Preparation process of large-diameter polycrystalline PCBN (Polycrystalline Cubic Boron Nitride) composite sheet

Abstract

The invention relates to a preparation process of a large-diameter polycrystalline PCBN (Polycrystalline Cubic Boron Nitride) composite sheet, which comprises the following steps of: 1, mixing a nano-metal binding agent, cubic boron nitride micro-powder and a hard alloy serving as raw materials, and mixing the cubic boron nitride micro-powder with the nano-metal binding agent; 2, the mixed materials are mixed in a three-dimensional mixer, and the mixed materials are put into a drying oven to be dried; 3, the screened powder and the hard alloy are put into a metal cup, a complex assembly is placed in vacuum equipment, heat preservation is conducted under the vacuum condition, and the complex assembly is assembled into a synthetic block through synthetic block assembling equipment; 4, a hinge type cubic press is adopted to control the sintering temperature and pressure by adjusting heating given parameters and pressure parameters under the high-temperature and high-pressure conditions, heating is conducted, and a sample is obtained; and 5, after the sample is sintered, carrying out a post-processing procedure to obtain a final product. The invention has the advantages of good wear resistance, low sintering condition, excellent bending strength and uniform and consistent hardness.

Description

Technical Field

[0001] The invention belongs to the technical field of PCBN materials, and in particular relates to a preparation process of a large-diameter polycrystalline PCBN composite sheet. Background Art

[0002] PCBN composite sheet is a superhard composite material made of cubic boron nitride particles and a binder composed in a certain proportion as raw materials, cemented carbide as the matrix, and sintered under high temperature and high pressure conditions through a specific assembly method. It has excellent properties such as high hardness, high wear resistance, high red hardness, and high chemical stability. It is mainly used in processing various hardened steels, thermal spray materials, chilled cast iron, and cobalt-based and nickel-based difficult-to-cut materials above HRC35; the composition of the binder in polycrystalline cubic boron nitride composite sheet (PCBN) plays a vital role in its performance. PCBN composite sheets with different binder components are used in different processing fields. At present, in the application field of high-temperature alloys, there is still a large gap between domestic products and foreign competitors, and the production capacity is also low. Most PCBN tools need to be imported from abroad; therefore, it is very necessary to provide a preparation process for a large-diameter polycrystalline PCBN composite sheet with good wear resistance, low sintering conditions, excellent bending strength, and uniform hardness. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a preparation process for a large-diameter polycrystalline PCBN composite sheet with good wear resistance, low sintering conditions, excellent bending strength and uniform hardness.

[0004] The technical solution of the present invention is: a preparation process of a large-diameter polycrystalline PCBN composite sheet, the preparation process comprising the following steps:

[0005] Step 1: Raw material preparation: Nano metal binder, cubic boron nitride powder and cemented carbide are used as raw materials, and the cubic boron nitride powder and the nano metal binder are mixed in a certain proportion, wherein the volume fraction of the cubic boron nitride powder accounts for 75-80%;

[0006] Step 2: Mix the mixed materials in a three-dimensional mixer by wet ball milling. After the materials are evenly mixed, pour out the balls at the same time, and put the mixed materials into an oven and bake them at 90-100° C. for 8 hours;

[0007] Step 3: Put the sieved powder and cemented carbide into a metal cup, assemble the composite by inverting three layers of heat-resistant metal cups, place the composite assembly in a vacuum device, keep it warm for 2 hours under vacuum conditions, and assemble it into a composite block using a composite block assembly device;

[0008] Step 4: Using a hinged six-sided top press under high temperature and high pressure conditions, the sintering temperature and pressure are controlled by adjusting the heating given parameters and the pressure parameters, and heating for 30-40 minutes to obtain a sample;

[0009] Step 5: After sintering, the sample undergoes post-processing to obtain a final size of 60 mm in diameter, 3.2-3.6 mm in total thickness, and 0.7-1.0 mm in polycrystalline CBN layer.

[0010] In the step 1, the particle size of the cubic boron nitride powder is a mixed particle size of 1-2 μm and 3-6 μm, with a purity of 99.9%; the cemented carbide is WC-11% to WC-13% Co.

[0011] The cubic boron nitride powder can be cubic boron nitride powder with an average particle size of 10 μm and 40 μm of magnesium-based catalyst.

[0012] The nano metal binder in step 1 is TiN powder with a particle size of 2-4 μm and a purity of 99.9%, Co powder with a particle size of 1-2 μm and a purity of 99.9%, and Al powder with a particle size of 1-2 μm and a purity of 99.8%.

[0013] The nano metal binder can be replaced by a high-purity β-Sialon phase, and the β-Sialon phase is prepared by spark plasma sintering.

[0014] The composite assembly in step 3 is placed in a vacuum device at a pressure of no more than 3×10 -4 The mixture was heated at 750 °C for 2 h under vacuum conditions of 1.34 °C.

[0015] The temperature control in step 4 uses a double platinum-rhodium B-type thermocouple of Pt6%Rh-Pt30%Rh to control the temperature range to 1480-1600°C, and the pressure range is 5.0-6.0GPa or 5.5-6.5GPa. Bi, Tl, and Ba are used for calibration at room temperature, and Ag is used for calibration at high temperature.

[0016] In step 4, the temperature range of 1480-1600° C. is divided into four sections by a temperature control method.

[0017] The post-processing steps in step 5 include outer circle peeling, alloy finishing, outer grinding, flat grinding, grinding and polishing.

[0018] The invention has the following advantages: when in use, the invention optimizes the ratio of the binder component and the cubic boron nitride (CBN) powder, assembles in a certain assembly mode, and then adds a certain amount of binder to the CBN powder, which can effectively reduce the sintering conditions and give the PCBN some specific properties; the invention utilizes a hinged six-sided top press to sinter a large-diameter PCBN composite sheet under high temperature and high pressure conditions, and ultrasonic scanning detection and analysis show that the sintered product is basically free of defects such as delamination and cracks; under the same processing conditions, from the comparative detection data of turning high-temperature alloys, it is analyzed that the PCBN tool of the sample has reached a relatively high level; the invention has the advantages of good wear resistance, low sintering conditions, excellent bending strength, and uniform hardness. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the embodiments.

[0020] Example 1

[0021] A preparation process of a large-diameter polycrystalline PCBN composite sheet, the preparation process comprising the following steps:

[0022] Step 1: Raw material preparation: Nano metal binder, cubic boron nitride powder and cemented carbide are used as raw materials, and the cubic boron nitride powder and the nano metal binder are mixed in a certain proportion, wherein the volume fraction of the cubic boron nitride powder accounts for 75%;

[0023] Step 2: Mix the mixed materials in a three-dimensional mixer by wet ball milling. After the materials are evenly mixed, pour out the balls at the same time, and put the mixed materials into an oven and bake them at 90° C. for 8 hours;

[0024] Step 3: Put the sieved powder and cemented carbide into a metal cup, assemble the composite by inverting three layers of heat-resistant metal cups, place the composite assembly in a vacuum device, keep it warm for 2 hours under vacuum conditions, and assemble it into a composite block using a composite block assembly device;

[0025] Step 4: Using a hinged six-sided top press under high temperature and high pressure conditions, the sintering temperature and pressure are controlled by adjusting the heating given parameters and the pressure parameters, and heating for 30 minutes to obtain a sample;

[0026] Step 5: After sintering, the sample was post-processed to obtain a final size of 60 mm in diameter, 3.2 mm in total thickness, and 0.7 mm in polycrystalline CBN layer.

[0027] In the step 1, the particle size of the cubic boron nitride powder is a mixed particle size of 1 μm and 3 μm, with a purity of 99.9%; the cemented carbide is WC-11%Co.

[0028] The nano metal binder in step 1 is TiN powder with a particle size of 2 μm and a purity of 99.9%, Co powder with a particle size of 1 μm and a purity of 99.9%, and Al powder with a particle size of 1 μm and a purity of 99.8%.

[0029] The composite assembly in step 3 is placed in a vacuum device at a pressure of no more than 3×10 -4 The mixture was heated at 750 °C for 2 h under vacuum conditions of 1.34 °C.

[0030] The temperature in step 4 is controlled at 1480°C by a double platinum-rhodium B-type thermocouple of Pt6%Rh-Pt30%Rh, with a pressure range of 5.0GPa. Bi, Tl, and Ba are used for calibration at room temperature, and Ag is used for calibration at high temperature.

[0031] The post-processing steps in step 5 include outer circle peeling, alloy finishing, outer grinding, flat grinding, grinding and polishing.

[0032] In this embodiment, performance test: In this experiment, three test points or positions are selected along the radial direction of the PCBN composite sheet to test the wear resistance, microhardness and bending strength respectively, and the uniformity of sample performance is judged according to the maximum difference of the test values ​​of the three test points or positions.

[0033] ① Wear resistance: For PCBN samples that have passed the appearance inspection and grinding and polishing, use electric spark wire cutting or laser cutting to process two test circles in the radial direction with a diameter of 1 / 2 of the sample radius, and mark the test positions of 1 point, 2 points and 3 points on the test circle (where 2 points are tangent to the two test circles, 1 point is tangent to the test circle and the center of the sample, and 3 points are tangent to another test circle and the sample and are symmetrical about 2 points and 1 point). According to the industry standard JB / T3235-1999, the wear resistance of the test points of the test circle is tested using a wear ratio tester. The test results are shown in Table 1.

[0034] Table 1 Wear ratio at different positions

[0035]

[0036] It can be seen from Table 1 that the wear ratio decreases gradually from the edge point to the center point in the radial direction, and the wear ratio of the center point relative to the edge point decreases by 8.2%. This is due to the uneven temperature and pressure along the radial direction, indicating that the wear resistance of the samples is basically uniform.

[0037] ② Microhardness: After the PCBN sample is polished, three microhardness test points are selected along the radial direction, and the test positions of point 1, point 2 and point 3 are marked (point 1 is at the center of the circle, point 3 is at the end point of the radius, and point 2 is at the midpoint of the radius). Then, the sample is placed on a HBRVU-187.5 type Burrows optical hardness tester. According to the standard ASTME384-2010, a diamond Vickers indenter is selected, and a force of 29.6N (F) is used to perform microhardness tests on the three points. Table 2 shows the hardness values ​​at different positions of the sample. The Vickers hardness tester measures the length d of the two diagonal lines of the indentation left by a regular pyramid diamond with a relative surface angle of 136° under a certain experimental pressure by optical magnification. 1 and d 2 , take the arithmetic mean d, according to the formula HV = 0.1891 × F / d 2 Find the hardness of the object being measured.

[0038] Table 2 Hardness values ​​at different positions

[0039]

[0040] It can be seen from Table 2 that the microhardness of the sample from the edge to the center shows a gradually decreasing trend, and the microhardness amplitude of the center point relative to the edge point is 6.6%, indicating that the microhardness values ​​of the samples are basically uniform.

[0041] ③ Bending strength: Cut three 35mm×4mm rectangular strips in the radial direction by wire EDM or laser (the same as the positions of 1, 2, and 3 marked when testing the microhardness), then remove the cemented carbide substrate by wire EDM, and make a 35×4×1 sample by surface grinder, and polish both sides of the CBN layer into a mirror surface, and then perform a bending strength test by the three-point bending method. According to the industry standard GB / T6569-2006, the bending strength of different positions of the PCBN composite sheet was measured. The results are shown in Table 3.

[0042] Table 3 Bending strength at different positions

[0043]

[0044] It can be seen from Table 3 that the bending strength values ​​of the samples along the radial direction gradually decrease from the center to the edge, and the bending strength decrease of the center relative to the edge is 9.25%, indicating that the bending performance of the samples is basically uniform.

[0045] ④Ultrasonic micro-imaging analysis: Ultrasonic non-destructive testing: The SO-NIX ultrasonic scanning microscope is used to perform ultrasonic scanning on the internal quality of PCBN piece by piece, and no defects such as cracks, delamination and inclusions are found in batches.

[0046] ⑤Cutting test: The standard cutting blade shape is made, the blade tip arc is 0.4, the blade is clamped on the MSSNL2525M12W tool holder, and the cutting test is carried out on the NEXUS200-ⅡL CNC lathe according to GB / T16461-1996 standard. The tool life is determined as the flank wear v b =0.3mm; compared with foreign PCBN tools, the cutting test rod material used is bearing steel GCr15 with a hardness of HRC61. During the test, the cutting speed is 100m / min, the cutting depth is 0.1mm, the feed rate is 0.1mm / r, and dry cutting is used; after cutting three times with each blade, the wear of the flank is observed, and the cutting depth is recorded for a total of 9 times; the cutting mileage and the wear of the flank are obtained according to the cutting results, and the surface roughness Ra value of the workpiece measured according to the wear test is obtained. From the experimental results, it can be seen that the tool made by the present invention can travel about 5000 meters, and the foreign tool can also travel about 4900 meters. The surface roughness Ra values ​​of the tool made by the present invention and the foreign tool in the initial wear stage and when the workpiece reaches the blunting standard are between 0.4μm and 0.7μm, and are all at the same quality grade.

[0047] In summary, ① the samples were tested for performance, with a wear ratio of 5425, a Vickers hardness of 5980HV, and a CBN layer bending strength of 516.6MPa. The wear ratio, Vickers hardness, and bending strength decreased by 8.2%, 6.6%, and 9.25% from the center to the edge, respectively, indicating that the performance of the samples was relatively uniform; ② the samples were analyzed by ultrasonic micro-imaging, and no defects such as cracks, inclusions, pores, delamination, and obvious uneven CBN thickness occurred in batches; ③ after the samples were made into tools, when cutting bearing steel Gr15, the cutting mileage was good and the service life was long.

[0048] The invention discloses a preparation process of a large-diameter polycrystalline PCBN composite sheet. When in use, the invention optimizes the ratio of a binder component to cubic boron nitride (CBN) powder, assembles the CBN powder in a certain assembly mode, and then adds a certain amount of a binder to the CBN powder, thereby effectively reducing the sintering conditions and giving the PCBN some specific properties. The invention utilizes a hinged six-sided top press to sinter a large-diameter PCBN composite sheet under high temperature and high pressure conditions. Ultrasonic scanning detection and analysis show that the sintered product has basically no defects such as delamination and cracks. Under the same processing conditions, from comparative detection data of turning high-temperature alloys, it is analyzed that the PCBN tool of the sample has reached a relatively high level. The invention has the advantages of good wear resistance, low sintering conditions, excellent bending strength, and uniform hardness.

[0049] Example 2

[0050] A preparation process of a large-diameter polycrystalline PCBN composite sheet, the preparation process comprising the following steps:

[0051] Step 1: Raw material preparation: Nano metal binder, cubic boron nitride powder and cemented carbide are used as raw materials, and the cubic boron nitride powder and the nano metal binder are mixed in a certain proportion, wherein the volume fraction of the cubic boron nitride powder accounts for 78%;

[0052] Step 2: Mix the mixed materials in a three-dimensional mixer by wet ball milling. After the materials are evenly mixed, pour out the balls at the same time, and put the mixed materials into an oven and bake them at 95° C. for 8 hours;

[0053] Step 3: Put the sieved powder and cemented carbide into a metal cup, assemble the composite by inverting three layers of heat-resistant metal cups, place the composite assembly in a vacuum device, keep it warm for 2 hours under vacuum conditions, and assemble it into a composite block using a composite block assembly device;

[0054] Step 4: Using a hinged six-sided top press under high temperature and high pressure conditions, the sintering temperature and pressure are controlled by adjusting the heating given parameters and the pressure parameters, and heating for 35 minutes to obtain a sample;

[0055] Step 5: After sintering, the sample was post-processed to obtain a final size of 60 mm in diameter, 3.4 mm in total thickness, and 0.85 mm in polycrystalline CBN layer.

[0056] In the step 1, the particle size of the cubic boron nitride powder is a mixed particle size of 1.5 μm and 3.5 μm, with a purity of 99.9%; the cemented carbide is WC-12%Co.

[0057] The nano metal binder in step 1 is TiN powder with a particle size of 3 μm and a purity of 99.9%, Co powder with a particle size of 1.5 μm and a purity of 99.9%, and Al powder with a particle size of 1.5 μm and a purity of 99.8%.

[0058] The composite assembly in step 3 is placed in a vacuum device at a pressure of no more than 3×10 -4 The mixture was heated at 750 °C for 2 h under vacuum conditions of 1.34 °C.

[0059] The temperature control in step 4 uses a double platinum-rhodium B-type thermocouple of Pt6%Rh-Pt30%Rh to control the temperature at 1540°C, the pressure range is 5.5GPa, Bi, Tl, and Ba are used for calibration at room temperature, and Ag is used for calibration at high temperature.

[0060] The post-processing steps in step 5 include outer circle peeling, alloy finishing, outer grinding, flat grinding, grinding and polishing.

[0061] In this embodiment, ① detection: the CBN layer of the PCBN composite sheet is analyzed by X-ray diffractometer (XRD), the morphology and energy spectrum analysis are performed by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), and the internal quality of the PCBN is inspected by ultrasonic scanner; after the turning experiment, the flank wear of each blade head is measured by high-definition microscope.

[0062] ② Microstructure and phase analysis: From the scanning microstructure of the PCBN composite sheet obtained under high temperature and high pressure sintering conditions, it can be seen that the binder is distributed around the CBN powder. At the same time, part of the binder reacts with the CBN powder. The product acts as a binding phase to firmly bind the CBN particles together to form a dense network structure. Analysis of the XRD spectrum of the PCBN sample shows that under high temperature and high pressure conditions, the binder A1 element first reaches the melting point and melts. The melted liquid Al reacts with other particles by flowing, and CBN reacts with Al and Ti as follows: BN(s)+Ti(s)+Al(l)→TiB 2 (s)+Al 1 N(s), where s is the solid phase; l is the liquid phase; AIN, TiB and Co form a bonding phase with a network structure filling around the CBN particles, firmly combining the CBN particles together, thereby increasing the strength of the sintered body and obtaining higher impact resistance and toughness.

[0063] ③ Ultrasonic scanning analysis: The thickness of the sample ranges from 0.85 to 1.1 mm, which indicates that the CBN layer of the sample has no obvious uneven thickness.

[0064] ④ Turning experiment analysis: Qualified PCBN large sheets were used for cutting, tool head thinning, vacuum welding, and rough grinding to make CNGA120408 standard tools. At the same time, the same CNGA120408 standard tools were made with PCBN large sheets of foreign samples A and B, and the external cylindrical continuous turning experiment of high-temperature alloy was carried out on a CNC lathe; under the same turning parameters, after the processing reached a certain stroke (1500m), the flank loss of each blade, turning parameters and main components of the cutter were compared (Table 4, Table 5).

[0065] Table 4 Cutting parameters

[0066]

[0067] Table 2 Main components of cutting workpiece

[0068]

[0069]

[0070] In this turning experiment, 5 tools for each type of tool were tested. Comprehensive comparison of the flank wear of the 5 groups of turning experiments showed that the flank wear of the sample's PCBN tool was lower than that of competitor products A and B. This indicates that in terms of high-temperature alloy processing, under the same processing conditions, the average service life of the sample's PCBN tool has reached a relatively high level.

[0071] The invention discloses a preparation process of a large-diameter polycrystalline PCBN composite sheet. When in use, the invention optimizes the ratio of a binder component to cubic boron nitride (CBN) powder, assembles the CBN powder in a certain assembly mode, and then adds a certain amount of a binder to the CBN powder, thereby effectively reducing the sintering conditions and giving the PCBN some specific properties. The invention utilizes a hinged six-sided top press to sinter a large-diameter PCBN composite sheet under high temperature and high pressure conditions. Ultrasonic scanning detection and analysis show that the sintered product has basically no defects such as delamination and cracks. Under the same processing conditions, from comparative detection data of turning high-temperature alloys, it is analyzed that the PCBN tool of the sample has reached a relatively high level. The invention has the advantages of good wear resistance, low sintering conditions, excellent bending strength, and uniform hardness.

[0072] Example 3

[0073] A preparation process of a large-diameter polycrystalline PCBN composite sheet, the preparation process comprising the following steps:

[0074] Step 1: Raw material preparation: Using nano-metal binder, cubic boron nitride powder and cemented carbide as raw materials, the cubic boron nitride powder and the nano-metal binder are mixed in a certain proportion, wherein the volume fraction of the cubic boron nitride powder accounts for 80%;

[0075] Step 2: The mixed materials are mixed in a three-dimensional mixer by wet ball milling. After the materials are mixed evenly, the balls are poured out at the same time, and the mixture is placed in an oven and dried at 100° C. for 8 hours;

[0076] Step 3: Put the sieved powder and cemented carbide into a metal cup, assemble the composite by inverting three layers of heat-resistant metal cups, place the composite assembly in a vacuum device, keep it warm for 2 hours under vacuum conditions, and assemble it into a composite block using a composite block assembly device;

[0077] Step 4: Using a hinged six-sided top press under high temperature and high pressure conditions, the sintering temperature and pressure are controlled by adjusting the heating given parameters and the pressure parameters, and heating for 40 minutes to obtain a sample;

[0078] Step 5: After sintering, the sample was post-processed to obtain a final size of 60 mm in diameter, 3.6 mm in total thickness, and 1.0 mm in polycrystalline CBN layer.

[0079] In the step 1, the particle size of the cubic boron nitride powder is a mixed particle size of 2 μm and 6 μm, with a purity of 99.9%; the cemented carbide is WC-13%Co.

[0080] The nano-metal binder in step 1 is a high-purity β-Sialon phase, and the β-Sialon phase is prepared by spark plasma sintering.

[0081] The composite assembly in step 3 is placed in a vacuum device at a pressure of no more than 3×10 -4 The mixture was heated at 750 °C for 2 h under vacuum conditions of 1.34 °C.

[0082] The temperature control in step 4 uses a double platinum-rhodium B-type thermocouple of Pt6%Rh-Pt30%Rh to control the temperature at 1600°C, the pressure range is 6.0GPa, Bi, Tl, and Ba are used for calibration at room temperature, and Ag is used for calibration at high temperature.

[0083] The post-processing steps in step 5 include outer circle peeling, alloy finishing, outer grinding, flat grinding, grinding and polishing.

[0084] In this embodiment, the experiment uses spark plasma sintering (SPS) to prepare PCBN with a high purity β-Sialon phase as a binder mixed with CBN under high temperature and high pressure (HTHP) conditions (6.0 GPa, about 1600°C); a variety of testing methods are used to test different properties of the prepared samples, and the test results are analyzed and studied.

[0085] The phase analysis of each sample was carried out using a D / max-rB rotating anode X-ray diffractometer (XRD). The microstructural characteristics of the samples were observed under a KYKY-2800 scanning electron microscope (SEM). The density of the samples was determined by the liquid static weighing method according to the Archimedean principle. The microhardness of the samples was tested using a HVS-1000 digital microhardness tester. The wear ratio of the samples was determined using a DHM-3 wear ratio tester.

[0086] ① Determination of volume density of PCBN samples: The volume density at 1500℃ and 1600℃ reached a stable value of 3.388g / cm3, which is also the highest value, indicating that PCBN has been completely sintered at 1500℃.

[0087] ②Measurement of microhardness of PCBN samples: The microhardness of the sample sintered at 1400℃ is the lowest value of 2030HV. When the sintering temperature is 1500℃ and 1600℃, the microhardness of the sample reaches 2125HV and 2136HV respectively. Since the more suitable sintering temperature is reached at 1500℃, the microhardness is not much different when the sintering temperature is further increased, and a more stable state is obtained.

[0088] ③Measurement of wear resistance of PCBN samples: When sintered at 1400℃, the sintering was not complete, and the holding ability of CBN particles was not strong, the wear ratio was the lowest, only 5276, which was consistent with the analysis of the microhardness measurement results; when the sintering temperature was 1500℃ and 1600℃, the wear ratios were 7178 and 7154 respectively; the wear ratio of the sample sintered at 1600℃ was slightly lower than that at 1500℃, which should be caused by errors.

[0089] In summary, (1) the β-Sialon phase obtained by SPS sintering can be strengthened under HTHP, and the relative content reaches 97.35w%, which is helpful to improve the wear resistance, hardness and strength of the material. Therefore, the β-Sialon phase obtained by SPS sintering is suitable as a binder for PCBN; (2) the optimal sintering temperature of the PcBN sintered body prepared under HTHP is 1500℃, and the bulk density at this time is 3.388g / cm 3 , microhardness is 2125HV, and wear ratio is 7178.

[0090] The invention discloses a preparation process of a large-diameter polycrystalline PCBN composite sheet. When in use, the invention optimizes the ratio of a binder component to cubic boron nitride (CBN) powder, assembles the CBN powder in a certain assembly mode, and then adds a certain amount of a binder to the CBN powder, thereby effectively reducing the sintering conditions and giving the PCBN some specific properties. The invention utilizes a hinged six-sided top press to sinter a large-diameter PCBN composite sheet under high temperature and high pressure conditions. Ultrasonic scanning detection and analysis show that the sintered product has basically no defects such as delamination and cracks. Under the same processing conditions, from comparative detection data of turning high-temperature alloys, it is analyzed that the PCBN tool of the sample has reached a relatively high level. The invention has the advantages of good wear resistance, low sintering conditions, excellent bending strength, and uniform hardness.

[0091] Example 4

[0092] A preparation process of a large-diameter polycrystalline PCBN composite sheet, the preparation process comprising the following steps:

[0093] Step 1: Raw material preparation: Using nano-metal binder, cubic boron nitride powder and cemented carbide as raw materials, the cubic boron nitride powder and the nano-metal binder are mixed in a certain proportion, wherein the volume fraction of the cubic boron nitride powder accounts for 80%;

[0094] Step 2: The mixed materials are mixed in a three-dimensional mixer by wet ball milling. After the materials are mixed evenly, the balls are poured out at the same time, and the mixture is placed in an oven and dried at 100° C. for 8 hours;

[0095] Step 3: Put the sieved powder and cemented carbide into a metal cup, assemble the composite by inverting three layers of heat-resistant metal cups, place the composite assembly in a vacuum device, keep it warm for 2 hours under vacuum conditions, and assemble it into a composite block using a composite block assembly device;

[0096] Step 4: Using a hinged six-sided top press under high temperature and high pressure conditions, the sintering temperature and pressure are controlled by adjusting the heating given parameters and the pressure parameters, and heating for 40 minutes to obtain a sample;

[0097] Step 5: After sintering, the sample was post-processed to obtain a final size of 60 mm in diameter, 3.62 mm in total thickness, and 1.1 mm in polycrystalline CBN layer.

[0098] The cubic boron nitride powder can be cubic boron nitride powder with an average particle size of 10 μm and 40 μm of magnesium-based catalyst.

[0099] The nano metal binder in step 1 is TiN powder with a particle size of 4 μm and a purity of 99.9%, Co powder with a particle size of 2 μm and a purity of 99.9%, and Al powder with a particle size of 2 μm and a purity of 99.8%.

[0100] The composite assembly in step 3 is placed in a vacuum device at a pressure of no more than 3×10 -4 The mixture was heated at 750 °C for 2 h under vacuum conditions of 1.34 °C.

[0101] The temperature control in step 4 uses a double platinum-rhodium B-type thermocouple of Pt6%Rh-Pt30%Rh to control the temperature range at 1600°C and the pressure range at 6.5GPa. Bi, Tl, and Ba are used for calibration at room temperature, and Ag is used for calibration at high temperature.

[0102] The post-processing steps in step 5 include outer circle peeling, alloy finishing, outer grinding, flat grinding, grinding and polishing.

[0103] In this embodiment, ① Bending strength: The bending strength test usually adopts the three-point bending method and is calculated according to the following formula: δ = 3PL / 2RS 2 , where δ is the bending strength of the sample; P is the load when the sample breaks; L is the span of the special bending fixture; R is the radius of the sample; R is the thickness of the sample; the samples prepared in this experiment were subjected to TRS tests on a universal testing machine at room temperature with a span of L = 7 mm, a roller diameter of Φ1.5 mm, and a force speed of v = 0.5 mm / min. The TRS values ​​were calculated according to the above formula, and the results are shown in Table 6.

[0104] Table 6 Bending strength values ​​of samples fired at different temperatures

[0105]

[0106] Under a constant pressure of 6.5 GPa, at a temperature of 1480, there is less bonding between CBN particles, most of the particles are surrounded by Co, in an under-fired state, and the sintering is uneven. At this time, the bonding strength between the particles is low, which is manifested as a small TRS value; as the temperature increases, the liquid phase Co begins to fully penetrate and diffuse into the entire PCBN layer. In this process, the CBN particles can better bond themselves, and at the same time, Co is excluded and gathered at the PCBN grain boundary, forming a vein-like distribution; at a high temperature of 1600°C, the bonding between CBN particles in the sintered PCBN composite sheet is significantly increased, Co gathers at the PCBN grain boundary, sintering is uniform, the CBN particles have been completely combined into a network skeleton structure, and Co is filled between the skeletons; this is because the bonding between CBN particles is formed by atomic bonding, which is highly dependent on temperature. When the CBN particles are bonded, most of the metal Co is excluded from the grain boundary of the CBN particles and retained at the boundary of the PCBN, which makes the CBN particles completely and directly bonded, and the bonding strength is high.

[0107] The invention discloses a preparation process of a large-diameter polycrystalline PCBN composite sheet. When in use, the invention optimizes the ratio of a binder component to cubic boron nitride (CBN) powder, assembles the CBN powder in a certain assembly mode, and then adds a certain amount of a binder to the CBN powder, thereby effectively reducing the sintering conditions and giving the PCBN some specific properties. The invention utilizes a hinged six-sided top press to sinter a large-diameter PCBN composite sheet under high temperature and high pressure conditions. Ultrasonic scanning detection and analysis show that the sintered product has basically no defects such as delamination and cracks. Under the same processing conditions, from comparative detection data of turning high-temperature alloys, it is analyzed that the PCBN tool of the sample has reached a relatively high level. The invention has the advantages of good wear resistance, low sintering conditions, excellent bending strength, and uniform hardness.

Claims

1. A process for preparing a large diameter polycrystalline PCBN composite sheet, characterized in that: The preparation process comprises the following steps: Step 1: Raw material preparation: Nano metal binder, cubic boron nitride powder and cemented carbide are used as raw materials, and the cubic boron nitride powder and the nano metal binder are mixed in a certain proportion, wherein the volume fraction of the cubic boron nitride powder accounts for 75-80%; Step 2: Mix the mixed materials in a three-dimensional mixer by wet ball milling. After the materials are evenly mixed, pour out the balls at the same time, and put the mixed materials into an oven and bake them at 90-100° C. for 8 hours; Step 3: Put the sieved powder and cemented carbide into a metal cup, assemble the composite by inverting three layers of heat-resistant metal cups, place the composite assembly in a vacuum device, keep it warm for 2 hours under vacuum conditions, and assemble it into a composite block using a composite block assembly device; Step 4: Using a hinged six-sided top press under high temperature and high pressure conditions, the sintering temperature and pressure are controlled by adjusting the heating given parameters and the pressure parameters, and heating for 30-40 minutes to obtain a sample; Step 5: After sintering, the sample undergoes post-processing to obtain a final size of 60 mm in diameter, 3.2-3.6 mm in total thickness, and 0.7-1.0 mm in polycrystalline CBN layer.

2. The process for preparing a large-diameter polycrystalline PCBN composite sheet according to claim 1, characterized in that: In the step 1, the particle size of the cubic boron nitride powder is a mixed particle size of 1-2 μm and 3-6 μm, with a purity of 99.9%; the cemented carbide is WC-11% to WC-13% Co.

3. The process for preparing a large-diameter polycrystalline PCBN composite sheet according to claim 2, characterized in that: The cubic boron nitride powder can be a magnesium-based catalyst cubic boron nitride powder with an average particle size of 10 μm and 40 μm.

4. The process for preparing a large-diameter polycrystalline PCBN composite sheet according to claim 3, characterized in that: The nano metal binder in step 1 is TiN powder with a particle size of 2-4 μm and a purity of 99.9%, Co powder with a particle size of 1-2 μm and a purity of 99.9%, and Al powder with a particle size of 1-2 μm and a purity of 99.8%.

5. The process for preparing a large-diameter polycrystalline PCBN composite sheet according to claim 4, characterized in that: The nano metal binder can be replaced by a high-purity β-Sialon phase, and the β-Sialon phase is prepared by spark plasma sintering.

6. The process for preparing a large-diameter polycrystalline PCBN composite sheet according to claim 1, characterized in that: The composite assembly in step 3 is placed in a vacuum device at a pressure of no more than 3×10 -4 The mixture was heated at 750 °C for 2 h under vacuum conditions of 1.34 °C.

7. The process for preparing a large diameter polycrystalline PCBN composite sheet according to claim 1, characterized in that: The temperature control in step 4 uses a double platinum-rhodium B-type thermocouple of Pt6%Rh-Pt30%Rh to control the temperature range to 1480-1600°C, and the pressure range is 5.0-6.0GPa or 5.5-6.5GPa. Bi, Tl, and Ba are used for calibration at room temperature, and Ag is used for calibration at high temperature.

8. The process for preparing a large-diameter polycrystalline PCBN composite sheet according to claim 7, characterized in that: In step 4, the temperature range of 1480-1600° C. is divided into four sections by a temperature control method.

9. The process for preparing a large-diameter polycrystalline PCBN composite sheet according to claim 1, characterized in that: The post-processing steps in step 5 include outer circle peeling, alloy finishing, outer grinding, flat grinding, grinding and polishing.

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