AU2017400313A1 - Nickel-coated hexagonal boron nitride composite powder, preparation and application thereof as well as self-lubricating ceramic cutter - Google Patents

Nickel-coated hexagonal boron nitride composite powder, preparation and application thereof as well as self-lubricating ceramic cutter Download PDF

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AU2017400313A1
AU2017400313A1 AU2017400313A AU2017400313A AU2017400313A1 AU 2017400313 A1 AU2017400313 A1 AU 2017400313A1 AU 2017400313 A AU2017400313 A AU 2017400313A AU 2017400313 A AU2017400313 A AU 2017400313A AU 2017400313 A1 AU2017400313 A1 AU 2017400313A1
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boron nitride
hexagonal boron
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Zhaoqiang CHEN
Changchao SHENG
Guangyong WU
Guangchun XIAO
Chonghai XU
Mingdong YI
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Qilu University of Technology
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Abstract

A nickel-coated hexagonal boron nitride composite powder and a preparation method therefor. The method comprises: after sensitization and activation, adding a hexagonal boron nitride (BN) powder into a chemical plating solution and plating the same in a water bath having a constant temperature. The components of the chemical plating solution being: nickel sulfate hexahydrate (NiSO

Description

Nickel-coated hexagonal boron nitride composite powder, preparation and application thereof and self-lubricating ceramic cutting tool
Technical Field
The invention relates to a nickel-coated hexagonal boron nitride composite powder, a preparation method and application thereof and a self-lubricating ceramic cutting tool, belonging to the technical field of solid self-lubricating composite materials and ceramic cutting tool.
Background Art
In modern mechanical processing technology, with the emergence of various difficult-to-machine materials and the improvement of efficiency, precision and environmental protection requirements, cutting tool technology has increasingly become one of the key factors affecting the development of mechanical manufacturing industry. Compared with traditional tool materials such as high speed steel and hard alloy, ceramic tool materials have the advantages of high hardness, wear resistance, high temperature resistance and good chemical stability. However, due to the inherent low toughness and low thermal shock resistance of ceramic materials, cutting fluid cannot be used for cooling and lubrication of ceramic tools during high-speed cutting, resulting in high cutting temperature and severe thermal wear of the cutting tools, leading relatively in low tool life. The development of self-lubricating ceramic cutting tool materials is an effective way to solve this problem.
The solid lubricants used to prepare self-lubricating ceramic tool materials should meet two basic requirements: First, at the sintering temperature of the tool materials (generally 1500-1800 °C), the solid lubricants do not decompose or have obvious chemical reactions with the ceramic matrix; Second, at the cutting temperature of the tool (generally 500-1000 °C), solid lubricant will not have obvious chemical reaction with air and workpiece materials and will lose its lubricating effect. In the commonly used solid lubricants graphite, molybdenum disulfide, hexagonal boron nitride and polytetrafluoroethylene, the decomposition temperatures of molybdenum disulfide and polytetrafluoroethylene are 1370 °C and 415 °C, respectively, which are lower than the sintering temperature of ceramic cutting tool materials. Graphite and hexagonal boron nitride do not decompose or sublimate at the sintering temperature of the cutting tool material, but graphite begins to oxidize at 450 °C in air and increases with the increase of temperature; Hexagonal boron nitride (h-BN) is called white graphite, and it has a layered structure similar to graphite and has good lubricity, thermal conductivity and chemical corrosion resistance. The performance of hexagonal boron nitride is still stable at 900 °C, and the temperature at which oxidation starts in air is 1000-1100 °C. Therefore, hexagonal boron nitride is an ideal solid lubricant for preparing selflubricating ceramic cutting tool materials. However, the direct addition of hexagonal boron nitride will have adverse effects on the mechanical properties of ceramic cutting tool materials.
The traditional preparation process of self-lubricating ceramic cutting tool materials is to directly mix ceramic powder and solid lubricant powder, and then make block materials through certain molding and sintering processes. The direct addition of hexagonal boron nitride can produce two effects on ceramic cutting tool materials: on the one hand, hexagonal boron nitride in the cutting tool material can form a selflubricating fdm on the surface of the cutting tool during cutting, thus reducing the friction coefficient between the cutting tool and chips;
The direct addition of hexagonal boron nitride has a great negative impact on the mechanical properties of solid self-lubricating composites, which limits its application range. (1) For the metal-based solid self-lubricating composite directly added with hexagonal boron nitride, on the one hand, hexagonal boron nitride has poor wettability with the metal matrix, and the interface bonding strength between the two is low, which has strong separation effect on the metal matrix. On the other hand, because the density of hexagonal boron nitride is much smaller than that of metal matrix, segregation inevitably occurs in the mixing process. Two aspects lead to the reduction of the mechanical strength ofthe composite material and affect its friction and wear properties.
(2) As hexagonal boron nitride is a soft material with low strength and hardness, its mechanical properties decrease due to its dispersion in the tool material, thus reducing the wear resistance of the tool. In addition, hexagonal boron nitride is a covalent bond compound with low solid phase diffusion coefficient at high temperature and is a material difficult to sinter. Some literatures pointed out that the card room structure formed by cross stacking of sheet hexagonal boron nitride is the main factor hindering the densification of composite ceramics containing hexagonal boron nitride. Only by adopting appropriate technology to eliminate the card room structure can it obtain high compactness and further have higher mechanical properties. In the related process, adding a component capable of generating a liquid phase during the sintering process can promote particle rearrangement of hexagonal boron nitride-containing composite ceramic and diffusion of the substance, which is conducive to eliminating the card room structure of hexagonal boron nitride, thus promoting densification of the composite ceramics. See Journal of the Chinese ceramic society, 1998,26(2):265-269.
Aiming at the defect of low mechanical properties of solid self-lubricating composites directly added with hexagonal boron nitride, it is found that the preparation of solid self-lubricating composites by adding coated hexagonal boron nitride composite powder can make up the above technical defects to a certain extent. The existing preparation methods of coated hexagonal boron nitride composite powder mainly include ceramic coated h-BN and cermet coated h-BN. Among them, ceramic coated h-BN mainly involves alumina-coated hexagonal boron nitride and nano-silica coated hexagonal boron nitride. For example, Chinese patent document CNI04974817A discloses a method for preparing spherical nano-silica coated hexagonal boron nitride composite powder by hydrolysis and condensation reaction of ethyl orthosilicate; CNI04892003A discloses a method for preparing alumina-coated hexagonal boron nitride composite powder by heterogeneous nucleation and vacuum calcination. Chinese patent document CNI04892005A discloses a silicon nitride-based self-lubricating ceramic cutting tool material added with aluminum oxide coated hexagonal boron nitride composite powder; CNI 04844178A provides a self-lubricating ceramic cutting tool material added with silica-coated hexagonal boron nitride composite powder; CNI04844225A discloses a self-lubricating ceramic cutting tool material added with silicon carbide coated hexagonal boron nitride composite powder. The mechanical properties of the ceramic-coated hexagonal boron nitride composite powder and the ceramic cutting tool material have been improved by the above technology, but the defects are as follows: (1) For metal-based solid self-lubricating composite materials, the ceramic coating layer and the metal matrix also have problems of poor wettability, low bonding strength and high density difference, so the addition of ceramic-coated hexagonal boron nitride composite powder has little effect on the mechanical properties and friction and wear properties of metal-based solid selflubricating composites. (2) Aluminum oxide, silicon dioxide and silicon carbide coated with hexagonal boron nitride powder are ceramic materials for ceramic-based solid selflubricating composite materials. On the one hand, the coating layer of ceramic material can not or seldom produce liquid phase during sintering, which has little effect on eliminating the card room structure of hexagonal boron nitride, and further has little effect on promoting densification of the prepared composite material. On the other hand, due to the inherent low fracture toughness characteristics of ceramic materials, the addition of ceramic-coated hexagonal boron nitride mainly improves the hardness and flexural strength of the composite material, and has less effect on the improvement of fracture toughness. However, the lower fracture toughness has become the bottleneck restricting the wide application of ceramic cutting tool materials, so the development of corresponding technologies should be emphasized to improve the fracture toughness of ceramic cutting tool materials.
Compared with the addition of ceramic coated h-BN, the addition of metal coated h-BN can better improve the mechanical properties and friction and wear properties of metal-based and ceramic-based solid self-lubricating composites. The Chinese patent document CN101214549A discloses a method for preparing a nickel-coated boron nitride composite powder by hydrothermal hydrogen reduction. In the method, a hexagonal boron nitride powder and a catalyst are added into a nickel salt solution, and nickel is reduced and deposited on the surface of hexagonal boron nitride powder by hydrogen gas at a certain temperature in an autoclave to form a composite powder. Literature (Chinese Journal of Materials Research, 2011,25 (5): 509-516) reported the preparation of nickel-plated h-BN powder by precipitation method. In the method, hBN powder is added into a nickel salt solution to prepare a suspension, and a precipitant is added into wrap the precipitate on the surface of the h-BN powder, washed with water and then subjected to high temperature reduction in hydrogen to obtain a nickel-plated h-BN powder. Both of these technologies have prepared metal-coated hexagonal boron nitride composite powder, but there are still deficiencies: (1) The hydrothermal hydrogen reduction method needs to be carried out in a closed container, the reaction process cannot be observed, it is not intuitive; The equipment requirements are high (the autoclave is made of high temperature resistant high pressure steel, corrosion resistant lining), and the technical difficulty is high (temperature and pressure are strictly controlled), and cost is high; High pressure hydrogen gas is required, and the safety performance is poor. (2) The coated h-BN powder prepared by the precipitation method has more serious agglomeration (multiple h-BN powders are gathered together and coated with some fine nickel particles on the outside), which affects the performance of the solid self-lubricating composite material prepared by the method; the step of high temperature reduction in hydrogen has higher requirements on equipment, poor safety performance and high cost.
Contents of the Invention
In order to overcome the defects of the prior technologies, the invention provides a nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder and a preparation method thereof.
The invention also provides application of nickel-coated hexagonal boron nitride composite powder for preparing metal-based and ceramic-based solid self-lubricating composite materials.
The invention also provides a self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride (h-BN@Ni) core-shell structure composite powder and a preparation method thereof. While improving the hardness and flexural strength of the self-lubricating ceramic cutting tool material, the fracture toughness is also significantly improved.
Terminology description:
h-BN: Hexagonal boron nitride h-BN@Ni: Nickel coated hexagonal boron nitride. Among them, h-BN is the core and Ni is the shell.
The invention is realized by the following technical scheme:
Nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder which has a core-shell structure with h-BN as core and Ni as shell;
The composite powder is prepared by added sensitized and activated h-BN powder into electroless plating solution and plating nickel on the surface of hexagonal boron nitride under the condition of ultrasonic oscillation; Among them, the components of the electroless plating solution are: 20-30 g/L of nickel sulfate hexahydrate (NiSCUfoHzO), 50-70 g/L of sodium citrate dihydrate (NasCeHsCh^HzO), 30-40 g/L of boric acid (H3BO3), 50-100 mL/L of hydrazine hydrate (Ν2Η4Ή2Ο) with a mass fraction of 50-80%, an appropriate amount of pH adjuster to make the electroless plating solution pH 11-12, the balance is distilled water.
A preparation method of the nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder comprises the following steps:
(1) The h-BN powder is added into the sensitizing solution, ultrasonically oscillated for 2-5 min, centrifugally dispersed and washed once with absolute ethanol, and then washed once with distilled water;
(2) The h-BN powder sensitized in step (1) is added into the activation solution, ultrasonically oscillated for 5-10 min, centrifugally dispersed and washed with absolute ethanol for 3-5 times, and drying in a vacuum drying oven at 40-60 °C for 7-10 h to obtain the activated h-BN powder;
(3) The activated h-BN powder is added into the electroless plating solution, and the electroless plating solution has a pH of 11-12, and is plated in a constant temperature water bath of 70-85 °C;
Ultrasonic oscillation is maintained in the plating process and pH regulator is dropped at any time to keep the pH value of the electroless plating solution at 11-12; After plating is completed, solid particles are separated and washed to neutrality by distilled water, then washed 2-3 times by absolute ethanol, and then dried for 7-10 h at 40-60 °C in a vacuum drying oven to obtain h-BN@Ni composite powder.
According to a preferred embodiment of the present invention, the components of the sensitizing solution described in the step (1) are: 20-30 g/L of stannous chloride dihydrate (SnC12’2H2O), the balance is absolute ethanol. Further preferably, the preparation step of the sensitizing solution in step (1) is: SnCh^FbO is weighed according to the proportion, added into an appropriate amount of absolute ethanol, stirred and dissolved, and then added with absolute ethanol to the total volume of sensitizing solution.
According to a preferred embodiment of the present invention, when h-BN is sensitized in step (1), the addition amount of the h-BN powder is 10-20 g/L per liter of sensitizing solution.
According to a preferred embodiment of the present invention, the components of the activating solution described in step (2) are: 0.5-1 g/L of palladium chloride (PdCb), 10-20 mL/L of concentrated hydrochloric acid with a mass fraction of 35-37% and the balance is distilled water.
Further preferably, the preparation step of the activating solution in step (2) is: PdCL is weighed according to proportion, added into concentrated hydrochloric acid measured according to proportion, stirred and dissolved, and distilled water is added into the total volume of the activating solution.
According to a preferred embodiment of the present invention, when the h-BN is activated in step (2), the addition amount of the h-BN powder is 10-20 g/L per liter of the activating solution.
According to a preferred embodiment of the present invention, the components of the electroless plating solution described in the step (3) are: 20-30 g/L of nickel sulfate hexahydrate (NiSCLAFFO), 50-70 g/L of sodium citrate dihydrate (NasCeHsCF^HzO), 30-40 g/L of boric acid (H3BO3), 50-100 mL/L of hydrazine hydrate (Ν2Η4Ή2Ο) with a mass fraction of 50-80%, an appropriate amount of pH adjuster makes the pH of the electroless plating solution 11-12, and the balance is distilled water.
According to a preferred embodiment of the invention, the pH adjuster described in step (3) is a 60-80 g/L NaOH solution. The pH adjuster in the electroless plating solution described in the step (3) is a 60-80 g/L NaOH solution.
Further preferably, the preparation step of the electroless plating solution in step (3) is as follows:
□ Weigh NaOH proportionally, add appropriate amount of distilled water, stir to dissolve and add distilled water to the required volume, and prepare 60-80 g/L NaOH solution, that is, pH adjuster.
□ NiSO4’6H2O, Na3C6HsO7’2H2O and H3BO3 are weighed in proportion, respectively, and added into an appropriate amount of distilled water, and stirred in a water bath of 30-40 °C to dissolve them, respectively, to obtain a clear solution.
□ NiSO4’6H2O solution is slowly added into Na3C6H5O7’2H2O solution, and solution A is obtained by stirring while adding.
□ H3BO3 solution is slowly added into the solution A, and stirring while adding to obtain a solution B.
□ The pH adjuster is added dropwise to the solution B, and the solution is stirring while adding, so that the pH value of the solution reaches 11-12, and solution C is obtained.
□ Hydrazine hydrate with a mass fraction of 50-80% is measured according to a proportion, added dropwise into the solution C, and stirring while adding to obtain solution D.
□ Distil water is added into the solution D to the total volume of the electroless plating solution and stirred evenly to obtain the electroless plating solution.
According to a preferred embodiment of the present invention, in the electroless plating step (3), the amount of the h-BN powder added is 2 to 5 g/L per liter of the electroless plating solution.
According to a preferred embodiment of the present invention, the h-BN powder raw material described in the step (1) is a commercially available product with an average particle diameter of 1-3 pm and a purity of more than 99%. Preferably, the chemical reagents used in the invention such as stannous chloride dihydrate, absolute ethanol and the like are all commercially available products and analytically pure, wherein the concentration of concentrated hydrochloric acid is 35-37% by mass and the concentration of hydrazine hydrate is 50-80% by mass.
The nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder prepared by the invention is used for preparing metal-based and ceramic-based solid self-lubricating composite materials.
The invention relates to a self-lubricating ceramic cutting tool material added with the nickel-coated hexagonal boron nitride core-shell structure composite powder, which is prepared by using a phase alumina (01-AI2O3) as a matrix, tungsten carbide titanium ((W,Ti)C) as a reinforcing phase, nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder of the invention as a solid lubricant, magnesium oxide (MgO) as a sintering aid through ball milling, mixing and hot pressing sintering; The mass percentage content of each component is: 25-45% of (X-AI2O3, 50-70% of (W,Ti)C, and 2-10% of the nickel-coated hexagonal boron nitride based on the mass of h-BN in the composite powder, 0.4-1.5% of MgO.
According to a preferred embodiment of the present invention, the raw material powders of the above components are all commercially available products, the average particle sizes of h-BN powder, 01-AI2O3 powder, (W,Ti)C powder and MgO powder are 1-3 pm, 0.2-0.5 pm, 1-1.5 pm and 1-2 pm respectively, and the purity is greater than 99%.
According to a preferred embodiment of the present invention, the self-lubricating ceramic cutting tool material of the above-mentioned the nickel-coated hexagonal boron nitride core-shell composite powder is characterized in that the mass percentage of each component is: 31-41% of (X-AI2O3, 52-66% of (W,Ti)C, 2-6% of h-BN@Ni based on the mass of h-BN in the composite powder, and 0.5-1% of MgO; The sum of the components are 100%.
Further preferably, the self-lubricating ceramic cutting tool material with the nickel-coated hexagonal boron nitride core-shell composite powder, the mass percentage of each component is: 36-38% of (X-AI2O3, 58-59% of (W,Ti)C, 3.5-4.5% of h-BN@Ni based on the mass of h-BN in the composite powder and 0.5% of MgO; The sum of the components are 100%.
According to the present invention, a method for preparing a self-lubricating ceramic cutting tool material for adding a nickel-coated hexagonal boron nitride coreshell composite powder, comprising the above-mentioned preparation step (1)-(3) of nickel-coated hexagonal boron nitride composite powder, also includes the following steps:
(4) Preparation of suspension
The (X-AI2O3 powder is weighed in proportion, added into an appropriate amount of polyethylene glycol-absolute ethanol solution, ultrasonically dispersed and stirred to form an 01-AI2O3 suspension;
The (W,Ti)C powder is weighed in proportion, added into an appropriate amount of absolute ethanol, ultrasonically dispersed and stirred to prepare (W,Ti)C suspension;
The h-BN@Ni powder is weighed in proportion, added into an appropriate amount of absolute ethanol, ultrasonically dispersed and stirred to prepare h-BN@Ni suspension;
(5) Preparation of multiphase suspension, ball milling
The prepared (X-AI2O3 suspension is mixed with the (W,Ti)C suspension, then the MgO powder is added in proportion, ultrasonically dispersed and stirred for 20-30 min, and the obtained multiphase suspension is poured into a ball mill tank ball mill 40-50 h; Then added the h-BN@Ni suspension obtained in the step (3), and continuing the ball milling to obtain a ball milled slurry;
(6) The ball milled slurry is vacuum dried and sieved to obtain a mixed powder, which is sealed and used; The mixed powder is charged into a graphite mold, and after cold press forming, it is placed in a vacuum furnace for hot press sintering.
According to the preparation method of the ceramic cutting tool material of the present invention, preferably, in the step (4), the mass of the polyethylene glycol is 24% of the mass of the (X-AI2O3 powder. The preparation method of polyethylene glycolabsolute ethanol solution is as follows: Firstly, polyethylene glycol is added into absolute ethanol and stirred and dissolved in a water bath at 30-40 °C. The amount of absolute ethanol solution is not necessarily strictly controlled, so that it can be made into a suspension. Further, the average molecular weight of polyethylene glycol is 40006000.
Further preferred:
In the step (4), the ultrasonic dispersion and stirred time are both 15-20 min.
In step (5), the ball milling conditions are as follows: The cemented carbide grinding balls are added at a ball weight ratio of 10:1, and ball milling is carried out under a protective atmosphere of nitrogen or argon.
In step (5), the continuous ball milling time is 2-4 h; The protective atmosphere is still nitrogen or argon.
In step (6), the ball milling slurry is dried in a vacuum drying oven at 90-110 °C for 20-2511, and then passed through a 100-200 mesh sieve.
The sintering process parameters of the hot pressing sintering in step (6) are as follows: The heating rate is 10-20 °C/min, the holding temperature is 1450-1550 °C, the holding time is 10-25 min, and the hot pressing pressure is 25-30 MPa.
Compared with the prior art, the invention has the following advantages:
1. Compared with the existing technology for preparing ceramic coated hexagonal boron nitride composite powder: (1) For the metal-based solid self-lubricating composite material, the invention not only can improve the wettability of the solid lubricant and the metal matrix and increase the interfacial bonding strength of the solid lubricant and the metal matrix, but also can reduce the density difference between the solid lubricant and the metal matrix, thereby improving the segregation in the mixing process and making the structure of the material uniform. Therefore, the mechanical properties and friction and wear properties of the metal-based solid self-lubricating composite material are improved. (2) For the ceramic-based solid self-lubricating composite material, the invention can produce a liquid phase at a lower sintering temperature, which can effectively eliminate the card room structure of the hexagonal boron nitride and thereby increase the density of the composite material, and the sintering temperature of the composite material is lowered, energy is saved, environmental protection is facilitated. The metal nickel coated hexagonal boron nitride powder solid lubricant prepared by the invention can greatly improve the fracture toughness of the ceramic-based solid self-lubricating composite material, thereby expanding the application range.
2. Compared with the existing hydrothermal hydrogen reduction method and n
precipitation method for preparing the metal-coated hexagonal boron nitride composite powder, the invention has the advantages of simple process equipment, simple and convenient operation, high safety, good powder coating effect and low cost. The hBN@Ni composite powder prepared by the invention has good dispersibility and no agglomeration, and is convenient for adding to the solid self-lubricating composite material during application, and does not adversely affect the performance of the solid self-lubricating composite material prepared by the method.
3. The invention prepares a self-lubricating ceramic cutting tool material by adding a h-BN@Ni composite powder having a core-shell structure instead of the h-BN powder as a solid lubricant; On the one hand, the flaky h-BN powder is easy to agglomerate and not easy to disperse. When directly added, it will form a cross-stacked card room structure in the ceramic matrix, resulting in low sintering density and uneven microstructure of ceramic tool materials. Electroless nickel plating of h-BN powder can improve its dispersibility and also produce liquid phase during sintering. Therefore, the addition of h-BN@Ni composite powder can avoid the formation of card room structure in ceramic matrix and improve the sintering density and microstructure uniformity of ceramic tool materials. On the other hand, the metal nickel coating of h-BN@Ni composite powder can toughen and reinforce the self-lubricating ceramic cutting tool material. The synergistic effect of the two aspects is to improve the mechanical properties and wear resistance of the self-lubricating ceramic tool materials by using the core-shell self-lubricating and reinforcing composite effects.
4. Compared with the prior technology for preparing the self-lubricating ceramic cutting tool material by adding ceramic material and coating hexagonal boron nitride composite powder, the invention can generate liquid phase at a lower sintering temperature, can effectively eliminate the card room type structure of hexagonal boron nitride and further improve the compactness of the ceramic cutting tool material, simultaneously reduces the sintering temperature of the ceramic cutting tool material, saves energy and is beneficial to environmental protection. In addition, the invention adopts the metal nickel as the coating material of the hexagonal boron nitride powder, and can greatly improve the fracture toughness of the self-lubricating ceramic cutting tool material by utilizing the high toughness of the metal nickel, thereby expanding the application range of the ceramic cutting tool.
Description of the Drawings
Fig. 1 is scanning electron microscope (SEM) photograph of h-BN raw material powders used in the example of the present invention.
Fig. 2 is 10,000-fold enlarged SEM photograph of h-BN@Ni composite powders prepared in example 1 of the present invention.
Fig. 3 is 40,000-fold enlarged SEM photograph of h-BN@Ni composite powders prepared in example 1 of the present invention.
Fig. 4 is x-ray diffraction pattern of h-BN@Ni composite powders and the h-BN raw material powder in example 1 of the present invention.
Fig. 5 is cross-sectional SEM photograph of the self-lubricating ceramic cutting too material added with h-BN@Ni composite powders prepared in example 4 of the present invention.
Fig. 6 is cross-sectional SEM photograph of a self-lubricating ceramic cutting tool material added with h-BN powders prepared in comparative example 1.
Mode of Carrying out the Invention
The technical scheme of the present invention will be further explained below with reference to the drawings and examples.
The raw material powders used in the examples were all commercially available products, the average particle sizes of h-BN powder raw materials was 2pm, and the purity was more than 99%; SEM photos and X-ray diffraction patterns of the used hBN raw material powder are shown in Fig. 1 and Fig. 4. The average particle sizes of (X-AI2O3 powder, (W,Ti)C powder and MgO powder were 0.2pm, 1.5pm and 2pm respectively, and the purity was more than 99%.
The chemical reagents used in the examples were all commercially available products and analytically pure, wherein the concentration of concentrated hydrochloric acid was 37% by mass, the concentration of hydrazine hydrate was 80% by mass, and the average molecular weight of polyethylene glycol was 4,000.
Example 1: The preparation method of nickel-coated hexagonal boron nitride composite powder is as follows:
(1) 2.5 g of SnCl2-2H2O was weighed, added into 50 mL of absolute ethanol, stirred and dissolved, and then absolute ethanol was added into 100 mL to obtain a sensitizing solution. 2 g of h-BN powder was weighed into a sensitizing solution, ultrasonically oscillated for 2 min, centrifugally separated and washed once with absolute ethanol, and then washed once with distilled water.
(2) 0.05g of PdCl2 was added into 1 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added into 100 mL to obtain an activation solution. The sensitized h-BN powder was added into the activation solution, ultrasonically oscillated for 5 min, centrifugally separated and washed with absolute ethanol for 3 times, and dried in a vacuum oven at 40 °C for 10 h to obtain activated hBN powder.
(3) Weigh 8 g NaOH, add 70 mL distilled water, stir and dissolve, add distilled water to 100 mL, and prepare 80 g/LNaOH solution, i.e. pH adjuster; Weighing 12.5 g NiSO4’6H2O, 25 g of NaA'eHsCh^^O and 15 g of H3BO3, respectively, added 70-100 mL of distilled water, stirred and dissolved in a water bath at 35 °C to respectively obtain clear solutions; NiSO4’6H2O solution was slowly added into the Na3C6H5O7’2H2O solution, and stirring while adding to obtain a solution A; H3BO3 solution was slowly added into the solution A, and stirring while adding to obtain a solution B; Added the pH adjuster dropwise to the solution B, stirring while adding, so that the pH value of the solution reaches 11 to obtain solution C; Measure 35 mL of hydrazine hydrate, add it drop by drop into the solution C, and stirring while adding it to obtain solution D; Distilled water was added into the solution D to 500 mL and stirred evenly to obtain electroless plating solution.
The h-BN powder activated in the step (2) was added into the above electroless plating solution, and plated in a constant temperature water bath at 80 °C. During the plating process, ultrasonic oscillation was maintained and pH adjuster was dropped at any time to keep the pH value of the electroless plating solution at 11. After the plating was completed, the solid particles were separated and washed with distilled water until neutral, and then washed twice with absolute ethanol, and then dried in a vacuum drying oven at 40 °C for 10 h to obtain a h-BN@Ni composite powder.
The SEM photograph and the X-ray diffraction pattern of nickel-coated hexagonal boron nitride composite powder prepared in example 1 are shown in Fig. 2, Fig. 3 and Fig. 4. The SEM photograph and the X-ray diffraction pattern of the h-BN raw material powder used are shown in Fig. 1 and Fig. 4.
It can be seen from Fig. 1 that the h-BN raw material powder had a sheet structure and the surface was flat. It can be seen from Fig. 2 that the h-BN@Ni composite powder was still in a sheet-like structure with good dispersibility and no agglomeration. It can be seen from Fig. 3 that the surface of the h-BN@Ni composite powder was coated with fine particles, and the coating layer was complete and compact. In Fig. 4, the xray diffraction pattern of the h-BN@Ni composite powder had the diffraction peak of h-BN and the diffraction peak of Ni, and no impurity peak appears, indicating that the cladding layer was crystalline metal Ni. From Fig. 2, Fig. 3 and Fig. 4, it can be seen that nickel-coated hexagonal boron nitride composite powder with core-shell structure was prepared in example 1.
Example 2: The preparation method of nickel-coated hexagonal boron nitride composite powder is as follows:
(1) 4 g of SnC12-2H2O was weighed, added into 100 mL of absolute ethanol, stirred and dissolved, and then absolute ethanol was added into 200 mL to obtain a sensitizing solution. 3 g of h-BN powder was weighed into a sensitizing solution, ultrasonically oscillated for 4 min, centrifugally separated and washed once with absolute ethanol, and then washed once with distilled water.
(2) 0.2g PdCb was added into 3 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added into 200 mL to obtain an activation solution. The sensitized h-BN powder was added into the activation solution, ultrasonically oscillated for 6 min, centrifugally separated and washed with absolute ethanol for 5 times, and dried in a vacuum oven at 50 °C for 9 h to obtain activated h-BN powder.
(3) Weigh 14 g NaOH, add 150 mL distilled water, stir and dissolve, add distilled water to 200 mL, and prepare 70 g/L NaOH solution, i.e. pH adjuster; Weighing 20 g NiSC>4’6H2O, 55 g of Na-XTHsChGI-hO and 35 g of H3BO3, respectively, added 1500200 mL of distilled water, stirred and dissolved in a water bath at 40 °C to respectively obtain clear solutions; NiSC>4’6H2O solution was slowly added into Na3C6HsO7-2H2O solution, and stirring while adding to obtain a solution A; H3BO3 solution was slowly added into the solution A, and stirring while adding to obtain a solution B; Added the pH adjuster dropwise to the solution B, stirring while adding, so that the pH value of the solution reaches 11 to obtain solution C; Measure 80 mL of hydrazine hydrate, add it drop by drop into the solution C, and stirring while adding it to obtain solution D; Distilled water was added into the solution D to 1000 mL and stirred evenly to obtain electroless plating solution. The h-BN powder activated in the step (2) was added into the above electroless plating solution, and plated in a constant temperature water bath at 85 °C. During the plating process, ultrasonic oscillation is maintained and pH adjuster was dropped at any time to keep the pH value of the electroless plating solution at 11. After the plating was completed, the solid particles were separated and washed with distilled water until neutral, and then washed twice with absolute ethanol, and then dried in a vacuum drying oven at 60 °C for 9 h to obtain a h-BN@Ni composite powder.
Example 3: The preparation method of nickel-coated hexagonal boron nitride composite powder is as follows:
(1) 10.5 g of SnC12’2H2O was weighed, added into 250 mL of absolute ethanol, stirred and dissolved, and then absolute ethanol was added into 350 mL to obtain a sensitizing solution. 5 g of h-BN powder was weighed into a sensitizing solution, ultrasonically oscillated for 4 min, centrifugally separated and washed once with absolute ethanol, and then washed once with distilled water.
(2) 0.3 g PdCb was added into 4 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added into 350mL to obtain an activation solution. The sensitized h-BN powder was added into the activation solution, ultrasonically oscillated for 8 min, centrifugally separated and washed with absolute ethanol for 3 times, and dried in a vacuum oven at 50 °C for 10 h to obtain activated h-BN powder.
(3) Weigh 21 g NaOH, add 250 mL distilled water, stir and dissolve, add distilled water to 300 mL, and prepare 70g/L NaOH solution, i.e. pH adjuster; Weighing 30 g NiSO4’6H2O, 70 g of Na/C/H/Ch^I-hO and 40 g of H3BO3, respectively, added 200250 mL of distilled water, stirred and dissolved in a water bath at 35 °C to respectively obtain clear solutions; NiSO4’6H2O solution was slowly added into Na3C6HsO7-2H2O solution, and stirring while adding to obtain a solution A; H3BO3 solution was slowly added into the solution A, and stirring while adding to obtain a solution B; Added the pH adjuster dropwise to the solution B, stirring while adding, so that the pH value of the solution reaches 12 to obtain solution C; Measure 80 mL of hydrazine hydrate, add it drop by drop into the solution C, and stirring while adding it to obtain solution D; Distilled water was added into the solution D to 1200 mL and stirred evenly to obtain electroless plating solution. The h-BN powder activated in the step (2) was added into the above electroless plating solution, and plated in a constant temperature water bath at 75 °C. During the plating process, ultrasonic oscillation is maintained and pH adjuster was dropped at any time to keep the pH value of the electroless plating solution at 12. After the plating was completed, the solid particles were separated and washed with distilled water until neutral, and then washed twice with absolute ethanol, and then dried in a vacuum drying oven at 50 °C for 8 h to obtain a h-BN@Ni composite powder.
Example 4: The self-lubricating ceramic cutting tool material of h-BN@Ni coreshell composite powder was added, and the mass percentage of each component is: 32.5% of (X-AI2O3, 65% of (W, Ti)C, 2% of h-BN@Ni based on the mass of h-BN in the composite powder (product prepared in example 1), 0.5% of MgO.
The preparation steps are as follows:
(1) - (3) same as example 1.
(4) preparation of suspension
Weighing 32.5 g of (X-AI2O3 powder and 0.65 g of polyethylene glycol, firstly added polyethylene glycol into 120 mL of absolute ethanol, stirred and dissolved in a water bath at 35 °C, then added (X-AI2O3 powder, ultrasonically dispersed and stirred for 15min to prepare (X-AI2O3 suspension.
g of (W, Ti)C powder was weighed, added into 100 mL of absolute ethanol, ultrasonically dispersed and stirred for 15 min to prepare a (W, Ti)C suspension.
The h-BN@Ni composite powder obtained in example 1 was added into 40 mL of absolute ethanol, ultrasonically dispersed and stirred for 15 min to prepare a h-BN@Ni suspension.
(5) Preparation of multiphase suspension, ball milling
The (X-AI2O3 suspension obtained in the step (4) and the (W, Ti)C suspension were mixed, then added 0.5 g MgO powder, ultrasonically dispersed and stirred for 20 min, poured the obtained multiphase suspension into a ball milling tank, added 1kg of hard alloy grinding balls, and performing ball milling for 48 h with nitrogen as a protective atmosphere; Then, the h-BN@Ni suspension obtained in the step (4) was added, and ball milling was continued for 4 h under nitrogen as a protective atmosphere to obtain a ball milled slurry.
(6) The ball milled slurry obtained in the step (5) was dried in a vacuum drying oven at 100 °C for 24 h, and then passed through a 120 mesh sieve to obtain a mixed powder; The mixed powder was put into a graphite mold, and after cold press forming, it was placed in a vacuum hot pressing sintering furnace for hot press sintering. The sintering process parameters are as follows: The heating rate is 15 °C/min, the holding temperature is 1500 °C, the holding time is 15 min, and the hot pressing pressure is 25 MPa.
Comparative example 1: The self-lubricating ceramic cutting tool material added with h-BN powders, wherein the mass percentage of each component is: 32.5% of aAI2O3, 65% of (W,Ti)C, 2% of h-BN, 0.5% of MgO. The preparation method is as follows:
(1) Preparation of suspension
Weighing 32.5 g of (X-AI2O3 powder and 0.65g of polyethylene glycol, firstly added polyethylene glycol into 120 mL of absolute ethanol, stirred and dissolved in a water bath at 35 °C, then added (X-AI2O3 powder, ultrasonically dispersed and stirred for 15 min to prepare (X-AI2O3 suspension. 65 g of (W, Ti)C powder was weighed, added into 100 mL of absolute ethanol, ultrasonically dispersed and stirred for 15 min to prepare a (W, Ti)C suspension. 2 g of h-BN raw material powder was weighed, added into 40 mL of absolute ethanol, ultrasonically dispersed and stirred for 15 min to prepare a h-BN suspension.
(2) Preparation of multiphase suspension, ball milling
The (X-AI2O3 suspension obtained in the step (1) and the (W,Ti)C suspension were mixed, then added 0.5g MgO powder, ultrasonically dispersed and stirred for 20min, poured the obtained multiphase suspension into a ball milling tank, added 1 kg of hard alloy grinding balls, and performing ball milling for 48h with nitrogen as a protective atmosphere; Then, the h-BN@Ni suspension obtained in the step (1) was added, and ball milling was continued for 4 h under nitrogen as a protective atmosphere to obtain a ball milled slurry.
(3) The ball milled slurry obtained in the step (2) was dried in a vacuum drying oven at 100 °C for 24 h, and then passed through a 120 mesh sieve to obtain a mixed powder; The mixed powder was put into a graphite mold, and after cold press forming, it was placed in a vacuum hot pressing sintering furnace for hot press sintering. The sintering process parameters are as follows: The heating rate is 15 °C/min, the holding temperature is 1500 °C, the holding time is 15 min, and the hot pressing pressure is 25 MPa.
It can be seen from Fig. 5 that the h-BN grain distribution of the self-lubricating ceramic cutting tool material with h-BN@Ni composite powder is relatively uniform and tightly combined with the ceramic matrix, and the ceramic matrix has uniform grain size and dense arrangement. It can be seen from Fig. 6 that the h-BN grains of the selflubricating ceramic cutting tool material added with h-BN powder (uncoated) have obvious agglomeration phenomenon, forming a card room structure, and the ceramic matrix has uneven grain size, abnormal growth phenomenon, non-compact arrangement and more pores. Fig. 5 and Fig. 6 show that the addition of nickel-coated hexagonal boron nitride instead of hexagonal boron nitride as a solid lubricant can improve the microstructure and sintering density of the self-lubricating ceramic cutting tool material.
According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool material prepared by adding the h-BN@Ni core-shell composite powder prepared in example 4 are: flexural strength 621 MPa, hardness 16.3 GPa, fracture toughness 5.5 MPa-m1/2; The mechanical properties of the self-lubricating ceramic cutting tool material added with h-BN powder prepared in comparative example 1 are: flexural strength 578 MPa, hardness 15.1 GPa, fracture toughness 4.8 MPa-m1/2. It can be seen that the flexural strength, hardness and fracture toughness of the former are 7.4%, 7.9% and 14.6% higher than those of the latter, respectively.
Example 5: The self-lubricating ceramic cutting tool material added with hBN@Ni core-shell structure composite powders, wherein the mass percentage of each component is: 37% of (X-AI2O3, 58.5% of (W,Ti)C, 4% of h-BN@Ni by mass of h-BN in the composite powder, 0.5% MgO. The preparation method is as follows:
(1) Sensitization and activation of h-BN powder g of SnC12’2H2O was weighed, added into 200 mL of absolute ethanol, and stirred to dissolve to obtain a sensitizing solution. 0.1 g of PdCb was added into 2 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added into 200 mL to obtain an activation solution. 4 g of h-BN raw material powder was weighed into a sensitizing solution, ultrasonically oscillated for 3 min, centrifugally separated and washed once with absolute ethanol, and then washed once with distilled water. The sensitized h-BN powder was added into the activation solution, ultrasonically oscillated for 7 min, centrifugally separated and washed 4 times with absolute ethanol, and dried in a vacuum oven at 50 °C for 8 h for standby.
(2) Preparation of h-BN@Ni composite powder by electroless plating
14g NaOH was weighed and added 150 mL of distilled water, stirred for dissolution and added distilled water to 200 mL to prepare 70 g/L NaOH solution; Weighing 20g of NiSO4-6H2O, 55g of Na3C6H5O7-2H2O and 35g of H3BO3, respectively, added 150-200 mL of distilled water, stirred in a water bath at 35 °C to dissolve them, respectively, to obtain clear solutions; NiSO4’6H2O solution was slowly added into Na3C6HsO7-2H2O solution, stirring while adding, and then H3BO3 solution was slowly added, and stirring while adding to obtain a mixed solution; NaOH solution was added dropwise to the mixed solution and stirring while adding, so that the pH value of the mixed solution reaches 12. Measure 70 mL of hydrazine hydrate, add it drop by drop into mixed solution, stirring while being added, and then distilled water was added into 1000 mL and stirred uniformly to obtain an electroless plating solution.
The h-BN powder activated in the step (1) was added into the above electroless plating solution, and plated in a constant temperature water bath at 75 °C. During the plating process, ultrasonic oscillation was maintained and NaOH solution was dropped at any time to keep the pH value of the electroless plating solution at 12. After the plating was completed, the solid particles were separated and washed with distilled water until neutral, and then washed 3 times with absolute ethanol, and then dried in a vacuum drying oven at 50 °C for 8 h to obtain a h-BN@Ni composite powder.
(3) Preparation of suspension
Weighing 37 g of (X-AI2O3 powder and 0.74 g of polyethylene glycol, firstly added polyethylene glycol into 120 mL of absolute ethanol, stirred and dissolved in a water bath at 40 °C, then added (X-AI2O3 powder, ultrasonically dispersed and stirred for 20 min to prepare (X-AI2O3 suspension. 58.5 g of (W, Ti)C powder was weighed, added into 90 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 min to prepare a (W,Ti)C suspension. The h-BN@Ni composite powder obtained in the step (2) was added into 60 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 minutes to prepare a h-BN@Ni suspension.
(4) Preparation of multiphase suspension, ball milling
The (X-AI2O3 suspension obtained in the step (3) and the (W,Ti)C suspension were mixed, then added 0.5g MgO powder, ultrasonically dispersed and stirred for 20 min, poured the obtained multiphase suspension into a ball milling tank, added 1 kg of hard alloy grinding balls, and performing ball milling for 45 h with nitrogen as a protective atmosphere; Then, the h-BN@Ni suspension obtained in the step (3) was added, and ball milling was continued for 3 h under nitrogen as a protective atmosphere to obtain a ball milled slurry.
(5) The ball milled slurry obtained in the step (4) was dried in a vacuum drying oven at 110 °C for 20 h, and then passed through a 100 mesh sieve to obtain a mixed powder; The mixed powder was put into a graphite mold, and after cold press forming, it was placed in a vacuum hot pressing sintering furnace for hot press sintering. The sintering process parameters are as follows: The heating rate is 10 °C/min, the holding temperature is 1550 °C, the holding time is 10 min, and the hot pressing pressure is 30
MPa.
Comparative example 2: The self-lubricating ceramic cutting tool material added with h-BN powders, wherein the mass percentage of each component is: 37% of aAI2O3, 58.5% of (W,Ti)C, 4% of h-BN, 0.5% of MgO. The preparation method is as follows:
(1) Preparation of suspension
Weighing 37 g of (X-AI2O3 powder and 0.74 g of polyethylene glycol, firstly added polyethylene glycol into 120 mL of absolute ethanol, stirred and dissolved in a water bath at 40 °C, then added (X-AI2O3 powder, ultrasonically dispersed and stirred for 20 min to prepare (X-AI2O3 suspension. 58.5 g of (W,Ti)C powder was weighed, added into 90 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 min to prepare a (W,Ti)C suspension. 4 g of h-BN raw material powder was weighed, added into 60 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 min to prepare a h-BN suspension.
(2) Preparation of multiphase suspension, ball milling
The (X-AI2O3 suspension obtained in the step (1) and the (W,Ti)C suspension were mixed, then added 0.5g MgO powder, ultrasonically dispersed and stirred for 20 min, poured the obtained multiphase suspension into a ball milling tank, adding 1 kg of hard alloy grinding balls, and performing ball milling for 45 h with nitrogen as a protective atmosphere; Then, the h-BN@Ni suspension obtained in the step (1) was added, and ball milling was continued for 3 h under nitrogen as a protective atmosphere to obtain a ball milled slurry.
(3) The ball milled slurry obtained in the step (2) was dried in a vacuum drying oven at 110 °C for 20 h, and then passed through a 100 mesh sieve to obtain a mixed powder; The mixed powder was put into a graphite mold, and after cold press forming, it was placed in a vacuum hot pressing sintering furnace for hot press sintering. The sintering process parameters are as follows: The heating rate is 10 °C/min, the holding temperature is 1550 °C, the holding time is 10 min, and the hot pressing pressure is 30 MPa.
According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool material prepared by adding the h-BN@Ni core-shell composite powder prepared in example 5 are: flexural strength 610 MPa, hardness 15.3 GPa, fracture toughness 5.1 MPa-m1/2; The mechanical properties of the self-lubricating ceramic cutting tool material added with h-BN powder prepared in comparative example 2 are: flexural strength 536 MPa, hardness 14.1 GPa, fracture toughness 4.2 MPa-m1/2. It can be seen that the flexural strength, hardness and fracture toughness of the former are 13.8%, 8.5% and 21.4% higher than those of the latter, respectively.
Example 6: The self-lubricating ceramic cutting tool material added with hBN@Ni core-shell structure composite powders, wherein the mass percentage of each component is: 40% of (X-AI2O3, 53% of (W,Ti)C, 6% of h-BN@Ni by mass of h-BN in the composite powder, 1% MgO. The preparation method is as follows:
(1) Sensitization and activation of h-BN powder
10.5 g of SnC12’2H2O was weighed, added into 350 mL of absolute ethanol, and stirred to dissolve to obtain a sensitizing solution. 0.3 g of PdCb was added into 4 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added into 350 mL to obtain an activation liquid. 6 g of h-BN raw material powder was weighed into a sensitizing solution, ultrasonically oscillated for 5 min, centrifugally separated and washed once with absolute ethanol, and then washed once with distilled water. The sensitized h-BN powder was added into the activation solution, ultrasonically oscillated for 7 min, centrifugally separated and washed 4 times with absolute ethanol, and dried in a vacuum oven at 60 °C for 7 h for standby.
(2) Preparation of h-BN@Ni composite powder by electroless plating
24g NaOH was weighed and added 250 mL of distilled water, stirred for dissolution and added distilled water to 300 mL to prepare 80 g/L NaOH solution; Weighing 30 g of NiSO4-6H2O, 70 g of NasCeHsOy^O and 40 g of H3BO3, respectively, added 200-250 mL of distilled water, stirred in a water bath at 40 °C to dissolve them, respectively, to obtain clear solutions; NiSO4’6H2O solution was slowly added into Na3C6HsO7-2H2O solution, stirring while adding, and then H3BO3 solution was slowly added, and stirring while adding to obtain a mixed solution; NaOH solution was added dropwise to the mixed solution and stirrig while adding, so that the pH value of the mixed solution reaches 12. Measure 100 mL of hydrazine hydrate, add it drop by drop into mixed solution, stirring while adding, and then distilled water was added into 1200 mL and stirred uniformly to obtain an electroless plating solution. The h-BN powder activated in the step (1) was added into the above electroless plating solution, and plated in a constant temperature water bath at 85 °C. During the plating process, ultrasonic oscillation was maintained and NaOH solution was dropped at any time to keep the pH value of the electroless plating solution at 12. After the plating was completed, the solid particles were separated and washed with distilled water until neutral, and then washed 3 times with absolute ethanol, and then dried in a vacuum drying oven at 50 °C for 9 h to obtain a h-BN@Ni composite powder.
(3) Preparation of suspension
Weighing 40 g of (X-AI2O3 powder and 1.2 g of polyethylene glycol, firstly added polyethylene glycol into 125 mL of absolute ethanol, stirred and dissolved in a water bath at 30 °C, then added (X-AI2O3 powder, ultrasonically dispersed and stirred for 20 min to prepare (X-AI2O3 suspension. 53 g of (W,Ti)C powder was weighed, added into 85 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 min to prepare a (W,Ti)C suspension. The h-BN@Ni composite powder obtained in the step (2) was added into 80 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 minutes to prepare a h-BN@Ni suspension.
(4) Preparation of multiphase suspension, ball milling
The (X-AI2O3 suspension obtained in the step (3) and the (W,Ti)C suspension were mixed, then added 1 g MgO powder, ultrasonically dispersed and stirred for 30 min, poured the obtained multiphase suspension into a ball milling tank, added 1 kg of hard alloy grinding balls, and performing ball milling for 40 h with nitrogen as a protective atmosphere; Then, the h-BN@Ni suspension obtained in the step (3) was added, and ball milling was continued for 2 h under nitrogen as a protective atmosphere to obtain a ball milled slurry.
(5) The ball milled slurry obtained in the step (4) was dried in a vacuum drying oven at 90 °C for 25 h, and then passed through a 100 mesh sieve to obtain a mixed powder; The mixed powder was put into a graphite mold, and after cold press forming, it was placed in a vacuum hot pressing sintering furnace for hot press sintering. The sintering process parameters are as follows: The heating rate is 20 °C/min, the holding temperature is 1500 °C, the holding time is 25 min, and the hot pressing pressure is 30 MPa.
Comparative example 3: The self-lubricating ceramic cutting tool material added with h-BN powders, wherein the mass percentage of each component is: 40% of aAI2O3, 53% of (W,Ti)C, 6% of h-BN, 1% of MgO. The preparation method is as follows:
(1) Preparation of suspension
Weighing 40 g of (X-AI2O3 powder and 1.2 g of polyethylene glycol, firstly added polyethylene glycol into 125 mL of absolute ethanol, stirred and dissolved in a water bath at 30 °C, then added (X-AI2O3 powder, ultrasonically dispersed and stirred for 20 min to prepare (X-AI2O3 suspension. 53 g of (W,Ti)C powder was weighed, added into 85 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 min to prepare a (W,Ti)C suspension. 6 g of h-BN raw material powder was weighed, added into 80 mL of absolute ethanol, ultrasonically dispersed and stirred for 20 min to prepare a h-BN suspension.
(2) Preparation of multiphase suspension, ball milling
The (X-AI2O3 suspension obtained in the step (1) and the (W,Ti)C suspension were mixed, then added 1 g MgO powder, ultrasonically dispersed and stirred for 30 min, poured the obtained multiphase suspension into a ball milling tank, added 1 kg of hard alloy grinding balls, and performing ball milling for 40 h with nitrogen as a protective atmosphere; Then, h-BN@Ni suspension obtained in the step (1) was added, and ball milling was continued for 2 h under nitrogen as a protective atmosphere to obtain a ball milled slurry.
(3) The ball milled slurry obtained in the step (2) was dried in a vacuum drying oven at 90 °C for 25 h, and then passed through a 100 mesh sieve to obtain a mixed powder; The mixed powder was put into a graphite mold, and after cold press forming, it was placed in a vacuum hot pressing sintering furnace for hot press sintering. The sintering process parameters are as follows: The heating rate is 20 °C/min, the holding temperature is 1500 °C, the holding time is 25 min, and the hot pressing pressure is 30
MPa.
According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool material prepared by adding the h-BN@Ni core-shell composite powder prepared in example 6 are: flexural strength 550 MPa, hardness 13.1 GPa, fracture 5 toughness 4.1 MPa-m1/2; The mechanical properties of the self-lubricating ceramic cutting tool material added with h-BN powder prepared in Comparative example 3 are: flexural strength 497 MPa, hardness 12.3 GPa, fracture toughness 3.5 MPa-m1/2. It can be seen that the flexural strength, hardness and fracture toughness of the former are 10.7%, 6.5% and 17.1% higher than those of the latter, respectively.

Claims (6)

  1. Claims
    1. A nickel-coated hexagonal boron nitride composite powder having a core-shell structure with h-BN as a core and Ni as a shell; The composite powder is prepared by added sensitized and activated h-BN powder into electroless plating solution and plating nickel on the surface of hexagonal boron nitride under the condition of ultrasonic oscillation; Wherein, the composition of the electroless plating solution is: 20-30 g/L of nickel sulfate hexahydrate (NiSCUfoHzO), 50-70 g/L of sodium citrate dihydrate (NasCeHsCh^HzO), 30-40 g/L of boric acid (H3BO3), 50-100 mL/L of hydrazine hydrate (Ν2Η4Ή2Ο) with a mass fraction of 50-80%, an appropriate amount of pH adjuster makes the pH of the electroless plating solution 11-12, and the balance is distilled water.
    2. A preparation method of nickel-coated hexagonal boron nitride composite powder as claimed in claim 1, comprises the following steps:
    (1) Added h-BN powder into sensitizing solution, ultrasonically oscillated for 2-5 min, centrifugally separated and washed with absolute ethanol once, then washed with distilled water once;
  2. (2) Added the h-BN powder sensitized in the step (1) into the activating solution, ultrasonically oscillated for 5-10 min, centrifugally separated and washed with absolute ethanol for 3-5 times, and drying in a vacuum drying oven at 40-60 °C for 7-10 h to obtain the activated h-BN powder;
  3. (3) Added the activated h-BN powder into the chemical plating solution, wherein the pH value of the electroless plating solution is 11-12, and plating is carried out in a constant temperature water bath at 70-85 °C;
    During the plating process, ultrasonic oscillation is maintained and pH adjuster is dropped at any time to keep the pH value of the electroless plating solution at 11-12; After plating is completed, solid particles are separated and washed to neutrality by distilled water, then washed 2-3 times by absolute ethanol, and then dried for 7-10 hours at 40-60 °C in a vacuum drying oven to obtain h-BN@Ni composite powder.
    3. The preparation method of nickel-coated hexagonal boron nitride composite powder as claimed in claim 2, characterized in that the components of the sensitizing solution in step (1) are: 20-30 g/L of stannous chloride dihydrate (SnC12’2H2O) and the balance is absolute ethanol; Preferably, when the h-BN is sensitized, the addition amount of the h-BN powder is 10-20 g/L per liter of sensitizing solution;
    4. The preparation method of nickel-coated hexagonal boron nitride composite powder as claimed in claim 2, characterized in that the components of the activating solution in step (2) are: 0.5-1 g/L of palladium chloride (PdCb), 10-20 mL/L of mass fraction 35-37% concentrated hydrochloric acid, the balance is distilled water; Preferably, when the h-BN is activated, the addition amount of the h-BN powder is 1020 g/L per liter of activation liquid.
    5. The preparation method of nickel-coated hexagonal boron nitride composite powder as claimed in claim 2, characterized in that the components of the electroless plating solution in step (3) are: 20-30 g/L of nickel sulfate hexahydrate (ΝΐΞΟυόίΒΟ), 50-70 g/L of sodium citrate dihydrate (NasCeHsOv^fBO), 30-40g/L of boric acid (H3BO3), 50-100 mL/L of hydrazine hydrate (Ν2Η4Ή2Ο) with a mass fraction of 5080%, an appropriate amount of pH adjuster makes the pH of the electroless plating solution 11-12, and the balance is distilled water.
    6. The preparation method of nickel-coated hexagonal boron nitride composite powder as claimed in claim 1 or 5, characterized in that the pH regulator in step (3) is 60-80 g/LNaOH solution; Preferably, the addition amount of h-BN powder is 2-5 g/L per liter of chemical plating solution during chemical plating in step (3).
    7. The preparation method of nickel-coated hexagonal boron nitride composite powder as claimed in claim 1 or 6, characterized in that the preparation step of electroless plating solution in step (3) is as follows:
    □ Weigh NaOH proportionally, add appropriate amount of distilled water, stir to dissolve and add distilled water to the required volume, and prepare 60-80 g/L NaOH solution, that is, pH adjuster.
    □ NiSO4’6H2O, Na3C6HsO7-2H2O and H3BO3 are weighed in proportion, respectively, and added into an appropriate amount of distilled water, and stirred in a water bath of 30-40 °C to dissolve them, respectively, to obtain a clear solution.
    □ NiSO4’6H2O solution is slowly added into Na3C6HsO7-2H2O solution, and the solution A is obtained by stirring while adding.
    □ Slowly added H3BO3 solution into solution A, and stirring while adding to obtain solution B.
    □ A pH adjuster is added dropwise to the solution B, and the solution is stirring while adding, so that the pH value of the solution reaches 11-12, and the solution C is obtained.
    □ Hydrazine hydrate with a mass fraction of 50-80% is measured according to a proportion, added dropwise into the solution C, and stirring while adding to obtain solution D.
    □ Distilled water is added into the solution D to the total volume of the electroless plating solution and stirred evenly to obtain the electroless plating solution.
    8. A self-lubricating ceramic cutting tool material with nickel-coated hexagonal boron nitride core-shell composite powder is prepared by taking α-phase alumina (aAI2O3) as a matrix, tungsten carbide titanium ((W,Ti)C) as a reinforcing phase, nickelcoated hexagonal boron nitride (h-BN@Ni) composite powder described in claim 1 or any one of claims 2 to 7 as a solid lubricant, magnesium oxide (MgO) as a sintering aid agent, and performing ball milling mixing and hot pressing sintering; The mass percentage of each component is: 25-45% of (X-AI2O3, 50-70% of (W,Ti)C, 2-10% of nickel-coated hexagonal boron nitride composite powder based on the mass of h-BN, and 0.4-1.5% of MgO.
    9. The self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride core-shell structure composite powder as claimed in claim 8, is characterized in that the mass percentage of each component is: 31-41% of (X-AI2O3, 52-66% of (W,Ti)C, 2-6% of h-BN@Ni based on the mass of h-BN in the composite powder, and 0.5-1% of MgO; Preferably, the mass percentage of each component is: 36-38% of (X-AI2O3, 58-59% of (W,Ti)C, 3.5-4.5% of h-BN@Ni based on the mass of h-BN in the composite powder, and 0.5% of MgO; The sum of the components is 100%.
    10. The preparation method of the self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride core-shell structure composite powder as claimed in claim 8 or 9 comprises the preparation steps (1)-(3) of nickel coated hexagonal boron nitride composite powder as claimed in claim 2, and further comprises the following steps:
  4. (4) Preparation of suspension
    The (X-AI2O3 powder is weighed in proportion, added into an appropriate amount of polyethylene glycol-absolute ethanol solution, ultrasonically dispersed and stirred to form an 01-AI2O3 suspension;
    The (W,Ti)C powder is weighed in proportion, added into an appropriate amount of absolute ethanol, ultrasonically dispersed and stirred to prepare (W,Ti)C suspension;
    The h-BN@Ni powder is weighed in proportion, added into an appropriate amount of absolute ethanol, ultrasonically dispersed and stirred to prepare h-BN@Ni suspension;
  5. (5) Preparation of multiphase suspension, ball milling
    The prepared (X-AI2O3 suspension is mixed with the (W,Ti)C suspension, then the MgO powder is added in proportion, ultrasonically dispersed and stirred for 20-30 min, and the obtained multiphase suspension is poured into a ball mill tank ball mill 40-5 Oh; Then added the h-BN@Ni suspension obtained in the step (3), and continuing the ball milling to obtain a ball milled slurry;
  6. (6) The prepared ball milled slurry is vacuum dried and sieved to obtain a mixed powder, which is sealed and used; The mixed powder is charged into a graphite mold, and after cold press forming, it is placed in a vacuum hot pressing sintering furnace for hot press sintering.
    Preferably, it is dried at 90-110 °C for 20-25 h; Further preferably, the sintering process parameters of the hot press sintering are: The heating rate is 10-20 °C/min, the holding temperature is 1450-1550 °C, the holding time is 10-25 min, and the hot pressing pressure is 25-30 MPa.
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