Polycrystalline cubic boron nitride

Abstract

A translucent polycrystalline cubic boron nitride body is provided. It contains no more than 2% by weight of hexagonal boron nitride grains and has a wavelength of less than 100 cm⁻¹ at 1064 nm. ‑1 The absorption coefficient.

Description

Invention Field

[0001] This invention relates to the field of polycrystalline cubic boron nitride and a method for preparing polycrystalline cubic boron nitride. Background of the Invention

[0003] Polycrystalline superhard materials such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PcBN) can be used in a wide variety of tools for cutting, machining, drilling, or degrading or abrasive materials such as rock, metal, ceramics, composites, and materials containing wood.

[0004] Abrasive briquettes are widely used in cutting, grinding, lapping, drilling, and other abrasive operations. They typically contain superhard abrasive particles dispersed in a second-phase matrix. The matrix can be metallic, ceramic, or cermet. The superhard abrasive particles can be diamond, cubic boron nitride (cBN), silicon carbide, or silicon nitride, etc. These particles can bond together to form polycrystalline materials during high-pressure and high-temperature compaction manufacturing processes, or they can be bonded together through a matrix of one (or more) second-phase materials to form sintered polycrystalline materials. Such objects are commonly known as polycrystalline diamond or polycrystalline cubic boron nitride, which respectively contain diamond or cBN as superhard abrasives. Examples of diamond and cubic boron nitride abrasive briquettes are described in U.S. Patent Nos. 3,745,623 and 5,328,875.

[0005] U.S. Patent No. 4,334,928 describes a sintered compact for use in tools, comprising essentially a matrix of 20-80 vol% cubic boron nitride and the balance at least one binder compound material selected from the group consisting of carbides, nitrides, carbonitrides, borides, and silicides of periodic table IVa or Va transition metals, mixtures thereof, and their solid solution compounds. In the sintered body with high-pressure boron nitride embedded within a continuous matrix, the matrix forms a continuously bonded structure. The methods outlined in this document all involve using mechanical milling / mixing techniques such as ball mills, mortars, etc., to combine the desired materials.

[0006] Polycrystalline superhard materials such as polycrystalline diamond (PCD) and PcBN can be used in a wide variety of tools for cutting, machining, drilling, or degrading or abrasive materials such as rock, metals, ceramics, composites, and materials containing wood. Sintered polycrystalline materials can be used as tool inserts to form abrasive or cutting edges.

[0007] PCD is not chemically stable relative to ferrous materials. This means that PCD cannot be used to machine ferrous materials such as steel. In such cases, PcBN is usually used instead of PCD. However, PcBN is not as hard or wear-resistant as PCD, mainly because it consists of a matrix phase other than cBN. Therefore, it is desirable to reduce or eliminate this matrix phase overall.

[0008] PcBN prepared without a binder has been reported. For example, CN104774591A describes binder-free PcBN abrasives prepared by high-pressure, high-temperature (HPHT) treatment of hexagonal boron nitride (hBN) to achieve the conversion of hBN into a binder-free PcBN body. JP2004200278 describes binder-free PcBN prepared using a pressure of 9.5 GPa and a temperature of 1700–1900 °C. The very high pressure means that it is difficult to scale up this product to a commercial method, and only very small samples can be prepared. It has been shown that it is very difficult to manufacture such PcBN bodies large enough to form usable tool inserts. Invention Overview

[0010] The aim is to provide a PcBN body that is essentially composed of cBN without a binder phase.

[0011] According to the first aspect, a translucent polycrystalline cubic boron nitride body is provided, comprising:

[0012] Polycrystalline cubic boron nitride grains;

[0013] No more than 2% by weight of hexagonal boron nitride grains;

[0014] At a wavelength of 1064 nm, less than 100 cm -1 The absorption coefficient.

[0015] Optionally, the polycrystalline cubic boron nitride body has wavelengths of 5 and 100 cm⁻¹ at 1064 nm. -1 Between, optionally at a wavelength of 1064 nm at 10 and 100 cm⁻¹ -1 Between, and optionally at a wavelength of 1064 nm at 20 and 100 cm⁻¹ -1 The absorption coefficient between them.

[0016] Alternatively, at least 50% of the cubic boron nitride grains are twinned.

[0017] The polycrystalline cubic boron nitride body is optionally disk-shaped and has a diameter selected between 10 mm and 25 mm and a height selected between 4 mm and 25 mm. These dimensions open up a range of practical applications for the object, particularly in the field of machining.

[0018] Alternatively, the polycrystalline cubic boron nitride body has a diameter selected between 12 mm and 16 mm and a height selected between 8 mm and 12 mm.

[0019] The polycrystalline cubic boron nitride body is optionally composed of polycrystalline cubic boron nitride grains and no more than 2% by weight of hexagonal boron nitride grains.

[0020] The polycrystalline cubic boron nitride body optionally includes any of the following: not more than 1.5 wt% hexagonal boron nitride grains, not more than 1.0 wt% hexagonal boron nitride grains, not more than 0.5 wt% hexagonal boron nitride grains, not more than 0.2 wt% hexagonal boron nitride grains, and not more than 0.1 wt% hexagonal boron nitride grains.

[0021] Alternatively, the polycrystalline cubic boron nitride body may have any of the following: a Knoop hardness greater than 3800 HK1 under a 1 kg load, a Knoop hardness greater than 4000 HK1 under a 1 kg load, a Vickers hardness greater than 35 GPa, a Vickers hardness greater than 40 GPa, a Vickers hardness greater than 45 GPa, and a Vickers hardness greater than 50 GPa.

[0022] Alternatively, the polycrystalline cubic boron nitride body has any of the following characteristics: less than 100 cm⁻¹ at a wavelength of 700 nm. -1 The absorption coefficient is less than 150 cm⁻¹ at a wavelength of 500 nm. -1 The absorption coefficient.

[0023] Alternatively, the polycrystalline cubic boron nitride body has any of the following characteristics: less than 50 cm⁻¹ at a wavelength of 1064 nm. -1 The absorption coefficient is less than 30 cm⁻¹ at a wavelength of 1064 nm. -1 The absorption coefficient.

[0024] According to the second aspect, a translucent polycrystalline cubic boron nitride body is provided, comprising:

[0025] Polycrystalline cubic boron nitride grains;

[0026] No more than 2% by weight of hexagonal boron nitride grains;

[0027] Less than 100cm at a wavelength of 350nm -1 The absorption coefficient.

[0028] Optionally, the polycrystalline cubic boron nitride body has wavelengths of 5 and 100 cm⁻¹ at 350 nm. -1 Between, optionally at a wavelength of 350 nm at 10 and 100 cm⁻¹ -1 Between, and optionally at a wavelength of 350 nm at 20 and 100 cm⁻¹ -1 The absorption coefficient between them.

[0029] Alternatively, at least 50% of the cubic boron nitride grains are twinned.

[0030] The polycrystalline cubic boron nitride body is optionally disk-shaped and has a diameter selected between 10 mm and 25 mm and a height selected between 4 mm and 25 mm.

[0031] Alternatively, the polycrystalline cubic boron nitride body has a diameter selected between 12 mm and 16 mm and a height selected between 8 mm and 12 mm.

[0032] Alternatively, the polycrystalline cubic boron nitride body is composed of polycrystalline cubic boron nitride grains and no more than 2% by weight of hexagonal boron nitride grains.

[0033] The polycrystalline cubic boron nitride body optionally includes any of the following: not more than 1.5 wt% hexagonal boron nitride grains, not more than 1.0 wt% hexagonal boron nitride grains, not more than 0.5 wt% hexagonal boron nitride grains, not more than 0.2 wt% hexagonal boron nitride grains, and not more than 0.1 wt% hexagonal boron nitride grains.

[0034] Alternatively, the polycrystalline cubic boron nitride body may have any of the following: a Knoop hardness greater than 3800 HK1 under a 1 kg load, a Knoop hardness greater than 4000 HK1 under a 1 kg load, a Vickers hardness greater than 35 GPa, a Vickers hardness greater than 40 GPa, a Vickers hardness greater than 45 GPa, and a Vickers hardness greater than 50 GPa.

[0035] The polycrystalline cubic boron nitride body optionally has any of the following characteristics: less than 100 cm⁻¹ at a wavelength of 700 nm. -1 The absorption coefficient is less than 150 cm⁻¹ at a wavelength of 500 nm. -1 The absorption coefficient.

[0036] According to a third aspect, a method for manufacturing polycrystalline cubic boron nitride is provided. The method includes:

[0037] Provide a green body containing hexagonal boron nitride particles, the green body having a density of at least 95% of the theoretical density of hexagonal boron nitride;

[0038] The green compact is subjected to a sintering process at a pressure of at least 7.7 GPa and a temperature of at least 2100 °C to transform hexagonal boron nitride into polycrystalline cubic boron nitride material.

[0039] Alternatively, the hexagonal boron nitride particles have an oxygen content selected from not less than 0.1% by weight and not more than 0.4% by weight.

[0040] As a further option, the hexagonal boron nitride particles have an oxygen content selected from no more than 0.3% by weight and no more than 0.2% by weight.

[0041] The temperature can be optionally selected from any of the following: between 2100°C and 2300°C, and between 2200°C and 2300°C.

[0042] Optionally, the pressure is selected from any of the following: 7.7 to 8.5 GPa and 8.0 to 8.5 GPa.

[0043] Alternatively, the sintering process may be maintained at maximum pressure and temperature for at least 3 minutes, at least 5 minutes, or at least 10 minutes.

[0044] The method optionally includes cold isostatic pressing of hexagonal boron nitride particles before sintering to densify the green body. As a further option, cold isostatic pressing is performed at a pressure between 0.2 GPa and 4 GPa. As a further option, cold isostatic pressing is performed at any pressure greater than 0.4 GPa and 0.6 GPa.

[0045] Alternatively, aside from unavoidable impurities, the green body is composed of hexagonal boron nitride particles.

[0046] Alternatively, the method further includes nitriding the hexagonal boron nitride particles in ammonia at a temperature between 900 and 1100°C before providing the green body containing the hexagonal boron nitride particles. This method may leave unavoidable impurities in green bodies otherwise composed of hexagonal boron nitride particles.

[0047] According to the fourth aspect, an apparatus comprising the polycrystalline cubic boron nitride body described in either the first or second aspect is provided.

[0048] As a further option, the device includes any one of an insert for machining tools, a wire drawing die, an optical transmission element, and a heat diffusion element.

[0049] Brief description of the attached diagram

[0050] To better understand the present invention and show how it can be practiced, embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0051] Figure 1 It is a flowchart outlining the steps to achieve a direct conversion from hBN to cBN;

[0052] Figure 2 These are X-ray diffraction traces from Example 2;

[0053] Figure 3 The Raman spectra of cBN disks synthesized from hBN powder AD sintered as detailed in Examples 1, 2, 3 and 4 are shown.

[0054] Figure 4 Raman spectra obtained from Examples 5, 6, 8 and 11 are shown;

[0055] Figure 5 These are scanning electron micrographs of Example 6;

[0056] Figure 6 These are scanning electron micrographs of Example 8;

[0057] Figure 7 The UV-Vis absorption spectra of Examples 6, 8, and 11 are shown;

[0058] Figure 8 Raman spectra obtained from Examples 13, 14 and 15 are shown;

[0059] Figure 9 The absorption coefficients of the materials in each embodiment are shown at different wavelengths.

[0060] Figure 10 The data shows the transmittance of the materials in each embodiment measured at different wavelengths.

[0061] Figure 11 Shows the Knoop hardness values ​​for the materials in each embodiment;

[0062] Figure 12 Displays the speed of sound measured for each sample;

[0063] Figure 13 The wear test results are shown for tool inserts made of PcBN material according to various embodiments; and

[0064] Figure 14 The results of a flank wear test are shown for a tool insert made of PcBN material used in the example.

[0065] Detailed description

[0066] A direct conversion from hexagonal boron nitride (hBN) to cubic boron nitride (cBN) was discovered, achievable under pressures exceeding 7.7 GPa and temperatures exceeding 2100 °C. This material exhibits no binder phase, and almost all hBN is converted to cBN. The final PcBN material has an hBN content of no more than 2% by weight. Due to the extremely low hBN content, the resulting PcBN material is translucent, exhibiting a wavelength of less than 100 cm⁻¹ at 1064 nm. -1 The absorption coefficient. Previously, binderless PcBN materials prepared by direct conversion of hBN to cBN were black, which was thought to be due to the large amount of unconverted hBN remaining at the grain boundaries between cBN grains.

[0067] Figure 1 This is a flowchart illustrating the process. The following numbers correspond to... Figure 1 The number.

[0068] S1. Provide hBN green blanks. This can be prepared, for example, by cold isostatic pressing at pressures between 0.2 and 4.0 GPa (with a minimum pressure of 0.4 or 0.6 GPa yielding better results). An oxygen content of greater than 0.1% by weight and not more than 0.4% by weight of oxygen in the hBN powder is considered advantageous. This includes free oxygen or other forms of oxygen such as water or -OH groups. While it is not desirable to be bound by a particular theory, small amounts of oxygen and / or water may act as catalysts in the conversion of hBN to cBN.

[0069] S2. Direct conversion of hBN to cBN was achieved during the HPHT process using a pressure of at least 7.7 GPa and a temperature of at least 2100 °C. Temperatures of up to 2300 °C and pressures of up to 8.5 GPa were found to be effective. The sintering process could be sustained for at least 3 minutes.

[0070] High twinning levels of the resulting cBN grains were observed in some samples. This is thought to occur during the nucleation process of cBN in the direct transformation, as it was observed in very short runs where incomplete transformation did not occur and some untransformed hBN remained.

[0071] The method described above allows for the production of large PcBN bodies. Disks with diameters of 10 mm to 18 mm and heights of 4 mm to 15 mm were prepared. Example

[0072] All examples were performed using hBN powder. Different hBN powders were tested, as listed in Table 1.

[0073] Table 1: Physical and chemical specifications of the hBN powder used in the examples presented herein

[0074]

[0075] To prepare Example 1, hBN powder A was compacted to form a green compact, which was then subjected to high pressure and temperature cycling for 3 minutes in an HPHT apparatus to directly convert hBN to cBN in a polycrystalline solid block. Initially, the pressure was varied between 7 and 7.5 GPa, and the temperature was varied between 2100°C and 2300°C to prepare sintered PcBN disks.

[0076] The presence of cBN was confirmed using Raman spectroscopy collected from the sintered disk, and the crystallinity quality within the disk was confirmed by signal-to-noise ratio. X-ray diffraction (XRD) was also used to confirm the presence of the cubic phase. This XRD data also revealed small amounts of unconverted hBN, such as... Figure 2 As shown in the image. Figure 2 The XRD spectrum shows a cBN 111 peak at 2θ angle 50.75 and a small residual hBN peak at 2θ angle 31.22.

[0077] Examples 2 to 4 are repetitions of the procedures detailed in Example 1, but each is performed using hBN powder (BD). Figure 3 The images show typical Raman spectra of cBN disks prepared from these materials.

[0078] The disks prepared in Examples 1 to 4 were opaque and black / dark gray in color. Examples 2 and 3 showed greater than 200 W / m. -1 K -1 (Using a Netzsch (RTM) laser flash device LFA 467 at 25°C) The high thermal conductivity (measured). High thermal conductivity is a desirable property in high-speed precision machining of high-resistivity superalloys (HRSA) because it allows heat generated during the machining process to dissipate or diffuse more quickly.

[0079] Based on the initial work performed in Examples 1 to 4, powder D was excluded from further work because it produced a poorly clear and noisy Raman spectrum, indicating poor crystallinity.

[0080] In Example 5, powder A underwent the same process as in Examples 1 to 4, however, the temperature was fixed at 2200°C and the pressure at 7.5 GPa. The resulting PcBN disk was translucent.

[0081] In Example 6, powder A underwent the same process as in Example 5, but at a pressure of 8 GPa. The resulting PcBN disk was translucent.

[0082] In Example 7, powder B underwent the same process as in Example 5. The resulting disk contained some cBN, but a significant amount of unconverted hBN remained.

[0083] In Example 8, powder B underwent the same process as in Example 6. The resulting PcBN disk was translucent and had a bluish tint.

[0084] In Example 9, powder C underwent the same process as in Example 5. The resulting PcBN disk was translucent and had a yellow / orange hue.

[0085] In Example 10, powder E underwent the same process as in Example 5. The resulting disk contained some cBN, but a significant amount of unconverted hBN remained.

[0086] As for Example 11, powder E underwent the same process as used in Example 6. The prepared cBN disk was translucent and had a blue / green hue.

[0087] The translucency observed in Examples 5, 6, 8, 9, and 11 (all falling within the scope of the claims) is due to the high purity of the prepared cBN and the reduction in scattering centers, such as residual hBN, and porosity. The Raman spectra obtained from these examples (in...) Figure 4 The good signal-to-noise ratio, resulting from the lack of scattering, indicates the high quality and crystallinity of the converted cBN. XRD spectra obtained from the surfaces of these disks also confirmed that the cubic phase was dominant with very little hBN remaining in these embodiments.

[0088] The microstructure of these embodiments also showed no identifiable porosity and numerous twins in the cBN grains. For Example 6... Figure 5 The scanning electron microscopy (SEM) images show a large number of twinned grains, and for Example 8... Figure 6 The SEM images similarly show a large number of twinned grains. Twins are advantageous in many machining applications because they increase Knoop microhardness. Average grain sizes ranging from 200 to 1000 nm were observed.

[0089] Examples 6 and 8 exhibit higher thermal conductivity than the previously synthesized examples (Examples 1 and 2) at lower pressures. The thermal conductivity measurements for Examples 6 and 8 are approximately 200 and 250 W / m², respectively. -1 K -1 This suggests that Examples 6 and 8 have lower porosity and lower impurities.

[0090] The translucency of PcBN sintered disks can be quantified by the absorption of UV-Vis light. Figure 7 The absorption spectra of Examples 6, 8, and 11 between 200 and 3200 nm are shown. The molar absorption coefficient α at 700 nm for Examples 6, 8, and 11 was calculated from this. (700nm) The measurements are 91.9, 89.7, and 24.4 cm respectively. -1 .

[0091] The average maximum dimension of the prepared part in any direction is 8.3 mm, and the average volume is 0.2 cm³. 3 This volume is impractical and inefficient for the mass production of precision workpieces.

[0092] To obtain larger material pieces from each HPHT cycle, where the minimum diameter of the recycled material is 13 mm, larger volumes of hBN are placed in the HPHT container. For the complete direct conversion of larger quantities of hBN powder, longer HPHT cycles are required. It was also found that densification of the hBN powder prior to HPHT cycling can maintain high pressure throughout the entire HPHT cycle.

[0093] In Example 12, hBN powder B was densified by cold isostatic pressing (CIP) cycling at approximately 3 GPa in a ceramic cup prior to HPHT sintering. The green body had a density greater than 95% of the theoretical hBN density, indicating low porosity. Higher pressures were used to achieve a density greater than 98% of the theoretical hBN density. The densified powder block was then subjected to the same HPHT cycling at 7.5 GPa as in Example 5. However, the cycling time (including heating and holding) was extended from 3 minutes to 10 minutes. The resulting disc was black and opaque, thus falling outside the scope of the claims. Raman spectroscopy and XRD confirmed the conversion from hBN to cBN and the presence of a small amount of hBN remaining in the sample.

[0094] As for Examples 13, 14, and 15, the hBN precursor powders B, A, and E underwent the same CIP and HPHT sintering processes as in Example 12, but at a maximum pressure of 8 GPa. The resulting PcBN disks were translucent and therefore fall within the scope of the claims. Raman spectroscopy, with a high signal-to-noise ratio, confirmed the presence of only cBN with good quality crystallinity. Figure 8 The Raman spectra from Examples 13, 14, and 15 are shown in the figure. XRD spectral data (not shown) also confirmed the presence of cBN alone.

[0095] As for Example 16, the hBN powder C underwent the same process as in Example 13. This sample failed to produce a single solid material piece. While it is undesirable to be bound by any particular theory, this is thought to be due to the high oxygen content in the hBN powder.

[0096] Examples 13, 14, and 15 have a minimum maximum dimension of 13 mm in any direction, and 0.7 cm. 3 The minimum volume and 3.469g cm -3 The average density. This density is 99.8% of the theoretical density of cBN (3.475 g cm³). -3 ).

[0097] To provide an indication of translucency, quantification is performed based on the absorption coefficient calculated from the absorption spectrum. Figure 9 The absorption coefficients of each sample are displayed. Absorption spectra of the samples were obtained between 200 nm and 1500 nm using a Perkin Elmer (RTM) UV-Vis / NIR Lamba 19 spectrophotometer, with the detector changed at 860 nm (PMT for 200 < λ < 860 nm and PbS for 860 < λ < 3200 nm) and the lamp changed at 319 nm (deuterium lamp for 200 < λ < 319 nm and halogen lamp for 319 < λ < 3200 nm), using a scan rate of 60 nm / min. -1Absorption modes with NIR sensitivity of 3 were also observed. Hot-pressed samples (HC) were also prepared, consisting of hot-pressed cBN containing residual hBN at the grain boundaries, which imparted its black color. It was observed that the black HC sample exhibited a significantly higher absorption coefficient at most wavelengths than the other samples.

[0098] Table 2 provides details of the absorption coefficients at various wavelengths.

[0099] Table 2: Absorption coefficients of various samples at specific wavelengths

[0100] Example 6 Example 8 Example 13 Example 14a Example 14 HC <![CDATA[α 200nm ]]> 205 216 219 294 205 202 <![CDATA[α 300nm ]]> 193 205 67.7 175 155 230 <![CDATA[α 350nm ]]> 159 187 37 115 129 204 <![CDATA[α 500nm ]]> 122 122 23.8 73.9 98.6 187 <![CDATA[α 700nm ]]> 91.9 89.7 23.4 63.5 82 174.6 <![CDATA[α 1064nm ]]> 59.5 58.7 20.3 53.8 72.3 Not measured

[0101] Examples 14a and 14b were prepared in the same manner as in Example 14, but both were prepared using a sintering pressure of 7.5 GPa. Examples 14a and 14b were prepared under the same nominal conditions but in different operations.

[0102] Figure 11 The Knoop hardness values ​​for each embodiment are shown. Example 6 has a Knoop hardness of approximately 3600 HK1 (38 GPa) under a 1 kg load, and Example 8 has a Knoop hardness of approximately 4000 HK1 (40 GPa) under a 1 kg load. Example 13 has a Knoop hardness greater than 4000 HK1 (40 GPa) under a 1 kg load.

[0103] For some embodiments, Vickers hardness was also measured, and the results are shown in Table 3.

[0104] Table 3: Vickers hardness of selected samples

[0105] Example Average / GPa SD 8 47 5.21 6 42 5.7 13 52 5.21

[0106] The effect of nitriding hBN powder prior to sintering was investigated to test its influence on reducing the oxygen content of the hBN powder. Six batches of Example 13 (referred to as Examples 13a to 13f) were prepared.

[0107] Prior to sintering, the hBN powders of Examples 13d, 13e, and 13f were heated to 900°C under nitrogen at a rate of 5°C. The powders were then held at 1000°C for 4 hours and nitrogen was replaced with ammonia at a flow rate of 2 L / min. The powders were then allowed to cool to room temperature. Nitriding of other samples was carried out for 1 to 4 hours using ammonia flow rates between 3 and 6 L / min and temperatures between 900 and 1100°C.

[0108] The nitrided examples were much less translucent than the unnitrided samples, were grayish-black in color, and had a lower measured oxygen content (between 0.038 and 0.131 wt%).

[0109] The speed of sound was measured using nitrided samples and control samples (Examples 13a, b, and c) and displayed. Figure 12 The speed of sound was measured using the "Olympus(RTM)38DL plus", which works by sending an acoustic excitation pulse through the sample and recording the time it takes for the pulse to return to the detector, taking into account the sample thickness.

[0110] It can be seen that the sound velocity of the nitrided examples is much lower than that of the unnitrided examples. This indicates that the samples were not fully sintered and that there is less bonding between adjacent grains of cBN compared to other samples.

[0111] While not wishing to be bound by any particular theory, it is believed that nitrided samples did not convert all hBN to cBN (this is supported by the color differences in the examples). It has been proposed (e.g., in JP2003192443 and WO2015194728) that a reduction in oxygen is beneficial for improving conversion. Nitriding replaces the oxygen / water ratio in the hBN powder, but in this case, a reduction to less than 0.1 wt% of oxygen / water is unfavorable and no complete conversion of hBN to cBN occurs. As mentioned above, water can act as a catalyst for cBN nucleation. This work proposes that oxygen levels between 0.1 and 0.4 wt% in the hBN powder, and particularly between 0.1 and 0.2 wt%, are optimized for providing sufficient catalysis for the conversion of hBN to cBN.

[0112] The binderless PcBN materials prepared as described above have numerous applications. Their hardness and toughness make them suitable for mechanical applications such as machining, turning, and wire drawing dies. Their translucency allows them to be used in optical applications. Their thermal conductivity allows them to be used in heat sink / heat diffusion applications.

[0113] To test mechanical properties, tool inserts were prepared using Examples 6, 8, 13, and 14 by cutting them into triangles and welding the triangles onto carbide tools. The inserts had a CNGA12040852020 geometry with a chamfer width of 200 μm, a chamfer angle of 20°, and a ground joint of 10 μm. Additionally, Examples 13a and 14c were prepared under the same conditions as Examples 13 and 14, respectively, and subsequently annealed under vacuum at a heating rate of 5 °C / min to a holding temperature of 900 °C. The samples were then held at 900 °C for two hours before air cooling to room temperature. A control sample CS was also provided. CS is a commercially available grade of PcBN containing 90% cBN in the binder phase.

[0114] The tool wear rate was measured using a Vanadus 10 steel workpiece at a cutting speed of 100 m / min, a feed rate of 0.1 mm / revolution, and a depth of cut of 0.2 mm. Lateral wear marks (Vb) were also measured. Smaller wear marks indicate higher wear resistance and can be expected to result in longer tool life. (The last sentence appears to be incomplete and possibly refers to a different tool.) Figure 13 and 14 The binder-free PcBN materials all exhibited lower wear rates than the control samples, indicating improved wear resistance.

[0115] Transparency indicates the amount of residual hBN in PcBN and is therefore considered to have a positive impact on the mechanical properties of the resulting PcBN. While the above discussion refers to the mechanical properties of binderless PcBN, it will be appreciated that transparency allows for applications previously unsuitable for PcBN-type materials. For example, a low absorption coefficient may allow for applications in laser or laser-guided machining. As used herein, the term "optical transmission element" refers to any type of device that allows the transmission of electromagnetic radiation, particularly in the ultraviolet, visible, or far-infrared spectral range.

[0116] definition

[0117] As used in this article, "superhard material" is a material with a Vickers hardness of at least 28 GPa. Diamond and cubic boron nitride (cBN) materials are examples of superhard materials.

[0118] As used herein, PcBN (polycrystalline cubic boron nitride) material refers to a type of superhard material containing cubic boron nitride (cBN) grains. Typically, cBN grains are dispersed within a matrix containing metal or ceramic. However, this literature discusses PcBN without a matrix or binder phase, sometimes referred to as "binder-free PcBN." "Binder material" is understood to mean a matrix material that completely or partially fills pores, interstitials, or interstitial regions within a polycrystalline structure.

[0119] A multi-peak size distribution of numerous grains is understood to mean that the grains have a size distribution with more than one peak, each peak corresponding to a different "mode". Multi-peak polycrystalline materials can be fabricated by providing multiple grains from more than one source, each source containing grains with substantially different average sizes, and blending the grains or particles from that source together. In one embodiment, the PcBN structure may comprise cBN grains with a multi-peak distribution.

[0120] While the invention has been specifically shown and described with reference to embodiments, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for manufacturing a translucent polycrystalline cubic boron nitride body, the method comprising: Provided a green body comprising hexagonal boron nitride particles, the green body having a density of at least 95% of the theoretical density of hexagonal boron nitride, wherein the hexagonal boron nitride particles have an oxygen content selected from not less than 0.1% by weight and not more than 0.4% by weight; The green compact is subjected to a sintering process at a pressure of 8.0 GPa to 8.5 GPa and a temperature of 2200°C to 2300°C, thereby transforming the hexagonal boron nitride into a translucent polycrystalline cubic boron nitride material. and The method also includes: The hexagonal boron nitride particles are cold isostatically pressed before sintering to densify the green body.

2. The method according to claim 1, wherein the hexagonal boron nitride particles have an oxygen content selected from not less than 0.1% by weight and not more than 0.3% by weight.

3. The method according to claim 1, wherein the hexagonal boron nitride particles have an oxygen content selected from not less than 0.1% by weight and not more than 0.2% by weight.

4. The method of claim 1, wherein the sintering process is maintained at maximum pressure and temperature for at least 3 minutes.

5. The method of claim 1, wherein the sintering process is maintained at maximum pressure and temperature for at least 5 minutes.

6. The method of claim 1, wherein the sintering process is maintained at maximum pressure and temperature for at least 10 minutes.

7. The method of claim 1, wherein cold isostatic pressing is performed at a pressure between 0.2 GPa and 4 GPa.

8. The method of claim 7, wherein cold isostatic pressing is performed at a pressure greater than 0.4 GPa.

9. The method of claim 7, wherein cold isostatic pressing is performed at a pressure greater than 0.6 GPa.

10. The method of claim 1, wherein the green body is composed of hexagonal boron nitride particles.

11. The method of claim 1, further comprising nitriding the hexagonal boron nitride particles in ammonia at a temperature between 900°C and 1100°C before providing a green body containing hexagonal boron nitride particles.

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