CN110527891B

CN110527891B - Diamond coating on the surface of low cobalt cemented carbide and preparation method thereof

Info

Publication number: CN110527891B
Application number: CN201910871141.3A
Authority: CN
Inventors: 张建国; 原一高; 阮钧; 张金江
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2019-09-16
Filing date: 2019-09-16
Publication date: 2021-11-02
Anticipated expiration: 2039-09-16
Also published as: CN110527891A

Abstract

The invention relates to a diamond coating on the surface of a low-cobalt hard alloy and a preparation method thereof. The hard alloy with low cobalt content is used as a base material to deposit a diamond film. Utilize the excellent physical properties of graphene to improve the toughness of low cobalt content cemented carbide, which is used as a matrix material for diamond coating. The chemical pretreatment time before diamond coating is reduced, the corrosion damage to the matrix material caused by the long-term chemical reaction is avoided, and the dimensional accuracy of the product is better maintained. At the same time, the thermal diffusion effect of cobalt in the deposition process of the diamond coating is alleviated, and the adhesion strength between the coating and the substrate is improved. The dual effects of improving the toughness of the diamond-coated cemented carbide substrate and eliminating the adverse effects of cobalt elements are realized, and an effective method is provided for improving the performance of the diamond-coated cemented carbide products.

Description

Low-cobalt hard alloy surface diamond coating and preparation method thereof

Technical Field

The invention belongs to the field of diamond coatings and preparation thereof, and particularly relates to a low-cobalt hard alloy surface diamond coating and a preparation method thereof.

Background

The diamond coating has a plurality of excellent performances such as high hardness, high wear resistance, high thermal conductivity, low friction coefficient, good chemical inertness and the like, so that the diamond coating can be widely applied to the field of tools and dies. The diamond coating is deposited on the surface of the hard alloy tool and die, so that the service life of the tool and die can be greatly prolonged, and the quality of the processed surface of a workpiece can be improved.

In order to balance the hardness and toughness of the matrix material, the cobalt content of the hard alloy matrix selected for the diamond coating is generally 6 wt.% to 8 wt.%. However, in order to eliminate the catalytic graphitization of cobalt in the substrate material during the deposition of the diamond coating, the cemented carbide substrate must be pretreated by "chemical etching to remove cobalt" prior to the preparation of the diamond coating. The higher the cobalt content of the substrate, the longer the chemical etching time. The cobalt removal brings inevitable damage to the tungsten carbide structure in the matrix, thereby affecting the performance of the matrix material. So that the properties of the diamond coated product cannot be expected.

Through the patent search of the prior art, Chinese patent application numbers 201510673007.4 and 03117958.4 propose that the gradient hard alloy with poor cobalt on the surface layer is used as a substrate material to prepare the diamond coating, so as to solve the influence of cobalt element on the deposition of the diamond coating and simultaneously take the strength and toughness of the substrate into consideration. However, during the deposition of the diamond coating, the cobalt-rich layer of the core of the gradient cemented carbide substrate still causes the diamond coating to be graphitized and the film-substrate adhesion strength to be reduced due to the thermal diffusion of cobalt caused by the heating of the substrate.

Disclosure of Invention

The invention aims to solve the technical problem of providing a hard alloy matrix toughening diamond coating and a preparation method thereof, and overcomes the defects that in the prior art, the cobalt content in hard alloy applied to the diamond coating is 6-8 wt.%, and long-time chemical pretreatment is needed to obtain a better pretreatment effect, and the structural performance of the matrix is damaged while cobalt is removed. In addition, the high cobalt content in the matrix has a strong thermal diffusion effect in the deposition process of the diamond coating, so that the technical problem of low bonding strength between the diamond coating and the matrix is solved. The low cobalt content hard alloy matrix in the invention toughens and deposits the diamond coating.

According to the diamond coating, the diamond film is deposited on the coating by taking the hard alloy as a base material;

the hard alloy is characterized by comprising the following raw material components in percentage by mass: 0.1-1 wt% of graphene (powder), 2-3 wt% of cobalt and 97.9-96 wt% of tungsten carbide (powder).

The invention relates to a preparation method of a diamond coating, which comprises the following steps:

(1) ball-milling and mixing the dispersed graphene and cobalt powder with tungsten carbide powder to obtain slurry, carrying out vacuum drying, and sintering and molding a matrix to obtain a hard alloy matrix material;

(2) and (3) pretreating the substrate, and depositing a diamond coating to obtain the diamond coating.

The preferred mode of the above preparation method is as follows:

the graphene dispersed in the step (1) is specifically: absolute ethyl alcohol is used as a dispersion solution, the ratio of the absolute ethyl alcohol to the graphene is 100mL (0.1-0.5 g), and an ultrasonic oscillation dispersion process is utilized, wherein the ultrasonic frequency is 40 KHz; the duty cycle of the ultrasonic working time is 1: 1; the ultrasonic oscillation time is 4-6 h.

The specific process parameters of the ball milling mixing in the step (1) are as follows: the adopted grinding balls are hard alloy WC-3 wt.% Co balls with the diameter of 5mm, the rotating speed of the ball mill is 300-500 rpm, and the ball milling time is 6-8 h; wherein the weight ratio of absolute ethyl alcohol: powder lot: the proportion of the grinding balls is as follows: (1-2) mL of 1g (7-10).

The vacuum drying in the step (1) comprises the following steps: and (3) placing the mixed and stirred slurry in a vacuum drying oven for drying, wherein in the drying process, the heating temperature is 90-100 ℃, when no visible liquid exists in the slurry, the heating is stopped (the heating function is closed), the slurry is naturally dried for 2-3 h, and in the whole drying process, the pressure in a vacuum chamber is kept at 10000-15000 Pa.

Sintering and forming in the step (1): pressing the dried powder into a shape required by design, and sintering and molding by adopting a vacuum pressure sintering method at 1380 ℃ and 40 MPa.

The pretreatment in the step (2) is specifically as follows: immersing the substrate in an alkali solution for 10min, cleaning, blow-drying, immersing the substrate subjected to alkali treatment in an acid solution for natural reaction for 10s, cleaning, and blow-drying; grinding by using a mixed solution of diamond powder and glycerol, cleaning and drying; wherein the alkali liquor is potassium ferricyanide: potassium hydroxide: water ═ 1g: 1g: 10 mL; the acid solution is hydrochloric acid: hydrogen peroxide 1 mL: 4 mL.

The deposition in the step (2) is specifically as follows: and (2) placing the pretreated substrate in chemical vapor deposition equipment by adopting a hot wire chemical vapor deposition method, inputting a reaction working gas of 10-20 sccm of methane flow and 1000-2000 sccm of hydrogen flow after the pressure of a vacuum chamber of the equipment reaches below 5Pa, adjusting the reaction pressure to 2000-4000 Pa, and setting the deposition time of the coating to be 6-10 h. The invention provides a diamond coating prepared by the method.

The invention provides an application of the diamond coating.

Advantageous effects

(1) The invention solves the problems that the high cobalt content in the hard alloy matrix of the diamond coating in the prior art has adverse effect on the coating and the strength and toughness of the matrix can not be coordinated, and provides a toughening process of the low cobalt content hard alloy matrix for the diamond coating and a preparation method of the coating;

(2) the toughness of the hard alloy matrix with low cobalt content is improved by utilizing the excellent characteristics of high strength, good toughness and the like of the graphene, the component of the graphene is carbon, and other impurity elements are not introduced in the preparation process of the hard alloy, so that the component of the hard alloy is not influenced;

(3) when the hard alloy with low cobalt content is used for diamond coating, the chemical corrosion time of alkali and acid in the pretreatment stage is reduced, the adverse effect of long-time chemical corrosion on the performance of the hard alloy material and the size precision of a finished workpiece are avoided, and the problem of poor coating quality and film-substrate bonding strength caused by thermal diffusion of high cobalt content in the traditional hard alloy in the deposition process is also avoided;

(4) the method utilizes the excellent physical properties of the graphene, improves the toughness of the low-cobalt-content hard alloy, is used for the base material of the diamond coating, reduces the chemical pretreatment time before the diamond coating, avoids the corrosion damage of long-time chemical reaction to the base material, and better maintains the dimensional precision of the product. Meanwhile, the thermal diffusion effect of cobalt in the deposition process of the diamond coating is relieved, the adhesion strength of the coating and the matrix is improved, the double effects of improving the toughness of the diamond coating hard alloy matrix and eliminating the adverse effect of cobalt elements are realized, and an effective method is provided for improving the performance of the diamond coating hard alloy product.

Drawings

FIG. 1 is an indentation pattern of a diamond coating on the surface of a conventional cemented carbide (6 wt.% Co) substrate prepared in a comparative example;

fig. 2 is an indentation pattern of a diamond coating on the surface of a substrate made of graphene-enhanced low cobalt (3 wt.% Co) cemented carbide (0.3 wt.% graphene) prepared in example 1.

Fig. 3 is an indentation pattern of the diamond coating on the surface of the substrate of the graphene-enhanced low cobalt (3 wt.% Co) cemented carbide (0.5 wt.% graphene) prepared in example 2.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

The graphene referred to in the examples and comparative examples is a commercial product, and has a sheet diameter of 5-10 micrometers and a thickness of 3-10 nanometers; the cobalt powder is a commercial product, and the particle diameter is 1 micron; the tungsten carbide powder is a commercial product, and the particle diameter is 0.8 micron.

Example 1

Graphene enhanced low cobalt (3 wt.% Co) cemented carbide (0.3 wt.% graphene) matrix diamond coating deposition.

(1) And (3) graphene dispersion: weighing 0.3g of graphene powder by using a precision electronic balance, pouring the graphene powder into 100mL of absolute ethyl alcohol, and setting ultrasonic frequency to be 40KHz by using a cell crushing instrument; the duty cycle of the ultrasonic working time is 1: 1; the time of ultrasonic oscillation is 4 h.

(2) Ball milling and mixing: 2.991g of cobalt powder and 96.709g of tungsten carbide powder were weighed by a precision electronic balance, and poured into a ball mill pot together with the graphene-alcohol solution in (1). 700g of cemented carbide (WC-wt. 3% Co) balls having a diameter of 5mm were weighed and placed in a ball mill jar. And adding 100mL of absolute ethyl alcohol into the ball milling tank, setting the rotating speed of the ball mill to be 400rpm, and ball milling time to be 8 h.

(3) And (3) vacuum drying: and (5) placing the slurry subjected to ball milling in a vacuum drying oven for drying. Setting the pressure in the drying oven at 15000Pa and the heating temperature at 90 ℃, turning off the heating function when no visible liquid exists in the slurry, and naturally drying for 3 h.

(4) Sintering and forming of a substrate: the dried powder was sieved through a 120-mesh sieve, and then the powder was preformed by a powder tableting machine. A vacuum sintering furnace is adopted, the sintering temperature is set to 1380 ℃, the pressure is set to 40MPa, and the sintering time is set to 40 min. And grinding and polishing the surface of the base body into a mirror surface by using a metallographic grinding and polishing machine for the sintered sample.

(5) Matrix pretreatment: and (4) ultrasonically cleaning the substrate in the step (4) by using absolute ethyl alcohol, and drying. The substrate was immersed in an alkali solution (potassium ferricyanide: potassium hydroxide: water 1g: 1g: 10mL) for 10min, washed, and dried. And immersing the base body subjected to alkali treatment in an acid solution (hydrochloric acid: hydrogen peroxide: 1 mL: 4mL) for natural reaction for 10s, cleaning and drying. Grinding with mixed solution of diamond powder and glycerol, cleaning, and blow-drying.

(6) Deposition of diamond coating: and (3) placing the substrate pretreated in the step (5) in chemical vapor deposition equipment by adopting a hot wire chemical vapor deposition method, inputting a reaction working gas of 15sccm for methane flow and 1000sccm for hydrogen flow after the vacuum chamber pressure of the equipment reaches below 5Pa, adjusting the reaction pressure to 3000Pa, and setting the coating deposition time to 6 h.

Example 2

Graphene enhanced low cobalt (3 wt.% Co) cemented carbide (0.5 wt.% graphene) matrix diamond coating deposition.

(1) And (3) graphene dispersion: weighing 0.5g of graphene powder by using a precision electronic balance, pouring the graphene powder into 100mL of absolute ethyl alcohol, and setting ultrasonic frequency to be 40KHz by using a cell crushing instrument; the duty cycle of the ultrasonic working time is as follows: 1: 1; the time of ultrasonic oscillation is 4 h.

(2) Ball milling and mixing: 2.985g of cobalt powder and 96.515g of tungsten carbide powder were weighed by a precision electronic balance, and poured into a ball mill pot together with the graphene-alcohol solution in (1). 1000g of cemented carbide (WC-wt. 3% Co) balls having a diameter of 5mm were weighed and placed in a ball mill jar. And adding 100mL of absolute ethyl alcohol into the ball milling tank, setting the rotating speed of the ball mill to be 400rpm, and ball milling time to be 8 h.

Comparative example

Common cemented carbide (6 wt.% Co) substrate diamond coating deposition.

(1) Ball milling and mixing: 6g of cobalt powder and 94g of tungsten carbide powder were weighed by a precision electronic balance and poured into a ball mill pot. 1000g of cemented carbide (WC-wt.6% Co) balls having a diameter of 5mm were weighed and placed in a ball mill jar. 200mL of absolute ethyl alcohol is added into a ball milling tank, the rotating speed of the ball mill is set to be 400rpm, and the ball milling time is set to be 8 h.

(2) And (3) vacuum drying: and (5) placing the slurry subjected to ball milling in a vacuum drying oven for drying. Setting the pressure in the drying oven at 15000Pa and the heating temperature at 90 ℃, turning off the heating function when no visible liquid exists in the slurry, and naturally drying for 3 h.

(3) Sintering and forming of a substrate: the dried powder was sieved through a 120-mesh sieve, and then the powder was preformed by a powder tableting machine. A vacuum sintering furnace is adopted, the sintering temperature is set to 1380 ℃, the pressure is set to 40MPa, and the sintering time is set to 40 min. And grinding and polishing the surface of the base body into a mirror surface by using a metallographic grinding and polishing machine for the sintered sample. Comparison of

(4) Matrix pretreatment: and (4) ultrasonically cleaning the substrate in the step (3) by using absolute ethyl alcohol, and drying. The substrate was immersed in an alkali solution (potassium ferricyanide: potassium hydroxide: water 1g: 1g: 10mL) for 10min, washed, and dried. And immersing the base body subjected to alkali treatment in an acid solution (hydrochloric acid: hydrogen peroxide: 1 mL: 4mL) for natural reaction for 10s, cleaning and drying. Grinding with mixed solution of diamond powder and glycerol, cleaning, and blow-drying.

(5) Deposition of diamond coating: and (3) placing the substrate pretreated in the step (4) in chemical vapor deposition equipment by adopting a hot wire chemical vapor deposition method, inputting a reaction working gas of 15sccm for methane flow and 1000sccm for hydrogen flow after the vacuum chamber pressure of the equipment reaches below 5Pa, adjusting the reaction pressure to 3000Pa, and setting the coating deposition time to 6 h.

The sample obtained in step (4) of example 1, the sample obtained in step (4) of example 2, and the sample obtained in step (3) of comparative example were measured with a microhardness meter, and the fracture toughness values in the three cases were calculated from the indentation load and the indentation crack propagation length to be 13.1. + -. 0.1MPa · m^1/2，12.9±0.1MPa·m^1/2And 10.9. + -. 0.1 MPa. m^1/2. The results show that the process method of the invention can improve the toughness of the hard alloy.

According to GB/T230.1-2018 part 1 of Rockwell hardness test of metal materials: test method "indentation test was performed using a diamond cone indenter (cone angle 120 °, top radius of curvature 0.2mm) with a test force of 980N. And detecting the appearance of the indentation by using a scanning electron microscope. The diamond coating samples of the common hard alloy substrate and the diamond coating samples prepared in the examples 1 and 2 are respectively detected by the method, and the indentation appearances are respectively shown in the figures 1, 2 and 3. It can be seen that the coating peeling area of the sample surface in fig. 1 is larger than that of the sample surface in fig. 2 and 3. The result shows that the coating adhesion strength of the surface of the low-cobalt-content graphene reinforced hard alloy matrix prepared by the method is higher than that of the common hard alloy with higher cobalt content.

Claims

1. a diamond coating, the coating is a matrix material deposition diamond film with cemented carbide;

It is characterized in that, by mass percentage, the raw material components of the cemented carbide include: 0.1-1% of graphene, 2-3% of cobalt, and 97.9-96% of tungsten carbide;

Wherein the diamond coating is prepared by the following method:

(1) Mix the dispersed graphene and cobalt powder with the tungsten carbide ball mill to obtain a slurry, vacuum dry, and sinter to form a cemented carbide substrate;

(2) Pretreating the above-mentioned substrate and depositing a diamond coating, the pretreatment is specifically: immersing the substrate in an alkaline solution for 10 min, cleaning, drying, and then immersing the alkaline-treated substrate in an acid solution to naturally Reaction for 10 s, washing, and drying; grinding with a mixed solution of diamond powder and glycerol, washing, and drying; the alkali solution is potassium ferricyanide: potassium hydroxide: water = 1 g: 1 g: 10 mL; acid The solution is hydrochloric acid: hydrogen peroxide = 1 mL: 4 mL;

The deposition is as follows: using the hot wire chemical vapor deposition method, the pretreated substrate is placed in the chemical vapor deposition equipment, and after the vacuum chamber pressure of the equipment reaches below 5Pa, the reaction working gas methane flow rate is 10~20 sccm, and the hydrogen gas flow is 10~20 sccm. The flow rate was 1000~2000 sccm, the reaction pressure was adjusted to 2000~4000 Pa, and the coating deposition time was 6~10 h.

2. a preparation method of the described diamond coating of claim 1, comprises:

(2) Pretreating the above-mentioned substrate and depositing a diamond coating.

3. preparation method according to claim 2, is characterized in that, the graphene dispersed in described step (1) is specially: adopt dehydrated alcohol to be dispersion solution, and the proportioning of dehydrated alcohol and graphene is 100 mL: (0.1~0.5) g, using the ultrasonic oscillation dispersion process, in which the ultrasonic frequency is 40KHz; the duty ratio of the ultrasonic working time is 1:1; the ultrasonic oscillation time is 4~6 h.

4. The preparation method according to claim 2, characterized in that, in the step (1), the specific process parameters of ball milling and mixing are: the grinding balls used are cemented carbide WC-3 wt.% Co balls with a diameter of 5 mm, and the ball mill The rotating speed of the ball is 300~500 rpm, and the ball milling time is 6~8 h.

5 . The preparation method according to claim 2 , wherein the vacuum drying in the step (1) is: during the drying process, the heating temperature is 90-100° C., and when there is no visible liquid in the slurry, the heating is stopped, 6 . Natural drying for 2~3h. During the whole drying process, keep the pressure in the vacuum chamber at 10000~15000 Pa.

6 . The preparation method according to claim 2 , wherein, in the step (1), the temperature of sintering and molding is 1380 ^° C, and the pressure is 40MPa. 7 .