CN110342943B - Method for synthesizing binderless polycrystalline boron nitride block under industrial pressure and application thereof - Google Patents

Method for synthesizing binderless polycrystalline boron nitride block under industrial pressure and application thereof Download PDF

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CN110342943B
CN110342943B CN201910651003.4A CN201910651003A CN110342943B CN 110342943 B CN110342943 B CN 110342943B CN 201910651003 A CN201910651003 A CN 201910651003A CN 110342943 B CN110342943 B CN 110342943B
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赵智胜
罗坤
韩俏怡
靳田野
孙磊
刘兵
何巨龙
于栋利
胡文涛
田永君
陈俊云
徐波
柳忠元
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Abstract

The invention discloses a method for synthesizing a binderless polycrystalline boron nitride block under industrial pressure and application thereof, belonging to the field of synthesis of polycrystalline boron nitride, wherein the method mainly comprises the steps of mixing any one or more of powders of cBN, hBN, oBN and pBN, purifying, performing vacuum heating pretreatment, prefabricating into a columnar blank body, and processing at high temperature and industrial pressure to obtain the polycrystalline boron nitride block; the application mainly lies in that the cutting tool is prepared by processing, and the cutting processing of high-hardness and difficult-to-process materials such as iron-based materials, hard alloys (WC) and the like is realized. The invention greatly reduces the synthesis pressure and is suitable for industrial production.

Description

Method for synthesizing binderless polycrystalline boron nitride block under industrial pressure and application thereof
Technical Field
The invention relates to the field of synthesis of polycrystalline boron nitride, in particular to a method for synthesizing binderless polycrystalline boron nitride under industrial pressure and application.
Background
At present, cubic boron nitride (cBN) and diamond are the two most widely used types of superhard materials. Diamond has excellent performances of ultrahigh hardness (60-120GPa), high melting point, high thermal conductivity and the like, but has poor thermal stability and chemical inertness, and graphitization occurs when the diamond is heated to more than 700 ℃ in air. cBN, however, has a hardness lower than that of diamond, has a Vickers hardness of only 66GPa, and a hardness of 33-43GPa, and a fracture toughness of only 2.8 MPa.m, which is lower than that of commercially available cBN single crystals1/2. cBN single crystals have severely limited their application in industry because of their limited synthesis size, presence of break-away planes and low fracture toughness. The development of isotropic, high-hardness, high-toughness polycrystalline cubic boron nitride (PcBN) blocks has become a major research goal in the scientific and industrial industries.
At present, the PcBN used industrially contains binders, wherein the mainly used binders comprise metal type (Co, Al and the like), ceramic type (Si and the like) and metal-based ceramics (TiN and the like), and the existence of the binders can effectively reduce the synthesis pressure and temperature, thereby realizing production under the condition of pressure (less than or equal to 6GPa) which can be achieved industrially. However, the presence of a metallic binder can reduce the thermal stability of PcBN; the addition of the ceramic binder can not only reduce the hardness of PcBN and shorten the service life of the cutter, but also deteriorate the thermal shock resistance, so that the edge breaking phenomenon is easy to occur in the high-speed cutting process, and the service performance requirement of high-speed hard dry cutting is difficult to meet. The PcBN hardness, fracture toughness and heat resistance are not ideal due to the existence of the binder, for example, the hardness is about 30GPa generally, and the fracture toughness is 3-5MPa·m1/2The oxidation resistance temperature is only 1000 ℃, and the application of the antioxidant is restricted. In summary, the addition of binders will reduce the hardness and fracture toughness of PcBN blocks and lead to a reduction in wear resistance and thermal stability, and the preparation of high performance, binder-free PcBN blocks has become a hot spot of recent research at home and abroad.
The preparation method of the binderless PcBN block mainly uses hexagonal boron nitride (hBN), boron nitride with onion structure (oBN), cubic boron nitride (cBN), pyrolytic boron nitride (pBN) and their mixed powder as raw materials, and the raw materials are directly sintered into the PcBN block at high temperature and high pressure. The direct conversion method without the adhesive can greatly improve various mechanical properties of the obtained PcBN. For example: in 2000, H.Sumiya.S. et al (document: Mechanical properties of high purity polycrystalline cBN synthesized by direct conversion method. journal of Materials science.35(2000) 1181-1186) fired into binderless polycrystalline PcBN blocks at a pressure of 7.7GPa and a temperature of 2200 ℃ to 2400 ℃ using high purity hBN as the starting material, had a high Vickers hardness (50-55GPa) and a high transverse rupture strength (1.6 GPa). In 2007, Natalia Dubrovinkasia et al (document: Superhard nano-composite of boron nitride: non-polymeric material has accessed diamond hard. applied Physics letters. 2007: 90:101912) synthesized nano-poly-crystalline boron nitride composite materials (ABNNCs) with a grain size of 14nm, a hardness of 85GPa, and a fracture toughness of 15 MPa. m.1/2And the thermal stability in the air reaches 1327 ℃. In 2009, Kazuhiro Fujisaki et al (Development of ultra-fine-grain binding cBN tool for precision Processing of Materials. journal of Materials Processing technology.2009,209: 5646-. In 2013, we have a topic group (literature: Ultrahard nanotwined cubicon n)itride, Nature, vol.493, No.7432, pp.385-8, Jan.2013) adopts oBN as raw material to synthesize the nano twin crystal cBN block material (nt-cBN) with the best performance at present by martensite phase change sintering, the hardness of the nano twin crystal cBN block material is as high as 108GPa, and the fracture toughness is 12.7 MPa.m1 /2And the thermal stability in air reaches 1294 ℃. In 2015, Guodutan Liu et al (documents: Submicron cubic boron nitride as hard as diamond applied Physics letters.2015,106:121901) synthesized by using Submicron (0.2-0.5 μm) cBN powder as raw material under the pressure of 8GPa and the temperature of 2000 ℃ can reach 75GPa, and the fracture toughness is 13.2MPa m1/2The oxidation resistance temperature in air was 1252 ℃. In 2017, Teng Liu et al (document: Preparation of super critical cubic boron nitride obtained from commercially available submicron powders, journal of Applied Physics, 2017,121:125902) synthesized pure phase PcBN block at 8-14GPa and 1750 ℃ by using submicron (0.4-1.0 μm) cBN as raw material, wherein the PcBN block synthesized under the conditions of 11GPa and 1750 ℃ has the best performance, the Vickers hardness reaches 72GPa, and the fracture toughness is 12.4 MPa.m1/2The thermal stability in air reaches 1275 ℃. In 2018, Ming Yang et al (literature: Polycrystalline diamond compact nitride prepared with cubic-hexagonal boron nitride under high pressure and high temperature Physics B.2018,27:056105) synthesized PcBN with submicron (0.4-1.0 μm) mixed powder of cBN and hBN at 7.7GPa and 1750 ℃, wherein the Vickers hardness of the block reaches 61.5GPa, the thermal stability in air reaches 1290 ℃ and the density reaches 3.46g/cm3。
In summary, the binderless PcBN block has an ultra-high hardness of (>40GPa) and the maximum fracture toughness of 12-15 MPa.m1/2And high thermal stability in air (about 1200 ℃), thereby showing wide application prospects. However, in the current literature and patent reports, the pressure for synthesizing the binderless high-performance PcBN block is at least 7.7GPa, the synthetic pressure is higher than the pressure (less than or equal to 6GPa) achieved by an industrial press, so that secondary pressurization is needed to realize the synthesis, the synthesis cost is high, the size of a synthesized sample is limited, and the common method cannot be carried out at presentIndustrial popularization and application. The synthesis of binderless, high performance blocks of polycrystalline boron nitride under industrial pressure has been a dream in the scientific and industrial sectors, but unfortunately has not been realized to date.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for synthesizing the binderless polycrystalline boron nitride block under industrial pressure and application thereof, which greatly reduce the synthesis pressure and are suitable for industrial production.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a process for synthesizing the non-adhesive block of polycrystalline boron nitride under industrial pressure includes such steps as mixing the powder of one or more of cBN, hBN, oBN and pBN, purifying, vacuum heating, pre-treating to obtain cylindrical blank, and treating at high temp and industrial pressure.
The technical scheme of the invention is further improved as follows: the method specifically comprises the following steps:
a, mixing any one or more of cBN, hBN, oBN and pBN powder for purification and vacuum heating pretreatment to remove oxygen, adsorbed water and bound water adsorbed in the raw material powder;
b, prefabricating the powder pretreated in the step a into a columnar blank;
c, filling the columnar blank into a crucible, and putting the crucible into a high-temperature high-pressure assembly block;
d, placing the high-temperature high-pressure assembly block into a press for high-temperature high-pressure treatment;
and e, obtaining the polycrystalline boron nitride block after the treatment at high temperature and industrial pressure is finished.
The technical scheme of the invention is further improved as follows: and d, selecting a cubic press for processing, wherein the pressure range is 1-6GPa, the temperature range is 800-2300 ℃, and the heat preservation time is 10-400 minutes.
The technical scheme of the invention is further improved as follows: and c, prefabricating a cylindrical blank with the diameter of 3.5mm and the height of 4mm in the step b.
Further improvement of the technical scheme of the inventionThe method is characterized in that: the method for purifying and vacuum heating pretreatment of the raw materials in the step a comprises the following steps: purifying by acid dissolution and impurity removal, filling the purified raw material powder into a mold of a vacuum hot-pressing furnace, wherein the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400 ℃ and 1600 ℃ and the pressure is 30-50 MPa.
The adhesive-free polycrystalline boron nitride block is synthesized under industrial pressure, and the polycrystalline boron nitride block is processed to prepare the cutting tool.
The application of the polycrystalline boron nitride block material is further improved as follows: cutting tools are used for cutting high-hardness and difficult-to-machine materials including iron-based materials and cemented carbides.
Due to the adoption of the technical scheme, the invention has the technical progress that:
compared with the PcBN material containing the adhesive, which is generally used commercially at present, the polycrystalline boron nitride prepared by the method has the advantages that the high-performance polycrystalline boron nitride block without the adhesive has higher hardness, toughness and thermal stability. Meanwhile, the preparation and synthesis are carried out under the industrial pressure (less than or equal to 6GPa), which is different from the synthesis of a binderless high-performance PcBN block material under the ultrahigh pressure (more than or equal to 7.7 GPa).
The PcBN block prepared by the invention has excellent mechanical properties, the hardness is 40-50GPa, and the fracture toughness is 8-10 MPa.m1/2The compression strength is 6.5GPa, the antioxidation temperature in the air is more than 1200 ℃, and the cutting fluid can be directly applied to the cutting processing of high-hardness and difficult-to-process materials such as iron series, hard alloy (WC) and the like, and the ultraprecise mirror surface cutting of the high-hardness and difficult-to-process materials such as hardened steel, hard alloy (WC) and the like is realized.
Drawings
FIG. 1 shows an X-ray diffraction pattern of a polycrystalline boron nitride bulk material obtained in examples 1, 2, 3, 4, 5 and 6 of the present invention;
FIG. 2 shows a Raman diagram of the polycrystalline boron nitride bulk obtained in examples 2 and 4 of the present invention;
FIG. 3 is a graph showing hardness and indentation of a polycrystalline boron nitride bulk material obtained in example 4 of the present invention;
FIG. 4 is a transmission electron micrograph of a polycrystalline boron nitride bulk material obtained in example 3 of the present invention;
FIG. 5 is a scanning electron micrograph of a polycrystalline boron nitride bulk material obtained in example 4 of the present invention;
FIG. 6 shows electron energy loss spectra of the polycrystalline boron nitride bulk materials obtained in examples 1, 2, 3 and 5 of the present invention;
FIG. 7 is an atomic force microscope photograph of tool-cut hardened steel made from the polycrystalline boron nitride blocks obtained in examples 1, 2, 3, 4, 5, and 6 of the present invention;
FIG. 8 is an atomic force microscope photograph of tool cutting cemented carbide (WC with Co binder) made of the polycrystalline boron nitride bulk material obtained in examples 1, 2, 3, 4, 5, and 6 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples:
the method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure specifically comprises the following steps of:
a, mixing any one or more of cBN, hBN, oBN and pBN powder for purification and vacuum heating pretreatment to remove oxygen, adsorbed water and bound water adsorbed in the raw material powder;
the raw material purification and vacuum heating pretreatment method comprises the following steps: purifying by acid dissolution and impurity removal, filling the purified raw material powder into a mold of a vacuum hot-pressing furnace, wherein the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400 ℃ and 1600 ℃ and the pressure is 30-50 MPa. Wherein, the acid dissolution impurity removal can obtain high-purity raw materials, and if the purity of the raw materials is high, the step can not be carried out;
b, prefabricating the powder pretreated in the step a into a columnar blank, wherein the size of the columnar blank is adjusted according to the model of a press;
c, filling the columnar blank into a crucible, and putting the crucible into a high-temperature high-pressure assembly block;
d, placing the high-temperature high-pressure assembly block into a press for high-temperature high-pressure treatment;
specifically, the treatment can be carried out in a cubic press, the pressure range is 1-6GPa, the temperature range is 800-2300 ℃, and the heat preservation time is 10-400 minutes;
and e, obtaining the polycrystalline boron nitride block after the treatment at high temperature and industrial pressure is finished.
The method for synthesizing the polycrystalline boron nitride bulk material according to the present invention will be described in detail with reference to several embodiments.
Example 1:
the method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure specifically comprises the following steps of:
a, mixing cBN with any one or more of hBN, oBN and pBN powder for purification and vacuum heating pretreatment to remove impurities such as oxygen, adsorbed water, bound water and the like adsorbed in the raw material powder; specifically, the purification is carried out by using an acid dissolution impurity removal mode, the purified raw material powder is filled into a mould of a vacuum hot-pressing furnace, and the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400-600 ℃, and the pressure is 30-50 MPa;
b, prefabricating the powder pretreated in the step a into a cylindrical blank body with the diameter of 3.5mm and the height of 4 mm;
c, filling the columnar blank into an hBN crucible, and then putting the crucible into a high-temperature high-pressure assembly block;
and e, putting the high-temperature and high-pressure assembly block into a domestic cubic press for treatment, heating for 10-400 minutes under the conditions that the pressure is 3-6 GPa and the temperature is 1000-2000 ℃ to synthesize the binderless high-performance polycrystalline boron nitride block.
The resulting blocks were analyzed by X-ray diffractometry (Bruker D8, Germany) and electron energy loss spectroscopy (see FIGS. 1 and 6), and it was found that these samples included cBN and an sp2-sp3A bonded BN phase. Measured by a KB-5BVZ microhardness tester, the Vickers hardness is 30-50GPa, and the fracture toughness is 5-10 MPa.m1/2. Indicating that these samples are a binderless high performance polycrystalline boron nitride bulk material.
Example 2:
the method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure specifically comprises the following steps of:
a, preprocessing cBN raw powder such as purification and vacuum heating to remove impurities such as oxygen, absorbed water and bonding water absorbed in the raw powder; specifically, the purification is carried out by using an acid dissolution impurity removal mode, the purified raw material powder is filled into a mould of a vacuum hot-pressing furnace, and the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400-1600 ℃, and the pressure is 30-50 MPa;
b, prefabricating the powder pretreated in the step a into a cylindrical blank body with the diameter of 3.5mm and the height of 4 mm;
c, filling the columnar blank into an hBN crucible, and then putting the crucible into a high-temperature high-pressure assembly block;
and e, loading the high-temperature and high-pressure assembled blocks into a domestic cubic press for treatment, heating for 10-40 minutes under the conditions that the pressure is 6GPa and the temperature is 1400 ℃, and synthesizing the binderless high-performance polycrystalline boron nitride block.
The obtained polycrystalline boron nitride block is analyzed by an X-ray diffractometer and an electron energy loss spectrum, and the polycrystalline boron nitride block can be seen to comprise cBN and an sp2-sp3A bonded BN phase (as shown in FIGS. 1 and 6); when the obtained bulk was analyzed by Raman spectroscopy (HORIBA Jobin Yvon), as shown in FIG. 2, it was found that Raman peak positions different from those of pure cBN and pure hBN exhibited an sp2-sp3A BN phase characteristic of hybrid bonding; the Vickers hardness was measured to be 27GPa using a KB-5BVZ microhardness tester. The sample is shown to be a high performance bulk amorphous boron nitride without binder.
Example 3:
the method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure specifically comprises the following steps of:
a, preprocessing cBN raw powder such as purification and vacuum heating to remove impurities such as oxygen, absorbed water and bonding water absorbed in the raw powder; specifically, the purification is carried out by using an acid dissolution impurity removal mode, the purified raw material powder is filled into a mould of a vacuum hot-pressing furnace, and the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2At a temperature of 400-16 deg.C00 ℃ and the pressure of 30-50 MPa;
b, prefabricating the powder pretreated in the step a into a cylindrical blank body with the diameter of 3.5mm and the height of 4 mm;
c, filling the columnar blank into an hBN crucible, and then putting the crucible into a high-temperature high-pressure assembly block;
and e, loading the high-temperature and high-pressure assembled blocks into a domestic cubic press for treatment, heating for 10-40 minutes under the conditions that the pressure is 6GPa and the temperature is 1800 ℃, and synthesizing the binderless high-performance polycrystalline boron nitride block.
The obtained bulk polycrystalline boron nitride was analyzed by an X-ray diffractometer and electron energy loss spectroscopy, and as shown in FIGS. 1 and 6, it was found that the bulk polycrystalline boron nitride includes cBN and an sp2-sp3A bonded BN phase upon hybridization; the resulting bulk was analyzed by Raman spectroscopy, which showed a Raman peak position similar to that at 1400 ℃ in FIG. 2, which showed an sp2-sp3A BN phase characteristic of hybrid bonding; the Vickers hardness of the steel measured by a KB-5BVZ microhardness tester was 36GPa, and the fracture toughness thereof was 7MPa m1/2. As shown in FIG. 4, which is a high resolution image of a bulk polycrystalline boron nitride material, sp can be seen2-sp3The boundary region of the BN phase and the cBN phase hybridized to form bonds. The sample is shown to be a high performance bulk amorphous boron nitride without binder.
Example 4:
the method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure specifically comprises the following steps of:
a, preprocessing cBN raw powder such as purification and vacuum heating to remove impurities such as oxygen, absorbed water and bonding water absorbed in the raw powder; specifically, the purification is carried out by using an acid dissolution impurity removal mode, the purified raw material powder is filled into a mould of a vacuum hot-pressing furnace, and the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400-1600 ℃, and the pressure is 30-50 MPa;
b, prefabricating the powder pretreated in the step a into a cylindrical blank body with the diameter of 3.5mm and the height of 4 mm;
c, filling the columnar blank into an hBN crucible, and then putting the crucible into a high-temperature high-pressure assembly block;
and e, loading the high-temperature and high-pressure assembled blocks into a domestic cubic press for treatment, heating for 10-40 minutes under the conditions that the pressure is 6GPa and the temperature is 1700 ℃, and synthesizing the binderless high-performance polycrystalline boron nitride block.
The obtained bulk material was analyzed by an X-ray diffractometer, as shown in fig. 1, it can be seen that its phase composition was cubic boron nitride; the obtained bulk was analyzed by a raman spectrometer, and as shown in fig. 2, characteristic peak positions (1057 and 1305) of cubic boron nitride appeared; the results of Vickers hardness measured by a KB-5BVZ microhardness tester are shown in FIG. 3, in which the asymptotic hardness is 45GPa and the maximum hardness is 50 GPa. FIG. 3 shows a graph of a Vickers hardness indentation under a load of 5Kg and a Knoop hardness indentation under a load of 0.8Kg, respectively, and the fracture toughness of PcBN is calculated to be 8-10MPa m by measuring the crack length of the indentation1/2. FIG. 5 is an SEM picture of a PcBN block, and it can be seen that sintering among crystal grains is excellent. We also measured the compressive strength of the PcBN blocks, which was 6.5 GPa. This sample is shown to be a binderless high performance PcBN block.
Example 5:
the method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure specifically comprises the following steps of:
a, preprocessing cBN raw powder such as purification and vacuum heating to remove impurities such as oxygen, absorbed water and bonding water absorbed in the raw powder; specifically, the purification is carried out by using an acid dissolution impurity removal mode, the purified raw material powder is filled into a mould of a vacuum hot-pressing furnace, and the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400-1600 ℃, and the pressure is 30-50 MPa;
b, prefabricating the powder pretreated in the step a into a cylindrical blank body with the diameter of 3.5mm and the height of 4 mm;
c, filling the columnar blank into an hBN crucible, and then putting the crucible into a high-temperature high-pressure assembly block;
and e, loading the high-temperature and high-pressure assembled blocks into a domestic cubic press for treatment, heating for 10-40 minutes under the conditions that the pressure is 6GPa and the temperature is 1200 ℃, and synthesizing the binderless high-performance polycrystalline boron nitride block.
The obtained bulk polycrystalline boron nitride was analyzed by an X-ray diffractometer and an electron energy loss spectrum (see FIGS. 1 and 6), and it was found that the bulk polycrystalline boron nitride consisted of cBN and an sp2-sp3A bonded BN phase upon hybridization; the obtained bulk was analyzed by Raman spectroscopy, and its Raman peak position was similar to that at 1400 ℃ in FIG. 2, showing an sp2-sp3A BN phase characteristic of hybrid bonding; the Vickers hardness was 18GPa as measured using a KB-5BVZ microhardness tester. The sample is shown to be a high performance bulk amorphous boron nitride without binder.
Example 6:
the method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure specifically comprises the following steps of:
a, preprocessing cBN raw powder such as purification and vacuum heating to remove impurities such as oxygen, absorbed water and bonding water absorbed in the raw powder; specifically, the purification is carried out by using an acid dissolution impurity removal mode, the purified raw material powder is filled into a mould of a vacuum hot-pressing furnace, and the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400-1600 ℃, and the pressure is 30-50 MPa;
b, prefabricating the powder pretreated in the step a into a cylindrical blank body with the diameter of 3.5mm and the height of 4 mm;
c, filling the columnar blank into an hBN crucible, and then putting the crucible into a high-temperature high-pressure assembly block;
and e, loading the high-temperature and high-pressure assembled blocks into a domestic cubic press for treatment, heating for 20-40 minutes under the conditions that the pressure is 6GPa and the temperature is 900 ℃, and synthesizing the binderless high-performance polycrystalline boron nitride block.
The obtained bulk was analyzed by an X-ray diffractometer, and as shown in fig. 1, it was found that the phase composition of the polycrystalline boron nitride bulk was cBN and hBN. The Vickers hardness was 10GPa as measured with a KB-5BVZ microhardness tester. Indicating that the sample has not been fully sintered.
Application of the polycrystalline boron nitride block material:
the binderless polycrystalline boron nitride block synthesized by the embodiment is processed to prepare the cutter, and the specific preparation process of the cutter comprises grinding and polishing on mechanical grinding equipment. Grinding parameters: rotation speed 1500rpm (revolutions per minute), grinding pressure 3.6N, grinding particle size 1 μm.
The prepared cutter is used for cutting hardened steel (the type of the hardened steel is AISI 4140 die steel, the diameter is 20mm, the test value of the average Vickers hardness after quenching is Hv 494, and the test value is about 4.8GPa after conversion) and WC hard alloy containing Co (the diameter is 11mm, the hardness is 13-18GPa, and the fracture toughness is 8-12 MPa.m1/2). Wherein the machining parameters of the cut quenched steel are as follows: the rotating speed is 5000rpm, the cutting depth is 3 mu m, and the feeding speed is 10mm/min (2 mu m/rev (micrometer/rev) after the rotation speed is converted); machining parameters for cutting the hard alloy: a rotation speed of 5000rpm, a cutting depth of 2 μm, and a feed rate of 3mm/min (0.6 μm/rev (μm/rev) after conversion from the rotation speed). The surfaces of the WC hard alloy containing Co and the quenched steel after cutting are both mirror surface effects. Surface roughness measurements were also carried out after the cutting process using an atomic force microscope and a scanning electron microscope (AFM, Dimension Icon model manufactured by Bruker; SEM, Scios model manufactured by ThermoFisher). The results are shown in FIGS. 7 and 8, where FIG. 7 shows the results of AFM test on hardened steel, and FIG. 8 shows the results of AFM test on cemented carbide, where R isaIs the arithmetic mean of the surface height deviations. The detection result after the mirror surface cutting of the quenched steel is as follows: ra24.80 nm; the detection result after the hard alloy mirror surface is cut is as follows: raIt was 8.66 nm. In summary, the binderless polycrystalline boron nitride block developed by the patent can be used for preparing a high-performance turning tool, and can realize ultra-precise mirror surface processing of iron-based and carbide-forming materials, high-hardness hard alloys and other difficult-to-process materials.

Claims (2)

1. The method for synthesizing the binderless polycrystalline boron nitride block under the industrial pressure is characterized by comprising the following steps of: mixing any one or more of cBN, hBN, oBN and pBN powder, purifying, performing vacuum heating pretreatment, prefabricating a columnar blank, and processing at high temperature and industrial pressure to obtain a polycrystalline boron nitride block;
the method specifically comprises the following steps:
a, mixing any one or more of cBN, hBN, oBN and pBN powder for purification and vacuum heating pretreatment to remove oxygen, adsorbed water and bound water adsorbed in the raw material powder;
b, prefabricating the powder pretreated in the step a into a columnar blank;
c, filling the columnar blank into a crucible, and putting the crucible into a high-temperature high-pressure assembly block;
d, placing the high-temperature high-pressure assembly block into a press for high-temperature high-pressure treatment;
e, obtaining a polycrystalline boron nitride block after the treatment at high temperature and industrial pressure is finished;
d, selecting a cubic press for processing, wherein the pressure range is 1-6GPa, the temperature range is 800-2300 ℃, and the heat preservation time is 10-400 minutes; the method for purifying and vacuum heating pretreatment of the raw materials in the step a comprises the following steps: purifying by acid dissolution and impurity removal, filling the purified raw material powder into a mold of a vacuum hot-pressing furnace, wherein the vacuum degree of the vacuum hot-pressing furnace is 4 x 10-2The temperature is 400 ℃ and 1600 ℃ and the pressure is 30-50 MPa.
2. The method of industrial pressure synthesis of binderless bulk polycrystalline boron nitride material of claim 1 wherein: and c, prefabricating a cylindrical blank with the diameter of 3.5mm and the height of 4mm in the step b.
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