WO2018153105A1 - Nickel-coated hexagonal boron nitride composite powder, preparation and application thereof as well as self-lubricating ceramic cutter - Google Patents

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 (NiSO4·6H2O) 20-30 g/L, sodium citrate dihydrate (Na3C6H5O7.2H2O) 50-70 g/L, boric acid (H3BO3) 30-40 g/L, 50-80% mass fraction of hydrazine hydrate (N2H4.H2O) 50-100 mL/L, a suitable amount of a pH value adjuster to adjust the pH value of the chemical plating solution to be between 11-12, the rest being distilled water. Further comprised is a self-lubricating ceramic cutter material and a method for preparing the same; the components of the self-lubricating ceramic cutter material are: α-Al2O3 25-45%, (W, Ti)C 50-70%, nickel-coated hexagonal boron nitride composite powder 2-10%, according to the mass of hexagonol boron nitride (h-BN), and MgO 0.4-1.5%.

Description

Nickel coated hexagonal boron nitride composite powder, preparation and application thereof and self-lubricating ceramic cutter 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 cutter, and belongs to the technical field of solid self-lubricating composite materials and ceramic cutters.

Background technique

In modern machining technology, with the emergence of various difficult-to-machine materials and the improvement of efficiency, precision and environmental protection requirements, tool technology has become one of the key factors affecting the development of the machinery 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, ceramic tools cannot be cooled and lubricated by cutting fluids during high-speed machining, resulting in high cutting temperatures and severe tool wear and tear, resulting in low tool life. The development of self-lubricating ceramic tool materials is an effective way to solve this problem.

The solid lubricant used to prepare the self-lubricating ceramic tool material should meet two basic requirements: First, the solid lubricant does not decompose or react with the ceramic matrix at the sintering temperature of the tool material (generally 1500-1800 ° C). Obvious chemical reaction; Second, at the cutting temperature of the tool (typically 500-1000 ° C), the solid lubricant does not have a significant chemical reaction with the air and the workpiece material and loses lubrication. 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 tool materials. . Graphite and hexagonal boron nitride do not decompose or sublime at the sintering temperature of the tool material, but graphite starts to oxidize from 450 ° C in air and increases with increasing temperature; hexagonal boron nitride (h-BN) has "White graphite", which has a layered structure similar to graphite, and has good lubricity, thermal conductivity and chemical resistance. The performance is still stable at 900 ° C. The temperature at which hexagonal boron nitride starts to oxidize in air is 1000. -1100 ° C. It can be seen that hexagonal boron nitride is an ideal solid lubricant for preparing self-lubricating ceramic tool materials. However, the direct addition of hexagonal boron nitride has an adverse effect on the mechanical properties of ceramic tool materials.

The traditional self-lubricating ceramic tool material is prepared by directly mixing ceramic powder and solid lubricant powder, and then forming a block material through a certain molding and sintering process. The direct addition of hexagonal boron nitride has two effects on the ceramic tool material: on the one hand, the hexagonal boron nitride in the tool material forms a self-lubricating film on the tool surface during the cutting process, thereby reducing the distance between the tool and the chip. Coefficient of friction;

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 material with hexagonal boron nitride added directly, on the one hand, the wettability of hexagonal boron nitride and the metal matrix is poor, the interface bonding strength between the two is low, and the metal matrix is strongly split. effect. The other side In addition, since the density of hexagonal boron nitride is much smaller than that of the metal matrix, segregation inevitably occurs during the mixing process. Two aspects lead to a decrease in the mechanical strength of the composite material, affecting its friction and wear properties.

(2) Since hexagonal boron nitride is a soft material, the strength and hardness are low, and the dispersion in the tool material causes the mechanical properties to decrease, thereby reducing the wear resistance of the tool. In addition, hexagonal boron nitride is a covalent bond compound which has a low solid phase diffusion coefficient at high temperatures and is a material which is difficult to sinter. It has been pointed out in the literature that the card-house structure formed by the cross-stacking of hexagonal boron nitride in sheet form is the main factor hindering the densification of composite ceramics containing hexagonal boron nitride, and the card-type structure can be eliminated by a suitable process to obtain high density. In turn, it has high mechanical properties. In the related process, adding a component capable of generating a liquid phase during the sintering process can promote particle rearrangement of the hexagonal boron nitride-containing composite ceramic and diffusion diffusion of the substance, and is advantageous for eliminating the card room structure of the hexagonal boron nitride. Therefore, it can promote the densification of composite ceramics. See Journal of Silicates, 1998, 26(2): 265-269.

Aiming at the low mechanical properties of solid self-lubricating composites with hexagonal boron nitride added directly, it is found that the preparation of solid self-lubricating composites by adding coated hexagonal boron nitride composite powder can make up for the above technical defects to some extent. . The preparation method of the existing coated hexagonal boron nitride composite powder mainly includes ceramic coated h-BN and cermet 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 CN104974817A discloses a method for preparing a spherical nano-silica-coated hexagonal boron nitride composite powder by hydrolysis and condensation reaction of ethyl orthosilicate; CN104892003A discloses a heterogeneous nucleation using CN104892003A A method of preparing an alumina-coated hexagonal boron nitride composite powder by vacuum calcination. Chinese patent document CN104892005A discloses a silicon nitride-based self-lubricating ceramic tool material with alumina-coated hexagonal boron nitride composite powder; CN104844178A provides a self-lubricating silica-coated hexagonal boron nitride composite powder. Lubricating ceramic tool material; CN104844225A discloses a self-lubricating ceramic tool material which is added with a silicon carbide-coated hexagonal boron nitride composite powder. The mechanical properties of the ceramic-coated hexagonal boron nitride composite powder and ceramic tool materials have been improved by the above techniques, but the disadvantages are: (1) for metal-based solid self-lubricating composite materials, ceramic coatings and metals The matrix also has the problems of poor wettability, low bonding strength and high density difference. Therefore, the mechanical properties and friction and wear properties of the metal-coated solid self-lubricating composites added by ceramic-coated hexagonal boron nitride composite powder are improved. not so useful. (2) Alumina, silica and silicon carbide coated with hexagonal boron nitride powder are ceramic materials. For ceramic-based solid self-lubricating composite materials, on the one hand, the ceramic material coating layer cannot or rarely is in the sintering process. The liquid phase is generated, and the card room structure of the hexagonal boron nitride is eliminated a little, and the promoting effect of the prepared composite material densification is small. 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, and has less effect on the improvement of fracture toughness. The lower fracture toughness has become a bottleneck restricting the wide application of ceramic tool materials, so the corresponding technology should be developed to improve the fracture toughness of ceramic tool materials.

Compared with the addition of ceramic coated h-BN, the addition of metal-coated h-BN can improve metal-based and ceramic-based solids. Mechanical properties and friction and wear properties of 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 to a nickel salt solution, and nickel is reduced and deposited on the surface of the hexagonal boron nitride powder by hydrogen gas at a certain temperature in an autoclave to form a composite powder. The literature (Journal of Materials Research, 2011, 25(5): 509-516) reports the preparation of nickel-plated h-BN powder by precipitation method by adding h-BN powder to a nickel salt solution to form a suspension and adding a precipitate. The precipitate is wrapped 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 techniques have prepared metal-coated hexagonal boron nitride composite powders, but there are still some shortcomings: (1) The hydrothermal hydrogen reduction method needs to be carried out in a closed container, and the reaction process cannot be observed, which is not intuitive; High equipment requirements (high-pressure autoclave with high-temperature and high-pressure resistant steel, corrosion-resistant lining), technical difficulty (strict temperature and pressure control), high cost; need to use higher pressure hydrogen, poor safety performance. (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 self-lubricating of the solids prepared by the method. The performance of the composite material; the step of high temperature reduction in hydrogen has higher requirements on equipment, poor safety performance and high cost.

Summary of the invention

In order to overcome the deficiencies of the prior art, the present invention provides a nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder and a preparation method thereof.

The invention also provides the use of the 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 tool material with nickel-coated hexagonal boron nitride (h-BN@Ni) core-shell composite powder and a preparation method thereof. While improving the hardness and bending strength of self-lubricating ceramic tool materials, the fracture toughness is also significantly improved.

Explanation of terms:

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 technical solution adopted by the present invention is as follows:

Nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder, the composite powder having a core-shell structure with h-BN as core and Ni as shell;

The composite powder is prepared by adding sensitized and activated h-BN powder to an electroless plating solution, and plating nickel onto the surface of hexagonal boron nitride under ultrasonic vibration conditions; wherein the electroless plating solution is The components are: nickel sulfate hexahydrate (NiSO ₄ · 6H ₂ O) 20-30 g / L, sodium citrate dihydrate (Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O) 50-70 g / L, boric acid (H ₃ BO ₃ ) 30-40g / L, mass fraction 50-80% hydrazine hydrate (N ₂ H ₄ · H ₂ O) 50-100mL / L, the right amount of pH adjuster to make the electroless plating solution pH 11-12 The balance is distilled water.

A preparation method of nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder, comprising the following steps:

(1) adding h-BN powder to the sensitizing solution, ultrasonically shaking for 2-5 minutes, centrifuging and washing once with absolute ethanol, and then washing once with distilled water;

(2) Adding the h-BN powder sensitized in step (1) to the activation solution, ultrasonically shaking for 5-10 minutes, centrifuging and washing with anhydrous ethanol for 3-5 times, in a vacuum drying oven at 40-60 ° C Drying for 7-10h to obtain activated h-BN powder;

(3) adding the activated h-BN powder to the electroless plating solution, the pH of the electroless plating solution is 11-12, and plating in a constant temperature water bath of 70-85 ° C;

Keep the ultrasonic vibration during the plating process and add the pH adjuster at any time to keep the pH of the electroless plating solution at 11-12. After the plating is completed, the solid particles are separated and washed with distilled water until neutral, and then ethanol is used. The mixture was washed 2-3 times, and then dried in a vacuum drying oven at 40-60 ° C for 7-10 h to obtain a h-BN@Ni composite powder.

According to the preferred embodiment of the present invention, the composition of the sensitizing liquid described in the step (1) is: stannous chloride dihydrate (SnCl ₂ · 2H ₂ O) 20-30 g/L, and the balance is anhydrous ethanol. Further preferably, the step of preparing the sensitizing liquid in the step (1) is: weighing SnCl ₂ · 2H ₂ O in proportion, adding an appropriate amount of absolute ethanol, stirring and dissolving, and adding anhydrous ethanol to the total volume of the sensitizing liquid.

According to the preferred embodiment of the present invention, when the h-BN is sensitized in the step (1), the amount of the h-BN powder added is 10-20 g/L per liter of the sensitizing liquid.

According to the preferred embodiment of the present invention, the composition of the activation liquid described in the step (2) is: palladium chloride (PdCl ₂ ) 0.5-1 g / L, mass fraction 35-37% concentrated hydrochloric acid 10-20 mL / L, The amount is distilled water.

Further preferably, the step of preparing the activation liquid in the step (2) is: weighing PdCl ₂ in proportion, adding the concentrated hydrochloric acid in a proportional manner, stirring and dissolving, and adding distilled water to the total volume of the activation liquid.

According to the preferred embodiment of the present invention, when the h-BN is activated in the step (2), the amount of the h-BN powder added is 10-20 g/L per liter of the activation liquid.

According to the preferred embodiment of the present invention, the composition of the electroless plating solution described in the step (3) is: nickel sulfate hexahydrate (NiSO ₄ · 6H ₂ O) 20-30 g / L, sodium citrate dihydrate (Na ₃ C ₆ H ₅ O ₇ ·2H ₂ O) 50-70g/L, boric acid (H ₃ BO ₃ ) 30-40g/L, mass fraction 50-80% hydrazine hydrate (N ₂ H ₄ ·H ₂ O) 50-100mL / L, the appropriate amount of pH adjuster makes the electroless plating solution pH 11-12, the balance is distilled water.

According to a preferred embodiment of the invention, the pH adjusting agent 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 step of preparing the electroless plating solution in the step (3) is as follows:

1 Weigh NaOH proportionally, add appropriate amount of distilled water, stir to dissolve and add distilled water to the required volume, and prepare 60-80g / L NaOH solution, that is, pH adjuster.

2 Weigh NiSO ₄ ·6H ₂ O, Na ₃ C ₆ H ₅ O ₇ ·2H ₂ O and H ₃ BO ₃ in proportion, respectively, add appropriate amount of distilled water, stir in a water bath at 30-40 ° C to dissolve, respectively A clear solution was obtained.

3 A solution of NiSO ₄ ·6H ₂ O was slowly added to a solution of Na ₃ C ₆ H ₅ O ₇ ·2H ₂ O, and stirred while stirring to obtain a solution A.

4 The H ₃ BO ₃ solution was slowly added to the solution A, and stirred while stirring to obtain a solution B.

5 The pH adjuster was added dropwise to the solution B, and while stirring, the pH of the solution was brought to 11-12 to obtain a solution C.

6 The hydrazine hydrate having a mass fraction of 50-80% is taken in proportion, added dropwise to the solution C, and stirred while stirring to obtain a solution D.

7 Add distilled water to the solution D to the total volume of the electroless plating solution and stir evenly to obtain an electroless plating solution.

According to the 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 the preferred embodiment of the present invention, the h-BN powder raw material described in the step (1) is a commercially available product having an average particle diameter of 1-3 μm and a purity of more than 99%. Preferably, the chemical reagents such as stannous chloride dihydrate and anhydrous ethanol used in the present invention are commercially available products and are analytically pure, wherein the concentration of concentrated hydrochloric acid is 35-37% by mass, and the concentration of hydrazine hydrate is 50 by mass. -80%.

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.

A self-lubricating ceramic tool material with nickel-coated hexagonal boron nitride core-shell composite powder is composed of α-phase alumina (α-Al ₂ O ₃ ) as matrix and tungsten carbide tungsten ((W, Ti) C) As the reinforcing phase, the nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder of the present invention is used as a solid lubricant, and magnesium oxide (MgO) is used as a sintering aid, and the mixture is ball-milled and heated. Made by pressure sintering; the mass percentage of each component is: α-Al ₂ O ₃ 25-45%, (W, Ti) C 50-70%, nickel-coated hexagonal boron nitride composite powder by h- The mass of BN is 2-10%, and MgO is 0.4-1.5%.

According to the preferred embodiment of the present invention, the raw material powders of the above respective components are all commercially available products, and the average particles of the h-BN powder, the α-Al ₂ O ₃ powder, the (W, Ti) C powder and the MgO powder. The diameters were 1-3 μm, 0.2-0.5 μm, 1-1.5 μm, and 1-2 μm, respectively, and the purity was more than 99%.

According to the preferred embodiment of the present invention, the self-lubricating ceramic tool material of the above-mentioned nickel-coated hexagonal boron nitride core-shell composite powder has a mass percentage of each component: α-Al ₂ O ₃ 31-41%, ( W, Ti) C 52-66%, h-BN@Ni is 2-6% by mass of h-BN in the composite powder, and MgO is 0.5-1%; the sum of the components is 100%.

Further preferably, the self-lubricating ceramic tool material with nickel-coated hexagonal boron nitride core-shell composite powder has a mass percentage of each component: α-Al ₂ O ₃ 36-38%, (W , Ti) C 58-59%, h-BN@Ni is 3.5-4.5% by mass of h-BN in the composite powder, and MgO is 0.5%; the sum of the components is 100%.

According to the present invention, a method for preparing a self-lubricating ceramic tool material for adding a nickel-coated hexagonal boron nitride core-shell composite powder, comprising the above-mentioned preparation step of nickel-coated hexagonal boron nitride composite powder (1)- (3), also includes the following steps:

(4) Preparation of suspension

The α-Al ₂ O ₃ powder is weighed in proportion, added to an appropriate amount of polyethylene glycol-anhydrous ethanol solution, ultrasonically dispersed and stirred to form an α-Al ₂ O ₃ suspension;

Weigh the (W, Ti) C powder in proportion, add an appropriate amount of absolute ethanol, ultrasonically disperse and stir to prepare a (W, Ti) C suspension;

The h-BN@Ni composite powder was weighed in proportion, added with an appropriate amount of absolute ethanol, ultrasonically dispersed and stirred to prepare a h-BN@Ni suspension;

(5) Preparation of multiphase suspension, ball milling

The prepared α-Al ₂ O ₃ 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 jar. Ball milling 40-50h; then adding the h-BN@Ni suspension obtained in step (3), continuing the ball milling to obtain a ball milling liquid;

(6) The prepared ball mill liquid is vacuum dried and sieved to obtain a mixed powder material, which is sealed for use; the mixed powder material is charged into a graphite mold, and after cold press forming, it is placed in a vacuum hot press sintering furnace for hot press sintering.

According to the method for preparing a ceramic cutter material of the present invention, preferably, in the step (4), the mass of the polyethylene glycol is 2-4% of the mass of the α-Al ₂ O ₃ powder. The polyethylene glycol-anhydrous ethanol solution is prepared by first adding polyethylene glycol to absolute ethanol and stirring and dissolving in a water bath at 30-40 ° C. The amount of anhydrous ethanol is not necessarily strictly controlled, so that it can be made into a suspension. Further, the polyethylene glycol has an average molecular weight of from 4,000 to 6,000.

Further preferred:

In the step (4), the ultrasonic dispersion and stirring time are both 15-20 min.

In the step (5), the ball milling conditions are as follows: a cemented carbide grinding ball is added at a ball weight ratio of 10:1, and ball milling is performed with nitrogen or argon as a protective atmosphere.

In the step (5), the ball milling time is 2-4 h; the nitrogen or argon is still used as the protective atmosphere.

In the step (6), the ball mill liquid is vacuum dried in a vacuum drying oven at 90-110 ° C for 20-25 h, and then passed through a 100-200 mesh sieve.

The sintering process parameters of the hot press sintering in the step (6) are: a heating rate of 10-20 ° C / min, a holding temperature of 1450-1550 ° C, a holding time of 10-25 min, and a hot pressing pressure of 25-30 MPa.

The present invention has the following advantages over the prior art:

1. Compared with the prior art technology for preparing ceramic coated hexagonal boron nitride composite powder, (1) for metal-based solid self-lubricating composite material, the invention can not only improve the wettability of the solid lubricant and the metal matrix, Increasing the interfacial bonding strength of the two, and reducing the density difference between the solid lubricant and the metal matrix, thereby improving the segregation during the mixing process and making the material uniform. Therefore, the mechanical properties and friction and wear properties of metal-based solid self-lubricating composites are improved. (2) For Tao Porcelain-based solid self-lubricating composite material, the invention can produce liquid phase at a lower sintering temperature, can effectively eliminate the card room structure of hexagonal boron nitride and thereby increase the density of the composite material, and reduce the sintering of the composite material. Temperature saves energy and is good for the environment. 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 thereof.

2. Compared with the existing hydrothermal hydrogen reduction method and precipitation method for preparing metal-coated hexagonal boron nitride composite powder, the invention has simple process equipment, simple operation, high safety, good powder coating effect and low cost. . The h-BN@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 same.

3. The present invention prepares a self-lubricating ceramic tool material by adding h-BN@Ni composite powder having a core-shell structure instead of h-BN powder as a solid lubricant. On the one hand, the flake-shaped h-BN powder is easily agglomerated. It is not easy to disperse. When directly added, a cross-stacked card room structure is formed in the ceramic matrix, resulting in low sintering density and uneven microstructure of the ceramic tool material. Electroless nickel plating of h-BN powder can improve its dispersibility and also produce liquid phase during sintering. Therefore, adding h-BN@Ni composite powder can avoid the formation of card house structure in ceramic matrix and improve ceramics. Sintering density of the tool material and uniformity of its microstructure. On the other hand, the cladding metal nickel of the h-BN@Ni composite powder can be toughened and reinforced by the self-lubricating ceramic 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 existing technology of adding a hexagonal boron nitride composite powder to prepare a self-lubricating ceramic tool material, the present invention can generate a liquid phase at a lower sintering temperature, and can effectively eliminate hexagonal nitriding. The card room structure of boron further increases the density of the ceramic tool material, and at the same time reduces the sintering temperature of the ceramic tool material, saves energy and is environmentally friendly. In addition, the present invention uses metallic nickel as a cladding material of the hexagonal boron nitride powder, and can utilize the high toughness of the metallic nickel to greatly improve the fracture toughness of the self-lubricating ceramic tool material, thereby expanding the application range of the ceramic tool.

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a scanning electron microscope (SEM) photograph of a h-BN raw material powder used in an example of the present invention.

Fig. 2 is a SEM photograph at 10,000 magnification of the h-BN@Ni composite powder prepared in Example 1 of the present invention.

Fig. 3 is a SEM photograph showing an enlargement of 40,000 times of the h-BN@Ni composite powder prepared in Example 1 of the present invention.

Fig. 4 is an X-ray diffraction spectrum of the h-BN@Ni composite powder and the h-BN raw material powder in Example 1 of the present invention.

Figure 5 is a cross-sectional SEM photograph of a self-lubricating ceramic tool material added with h-BN@Ni composite powder prepared in Example 4 of the present invention.

Figure 6 is a cross-sectional SEM photograph of a self-lubricating ceramic tool material added with h-BN powder prepared in Comparative Example 1.

detailed description

The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

The raw material powders used in the examples are all commercially available products, and the average particle diameter of the h-BN powder raw material is 2 μm, and the purity is more than 99%; the SEM photograph and the X-ray diffraction spectrum of the h-BN raw material powder used are as shown in FIG. 4 is shown. The average particle diameters of the α-Al ₂ O ₃ powder, the (W, Ti) C powder, and the MgO powder were 0.2 μm, 1.5 μm, and 2 μm, 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: Preparation method of nickel-coated hexagonal boron nitride composite powder, the steps are as follows:

(1) 2.5 g of SnCl ₂ · 2H ₂ O was weighed, added to 50 mL of absolute ethanol, stirred and dissolved, and then anhydrous ethanol was added to 100 mL to obtain a sensitizing solution. 2 g of h-BN powder was weighed into a sensitizing solution, ultrasonically shaken for 2 min, centrifuged and washed once with absolute ethanol, and then washed once with distilled water.

(2) 0.05 g of PdCl _{2 was} added to 1 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added to 100 mL to obtain an activation liquid. The sensitized h-BN powder was added to the activation solution, ultrasonically shaken for 5 min, centrifuged and washed three times with absolute ethanol, and dried in a vacuum oven at 40 ° C for 10 h to obtain activated h-BN powder.

(3) Weigh 8g NaOH, add 70mL of distilled water, stir to dissolve and add distilled water to 100mL, and prepare 80g / L NaOH solution, that is, pH adjuster; weigh 12.5g NiSO ₄ ·6H ₂ O, 25g Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O and 15 g of H ₃ BO ₃ were added to 70-100 mL of distilled water, respectively, and stirred and dissolved in a water bath at 35 ° C to obtain a clear solution; the NiSO ₄ ·6H ₂ O solution was slowly added to Na. ₃ C ₆ H ₅ O ₇ · 2H ₂ O solution, while stirring, to obtain solution A; H ₃ BO ₃ solution is slowly added to solution A, while stirring, to obtain solution B; drop to solution B Add the pH adjuster, stir while stirring, the pH value of the solution reaches 11 to obtain the solution C; measure 35 mL of hydrazine hydrate, add dropwise to the solution C, and stir while stirring to obtain the solution D; add to the solution D Distilled water to 500 mL and stirred well to obtain an electroless plating solution.

The h-BN powder activated in the step (2) was added to the above electroless plating solution, and plated in a constant temperature water bath at 80 °C. Ultrasonic vibration was maintained during the plating process and the pH adjuster was added dropwise at any time to maintain the pH 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 hours to obtain a h-BN@Ni composite powder.

The SEM photograph and the X-ray diffraction pattern of the nickel-coated hexagonal boron nitride composite powder obtained 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 has a sheet structure and the surface is flat. It can be seen from Fig. 2 that the h-BN@Ni composite powder is 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 is coated with fine particles, and the coating layer is completely dense. The X-ray diffraction pattern of the h-BN@Ni composite powder in Fig. 4 has a diffraction peak of h-BN and a diffraction peak of Ni, and no impurity peak appears, indicating that the cladding layer is a crystalline metal Ni. A nickel-coated hexagonal boron nitride composite powder having a core-shell structure was obtained as shown in Fig. 2, Fig. 3 and Fig. 4 .

Example 2: Preparation method of nickel-coated hexagonal boron nitride composite powder, the steps are as follows:

(1) 4 g of SnCl ₂ · 2H ₂ O was weighed, added to 100 mL of absolute ethanol, stirred and dissolved, and then anhydrous ethanol was added to 200 mL to obtain a sensitizing solution. 3 g of h-BN powder was weighed into a sensitizing solution, ultrasonically shaken for 4 min, centrifuged and washed once with absolute ethanol, and then washed once with distilled water.

(2) 0.2 g of PdCl _{2 was} added to 3 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added to 200 mL to obtain an activation liquid. The sensitized h-BN powder was added to the activation solution, ultrasonically shaken for 6 min, centrifuged 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 14g NaOH, add 150mL of distilled water, stir to dissolve and add distilled water to 200mL, and prepare 70g / L NaOH solution, that is, pH adjuster; weigh 20g NiSO ₄ · 6H ₂ O, 55g Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O and 35 g of H ₃ BO ₃ were respectively added to 150-200 mL of distilled water, and stirred in a water bath of 40 ° C to dissolve to obtain a clear solution; the NiSO ₄ ·6H ₂ O solution was slowly added to Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O solution, while stirring, to obtain solution A; H ₃ BO ₃ solution is slowly added to solution A, while stirring, to obtain solution B; drop to solution B Adding pH adjuster, stirring while stirring, the pH value of the solution reaches 11 to obtain solution C; measuring 80 mL of hydrazine hydrate, adding dropwise to solution C, stirring while stirring to obtain solution D; adding to solution D Distilled water to 1000 mL and stirred well to obtain an electroless plating solution. The h-BN powder activated in the step (2) was added to the above electroless plating solution, and plated in a constant temperature water bath at 85 °C. Ultrasonic vibration was maintained during the plating process and the pH adjuster was added dropwise at any time to maintain the pH 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 hours to obtain a h-BN@Ni composite powder.

Example 3: Preparation method of nickel-coated hexagonal boron nitride composite powder, the steps are as follows:

(1) 10.5 g of SnCl ₂ · 2H ₂ O was weighed, added to 250 mL of absolute ethanol, stirred and dissolved, and then anhydrous ethanol was added to 350 mL to obtain a sensitizing solution. 5 g of h-BN powder was weighed into a sensitizing solution, ultrasonically shaken for 4 min, centrifuged and washed once with absolute ethanol, and then washed once with distilled water.

(2) 0.3 g of PdCl _{2 was} added to 4 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added to 350 mL to obtain an activation liquid. The sensitized h-BN powder was added to the activation solution, ultrasonically shaken for 8 min, centrifuged 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 21g NaOH, add 250mL of distilled water, stir to dissolve and add distilled water to 300mL, and prepare 70g / L NaOH solution, that is, pH adjuster; weigh 30g NiSO ₄ · 6H ₂ O, 70g Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O and 40 g of H ₃ BO ₃ were respectively added to 200-250 mL of distilled water, and stirred in a water bath of 35 ° C to dissolve to obtain a clear solution; the NiSO ₄ ·6H ₂ O solution was slowly added to Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O solution, while stirring, to obtain solution A; H ₃ BO ₃ solution is slowly added to solution A, while stirring, to obtain solution B; drop to solution B Adding a pH adjuster, stirring while stirring, the pH of the solution reaches 12, to obtain a solution C; measuring 90 mL of hydrazine hydrate, adding dropwise to the solution C while stirring, to obtain a solution D; adding to the solution D Distilled water to 1200 mL and stirred well to obtain an electroless plating solution. The h-BN powder activated in the step (2) was added to the above electroless plating solution, and plated in a constant temperature water bath at 75 °C. The ultrasonic oscillate was maintained during the plating process and the pH adjuster was added dropwise at any time to maintain the pH 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 oven at 50 ° C for 8 hours to obtain a h-BN@Ni composite powder.

Example 4: Self-lubricating ceramic tool material with h-BN@Ni core-shell composite powder added, the mass percentage of each component is: α-Al ₂ O ₃ 32.5%, (W, Ti) C 65% h-BN@Ni was 2% by mass of h-BN in the composite powder (product prepared in Example 1), and MgO was 0.5%.

The preparation steps are as follows:

(1)–(3) Same as Example 1.

(4) Preparation of suspension

Weigh 32.5g α-Al ₂ O ₃ powder and 0.65g polyethylene glycol, first add polyethylene glycol to 120mL absolute ethanol, stir and dissolve in 35°C water bath, then add α-Al ₂ O ₃ powder. The mixture was ultrasonically dispersed and stirred for 15 min to prepare an α-Al ₂ O ₃ suspension.

65 g of (W, Ti) C powder was weighed, added to 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 to 40 mL of absolute ethanol, ultrasonically dispersed and stirred for 15 minutes to prepare a h-BN@Ni suspension.

(5) Preparation of multiphase suspension, ball milling

The α-Al ₂ O ₃ suspension obtained in the step (4) and the (W, Ti) C suspension are mixed, then 0.5 g of MgO powder is added, ultrasonically dispersed and stirred for 20 min, and the obtained multiphase suspension is poured into a ball mill. The cans were filled with 1 kg of cemented carbide grinding balls and ball-milled for 48 hours with nitrogen as a protective atmosphere. Then, the h-BN@Ni suspension obtained in the step (4) was added, and the ball milling was continued for 4 hours with nitrogen as a protective atmosphere to obtain a ball-milling liquid.

(6) The ball mill obtained in the step (5) is 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 is charged into a graphite mold, and after cold pressing, it is placed. Hot press sintering is carried out in a vacuum hot press sintering furnace. The sintering process parameters are: heating rate 15 ° C / min, holding temperature 1500 ° C, holding time 15 min, hot pressing pressure 25 MPa.

Comparative Example 1: Self-lubricating ceramic tool material with h-BN powder added, the mass percentage of each component was: α-Al ₂ O ₃ 32.5%, (W, Ti) C 65%, h-BN 2% , MgO 0.5%. The preparation method is as follows:

(1) Preparation of suspension

Weigh 32.5g α-Al ₂ O ₃ powder and 0.65g polyethylene glycol, first add polyethylene glycol to 120mL absolute ethanol, stir and dissolve in 35°C water bath, then add α-Al ₂ O ₃ powder. The mixture was ultrasonically dispersed and stirred for 15 min to prepare an α-Al ₂ O ₃ suspension. 65 g of (W, Ti) C powder was weighed, added to 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 to 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 α-Al ₂ O ₃ suspension obtained in the step (1) and the (W, Ti) C suspension are mixed, then 0.5 g of MgO powder is added, ultrasonically dispersed and stirred for 20 min, and the obtained multiphase suspension is poured into a ball mill. The cans were filled with 1 kg of cemented carbide grinding balls and ball-milled for 48 hours with nitrogen as a protective atmosphere. Then, the h-BN suspension obtained in the step (1) was added, and the ball milling was continued for 4 hours with nitrogen as a protective atmosphere to obtain a ball-milling liquid.

(3) The ball milling liquid obtained in the step (2) is dried in a vacuum drying oven at 100 ° C for 24 hours, and then passed through a 120 mesh sieve to obtain a mixed powder, and the obtained mixed powder is charged into a graphite mold, and after cold pressing, It is placed in a vacuum hot press sintering furnace for hot press sintering. The sintering process parameters are: heating rate 15 ° C / min, holding temperature 1500 ° C, holding time 15 min, hot pressing pressure 25 MPa.

It can be seen from Fig. 5 that the h-BN grain distribution of the self-lubricating ceramic 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 self-lubricating ceramic tool material with h-BN powder (uncoated) have obvious agglomeration phenomenon, forming a card room structure, and the ceramic matrix has uneven grain size and abnormality. When growing up, the arrangement is not dense and the pores are more. Figures 5 and 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 tool material.

The mechanical properties of the self-lubricating ceramic tool material prepared by adding the h-BN@Ni core-shell composite powder prepared in Example 4 were as follows: bending strength 621 MPa, hardness 16.3 GPa, fracture toughness 5.5 MPa·m ^1/2 ; The mechanical properties of the self-lubricating ceramic tool material prepared by adding the h-BN powder prepared in Comparative Example 1 were: bending strength 578 MPa, hardness 15.1 GPa, and fracture toughness 4.8 MPa·m ^1/2 . 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 the latter, respectively.

Example 5: Self-lubricating ceramic tool material with h-BN@Ni core-shell composite powder added, the mass percentage of each component is: α-Al ₂ O ₃ 37%, (W, Ti) C 58.5% , h-BN@Ni is 4% by mass of h-BN in the composite powder, and MgO is 0.5%. The preparation method is as follows:

(1) Sensitization and activation of h-BN powder

5 g of SnCl ₂ · 2H ₂ O was weighed, added to 200 mL of absolute ethanol, and stirred to dissolve to obtain a sensitizing solution. 0.1 g of PdCl _{2 was} added to 2 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added to 200 mL to obtain an activation liquid. 4 g of h-BN raw material powder was weighed into a sensitizing solution, ultrasonically shaken for 3 min, centrifuged and washed once with absolute ethanol, and then washed once with distilled water. The sensitized h-BN powder was added to the activation solution, ultrasonically shaken for 7 min, centrifuged and washed 4 times with absolute ethanol, and dried in a vacuum oven at 50 ° C for 8 h, and used.

(2) Preparation of h-BN@Ni composite powder by electroless plating

Weigh 14g NaOH, add 150mL of distilled water, stir to dissolve and add distilled water to 200mL, and prepare 70g / L NaOH solution; weigh 20g NiSO ₄ · 6H ₂ O, 55g Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O And 35g of H ₃ BO ₃ , respectively, were added to 150-200mL of distilled water, stirred in a water bath of 35 ° C to dissolve, respectively, to obtain a clear solution; the NiSO ₄ · 6H ₂ O solution was slowly added to Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O solution, while stirring, then slowly add H ₃ BO ₃ solution, while stirring, to obtain a mixed solution; add NaOH solution to the mixed solution, while stirring, to make the pH of the mixed solution Reached 12. 70 mL of hydrazine hydrate was weighed, added dropwise to the mixed solution, stirred while being added, and then distilled water was added to 1000 mL and stirred uniformly to obtain an electroless plating solution. The h-BN powder activated in the step (1) was added to the above electroless plating solution, and electroless plating was performed in a constant temperature water bath at 75 °C. Ultrasonic vibration was maintained during the plating process and the NaOH solution was added dropwise to keep the pH of the electroless plating solution at 12. After the plating was completed, the solid particles were centrifuged and washed with distilled water until neutral, and then washed with absolute ethanol for 3 times, and then dried in a vacuum oven at 50 ° C for 8 hours to obtain a h-BN@Ni composite powder.

(3) Preparation of suspension

37 g of α-Al ₂ O ₃ powder and 0.74 g of polyethylene glycol were weighed, and polyethylene glycol was first added to 120 mL of absolute ethanol, stirred and dissolved in a 40 ° C water bath, and then α-Al ₂ O ₃ powder was added. The mixture was ultrasonically dispersed and stirred for 20 min to prepare an α-Al ₂ O ₃ suspension. 58.5 g of (W, Ti) C powder was weighed, added to 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 to 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 α-Al ₂ O ₃ suspension obtained in the step (3) and the (W, Ti) C suspension are mixed, then 0.5 g of MgO powder is added, ultrasonically dispersed and stirred for 20 min, and the obtained multiphase suspension is poured into a ball mill. The cans were filled with 1 kg of cemented carbide grinding balls and ball-milled for 45 hours 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 hours with nitrogen as a protective atmosphere to obtain a ball-milling liquid.

(5) The ball mill obtained in the step (4) is 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, and the obtained mixed powder is charged into a graphite mold, and after cold press molding. It is placed in a vacuum hot press sintering furnace for hot press sintering. The sintering process parameters are: heating rate 10 ° C / min, holding temperature 1550 ° C, holding time 10 min, hot pressing pressure 30 MPa.

Comparative Example 2: Self-lubricating ceramic tool material with h-BN powder added, the mass percentage of each component was: α-Al ₂ O ₃ 37%, (W, Ti) C 58.5%, h-BN 4% , MgO 0.5%. The preparation method is as follows:

(1) Preparation of suspension

37 g of α-Al ₂ O ₃ powder and 0.74 g of polyethylene glycol were weighed, and polyethylene glycol was first added to 120 mL of absolute ethanol, stirred and dissolved in a 40 ° C water bath, and then α-Al ₂ O ₃ powder was added. The mixture was ultrasonically dispersed and stirred for 20 min to prepare an α-Al ₂ O ₃ suspension. 58.5 g of (W, Ti) C powder was weighed, added to 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 to 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 α-Al ₂ O ₃ suspension obtained in the step (1) and the (W, Ti) C suspension are mixed, then 0.5 g of MgO powder is added, ultrasonically dispersed and stirred for 20 min, and the obtained multiphase suspension is poured into a ball mill. The cans were filled with 1 kg of cemented carbide grinding balls and ball-milled for 45 hours with nitrogen as a protective atmosphere. Then, the h-BN suspension obtained in the step (1) was added, and the ball milling was continued for 3 hours with nitrogen as a protective atmosphere to obtain a ball-milling liquid.

(3) The ball mill obtained in the step (2) is 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 obtained mixed powder is charged into a graphite mold, and after cold press forming It is placed in a vacuum hot press sintering furnace for hot press sintering. The sintering process parameters are: heating rate 10 ° C / min, holding temperature 1550 ° C, holding time 10 min, hot pressing pressure 30 MPa.

The mechanical properties of the self-lubricating ceramic tool material prepared by adding the h-BN@Ni core-shell composite powder prepared in Example 5 were as follows: bending strength 610 MPa, hardness 15.3 GPa, fracture toughness 5.1 MPa·m ^1/2 ; The mechanical properties of the self-lubricating ceramic tool material prepared by adding the h-BN powder prepared in Comparative Example 2 were: bending strength 536 MPa, hardness 14.1 GPa, and fracture toughness 4.2 MPa·m ^1/2 . It can be seen that the flexural strength, hardness and fracture toughness of the former are increased by 13.8%, 8.5% and 21.4%, respectively.

Example 6: Self-lubricating ceramic tool material with h-BN@Ni core-shell composite powder added, the mass percentage of each component is: α-Al ₂ O ₃ 40%, (W, Ti) C 53% , h-BN@Ni is 6% by mass of h-BN in the composite powder, and MgO is 1%. The preparation method is as follows:

(1) Sensitization and activation of h-BN powder

10.5 g of SnCl ₂ ·2H ₂ O was weighed, added to 350 mL of absolute ethanol, and stirred to dissolve to obtain a sensitizing solution. 0.3 g of PdCl _{2 was} added to 4 mL of concentrated hydrochloric acid, stirred and dissolved, and distilled water was added to 350 mL to obtain an activation liquid. 6 g of h-BN raw material powder was weighed into a sensitizing solution, ultrasonically shaken for 5 min, centrifuged and washed once with absolute ethanol, and then washed once with distilled water. The sensitized h-BN powder was added to the activation solution, ultrasonically shaken for 7 min, centrifuged and washed 4 times with absolute ethanol, and dried in a vacuum oven at 60 ° C for 7 h, and used.

(2) Preparation of h-BN@Ni composite powder by electroless plating

Weigh 24g NaOH, add 250mL of distilled water, stir to dissolve and add distilled water to 300mL, and prepare 80g / L NaOH solution; weigh 30g NiSO ₄ · 6H ₂ O, 70g Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O And 40g of H ₃ BO ₃ , respectively, added to 200-250mL of distilled water, stirred in a water bath of 40 ° C to dissolve, respectively, to obtain a clear solution; the NiSO ₄ · 6H ₂ O solution was slowly added to Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O solution, while stirring, then slowly add H ₃ BO ₃ solution, while stirring, to obtain a mixed solution; add NaOH solution to the mixed solution, while stirring, to make the pH of the mixed solution Reached 12. 100 mL of hydrazine hydrate was weighed, added dropwise to the mixed solution, stirred while being added, and then distilled water was added to 1200 mL and stirred uniformly to obtain an electroless plating solution. The h-BN powder activated in the step (1) was added to an electroless plating solution, and electroless plating was performed in a constant temperature water bath at 85 °C. Ultrasonic vibration was maintained during the plating process and the NaOH solution was added dropwise to keep the pH of the electroless plating solution at 12. After the plating was completed, the solid particles were centrifuged and washed with distilled water until neutral, and then washed with absolute ethanol for 3 times, and then dried in a vacuum oven at 50 ° C for 9 hours to obtain a h-BN@Ni composite powder.

(3) Preparation of suspension

40 g of α-Al ₂ O ₃ powder and 1.2 g of polyethylene glycol were weighed, polyethylene glycol was first added to 125 mL of absolute ethanol, stirred and dissolved in a water bath at 30 ° C, and then α-Al ₂ O ₃ powder was added. The mixture was ultrasonically dispersed and stirred for 20 min to prepare an α-Al ₂ O ₃ suspension. 53 g of (W, Ti) C powder was weighed, added to 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 to 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 α-Al ₂ O ₃ suspension obtained in the step (3) and the (W, Ti) C suspension are mixed, then 1 g of MgO powder is added, ultrasonically dispersed and stirred for 30 min, and the obtained multiphase suspension is poured into a ball mill jar. 1 kg of cemented carbide grinding balls were added, and ball milling was carried out 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 hours with nitrogen as a protective atmosphere to obtain a ball milling liquid.

(5) The ball mill obtained in the step (4) was dried in a vacuum oven at 90 ° C for 25 hours, and then passed through a 100 mesh sieve to obtain a mixed powder. The obtained mixed powder is charged into a graphite mold, and after cold press forming, it is placed in a vacuum hot press sintering furnace for hot press sintering. The sintering process parameters are: heating rate 20 ° C / min, holding temperature 1500 ° C, holding time 25 min, hot pressing pressure 30 MPa.

Comparative Example 3: Self-lubricating ceramic tool material with h-BN powder added, the mass percentage of each component is: α-Al ₂ O ₃ 40%, (W, Ti) C 53%, h-BN 6% , MgO 1%. The preparation method is as follows:

(1) Preparation of suspension

40 g of α-Al ₂ O ₃ powder and 1.2 g of polyethylene glycol were weighed, polyethylene glycol was first added to 125 mL of absolute ethanol, stirred and dissolved in a water bath at 30 ° C, and then α-Al ₂ O ₃ powder was added. The mixture was ultrasonically dispersed and stirred for 20 min to prepare an α-Al ₂ O ₃ suspension. 53 g of (W, Ti) C powder was weighed, added to 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 to 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 α-Al ₂ O ₃ suspension obtained in the step (1) and the (W, Ti) C suspension are mixed, then 1 g of MgO powder is added, ultrasonically dispersed and stirred for 30 min, and the obtained multiphase suspension is poured into a ball mill jar. 1 kg of cemented carbide grinding balls were added, and ball milling was carried out for 40 hours with nitrogen as a protective atmosphere; then the h-BN suspension obtained in the step (1) was added, and ball milling was continued for 2 hours with nitrogen as a protective atmosphere to obtain a ball milling liquid.

(3) The ball mill obtained in the step (2) was dried in a vacuum oven at 90 ° C for 25 hours, and then passed through a 100 mesh sieve to obtain a mixed powder. The obtained mixed powder is charged into a graphite mold, and after cold press forming, it is placed in a vacuum hot press sintering furnace for hot press sintering. The sintering process parameters are: heating rate 20 ° C / min, holding temperature 1500 ° C, holding time 25 min, hot pressing pressure 30 MPa.

The mechanical properties of the self-lubricating ceramic tool material prepared by adding the h-BN@Ni core-shell composite powder prepared in Example 6 were: bending strength 550 MPa, hardness 13.1 GPa, fracture toughness 4.1 MPa·m ^1/2 ; The mechanical properties of the self-lubricating ceramic tool material prepared by adding the h-BN powder prepared in Comparative Example 3 were: bending strength 497 MPa, hardness 12.3 GPa, and fracture toughness 3.5 MPa·m ^1/2 . It can be seen that the flexural strength, hardness and fracture toughness of the former are increased by 10.7%, 6.5% and 17.1%, respectively.

Claims (10)

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 a sensitized and activated h-BN powder The body is added to the electroless plating solution, and the nickel is plated on the surface of the hexagonal boron nitride under ultrasonic vibration conditions; wherein the composition of the electroless plating solution is: nickel sulfate hexahydrate (NiSO ₄ · 6H ₂ O) 20-30g/L, sodium citrate dihydrate (Na ₃ C ₆ H ₅ O ₇ ·2H ₂ O) 50-70g/L, boric acid (H ₃ BO ₃ ) 30-40g/L, mass fraction 50-80% Hydrazine hydrate (N ₂ H ₄ ·H ₂ O) 50-100 mL / L, an appropriate amount of pH adjuster to make the electroless plating solution pH 11-12, the balance is distilled water.
2. A method for preparing a nickel-coated hexagonal boron nitride composite powder according to claim 1, comprising the steps of:

   (1) adding h-BN powder to the sensitizing solution, ultrasonically shaking for 2-5 minutes, centrifuging and washing once with absolute ethanol, and then washing once with distilled water;

   (2) Adding the h-BN powder sensitized in step (1) to the activation solution, ultrasonically shaking for 5-10 minutes, centrifuging and washing with anhydrous ethanol for 3-5 times, in a vacuum drying oven at 40-60 ° C Drying for 7-10h to obtain activated h-BN powder;

   (3) adding the activated h-BN powder to the electroless plating solution, the pH of the electroless plating solution is 11-12, and plating in a constant temperature water bath of 70-85 ° C;

   Keep the ultrasonic vibration during the plating process and add the pH adjuster at any time to keep the pH of the electroless plating solution at 11-12. After the plating is completed, the solid particles are separated and washed with distilled water until neutral, and then ethanol is used. The mixture was washed 2-3 times, and then dried in a vacuum drying oven at 40-60 ° C for 7-10 h to obtain a h-BN@Ni composite powder.
3. The method for preparing a nickel-coated hexagonal boron nitride composite powder according to claim 2, wherein the composition of the sensitizing liquid in the step (1) is: stannous chloride dihydrate (SnCl ₂ · 2H ₂ O) 20-30 g / L, the balance is anhydrous ethanol; preferably, when the h-BN is sensitized, the amount of h-BN powder added is 10-20 g per liter of sensitizing liquid. L.
4. The method for preparing a nickel-coated hexagonal boron nitride composite powder according to claim 2, wherein the composition of the activation liquid in the step (2) is: palladium chloride (PdCl ₂ ) 0.5-1 g/ L, a mass fraction of 35-37% concentrated hydrochloric acid 10-20mL / L, the balance is distilled water; preferably, when the h-BN is activated, the amount of h-BN powder added is 10 per liter of activation liquid -20g/L.
5. The method for preparing a nickel-coated hexagonal boron nitride composite powder according to claim 2, wherein the composition of the electroless plating solution in the step (3) is: nickel sulfate hexahydrate (NiSO ₄ · 6H ₂ O) 20-30g/L, sodium citrate dihydrate (Na ₃ C ₆ H ₅ O ₇ ·2H ₂ O) 50-70g/L, boric acid (H ₃ BO ₃ ) 30-40g/L, mass fraction 50- 80% hydrazine hydrate (N ₂ H ₄ ·H ₂ O) 50-100 mL / L, an appropriate amount of pH adjuster to make the electroless plating solution pH 11-12, the balance is distilled water.
6. The method for preparing a nickel-coated hexagonal boron nitride composite powder according to claim 1 or 5, wherein the pH adjusting agent in the step (3) is a 60-80 g/L NaOH solution; In the step (3), the amount of the h-BN powder added is 2-5 g/L per liter of the electroless plating solution.
7. The method for preparing a nickel-coated hexagonal boron nitride composite powder according to claim 1 or 6, wherein the step (3) The preparation steps of the medium electroless plating solution are as follows:

   1 Weigh NaOH proportionally, add appropriate amount of distilled water, stir to dissolve and add distilled water to the required volume, and prepare 60-80g / L NaOH solution, that is, pH adjuster;

   2 Weigh NiSO ₄ ·6H ₂ O, Na ₃ C ₆ H ₅ O ₇ ·2H ₂ O and H ₃ BO ₃ in proportion, respectively, add appropriate amount of distilled water, stir in a water bath at 30-40 ° C to dissolve, respectively Obtaining a clear solution;

   3, the NiSO ₄ · 6H ₂ O solution was slowly added to the Na ₃ C ₆ H ₅ O ₇ · 2H ₂ O solution, while stirring, to obtain a solution A;

   4 slowly add H ₃ BO ₃ solution to solution A, while stirring, to obtain solution B;

   5 to the solution B was added dropwise to the pH adjuster, while stirring, so that the pH of the solution reached 11-12, to obtain a solution C;

   6 proportionally take a mass fraction of 50-80% hydrazine hydrate, add dropwise to the solution C, while stirring, to obtain a solution D;

   7 Add distilled water to the solution D to the total volume of the electroless plating solution and stir evenly to obtain an electroless plating solution.
8. A self-lubricating ceramic tool material with nickel-coated hexagonal boron nitride core-shell composite powder is composed of α-phase alumina (α-Al ₂ O ₃ ) as matrix and tungsten carbide tungsten ((W, Ti) C) as a reinforcing phase, the nickel-coated hexagonal boron nitride (h-BN@Ni) composite powder according to any one of claims 1 to 2-7 as a solid lubricant, and magnesium oxide (MgO) As a sintering aid, it is made by ball milling and hot pressing sintering; the mass percentage of each component is: α-Al ₂ O ₃ 25-45%, (W, Ti) C50-70%, nickel coated The hexagonal boron nitride composite powder is 2-10% by mass of h-BN, and MgO is 0.4-1.5%.
9. The self-lubricating ceramic tool material according to claim 8, wherein the mass percentage of each component is: α-Al ₂ O ₃ 31-41 %, (W, Ti) C 52-66%, h-BN@Ni is 2-6% by mass of h-BN in the composite powder, MgO 0.5-1%; preferably, mass percentage of each component The content is: α-Al ₂ O ₃ 36-38%, (W, Ti) C 58-59%, h-BN@Ni is 3.5-4.5% by mass of h-BN in the composite powder, MgO 0.5%; The sum of the components is 100%.
10. The method for preparing a self-lubricating ceramic tool material for adding a nickel-coated hexagonal boron nitride core-shell composite powder according to claim 8 or 9, comprising the nickel-coated hexagonal boron nitride composite powder according to claim 2. The preparation steps (1)-(3) further include the following steps:

    (4) Preparation of suspension

    The α-Al ₂ O ₃ powder is weighed in proportion, added to an appropriate amount of polyethylene glycol-anhydrous ethanol solution, ultrasonically dispersed and stirred to form an α-Al ₂ O ₃ suspension;

    Weigh the (W, Ti) C powder in proportion, add an appropriate amount of absolute ethanol, ultrasonically disperse and stir to prepare a (W, Ti) C suspension;

    The h-BN@Ni composite powder was weighed in proportion, added with an appropriate amount of absolute ethanol, dispersed by ultrasonication and stirred to form h-BN@Ni. suspension;

    (5) Preparation of multiphase suspension, ball milling

    The prepared α-Al ₂ O ₃ 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 jar. Ball milling 40-50h; then adding the h-BN@Ni suspension obtained in step (3), continuing the ball milling to obtain a ball milling liquid;

    (6) The obtained ball mill liquid is vacuum dried and sieved to obtain a mixed powder material, and sealed for use; the mixed powder material is charged into a graphite mold, and after cold press forming, it is placed in a vacuum hot pressing sintering furnace for hot pressing sintering;

    Preferably, drying at 90-110 ° C for 20-25 h; further preferably, the sintering process parameters of the hot press sintering are: heating rate 10-20 ° C / min, holding temperature 1450-1550 ° C, holding time 10-25 min, heat The pressure is 25-30 MPa.

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