MPan for a thickness of 500 to 750 m; 275 MPan for a thickness of 750 to 1000 m; 250 MPan for a thickness of 1000 to 1250 m; 225 MPan for a thickness of 1250 to 1500 m; 200 MPan for a thickness of 1500 to 1750 m; 175 MPan for a thickness of 1750 to 2000 m; or 150 MPan for a thickness of 2000 m, wherein multiplying factor n is 1.0 1.1, 1.2, 1.4, 1.6, 1.8, or 2.
(18) In addition to thickness and robustness as described above, a relatively large working surface, at least in one dimension, is required for certain applications and embodiments of this invention are particularly suited to applications where a very high quality machined surface finish is required approaching that achievable using a single crystal diamond tool but also when the size of the working surface is larger than that which is readily available in single crystal diamond form, at least at reasonable cost. As such, the working surface of the polycrystalline CVD diamond work piece may have at least one linear dimension of at least 6 mm, 8 mm, 10 mm, 12 mm, 15 mm, 20 mm, 30 mm, or 50 mm. Such dimensions are readily achievable using polycrystalline CVD diamond material.
(19) Further still, during fabrication the polycrystalline CVD synthetic diamond work piece may be processed to have a well-defined, flat, smooth, working surface which is advantageous for achieving a very high quality machined surface finish. For example, the working surface may have a surface flatness as defined by a peak to valley deviation from a desired form of 5 m, 4 m, 3 m, 2 m, 1 m, 0.5 m, 0.2 m, or 0.1 m and/or a surface roughness R.sub.a20 nm, 10 nm, 5 nm, 2 nm, or 1 nm. The term surface roughness R.sub.a (sometimes referred to as centre line average or c.l.a.) refers to the arithmetic mean of the absolute deviation of surface profile from the mean line measured, for example, by stylus profilometer over a length of 0.08 mm according to British Standard BS 1134 Part 1 and Part 2.
(20) It is envisaged that polycrystalline CVD synthetic diamond work pieces as described above may be used in a range of mechanical tool applications. For example, the polycrystalline CVD synthetic diamond work piece may be in the form of a wear part, a dresser, a wire drawing die, a gauge stone, or a cutter. A particularly preferred application is for high precision metal machining, e.g. aluminium machining. In such cases, the polycrystalline CVD synthetic diamond work piece may comprise a cutting edge 8 and a working surface 4 extending, for example in a perpendicular direction, from the cutting edge as illustrated in
(21) In such tool applications a polycrystalline CVD synthetic diamond work piece 2 as described above is mounted to a holder 20 as illustrated in
(22) The polycrystalline CVD synthetic diamond work piece 2 may be mounted to the holder via, for example, a metal braze bond 22. As previously described, a rear mounting surface of the polycrystalline CVD synthetic diamond work piece 2 may be provided with a metallization coating 10 to allow good adhesion of the metal braze. The metallization coating may comprise a carbide forming metal such as titanium which adherers to the diamond surface. A further bonding layer, such as gold, may be provided over the carbide forming layer to achieve good adhesion with typical metal braze bonds. An inert barrier layer, such as platinum, may be provided between the carbide forming layer and the bonding layer to prevent adverse reactions between the titanium and the gold layers at high temperatures in use. The braze join to the holder may comprise gold or alternatively may comprise copper and silver. Other alternatives are also known in the art.
(23)
(24)
(25) The layer of polycrystalline CVD synthetic diamond material may be in the form of a free-standing wafer or may be in the form of a layer of polycrystalline CVD synthetic diamond material disposed on a support substrate with the nucleation face exposed and the growth face bonded to the support substrate. The polycrystalline CVD synthetic diamond work pieces will therefore either be in the form of a freestanding piece of polycrystalline CVD synthetic diamond material or in the form of a layer of polycrystalline CVD synthetic diamond material disposed on a support substrate with the working surface exposed and a rear mounting surface bonded to the support substrate.
(26) Suitable free-standing wafers of polycrystalline CVD synthetic diamond material used as the starting point for embodiments of this invention are available from Element Six Limited. A variety of grades of polycrystalline CVD synthetic diamond material are available including mechanical grades, thermal grades, and optical grades. While mechanical grades are suitable for use in embodiments of the present invention, the present inventors have noted that many different grades of polycrystalline CVD diamond material may share a similar grain structure and size at and near the nucleation surface. As such, the grade of polycrystalline CVD diamond material used in embodiments of the present invention may not be limited to those previously identified as mechanical grades. For example, it is also envisaged that higher thermal conductivity grades, which have typically been shown to perform poorly in abrasives/mechanical testing, may be useful in certain embodiments of the present invention to achieve a very high quality machined surface finish as the higher thermal conductivity of such polycrystalline CVD diamond grades will result in a lower local tool tip temperature. As such, optionally the thermal conductivity of the polycrystalline CVD diamond material may be no less than 1000 Wm.sup.1K.sup.1, 1200 Wm.sup.1K.sup.1, 1400 Wm.sup.1K.sup.1, 1600 Wm.sup.1K.sup.1, 1800 Wm.sup.1K.sup.1, 1900 Wm.sup.1K.sup.1, 2000 Wm.sup.1K.sup.1, 2100 Wm.sup.1K.sup.1, or 2200 Wm.sup.1K.sup.1.
(27) Having regard to the nucleation face processing step, lower quality nucleation diamond material is removed by processing the surface to a depth in a range 50 nm and 30 m. If this processing step is too shallow then poor quality nucleation diamond material may remain on the surface which will ultimately form the working surface of the diamond tool piece leading to poor performance and tool lifetime. As previously described, Raman spectroscopy can be used to measure the quality of the diamond material of the processed nucleation surface to ensure that very little sp2 carbon remains at the surface which will for the working surface of the diamond work piece. Conversely, if the processing step is too deep then the average lateral grain size of the diamond grains which will ultimately form the working surface of the diamond work piece becomes too large and a very high quality machined surface finish is not possible. SEM analysis can be used to ensure that the correct granular surface structure is achieved. As such, the present inventors have found that there is an optimum depth range which allows the removal of poor quality nucleation diamond material while also retaining a surface which has a suitable grain size to achieve a very high quality machined surface finish.
(28) Within the aforementioned depth range, the specific depth to which the nucleation face is processed will depend to some extent on the particular application and the desired granular structure for that particular application. For example, the depth of the portion of the polycrystalline CVD synthetic diamond material removed from the nucleation face may be no more than 20 m, 15 m, 10 m, or 5 m and/or no less than 100 nm, 200 nm, 300 nm, 500 nm, or 1 m.
(29) Suitable surface processing steps for removing a portion of the nucleation face of the polycrystalline CVD diamond material to a desired depth are known in the art and include one or more of the following: mechanical lapping and polishing techniques; chemical techniques include etching techniques such as plasma etching using suitable gas chemistries including, for example, one or more of hydrogen, oxygen, argon (or other inert gases), and chlorine (or other halides)an example of an etching technique for achieving low surface roughness diamond surface finishes is described in WO2008/090511; chemo-mechanical processing (CMP) techniques which combine mechanical and chemical processing mechanisms utilizing CMP slurries including abrasive grit particles and chemical components which react with the surface of the super-hard material being processed to change the chemical composition of the surface making it easier to removesuch processes having being utilized for other materials and are now currently under development for super-hard materials such as those comprising diamond; laser beam cutting/ablatinglaser cutting is the industry standard for cutting of synthetic diamond products; high energy particle beam cutting/ablatingelectron beam cutting has been proposed for cutting diamond products in the past and has recently been adapted to cut super-hard materials at significantly faster rates when compared with laser cutting; electric discharge machining (EDM)this technique is useful for cutting electrically conductive super-hard materials such as boron doped diamond materials; and focussed ion beam (FIB) surface processingthis technique is known in the art for processing super-hard materials such as diamond.
(30) Ideally, a processing method that imparts very little sub-surface damage should be used to remove the desired amount in a controlled and uniform manner. Such a technique may include polishing with a fine grade polishing wheel or a CMP processes. The growth surface of the polycrystalline CVD diamond wafer is also generally processed to provide a smooth, flat reference surface for mounting the diamond work pieces.
(31) In addition, or even as an alternative, to removal of nucleation surface material as described above, it is also possible to control early stage growth of the polycrystalline CVD diamond material to reduce sp2 carbon content of the nucleation surface material and achieve a working surface which has the above described combination of low grain size and low sp2 content. For example, the polycrystalline CVD diamond material may be grown using a methodology which comprises: providing a substrate; seeding a surface of said substrate; growing a diamond nucleation layer on said surface using a chemical vapour deposition (CVD) technique; and growing a thicker layer of polycrystalline CVD diamond material over the diamond nucleation layer, wherein the method further comprises applying at least one of the following techniques: (a) using a nanocrystalline diamond powder for the seeding step, the nanocrystalline diamond powder having an average particle size of no more than 200 nm and a D90 particle size of no more than 500 nm thereby reducing the size of grooves formed in the substrate surface and consequently reducing void formation during diamond growth thereon when compared with a seeding process which utilizes larger seed particles; (b) using alternating CVD diamond growth and non-diamond carbon etch steps to fabricate the diamond nucleation layer, the technique comprising growing a diamond layer of a first thickness by chemical vapor deposition, etching at least a part of said diamond layer, repeating said steps of growing and etching at least a part of said diamond layer until an overall thickness of said diamond layer reaches a second thickness, wherein said step of etching at least a part of said diamond layer etches non-diamond phases preferentially over diamond phases thereby increasing the proportion of diamond phase in the diamond nucleation layer relative to non-diamond phases; (c) using a pre-growth etching step applied to the substrate surface after seeding and prior to growth of the diamond nucleation layer thereon, wherein crystalline seeds are deposited on the substrate surface during seeding and the pre-growth etching step comprises etching using a chemistry which is selected to etch the substrate surface preferentially over crystalline seeds on the substrate surface and to smooth the substrate surface thereby reducing nucleation sites formed by sharp groove edges on the substrate surface relative to nucleation sites provided by the crystalline seeds.
(32) The aforementioned techniques involve: increasing nucleation densities and reducing grooves in the substrate using fine nanoparticle seeding to reduce void formation and non-diamond carbon phases; using an alternating growth and etching procedure during early stage growth to reduce non-diamond carbon and increase grain size; and using a pre-growth etch selected to reduce nucleation on the substrate surface relative to the seeds to increase crystal domains and consequently diamond grain size during early stage growth. Advantageously these techniques can be used in combination with either two or all three techniques being applied together. For example, while a nanocrystalline powder can increase nucleation densities, reduce void formation and non-diamond carbon, and thus increasing thermal conductivity, if the nucleation density is too high then the crystal domain size can be reduced resulting in more grain boundaries which will reduce thermal conductivity. As such, techniques (a) and (c) may be applied in combination to allow a high but controlled nucleation to be provided allowing optimization of nucleation density versus crystal domain size while also lowering void formation, non-diamond carbon, and other defects. Technique (b) may then be used to further reduce the amount of non-diamond carbon during the early stages of polycrystalline CVD diamond growth and reduce the thickness of the nucleation layer before moving into a higher quality bulk polycrystalline CVD diamond growth phase.
(33) After growth and processing of a wafer of polycrystalline CVD diamond material as described above, the wafer is cut into a plurality of diamond work pieces. Cutting will typically be performed using a laser although other cutting methods such as e-beam cutting may be utilized. In certain embodiments, the diamond work pieces may be further surface processed after cutting. For example, edge preparation may be completed using standard fine grinding techniques. The edge quality and lifetime of the diamond tool may be further enhanced by using processes that impart less surface and sub-surface damage such as laser shaping processes.
(34) Another synthesis method for achieving the polycrystalline CVD diamond work pieces as described herein may be used which avoids the need for post-synthesis processing of the nucleation face of the as-grown polycrystalline CVD diamond material. Such a method may utilize a very flat, low surface roughness growth substrate and careful control of early stage diamond growth using seeding and early stage diamond growth techniques such as those described above to achieve good quality nucleation face diamond material. In this case, the nucleation face of the as-grown polycrystalline CVD diamond material may be sufficiently well formed that surface processing of the nucleation face is not required after removal of the growth substrate.
(35) For example, the growth substrate may have a surface flatness as measured over a length of 5 mm across the growth substrate of 5 m, 4 m, 3 m, 2 m, 1 m, 0.5 m, 0.2 m, or 0.1 m. Furthermore, the growth substrate may have a surface roughness R.sub.a20 nm, 10 nm, 5 nm, 2 nm, or 1 nm. Such a growth substrate may be formed, for example, of a carbide forming refractory metal substrate such as tungsten or a silicon wafer. The growth surface of the growth substrate is processed to a high degree of flatness and low surface roughness prior to diamond growth thereon. When used in combination with the seeding and early stage diamond growth processes as described previously a low sp2 diamond nucleation face can be achieved having a high degree of flatness and a low surface roughness. As such, another method of fabricating a plurality of polycrystalline CVD synthetic diamond work pieces as described herein is provided, the method comprising: growing a layer of polycrystalline CVD synthetic diamond material on a growth substrate, the layer of polycrystalline CVD synthetic diamond material having a nucleation face and a growth face, the nucleation face comprising smaller grains than the growth face, wherein the average lateral grain size of the growth face is no less than 10 m; wherein the growth substrate has a surface flatness 5 m as measured over a length of 5 mm across the growth substrate and a surface roughness R.sub.a20 nm; wherein growth of the polycrystalline CVD synthetic diamond material is controlled such that after removal of the growth substrate the nucleation face of the layer of polycrystalline CVD synthetic diamond material has: (a) smaller diamond grains than the growth face; (b) an average lateral grain size in a range 10 nm to 15 m; and (c) a Raman signal generated by a laser focused on the processed nucleation surface which exhibits one or more of the following characteristics: (1) an sp3 carbon peak at 1332 cm.sup.1 having a full width half-maximum of no more than 8.0 cm.sup.1, (2) an sp2 carbon peak at 1550 cm.sup.1 having a height which is no more than 20% of a height of an sp3 carbon peak at 1332 cm.sup.1 after background subtraction when using a Raman excitation source at 633 nm; and (3) an sp3 carbon peak at 1332 cm.sup.1 is no less than 10% of local background intensity in a Raman spectrum using a Raman excitation source at 785 nm, and cutting the layer of polycrystalline CVD synthetic diamond material to form a plurality of polycrystalline CVD synthetic diamond work pieces such that a working surface of each of the polycrystalline CVD synthetic diamond work pieces is formed of said nucleation face.
(36) In summary, embodiments of this invention utilize the anisotropic material properties of polycrystalline CVD diamond material in combination with careful growth and/or processing control to provide a diamond tool capable of very high quality machined surface finishing. Embodiments of the present invention complement single crystal diamond tools in aluminium and other material machining applications and also provide a solution for applications requiring long edge length tools capable of achieving very high quality machined surface finishing.
(37) While this invention has been particularly shown and described with reference to embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appendant claims.