Nickel-coated hexagonal boron nitride nanosheet composite powder, preparation and high performance composite ceramic cutting tool material

Abstract

The invention relates to nickel-coated hexagonal boron nitride nanosheet composite powder, its preparation and high-performance composite ceramic cutting tool material. The composite powder has a core-shell structure with BNNS as the core and Ni as the shell. The self-lubricating ceramic cutting tool material is prepared by wet ball milling mixing and vacuum hot-pressing sintering with a phase alumina as the matrix, tungsten-titanium carbide as the reinforcing phase, nickel-coated hexagonal boron nitride nanosheet composite powder as the solid lubricant and magnesium oxide and yttrium oxide as the sintering aids. The invention also provides preparation methods of the nickel-coated hexagonal boron nitride nanosheet composite powder and the self-lubricating ceramic cutting tool material.

Claims

1. A method for preparing a nickel-coated hexagonal boron nitride nanosheet composite powder (BNNS@Ni) comprising the following steps: (1) adding BNNS powder into isopropanol, ultrasonically dispersing for 20-30 min, and then centrifugally separatinge to obtain dispersed BNNS powder; (2) adding the dispersed BNNS powder into a sensitizing solution, ultrasonically oscillating and stirring for 10-15 min, centrifugally separating after tin particles in a sensitizing solution are filtered out, and washing once with distilled water to obtain sensitized BNNS powder; wherein the sensitizing solution comprises: 10-15 g/L of stannous chloride dihydrate, the balance is isopropanol, and 3-5 g/L of tin particles are added; (3) the sensitized BNNS powder obtained in step (2) is added into an activating solution, ultrasonically oscillated and stirred for 10-20 min, centrifugally separated and washed to neutrality with distilled water to obtain activated BNNS powder; then it is added into a PVP solution, ultrasonically oscillated and stirred for 5-10 min to prepare an activated BNNS suspension, which is sealed for later use; the components of the activating solution are: 0.2-0.5 g/L of palladium chloride (PdCl.sub.2), 5-10 mL/L of concentrated hydrochloric acid, 5-10 mg/L of polyvinylpyrrolidone (PVP), and the balance is distilled water; (4) electroless plating solution is prepared, and the components of the electroless plating solution are: 15-25 g/L of nickel sulfate hexahydrate, 50-60 g/L of ethylenediamine tetraacetic acid disodium dihydrate, 40-50 g/L of ammonium sulfate, 15-25 mL/L of a first dose of hydrazine hydrate, 5-10 mg/L of polyvinylpyrrolidone, 0.2-0.5 mg/L of potassium iodide, a pH adjuster that makes the pH value of the electroless plating solution at 10-11, and the balance is distilled water; in addition, 15-25 mL/L of a second dose of equal amount of hydrazine hydrate is prepared for later use; the activated BNNS suspension obtained in step (3) is added into the prepared electroless plating solution; first, the plating is carried out for 5-10 min in a constant temperature water bath at 85-90° C. and under ultrasonic oscillation condition, then the second dose of hydrazine hydrate is added dropwise under stirring condition; afterwards the plating is carried out in a constant temperature water bath at 50-60° C. and under ultrasonic oscillation condition, and the pH adjuster is dripped at any time to keep the pH value of the electroless plating solution at 10-11; (5) after the plating in step (4) is completed, the solid particles are centrifugally separated and washed to neutrality with distilled water, then washed with absolute ethanol for 2-3 times, and dried in a vacuum drying oven at 30-40° C. for 10-15 h to obtain nickel-coated hexagonal boron nitride nanosheet composite powder.

2. The method for preparing the nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 1, wherein the average particle size of the tin particles in step (2) is 1-2 mm; when the BNNS powder is sensitized in step (2), BNNS powder is added by 1-2 g/L per liter of the sensitizing solution.

3. The method for preparing the nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 1, wherein when the BNNS powder is activated in step (3), the addition amount of BNNS powder is added by 0.5-1 g/L per liter of the activating solution.

4. The method for preparing the nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 1, wherein the concentration of the PVP solution in step (3) is 5-10 mg/L in the distilled water.

5. The method for preparing the nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 1, wherein in step (4), the pH adjuster of the electroless plating solution is NaOH solution with a mass fraction of 7-8%.

6. The method for preparing the nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 1, wherein in step (4), the components of the electroless plating solution are: 20 g/L of nickel sulfate hexahydrate, 55 g/L of ethylenediamine tetraacetic acid disodium dihydrate, 45 g/L of ammonium sulfate, 20 mL/L of the first dose of hydrazine hydrate, 7 mg/L of PVP, 0.3 mg/L of potassium iodide, pH adjuster to makes the pH value of the electroless plating solution 10-11, and the balance is the distilled water; wherein 20 mL/L of the second dose of equal amount of hydrazine hydrate is prepared for later use.

7. The method for preparing the nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 1, wherein the preparation steps of the electroless plating solution in step (4) are as follows: 1) NiSO.sub.4.6H.sub.2O and Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O are weighed, respectively added into the distilled water, ultrasonically oscillated and stirred for dissolution to obtain NiSO.sub.4.6H.sub.2O solution and Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, respectively; 2) under ultrasonically oscillating and stirring conditions, NiSO.sub.4.6H.sub.2O solution is added into Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution to obtain solution a; 3) (NH.sub.4).sub.2SO.sub.4 is added into solution a, ultrasonically oscillated and stirred for dissolution to obtain solution b; 4) NaOH is added into the distilled water, ultrasonically oscillated and stirred for dissolution to prepare NaOH solution with mass fraction of 7-8%; 5) under the conditions of ultrasonically oscillating and stirring, the NaOH solution obtained in step 4) is added dropwise to solution b until the pH value reaches 10-11 to obtain solution c; 6) the first dose of hydrazine hydrate is dripped into the solution c under the conditions of ultrasonically oscillating and stirring, and the distilled water is added to the total volume of the electroless plating solution to obtain solution d; 7) PVP and KI are added into the solution d successively, ultrasonically oscillated and stirred for dissolution to obtain the electroless plating solution.

8. The method for preparing the nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 1, wherein during the electroless plating in step (4), the BNNS powder is added by 0.2-0.5 g/L per liter of the electroless plating solution.

9. A self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder, which is prepared by wet ball milling mixing and vacuum hot-pressing sintering with a phase alumina (α-Al.sub.2O.sub.3) as the matrix, tungsten-titanium carbide ((W,Ti)C) as the reinforcing phase, magnesium oxide (MgO) and yttrium oxide (Y.sub.2O.sub.3) as the sintering aids; wherein the nickel-coated hexagonal boron nitride nanosheet (BNNS@Ni) composite powder is used as a solid lubricant; the mass percentage of each component is: 28-50% of α-Al.sub.2O.sub.3, 46-70% of (W,Ti)C, 0.2-3% of the nickel-coated hexagonal boron nitride nanosheet composite powder based on the mass of BNNS in the composite powder, 0.4-1% of MgO and 0.4-1% of Y.sub.2O.sub.3.

10. The self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 9, wherein the mass percentage of each component is: 30-46% of α-Al.sub.2O.sub.3, 51-68% of (W,Ti)C, 0.2-1% of BNNS@Ni based on the mass of BNNS in the composite powder, 0.5-1% of MgO, and 0.5-1% of Y.sub.2O.sub.3; the sum of the components is 100%; alternatively, the self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder, wherein the mass percentage of each component is: 32.6-32.7% of α-Al.sub.2O.sub.3, 65-67% of (W,Ti)C, 0.3-0.4% of BNNS@Ni based on the mass of BNNS in the composite powder, 0.5% of MgO, and 0.5% of Y.sub.2O.sub.3; the sum of the components is 100%.

11. A method for preparing the self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 9, comprising the following steps: (1) preparation of sensitizing solution: stannous dichloride dihydrate is weighed in proportion, added into isopropanol and stirred for dissolution, then the isopropanol is added the sensitizing solution; ultrasonically oscillating and stirring uniformly, sensitizing solution is obtained, and then 3-5 g of tin particles are added; a BNNS powder is added into isopropanol and ultrasonically dispersed for 20-30 min; after centrifugal separation, the BNNS powder is added into the sensitizing solution, ultrasonically oscillated and stirred for 10-15 min, centrifugally separated after tin particles are filtered out, and washed once with distilled water to obtain a sensitized BNNS powder; (2) preparation of activating solution: PdCl.sub.2 is added into concentrated hydrochloric acid and stirred for dissolution, then distilled water is added to an activating solution; then, polyvinylpyrrolidone is added, ultrasonically oscillated and stirred for dissolution to obtain an activating solution; the sensitized BNNS powder obtained in step (1) is added into the activating solution, ultrasonically oscillated and stirred for 10-20 min, centrifugally separated and washed to neutrality with distilled water to obtain an activated BNNS powder, and the activated BNNS powder is added into a polyvinylpyrrolidone solution, ultrasonically oscillated and stirred for 5-10 min to prepare an activated BNNS suspension, which is sealed for later use; (3) the activated BNNS suspension obtained in step (2) is added into the electroless plating solution; first, the plating is performed for 5-10 min in a constant temperature water bath at 85-90° C. and under ultrasonic oscillation condition, then tea second dose of hydrazine hydrate is added dropwise under stirring condition; afterwards the plating is carried out in a constant temperature water bath at 50-60° C. and under the condition of ultrasonic oscillation, and a pH adjuster is dripped at any time to keep the pH value of the electroless plating solution at 10-11; after the plating is completed, the solid particles are centrifugally separated and washed to neutrality with distilled water, and then washed with absolute ethanol for 2-3 times to obtain a BNNS@Ni composite powder; then the BNNS@Ni composite powder is added into polyvinylpyrrolidone absolute ethanol solution, ultrasonically oscillated and stirred for 5-10 min to prepare a BNNS@Ni suspension, which is sealed for later use; (4) the Al.sub.2O.sub.3 powder and (W,Ti)C powder are added into absolute ethanol, respectively, then ultrasonically dispersed and stirred for 15-20 min to prepare an Al.sub.2O.sub.3 suspension and a (W,Ti)C suspension; the Al.sub.2O.sub.3 suspension and (W,Ti)C-suspensions are mixed, and then MgO and Y.sub.2O.sub.3 powders are added, ultrasonically dispersed and stirred for 10-15 min to obtain a multiphase suspension; (5) the multiphase suspension obtained in step (4) is poured into a ball milling tank, added with cemented carbide milling balls according to the weight ratio of ball to material of 9-12:1, and ball milled for 45-50 h under the protective atmosphere of nitrogen; (6) the BNNS@Ni suspension obtained in step (3) is ultrasonically dispersed and stirred for 5-10 min, added into the ball milling tank in step (5), and ball milling is continued for 1.5-3 h under the protective atmosphere of nitrogen to obtain a ball milled slurry; (7) the ball milled slurry obtained in step (6) is dried in vacuum and sieved to obtain a mixed powder; (8) the mixed powder obtained in step (7) is loaded into a graphite mold, cold pressed for molding, and put into a vacuum hot-pressing sintering furnace for hot-pressing sintering.

12. The method for preparing the self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 11, wherein the concentration of concentrated hydrochloric acid in step (2) is 35-37% by mass.

13. The method for preparing the self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 11, wherein the concentration of hydrazine hydrate in step (3) is 50-80% by mass.

14. The method for preparing the self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 11, wherein the drying and sieving in step (7) is to dry in a vacuum drying oven at 60-70° C. for 30-35 h, and pass through a 100-200 mesh sieve to obtain a mixed powder.

15. The method for preparing the self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder as claimed in claim 11, wherein the hot-pressing sintering process conditions are: the heating rate is 15-25° C./min, the holding temperature is 1500-1600° C., the holding time is 15-25 min, and the hot-pressing pressure is 25-30 MPa.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is scanning electron microscope (SEM) photograph of the BNNS powder used in the examples of the present invention.

(2) FIG. 2 is transmission electron microscope (TEM) photograph of the BNNS powder used in the examples of the present invention.

(3) FIG. 3 is SEM photograph of BNNS@Ni composite powder prepared in example 1 of the present invention.

(4) FIG. 4 is TEM photograph of the BNNS@Ni composite powder prepared in example 1 of the present invention.

(5) FIG. 5 is X ray diffraction (XRD) pattern of the BNNS@Ni composite powder prepared in example 1 of the present invention.

(6) FIG. 6 is scanning electron microscope (SEM) photograph of fracture surface of the self-lubricating ceramic cutting tool material added with BNNS@Ni composite powder prepared in example 4 of the present invention.

(7) FIG. 7 is SEM photograph of fracture surface of the self-lubricating ceramic cutting tool material added with BNNS powder prepared in comparative example 1.

(8) FIG. 8 is SEM photograph of fracture surface of the self-lubricating ceramic cutting tool material added with h-BN@Ni composite powder prepared in comparative example 2.

MODE OF CARRYING OUT THE INVENTION

(9) The technical scheme of the present invention will be further described with reference to the drawings and examples.

(10) The BNNS raw material powder used in the examples is prepared according to the prior technology. The nanosheet diameter of the BNNS raw material powder is 200-350 nm, and the sheet thickness is 3-6 nm. The SEM photograph and TEM photograph of the BNNS raw material powder used are shown in FIG. 1 and FIG. 2, respectively. The preparation method is referred to the example 2 in Chinese patent document CN107716002A, and the steps are as follows:

(11) (1) The ball milling bucket is placed in the working chamber of the oscillating tank, the beam height of the bracket is adjusted, so that the distance between the bottom end of the stirring rod and the bottom of the ball milling bucket is 5 mm;

(12) (2) The milling balls are added into the ball milling bucket. The height of the milling ball layer is ½ of the height of the ball milling bucket. The stirring device is placed, so that the stirring rod extends into the milling ball layer;

(13) (3) Ball milling medium liquid is added into the ball milling bucket, and the liquid level of the ball milling medium liquid is 20 mm higher than the pressing plate; The ball milling medium liquid is isopropanol;

(14) (4) Hexagonal boron nitride (h-BN) raw material powder is added according to the volume of the added ball milling medium liquid, and the concentration of the h-BN raw material powder in the ball milling medium liquid is 3 g/L; The average particle size of the h-BN raw material powder is 10 μm and the purity is greater than 99.9%.

(15) (5) The ultrasonic medium liquid is added into the holding chamber outside the ball milling bucket; The ball milling bucket is fixed by the holder of the bracket, and the ball milling bucket cover is inserted through the central circular hole from the top of the stirring rod, covering the opening of the ball milling bucket, and then the stirring rod and the speed regulating motor are connected with the coupling; The ultrasonic medium liquid is water; The liquid level of the ultrasonic medium liquid in the holding chamber is equal to that of ball milling medium liquid in the ball milling bucket.

(16) (6) The speed regulating motor is started, and the rotating speed is regulated to carry out ball milling; At the same time, the ultrasonic generator is started to perform ultrasonic oscillation; The rotating speed of the speed regulating motor is 1000 r/min, the power is 300 W, and the speed regulating range is 0-3000 r/min with stepless speed regulation. The power of the ultrasonic generator is 200 W and the frequency is 40 kHz; The processing time of ball milling and ultrasonic oscillation is 5 h.

(17) (7) After the ball milling and ultrasonic oscillation in step (6) are completed, the milling balls are separated and the resulting ball milling fluid is centrifuged at a speed of 2500 r/min for 45 min. The upper suspension is taken and centrifuged at a speed of 3500 r/min for 30 min, and the precipitate is taken and dried for 20 h under the vacuum condition of 40° C. to obtain hexagonal boron nitride nanosheet (BNNS) powder.

(18) The rest of raw material powders used in the examples are all commercially available products. The average particle sizes of α-Al.sub.2O.sub.3 powder, (W,Ti)C powder, MgO powder and Y.sub.2O.sub.3 powder are 0.2 μm, 1.5 μm, 2 μm and 1 μm, respectively, and the purity of each is greater than 99%.

(19) The chemical reagents used in the examples are all commercially available and analytically pure, wherein the concentration of concentrated hydrochloric acid is 37% by mass, the concentration of hydrazine hydrate is 80% by mass, the specification of polyvinylpyrrolidone is K30, and the average particle size of tin particles is 1 mm.

(20) Example 1: The preparation method of nickel-coated hexagonal boron nitride nanosheet composite powder comprises the following steps:

(21) (1) Ultrasonic Dispersion

(22) 0.35 g of BNNS powder raw material was weighed, added into 300 mL of isopropanol, ultrasonically dispersed for 20 min, and then centrifugally separated to obtain dispersed BNNS powder.

(23) (2) Sensitization

(24) 3.5 g of SnCl.sub.2.2H.sub.2O was weighed, added into 100 mL of isopropanol and stirred for dissolution, then isopropanol was added to 350 mL. After ultrasonically oscillating and stirring uniformly, 3 g of tin particles were added to obtain sensitizing solution; The dispersed BNNS powder obtained in step (1) was added into the sensitizing solution, ultrasonically oscillated and stirred for 10 min, centrifugally separated after the tin particles were filtered out, and then washed once with distilled water to obtain sensitized BNNS powder.

(25) (3) Activation

(26) 0.15 g of PdCl.sub.2 was weighed, added into 3 mL of concentrated hydrochloric acid, stirred for dissolution, then distilled water was added to 500 mL. Afterwards, 2.5 mg of PVP was weighed, ultrasonically oscillated and stirred for dissolution to obtain activating solution; The sensitized BNNS powder obtained in step (2) was added into the activating solution, ultrasonically oscillated and stirred for 10 min, centrifugally separated and washed to neutrality with distilled water to obtain activated BNNS powder;

(27) 0.3 mg of PVP was weighed and dissolved in 50 mL of distilled water to obtain PVP solution. Then the activated BNNS powder was added, ultrasonically oscillated and stirred for 5 min to prepare activated BNNS suspension, which was sealed for later use.

(28) (4) Electroless Plating

(29) 15 g of NiSO.sub.4.6H.sub.2O and 50 g of Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O were weighed, respectively added into 300 mL of distilled water, ultrasonically oscillated and stirred for dissolution to obtain NiSO.sub.4.6H.sub.2O solution and Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, respectively; Under ultrasonically oscillating and stirring conditions, NiSO.sub.4.6H.sub.2O solution was slowly added into Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution to obtain solution a; 40 g of (NH.sub.4).sub.2SO.sub.4 was weighed, added into the solution a, ultrasonically oscillated and stirred for dissolution to obtain solution b; 21 g of NaOH was weighed, added into 279 mL of distilled water, ultrasonically oscillated and stirred for dissolution to prepare NaOH solution with mass fraction of 7%; Under the conditions of ultrasonically oscillating and stirring, the NaOH solution was added dropwise into the solution b until the pH value reached 10 to obtain solution c; 15 mL of hydrazine hydrate was measured, dripped into the solution c under the conditions of ultrasonically oscillating and stirring, and then distilled water was added to 1000 mL to obtain solution d; 5 mg of PVP and 0.2 mg of KI were weighed, added into the solution d successively, ultrasonically oscillated and stirred for dissolution to obtain the electroless plating solution. The activated BNNS suspension obtained in step (3) was added into the electroless plating solution. First, the plating was carried out for 5 min in a constant temperature water bath at 90° C. and under ultrasonic oscillation condition, then 15 mL of hydrazine hydrate was added dropwise under stirring condition. Afterwards the plating was carried out in a constant temperature water bath at 60° C. and under ultrasonic oscillation condition, and the NaOH solution was dripped at any time to keep the pH value of the electroless plating solution at 10.

(30) (5) Drying

(31) After the plating was completed, the solid particles were centrifugally separated and washed to neutrality with distilled water, then washed twice with absolute ethanol, and dried in a vacuum drying oven at 30° C. for 15 h to obtain BNNS@Ni composite powder.

(32) It can be seen from the SEM photograph in FIG. 1 that the BNNS raw material powder is in a folded sheet shape and is laminated together. It can be seen from FIG. 2 that the TEM image of the BNNS raw material powder is translucent and the edge is curled, indicating that its thickness is very small. It can be seen from FIGS. 3 and 4 that fine particles are distributed on the BNNS surface of the BNNS@Ni composite powder, which is nickel coating. From the XRD pattern in FIG. 5, the diffraction peaks of BNNS and Ni can be clearly seen, indicating that both the BNNS raw material powder and the Ni coating are in crystalline state.

(33) Example 2: The preparation method of nickel-coated hexagonal boron nitride nanosheet composite powder comprises the following steps:

(34) (1) Ultrasonic Dispersion

(35) 0.6 g of BNNS powder was weighed, added into 400 mL of isopropanol, ultrasonically dispersed for 25 min, and then centrifugally separated to obtain dispersed BNNS powder.

(36) (2) Sensitization

(37) 7 g of SnCl.sub.2.2H.sub.2O was weighed, added into 200 mL of isopropanol and stirred for dissolution, then isopropanol was added to 500 mL. After ultrasonically oscillating and stirring uniformly, 4 g of tin particles were added to obtain sensitizing solution; The dispersed BNNS powder obtained in step (1) was added into the sensitizing solution, ultrasonically oscillated and stirred for 15 min, centrifugally separated after the tin particles were filtered out, and then washed once with distilled water to obtain sensitized BNNS powder.

(38) (3) Activation

(39) 0.25 g of PdCl.sub.2 was weighed, added into 5 mL of concentrated hydrochloric acid, stirred for dissolution, then distilled water was added to 600 mL. Afterwards, 4.2 mg of PVP was weighed, ultrasonically oscillated and stirred for dissolution to obtain activating solution; The sensitized BNNS powder obtained in step (2) was added into the activating solution, ultrasonically oscillated and stirred for 12 min, centrifugally separated and washed to neutrality with distilled water to obtain activated BNNS powder. 0.6 mg of PVP was weighed and dissolved in 60 mL of distilled water to obtain PVP solution. Then the activated BNNS powder was added, ultrasonically oscillated and stirred for 8 min to prepare activated BNNS suspension, which was sealed for later use.

(40) (4) Electroless Plating

(41) 24 g of NiSO.sub.4.6H.sub.2O and 66 g of Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O were weighed, respectively added into 350 mL of distilled water, ultrasonically oscillated and stirred for dissolution to obtain NiSO.sub.4.6H.sub.2O solution and Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, respectively; Under ultrasonically oscillating and stirring conditions, NiSO.sub.4.6H.sub.2O solution was slowly added into Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution to obtain solution a; 56 g of (NH.sub.4).sub.2SO.sub.4 was weighed, added into the solution a, ultrasonically oscillated and stirred for dissolution to obtain solution b; 28 g of NaOH was weighed, added into 372 mL of distilled water, ultrasonically oscillated and stirred for dissolution to prepare NaOH solution with mass fraction of 7%; Under the conditions of ultrasonically oscillating and stirring, the NaOH solution was added dropwise into the solution b until the pH value reached 10.5 to obtain solution c; 24 mL of hydrazine hydrate was measured, dripped into the solution c under the conditions of ultrasonically oscillating and stirring, and then distilled water was added to 1200 mL to obtain solution d; 7 mg of PVP and 0.3 mg of K1 were weighed, added into the solution d successively, ultrasonically oscillated and stirred for dissolution to obtain the electroless plating solution. The activated BNNS suspension obtained in step (3) was added into the electroless plating solution. First, the plating was carried out for 6 min in a constant temperature water bath at 85° C. and under ultrasonic oscillation condition, then 24 mL of hydrazine hydrate was added dropwise under stirring condition. Afterwards the plating was carried out in a constant temperature water bath at 58° C. and under ultrasonic oscillation condition, and the NaOH solution was dripped at any time to keep the pH value of the electroless plating solution at 10.5.

(42) (5) Drying

(43) After the plating was completed, the solid particles were centrifugally separated and washed to neutrality with distilled water, then washed twice with absolute ethanol, and dried in a vacuum drying oven at 35° C. for 12 h to obtain BNNS@Ni composite powder.

(44) Example 3: The preparation method of nickel-coated hexagonal boron nitride nanosheet composite powder comprises the following steps:

(45) (1) Ultrasonic Dispersion

(46) 0.8 g of BNNS powder was weighed, added into 500 mL of isopropanol, ultrasonically dispersed for 30 min, and then centrifugally separated to obtain dispersed BNNS powder.

(47) (2) Sensitization

(48) 7.5 g of SnCl.sub.2.2H.sub.2O was weighed, added into 300 mL of isopropanol and stirred for dissolution, then isopropanol was added to 500 mL. After ultrasonically oscillating and stirring uniformly, 5 g of tin particles were added to obtain sensitizing solution; The dispersed BNNS powder obtained in step (1) was added into the sensitizing solution, ultrasonically oscillated and stirred for 15 min, centrifugally separated after the tin particles were filtered out, and then washed once with distilled water to obtain sensitized BNNS powder.

(49) (3) Activation

(50) 0.35 g of PdCl.sub.2 was weighed, added into 7 mL of concentrated hydrochloric acid, stirred for dissolution, then distilled water was added to 800 mL. Afterwards, 6 mg of PVP was weighed, ultrasonically oscillated and stirred for dissolution to obtain activating solution; The sensitized BNNS powder obtained in step (2) was added into the activating solution, ultrasonically oscillated and stirred for 20 min, centrifugally separated and washed to neutrality with distilled water to obtain activated BNNS powder. 0.7 mg of PVP was weighed and dissolved in 70 mL of distilled water to obtain PVP solution. Then the activated BNNS powder was added, ultrasonically oscillated and stirred for 8 min to prepare activated BNNS suspension, which was sealed for later use.

(51) (4) Electroless Plating

(52) 30 g of NiSO.sub.4.6H.sub.2O and 90 g of Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O were weighed, respectively added into 500 mL of distilled water, ultrasonically oscillated and stirred for dissolution to obtain NiSO.sub.4.6H.sub.2O solution and Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, respectively; Under ultrasonically oscillating and stirring conditions, NiSO.sub.4.6H.sub.2O solution was slowly added into Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution to obtain solution a; 70 g of (NH.sub.4).sub.2SO.sub.4 was weighed, added into the solution a, ultrasonically oscillated and stirred for dissolution to obtain solution b; 32 g of NaOH was weighed, added into 368 mL of distilled water, ultrasonically oscillated and stirred for dissolution to prepare NaOH solution with mass fraction of 8%; Under the conditions of ultrasonically oscillating and stirring, the NaOH solution was added dropwise into the solution b until the pH value reached 10 to obtain solution c; 38 mL of hydrazine hydrate was measured, dripped into the solution c under the conditions of ultrasonically oscillating and stirring, and then distilled water was added to 1600 mL to obtain solution d; 10 mg of PVP and 0.7 mg of KI were weighed, added into the solution d successively, ultrasonically oscillated and stirred for dissolution to obtain the electroless plating solution. The activated BNNS suspension obtained in step (3) was added into the electroless plating solution. First, the plating was carried out for 8 min in a constant temperature water bath at 87° C. and under ultrasonic oscillation condition, then 38 mL of hydrazine hydrate was added dropwise under stirring condition. Afterwards the plating was carried out in a constant temperature water bath at 56° C. and under ultrasonic oscillation condition, and the NaOH solution was dripped at any time to keep the pH value of the electroless plating solution at 10.

(53) (5) Drying

(54) After the plating was completed, the solid particles were centrifugally separated and washed to neutrality with distilled water, then washed three times with absolute ethanol, and dried in a vacuum drying oven at 40° C. for 10 h to obtain BNNS@Ni composite powder.

(55) Example 4: The self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder, wherein the raw materials were 0.2 μm α-Al.sub.2O.sub.3 powder, 1.5 μm (W,Ti)C powder, 2 μm MgO powder, Y.sub.2O.sub.3 powder and BNNS@Ni composite powder prepared in example 1. The mass percentage of each component is: 32.65% of α-Al.sub.2O.sub.3, 66% of (W,Ti)C, 0.35% of BNNS@Ni based on the mass of BNNS in the composite powder, 0.5% of MgO, and 0.5% of Y.sub.2O.sub.3.

(56) The preparation method is as follows:

(57) (1) 32.65 g of α-Al.sub.2O.sub.3 powder and 66 g of (W,Ti)C powder were weighed and added into 200 mL of absolute ethanol, respectively, then ultrasonically dispersed and stirred for 15 min to prepare α-Al.sub.2O.sub.3 suspension and (W,Ti)C suspension; the two suspensions were mixed, and then 0.5 g of MgO and 0.5 g of Y.sub.2O.sub.3 powders were added, ultrasonically dispersed and stirred for 10 min to obtain a multiphase suspension.

(58) (2) The multiphase suspension obtained in step (1) was poured into a ball milling tank, added with cemented carbide milling balls according to the weight ratio of ball to material of 9:1, and ball milled for 45 h under the protective atmosphere of nitrogen.

(59) (3) 0.05 g of PVP was weighed and dissolved in 100 mL of absolute ethanol to obtain PVP-absolute ethanol solution. Then the BNNS@Ni composite powder was added into the PVP-absolute ethanol solution, ultrasonically oscillated and stirred for 5 min to prepare BNNS@Ni suspension, then added into the ball milling tank in step (2), and ball milling was continued for 2 h under the protective atmosphere of nitrogen to obtain ball milled slurry.

(60) (4) The ball milled slurry obtained in step (3) was dried in a vacuum drying oven at 60° C. for 35 h, and then passed through a 200 mesh sieve to obtain a mixed powder.

(61) (5) The mixed powder obtained in step (4) was loaded into the graphite mold, cold pressed for molding, and put into a vacuum hot-pressing sintering furnace for hot-pressing sintering. The sintering process parameters were: the heating rate was 15° C./min, the holding temperature was 1600° C., the holding time was 15 min, and the hot-pressing pressure was 25 MPa.

(62) The SEM photograph of fracture surface of the obtained self-lubricating ceramic cutting tool material is shown in FIG. 6.

(63) As can be seen from FIG. 6, the self-lubricating ceramic cutting tool material added with BNNS@Ni composite powder prepared in example 4 has dense microstructure. The grain size and distribution of each phase of the ceramic matrix are relatively uniform. The flaky grains are BNNS, which are closely bound with the ceramic matrix grains without obvious pores. The phenomenon of BNNS being pulled off can also be seen, indicating that the bonding strength between the BNNS and the ceramic matrix is relatively large.

(64) According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool material added with BNNS@Ni composite powder prepared in example 4 are: flexural strength 760 MPa, hardness 18.7 GPa, fracture toughness 6.7 MPa.Math.M.sup.1/2.

(65) Example 5: The self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder, wherein the mass percentage of each component is: 34% of α-Al.sub.2O.sub.3, 64.5% of (W,Ti)C, 0.5% of BNNS@Ni based on the mass of BNNS in the composite powder, 0.5% of MgO, and 0.5% of Y.sub.2O.sub.3. The preparation method is as follows:

(66) (1) 6 g of SnCl.sub.2.2H.sub.2O was weighed, added into 200 mL of isopropanol and stirred for dissolution, then isopropanol was added to 500 mL. After ultrasonically oscillating and stirring uniformly, sensitizing solution was obtained, and then 4 g of tin particles were added; 0.5 g of BNNS powder was weighed, added into 400 mL of isopropanol, ultrasonically dispersed for 25 min. After centrifugal separation, the powder was added into the sensitizing solution, ultrasonically oscillated and stirred for 12 min, centrifugally separated after the tin particles were filtered out, and then washed once with distilled water to obtain sensitized BNNS powder.

(67) (2) 0.2 g of PdCl.sub.2 was weighed, added into 4 mL of concentrated hydrochloric acid, stirred for dissolution, then distilled water was added to 500 mL. Afterwards, 3.5 mg of polyvinylpyrrolidone was weighed, ultrasonically oscillated and stirred for dissolution to obtain activating solution; The sensitized BNNS powder obtained in step (1) was added into the activating solution, ultrasonically oscillated and stirred for 15 min, centrifugally separated and washed to neutrality with distilled water to obtain activated BNNS powder; 0.6 mg of polyvinylpyrrolidone was weighed and dissolved in 60 mL of distilled water to obtain polyvinylpyrrolidone solution. Then the activated BNNS powder was added, ultrasonically oscillated and stirred for 7 min to prepare activated BNNS suspension, which was sealed for later use.

(68) (3) 20 g of NiSO.sub.4.6H.sub.2O and 55 g of Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O were weighed, respectively added into 350 mL of distilled water, ultrasonically oscillated and stirred for dissolution to obtain NiSO.sub.4.6H.sub.2O solution and Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, respectively; Under ultrasonically oscillating and stirring conditions, NiSO.sub.4.6H.sub.2O solution was slowly added into Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, and then 45 g of (NH.sub.4).sub.2SO.sub.4 were added, ultrasonically oscillated and stirred for dissolution to obtain solution A; 24 g of NaOH was weighed, added into 276 mL of distilled water, ultrasonically oscillated and stirred for dissolution to prepare NaOH solution with mass fraction of 8%; Under the conditions of ultrasonically oscillating and stirring, the NaOH solution was added dropwise into the solution A until the pH value reached 10.5 to obtain solution B; 20 mL of hydrazine hydrate was measured, dripped into the solution B under the conditions of ultrasonically oscillating and stirring, and then distilled water was added to 1000 mL to obtain solution C; 7 mg of polyvinylpyrrolidone and 0.3 mg of potassium iodide were weighed, added into the solution C successively, ultrasonically oscillated and stirred for dissolution to obtain the electroless plating solution. The activated BNNS suspension obtained in step (2) was added into the electroless plating solution. First, the plating was carried out for 7 min in a constant temperature water bath at 87° C. and under ultrasonic oscillation condition, then 20 mL of hydrazine hydrate was added dropwise under the stirring condition. Afterwards the plating was carried out in a constant temperature water bath at 55° C. and under ultrasonic oscillation condition, and the NaOH solution was dripped at any time to keep the pH value of the electroless plating solution at 10.5. After the plating was completed, the solid particles were centrifugally separated and washed to neutrality with distilled water, then washed three times with absolute ethanol to obtain BNNS@Ni composite powder; 0.07 g of polyvinylpyrrolidone was weighed and dissolved in 100 mL of absolute ethanol to obtain polyvinylpyrrolidone absolute ethanol solution. Then the BNNS@Ni composite powder was added into the polyvinylpyrrolidone absolute ethanol solution, ultrasonically oscillated and stirred for 7 min to prepare BNNS@Ni suspension, which was sealed for later use.

(69) (4) 34 g of α-Al.sub.2O.sub.3 powder and 64.5 g of (W,Ti)C powder were weighed and added into 200 mL of absolute ethanol, respectively, then ultrasonically dispersed and stirred for 17 min to prepare α-Al.sub.2O.sub.3 suspension and (W,Ti)C suspension; the two suspensions were mixed, and then 0.5 g of MgO and 0.5 g of Y.sub.2O.sub.3 powders were added, ultrasonically dispersed and stirred for 12 min to obtain a multiphase suspension.

(70) (5) The multiphase phase suspension obtained in step (4) was poured into a ball milling tank, added with cemented carbide milling balls according to the weight ratio of ball to material of 10:1, and ball milled for 47 h under the protective atmosphere of nitrogen.

(71) (6) The BNNS@Ni suspension obtained in step (3) was ultrasonic dispersed and stirred for 7 min, added into the ball milling tank in step (5), and ball milling was continued for 2.5 h under the protective atmosphere of nitrogen to obtain ball milled slurry.

(72) (7) The ball milled slurry obtained in step (6) was dried in a vacuum drying oven at 65° C. for 32 h, and then passed through a 100 mesh sieve to obtain a mixed powder.

(73) (8) The mixed powder obtained in step (7) was loaded into a graphite mold, cold pressed for molding, and put into a vacuum hot-pressing sintering furnace for hot-pressing sintering. The sintering process parameters were: the heating rate was 20° C./min, the holding temperature was 1550° C., the holding time was 20 min, and the hot-pressing pressure was 25 MPa.

(74) According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool material added with BNNS@Ni composite powder prepared in example 5 are: flexural strength 715 MPa, hardness 18.3 GPa, fracture toughness 6.9 MPa.Math.M.sup.1/2.

(75) Example 6: The self-lubricating ceramic cutting tool material added with nickel-coated hexagonal boron nitride nanosheet composite powder, wherein the mass percentage of each component is: 38.3% of α-Al.sub.2O.sub.3, 60% of (W,Ti)C, 0.7% of BNNS@Ni based on the mass of BNNS in the composite powder, 0.5% of MgO, and 0.5% of Y.sub.2O.sub.3. The preparation method is as follows:

(76) (1) 7.5 g of SnCl.sub.2.2H.sub.2O was weighed, added into 300 mL of isopropanol and stirred for dissolution, then isopropanol was added to 500 mL. After ultrasonically oscillating and stirring uniformly, sensitizing solution was obtained, and then 5 g of tin particles were added; 0.7 g of BNNS powder was weighed, added into 500 mL of isopropanol, ultrasonically dispersed for 30 min. After centrifugal separation, the powder was added into the sensitizing solution, ultrasonically oscillated and stirred for 15 min, centrifugally separated after the tin particles were filtered out, and then washed once with distilled water to obtain sensitized BNNS powder.

(77) (2) 0.4 g of PdCl.sub.2 was weighed, added into 8 mL of concentrated hydrochloric acid, stirred for dissolution, then distilled water was added to 800 mL. Afterwards, 8 mg of polyvinylpyrrolidone was weighed, ultrasonically oscillated and stirred for dissolution to obtain activating solution; The sensitized BNNS powder obtained in step (1) was added into the activating solution, ultrasonically oscillated and stirred for 20 min, centrifugally separated and washed to neutrality with distilled water to obtain activated BNNS powder; 0.7 mg of polyvinylpyrrolidone was weighed and dissolved in 70 mL of distilled water to obtain polyvinylpyrrolidone solution. Then the activated BNNS powder was added, ultrasonically oscillated and stirred for 10 min to prepare activated BNNS suspension, which was sealed for later use.

(78) (3) 45 g of NiSO.sub.4.6H.sub.2O and 108 g of Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O were weighed, respectively added into 650 mL of distilled water, ultrasonically oscillated and stirred for dissolution to obtain NiSO.sub.4.6H.sub.2O solution and Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, respectively; Under ultrasonically oscillating and stirring conditions, NiSO.sub.4.6H.sub.2O solution was slowly added into Na.sub.2C.sub.10H.sub.14N.sub.2O.sub.8.2H.sub.2O solution, and then 90 g of (NH.sub.4).sub.2SO.sub.4 were added, ultrasonically oscillated and stirred for dissolution to obtain solution A; 42 g of NaOH was weighed, added into 558 mL of distilled water, ultrasonically oscillated and stirred for dissolution to prepare NaOH solution with mass fraction of 7%; Under the conditions of ultrasonically oscillating and stirring, the NaOH solution was added dropwise into the solution A until the pH value reached 11 to obtain solution B; 45 mL of hydrazine hydrate was measured, dripped into the solution B under the conditions of ultrasonically oscillating and stirring, and then distilled water was added to 1800 mL to obtain solution C; 18 mg of polyvinylpyrrolidone and 0.9 mg of potassium iodide were weighed, added into the solution C successively, ultrasonically oscillated and stirred for dissolution to obtain the electroless plating solution. The activated BNNS suspension obtained in step (2) was added into the electroless plating solution. First, the plating was carried out for 10 min in a constant temperature water bath at 85° C. and under ultrasonic oscillation condition, then 45 mL of hydrazine hydrate was added dropwise under the stirring condition. Afterwards the plating was carried out in a constant temperature water bath at 50° C. and under ultrasonic oscillation condition, and the NaOH solution was dripped at any time to keep the pH value of the electroless plating solution at 11. After the plating was completed, the solid particles were centrifugally separated and washed to neutrality with distilled water, then washed three times with absolute ethanol to obtain BNNS@Ni composite powder; 0.15 g of polyvinylpyrrolidone was weighed and dissolved in 150 mL of absolute ethanol to obtain polyvinylpyrrolidone absolute ethanol solution. Then the BNNS@Ni composite powder was added into the polyvinylpyrrolidone absolute ethanol solution, ultrasonically oscillated and stirred for 10 min to prepare BNNS@Ni suspension, which was sealed for later use.

(79) (4) 38.3 g of α-Al.sub.2O.sub.3 powder and 60 g of (W,Ti)C powder were weighed and added into 220 mL of absolute ethanol, respectively, then ultrasonically dispersed and stirred for 20 min to prepare α-Al.sub.2O.sub.3 suspension and (W,Ti)C suspension; the two suspensions were mixed, and then 0.5 g of MgO and 0.5 g of Y.sub.2O.sub.3 powders were added, ultrasonically dispersed and stirred for 15 min to obtain a multiphase suspension.

(80) (5) The multiphase phase suspension obtained in step (4) was poured into a ball milling tank, added with cemented carbide milling balls according to the weight ratio of ball to material of 11:1, and ball milled for 50 h under the protective atmosphere of nitrogen.

(81) (6) The BNNS@Ni suspension obtained in step (3) was ultrasonic dispersed and stirred for 10 min, added into the ball milling tank in step (5), and ball milling was continued for 3 h under the protective atmosphere of nitrogen to obtain ball milled slurry.

(82) (7) The ball milled slurry obtained in step (6) was dried in a vacuum drying oven at 70° C. for 30 h, and then passed through a 100 mesh sieve to obtain a mixed powder.

(83) (8) The mixed powder obtained in step (7) was loaded into a graphite mold, cold pressed for molding, and put into a vacuum hot-pressing sintering furnace for hot-pressing sintering. The sintering process parameters were: the heating rate was 25° C./min, the holding temperature was 1500° C., the holding time was 15 min, and the hot-pressing pressure was 30 MPa.

(84) According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool material added with BNNS@Ni composite powder prepared in example 6 are: flexural strength 683 MPa, hardness 17.5 GPa, fracture toughness 6.4 MPa.Math.M.sup.1/2.

(85) The following comparative examples were prepared according to the composition ratio of example 4.

Comparative Example 1: A Self-Lubricating Ceramic Cutting Tool Material Added with Uncoated Hexagonal Boron Nitride Nanosheets

(86) The difference from example 4 is that BNNS raw material powder is added instead of BNNS@Ni composite powder, 0.35% of BNNS, and the proportion of the other components is the same as that of example 4.

(87) The preparation method is as follows:

(88) (1) 0.05 g of polyvinylpyrrolidone was weighed and dissolved in 100 mL of absolute ethanol to obtain polyvinylpyrrolidone absolute ethanol solution, then 0.35 g of BNNS powder was added into the polyvinylpyrrolidone absolute ethanol solution to prepare BNNS suspension; 32.65 g of α-Al.sub.2O.sub.3 powder and 66 g of (W,Ti)C powder were weighed and added into 200 mL of absolute ethanol, respectively, then ultrasonically dispersed and stirred for 15 min to prepare α-Al.sub.2O.sub.3 suspension and (W,Ti)C suspension; The three suspensions were mixed, and then 0.5 g of MgO and 0.5 g of Y.sub.2O.sub.3 powders were added, ultrasonically dispersed and stirred for 10 min to obtain a multiphase suspension.

(89) (2) The multiphase suspension obtained in step (1) was poured into a ball milling tank, added with cemented carbide milling balls according to the weight ratio of ball to material of 9:1, and ball milled for 45 h under the protective atmosphere of nitrogen. to obtain ball milled slurry.

(90) (3) The ball milled slurry obtained in step (2) was dried in a vacuum drying oven at 60° C. for 35 h, and then passed through a 200 mesh sieve to obtain a mixed powder.

(91) (4) The mixed powder obtained in step (3) was loaded into a graphite mold, cold pressed for molding, and put into a vacuum hot-pressing sintering furnace for hot-pressing sintering. The sintering process conditions are the same as in step (5) of example 4. The SEM photograph of fracture surface of the obtained self-lubricating ceramic cutting tool material is shown in FIG. 7.

(92) It can be seen from FIG. 7 that the microstructure of ceramic matrix in the self-lubricating ceramic cutting tool material added with BNNS is relatively uniform and dense, but the BNNS is not closely bounded with the ceramic matrix grains and obvious pores exist. The phenomenon of BNNS being pulled out can also be seen, indicating that the bonding strength between the BNNS and the ceramic matrix is relatively small. According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool materials added with BNNS in comparative example 1 are: flexural strength 735 MPa, hardness 18.1 GPa, fracture toughness 6.0 MPa.Math.m.sup.1/2.

Comparative Example 2: A Self-Lubricating Ceramic Cutting Tool Material Added with Nickel-Coated Hexagonal Boron Nitride Composite Powder

(93) The difference from example 4 is that the BNNS raw material powder of example 4 is replaced by h-BN raw material powder, and the h-BN raw material powder is a commercially available product with an average sheet diameter of 0.5 μm, an average sheet thickness of 100 nm, and a purity of greater than 99%. The mass percentage of each component is: 32.65% of α-Al.sub.2O.sub.3, 66% of (W,Ti)C, 0.35% of h-BN@Ni based on the mass of h-BN in the composite powder, 0.5% of MgO, and 0.5% of Y.sub.2O.sub.3. The preparation method is the same as that of example 4. The SEM photograph of fracture surface of the obtained self-lubricating ceramic cutting tool material is shown in FIG. 8.

(94) It can be seen from FIG. 8 that the microstructure of the self-lubricating ceramic cutting tool material added with h-BN@Ni composite powder is relatively uniform and dense, and the h-BN grains are closely bounded with the ceramic matrix grains without obvious pores. According to the tests, the mechanical properties of the self-lubricating ceramic cutting tool material added with h-BN@Ni composite powder prepared in comparative example 2 are: flexural strength 676 MPa, hardness 17.4 GPa, fracture toughness 5.6 MPa.Math.m.sup.1/2.