CN114315354A

CN114315354A - Diamond-B4Two-step sintering method of C-SiC three-phase composite ceramic

Info

Publication number: CN114315354A
Application number: CN202111641915.7A
Authority: CN
Inventors: 王为民; 唐荣; 解晶晶; 何强龙; 邹冀
Original assignee: Wuhan University of Technology WUT
Current assignee: Wuhan University of Technology WUT
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-04-12
Anticipated expiration: 2041-12-29
Also published as: CN114315354B

Abstract

The invention relates to a diamond-B₄The two-step sintering method of the C-SiC three-phase composite ceramic comprises the steps of taking a mixture of diamond powder, Si powder and B powder as raw materials, carrying out in-situ sintering by adopting a two-step method in discharge plasma sintering, and heating the temperature to the highest temperature T at the speed of 100-200 ℃/min at the front sintering stage₁(ii) a Then, cooling for 5-15min from the highest temperature to T₂Thereby obtaining diamond-B₄C-SiC three-phase composite ceramic; wherein, T₁At 1550-1600 ℃ and T₂At 1500-1550 deg.C, T₁And T₂The difference of (A) is not less than 40 ℃. The invention replaces the traditional heat preservation stage with the stage of reducing the temperature to 1500-1550 ℃ at a constant speed, effectively prevents diamond graphitization, solves the problem of diamond graphitization at the temperature lower than the densification temperature of boron carbide, and effectively inhibits SiO in a sample₂The residue of the three-phase composite ceramic promotes the densification of a sample, improves the mechanical property, and the obtained three-phase composite ceramic has the characteristics of compact structure, good interface combination, no graphite residue, light weight, super hardness, high strength and high toughness.

Description

Diamond-B4Two-step sintering method of C-SiC three-phase composite ceramic

Technical Field

The invention relates to a three-phase composite ceramic, in particular to a diamond-B₄A two-step sintering method of C-SiC three-phase composite ceramic.

Background

B₄C due to its high hardness (third hard substance) and low density (2.52 g/cm)³) It is an excellent engineering structure material. Aiming at solving the problems of poor sintering capability (higher than 2000 ℃) and low fracture toughness (2-3 MPa.m)^1/2) And the like, and sintering at low temperature obtains dense B with high toughness₄The C block material is widely concerned, and is mainly at present in B₄The introduction of a second phase into the C matrix is effective to lower the sintering temperature or increase fracture toughness, but this in turn lowers B₄C inherent lightweight and high stiffness properties.

Diamond is the hardest engineering material and can be used as a reinforcing phase to improve B₄The properties of C thus do not increase weight and decrease hardness. However, the diamond covalent bond component is large and difficult to sinter and compact, while B₄The sintering condition of C is harsh, the minimum sintering temperature is more than 1700 ℃, and diamond is easy to graphitize (above 1600 ℃) under the conditions of high temperature and non-high pressure, so that B is used₄Directly mixing and sintering the ceramic C and the diamond powder to obtain the diamond/B with compact structure and no graphite residue₄C ceramics are difficult to achieve. B, Si active element is added to react with diamond in situ to generate B₄The C and the SiC can effectively absorb graphite generated by high-temperature sintering on the basis of enhancing the formability and the sinterability of the diamond micro powder.

CA112159231A discloses a super-hard light diamond-B₄Rapid preparation method of C-SiC ternary composite ceramic, and preparation of three-phase diamond-B₄In the case of C-SiC composite ceramics, in the samplePresence of SiO₂The glass phase affects the material properties, and when the sintering temperature is higher than 1550 ℃, a large amount of graphite residues around the diamond affect the interface bonding and thus the mechanical properties of the material.

Disclosure of Invention

The technical problem to be solved by the invention is to provide diamond-B₄A two-step sintering method of C-SiC three-phase composite ceramic. In the sintering process, firstly, the temperature is quickly raised to the sintering temperature T₁Then cooling to the sintering temperature T₂And completing the sintering densification process. In the present invention, when the sintering temperature T is reached₁(1550 ℃ to 1600 ℃) and then is reduced to T at a constant speed₂The process (1500-1550 ℃) replaces the traditional heat preservation stage, effectively prevents the graphitization of the diamond, solves the graphitization problem of the diamond at the temperature lower than the densification temperature of boron carbide, and effectively inhibits SiO in the sample₂The residual of the sample promotes the densification of the sample and improves the mechanical property of the sample.

The technical scheme adopted by the invention for solving the technical problems is as follows:

Diamond-B₄The two-step sintering method of the C-SiC three-phase composite ceramic comprises the following steps:

s1, mixing and ball-milling the diamond powder, the Si powder and the B powder uniformly, and drying to obtain mixed powder; wherein the diamond powder accounts for 30-50% of the total mass of the diamond powder, the Si powder and the B powder; the mass ratio of the Si powder to the B powder is 1-2;

s2, sieving the mixed powder, then loading the powder into a graphite die, pre-pressing, then placing the die into a discharge plasma sintering device, separating the inner wall of the graphite die, a pressure head and the powder by graphite paper, flushing argon gas in a high vacuum state (vacuum degree is less than 100Pa), axially pressurizing (pressure intensity is 50-100 MPa), applying pulse current, and performing 'two-step' multi-temperature-section in-situ reaction sintering: the sintering front section adopts higher temperature, the temperature is raised to the highest temperature section at a certain speed, then the temperature is lowered to a certain temperature section from the highest temperature through the temperature lowering process, and the required block sample is obtained after furnace cooling.

S3, removing the graphite paper on the surface of the block sample, and grinding and polishing the surface of the block sample to obtain the diamond-B₄C-SiC three-phase composite ceramic.

According to the scheme, in the step S1, diamond powder with the purity of more than 95% and the average particle size of 25-40 mu m, element B powder with the particle size of 1-3 mu m and element Si powder with the particle size of 1-3 mu m are selected.

According to the scheme, in the step S1, the ball milling time is 6-12 h, and the rotating speed is 100-200 r/min; the ball material ratio is 4-6, and the material of the grinding ball is SiC.

According to the scheme, in the step S1, the drying temperature is 70 ℃, the drying time is 12-24 hours, and after drying, the obtained mixed powder is screened by a 100-200-mesh sieve for granulation to obtain fully dried mixed powder; the drying equipment is an air-blast drying oven or a vacuum drying oven and the like.

According to the scheme, the step S2 of the two-step method multi-temperature-section in-situ reaction sintering comprises the following steps: the sintering front section adopts higher temperature, and the temperature is increased to the highest temperature T at the speed of 100-200 ℃/min₁(1550 ℃ C. to 1600 ℃ C.); then cooling for 5-15min from the highest temperature to a certain temperature stage T₂(1500 ℃ C. -1550 ℃ C.), wherein T₁And T₂The difference of (A) is not less than 40 ℃; the temperature reduction process is uniform temperature reduction, the temperature reduction rate is preferably set to be 5-7 ℃/min, the temperature reduction rate is inversely proportional to the temperature reduction time, and the liquid phase viscosity is reduced due to the excessively high temperature reduction rate, so that the reaction rate is reduced, the capillary is blocked, and the pore formation influence performance is reduced.

Compared with the prior art, the two-step sintering method of the diamond-B4C-SiC three-phase composite ceramic has the following beneficial effects:

1. compared with the traditional method, the method adopts a new sintering process of a two-step method, effectively promotes low-temperature densification, inhibits graphitization of diamond, and forms a large amount of liquid phase to accelerate diffusion of atoms by quickly heating to high temperature so as to greatly reduce oxygen content and play a role in promoting low-temperature densification; then the traditional heat preservation stage is replaced by the stage of reducing the temperature to 1500-1550 ℃ at a constant speed, thereby effectively preventing the graphitization of the diamond and ensuring that the diamond is densified at a temperature lower than the densification temperature of boron carbide (at the temperature lower than the densification temperature of boron carbide)On the premise of ensuring the realization of material densification) solves the problem of diamond graphitization; on the other hand, studies have shown that SiO₂The presence of (2) hinders the densification of the carbide ceramic to some extent, and the SiO that remains at the end₂The mechanical property of the material is reduced, and thermodynamic calculation shows that when the sintering temperature reaches 1550 ℃, the system has no SiO₂The two-step method provided by the invention adopts higher temperature (1550 ℃ -1650 ℃) in the early stage of sintering, and effectively inhibits SiO in the sample₂The residue promotes the densification of the sample and improves the mechanical property of the sample;

2. the invention provides a two-step method for preparing diamond-B by sintering₄Compared with the traditional method, the C-SiC composite ceramic has higher density and more excellent mechanical property, and the density is 2.8g/cm³Left and right; bending strength up to 502MPa, hardness up to 43.6GPa, and fracture toughness up to 7.07 MPa.m^1/2Much higher than the existing B₄C, composite ceramic; in addition, the diamond particles are well combined with the matrix interface, no graphite residue is left, the cutting and grinding performance is good, and the application prospect is wide.

Drawings

FIG. 1 is a view showing diamond-B prepared in examples 1 to 4 of the present invention₄XRD spectrogram of C-SiC three-phase composite ceramic:

a-Diamond-B prepared in example 1₄An XRD spectrogram of the C-SiC three-phase composite ceramic,

B-Diamond-B prepared in example 2₄An XRD spectrogram of the C-SiC three-phase composite ceramic,

c-Diamond prepared in example 3-_B4An XRD spectrogram of the C-SiC three-phase composite ceramic,

d-Diamond-B prepared in example 4₄XRD spectrogram of the C-SiC three-phase composite ceramic;

FIG. 2 shows diamond-B prepared in example 1 of the present invention₄SEM picture of C-SiC three-phase composite ceramic;

FIG. 3 shows diamond-B prepared according to example 2 of the present invention₄SEM picture of C-SiC three-phase composite ceramic;

FIG. 4 is a graph of a copolymer prepared in example 3 of the present inventionDiamond-B₄SEM picture of C-SiC three-phase composite ceramic;

FIG. 5 shows diamond-B prepared in example 4 of the present invention₄SEM picture of C-SiC three-phase composite ceramic;

FIG. 6 shows diamond-B prepared according to example 1 of the present invention₄EPMA diagram of C-SiC three-phase composite ceramic;

FIG. 7 shows diamond-B prepared according to example 2 of the present invention₄EPMA diagram of C-SiC three-phase composite ceramic.

Detailed Description

In order to better understand the present invention, the following examples are further provided to illustrate the content of the present invention, but the present invention is not limited to the following examples.

Example 1 (comparative example)

Diamond-B₄The preparation method of the C-SiC three-phase composite ceramic comprises the following steps:

(1) weighing 40% of diamond powder, 30% of Si powder and 30% of B powder according to the mass percentage, wherein the particle size of the diamond powder is 40 micrometers, the particle size of the B powder is 1 micrometer, the particle size of the Si powder is 1 micrometer, a grinding ball is SiC, the ball-to-material ratio is 5, dispersing by using absolute ethyl alcohol, drying by a rotary evaporation device after ball milling for 6 hours, and drying the dried mixed powder (namely the diamond-Si-B ternary mixed powder) in a vacuum drying oven for 24 hours.

(2) Dispersing the diamond-Si-B ternary mixed powder through a 100-mesh sieve to prevent hard agglomeration of the powder, weighing the powder and filling the powder

In the graphite mold, the inner wall of the graphite mold, the pressure head and the powder are separated by graphite paper, and the graphite mold is wrapped by graphite felt.

(3) Placing the graphite mould into a discharge plasma sintering device, pumping air until the vacuum degree is less than 100Pa, then flushing argon, axially loading the pressure to 75MPa, then applying pulse current, carrying out in-situ reaction sintering, heating to the maximum temperature of 1550 ℃ at the heating rate of 100 ℃/min, preserving heat for 10min to complete the sintering process, and cooling along with the furnace; removing graphite paper on the surface of the sample, cutting, grinding and polishing to obtainDiamond-B₄C-SiC three-phase composite ceramic.

Diamond-B obtained in this example₄The phase components of the C-SiC three-phase composite ceramic are mainly diamond and B by XRD detection₄C. SiC, Si residue exists, and a graphite peak (see a spectral line a in figure 1) does not appear in a map because the content of graphite is less and the graphite is in an amorphous state; SEM analysis shows that the diamond particles are uniformly distributed in B₄In C-SiC ceramics, pores exist in a matrix, the matrix is not completely compact, graphite residues appear around diamond (see figure 2), and EPMA shows that the content of silicon dioxide is high, and the mechanical property is greatly influenced (see figure 6).

Diamond-B obtained in this example₄The density of the C-SiC three-phase composite ceramic is 2.77g/cm³(ii) a The hardness is 36.4 GPa; the bending strength is 410 MPa; the fracture toughness is 5.52 MPa.m^1/2。

Example 2

(2) Dispersing the diamond-Si-B three-phase mixed powder through a 100-mesh sieve to prevent hard agglomeration of the powder, weighing the powder and filling the powder

(3) Placing the graphite mold into a discharge plasma sintering device, pumping air until the vacuum degree is less than 100Pa, then flushing argon, axially loading the pressure to 75MPa, then applying pulse current, carrying out in-situ reaction sintering, heating to the temperature at the heating rate of 100 ℃/minAfter the maximum temperature is 1600 ℃, the temperature is reduced at a constant speed for 10min to 1550 ℃, the sintering process is completed, and furnace cooling is carried out. Removing graphite paper on the surface of the sample, cutting, grinding and polishing to obtain diamond-B₄C-SiC three-phase composite ceramic.

Diamond-B obtained in this example₄The phase components of the C-SiC three-phase composite ceramic are mainly diamond and B by XRD detection₄C. SiC, no obvious change compared with example 1, no graphite peak (see line b in figure 1); SEM analysis shows that the diamond particles are uniformly distributed in B₄Among C-SiC ceramics, the density of a ceramic matrix is obviously improved compared with that of the ceramic matrix in the embodiment 1 (comparative example), and no graphite residue exists (see attached figure 3), mainly because the temperature is improved, the liquid phase viscosity is reduced, the inter-particle sliding resistance is reduced, and the densification process is promoted; EPMA shows that the silicon dioxide content is lower and the oxygen-scavenging effect is evident (see FIG. 7) compared to example 1 (comparative), mainly because of the SiO after temperature increase₂Is discharged in gaseous form. The diamond-B₄The density of the C-SiC three-phase composite ceramic is 2.82g/cm³(ii) a The hardness is 43.6 GPa; bending strength of 502MPa and fracture toughness of 7.07 MPa-m^1/2The mechanical properties are greatly increased compared with those of the comparative examples.

Example 3

(1) weighing 55% of diamond powder, 30% of Si powder and 15% of B powder according to mass percentage, wherein the particle size of the diamond powder is 25 micrometers, the particle size of the B powder is 3 micrometers, the particle size of the Si powder is 3 micrometers, a grinding ball is SiC, the ball-to-material ratio is 4, dispersing by using absolute ethyl alcohol, drying by a rotary evaporation device after ball milling for 12 hours, and drying the dried mixed powder (namely the diamond-Si-B ternary mixed powder) in a vacuum drying oven for 12 hours.

In the graphite mould, graphite is adopted among the inner wall of the graphite mould, the pressure head and the powderThe paper is separated, and the graphite mold is wrapped by graphite felt.

(3) Placing the graphite mold into a discharge plasma sintering device, pumping air until the vacuum degree is less than 100Pa, then flushing argon, axially loading the pressure to 100MPa, then applying pulse current, carrying out in-situ reaction sintering, heating to 1575 ℃ at the maximum temperature at the heating rate of 200 ℃/min, then cooling at constant speed for 10min to 1525 ℃, completing the sintering process, and cooling along with the furnace. Removing graphite paper on the surface of the sample, cutting, grinding and polishing to obtain diamond-B₄C-SiC three-phase composite ceramic.

Diamond-B obtained in this example₄The phase components of the C-SiC three-phase composite ceramic are mainly diamond and B by XRD detection₄C. SiC, with a small amount of Si residues, (see line c of fig. 1); SEM analysis shows that the diamond particles are well combined with the matrix, no obvious holes are formed, and no graphite residue is left (see figure 4); the diamond-B₄The density of the C-SiC three-phase composite ceramic is 2.80g/cm³(ii) a The hardness is 40 GPa; the bending strength is 474 MPa; the fracture toughness is 7.02 MPa.m^1/2。

Example 4

(1) weighing 45% of diamond powder, 27.5% of Si powder and 27.5% of B powder according to the mass percentage, wherein the particle size of the diamond powder is 30 micrometers, the particle size of the B powder is 2 micrometers, the particle size of the Si powder is 2 micrometers, a grinding ball is SiC, the ball-to-material ratio is 6, dispersing by using absolute ethyl alcohol, drying by a rotary evaporation device after ball milling for 8 hours, and putting the dried mixed powder (namely the diamond-Si-B ternary mixed powder) into a vacuum drying box for drying for 18 hours.

(3) Placing the graphite mold into a discharge plasma furnaceIn the sintering device, air is pumped until the vacuum degree is less than 100Pa, argon gas is injected, the axial loading pressure is 50MPa, then pulse current is applied, in-situ reaction sintering is carried out, after the temperature is heated to the maximum temperature of 1600 ℃ at the heating rate of 200 ℃/min, the temperature is reduced at a constant speed for 15min to 1500 ℃, furnace cooling is carried out, and the sintering process is completed. Removing graphite paper on the surface of the sample, cutting, grinding and polishing to obtain diamond-B₄C-SiC three-phase composite ceramic.

Diamond-B obtained in this example₄The phase components of the C-SiC three-phase composite ceramic are mainly diamond and B by XRD detection₄C. SiC, (see line d in fig. 1); SEM analysis shows that the diamond particles are well combined with the matrix, the matrix is compact, no obvious holes exist, and no graphite residue exists (see figure 5); the diamond-B₄The density of the C-SiC three-phase composite ceramic is 2.80g/cm³(ii) a The hardness is 41.8 GPa; the bending strength is 461 MPa; the fracture toughness is 7.00 MPa.m^1/2。

In summary, the diamond-B prepared in examples 2 to 4 above₄The density of the C-SiC three-phase composite ceramic is 2.80-2.82 g/cm³(ii) a The hardness is 40-43.6 GPa; the bending strength is 461-502 MPa; the fracture toughness is 7.00-7.07 MPa m^1/2Both are improved over the comparative example (example 1); meanwhile, the diamond particles are uniformly distributed in the B₄The combination of diamond particles and a matrix among C-SiC ceramics is good, the density of the ceramic matrix is obviously improved compared with that of a comparative example, and the ceramic matrix has no obvious holes and no graphite residue.

While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. Diamond-B₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized in that diamond powder, Si powder and B powder are usedThe mixture is used as a raw material, the discharge plasma sintering adopts a two-step method to carry out in-situ sintering, and the temperature is raised to the highest temperature T at the speed of 100-200 ℃/min in the front sintering section₁(ii) a Then, cooling for 5-15min from the highest temperature to T₂Thereby obtaining diamond-B₄C-SiC three-phase composite ceramic; wherein, T₁At 1550-1600 ℃ and T₂At 1500-1550 deg.C, T₁And T₂The difference of (A) is not less than 40 ℃.

2. Diamond-B₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized by comprising the following steps of:

s2, sieving the mixed powder, filling the sieved mixed powder into a mold, putting the mold into a discharge plasma sintering device, flushing protective atmosphere and axially pressurizing the mold in a high vacuum state, applying pulse current to perform in-situ reaction sintering, and heating the sintering front section to the highest temperature T at the speed of 100-200 ℃/min₁(ii) a Then, cooling for 5-15min from the highest temperature to T₂Cooling along with the furnace to obtain the diamond-B4C-SiC ternary composite ceramic; wherein, T₁At 1550-1600 ℃ and T₂At 1500-1550 deg.C, T₁And T₂The difference of (A) is not less than 40 ℃.

3. A diamond-B according to claim 2₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized in that the average grain diameter of diamond powder is 25-40 mu m, and the average grain diameters of B powder and Si powder are both 1-3 mu m; the purities of the diamond powder, the Si powder and the B powder are all more than 95%.

4. Diamond-B according to claim 2₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized in that in step S1The ball milling time is 6-12 h, and the rotating speed is 100-200 r/min; the ball material ratio is 4-6, and the material of the grinding ball is SiC.

5. Diamond-B according to claim 2₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized in that in the step S1, the drying temperature is 70 ℃, the drying time is 12-24 hours, and after drying, the obtained mixed powder is screened by a 100-200-mesh sieve for granulation to obtain fully dried mixed powder.

6. Diamond-B according to claim 2₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized in that mixed powder in the step S2 is screened and then placed into a graphite mold, the mold is placed into a discharge plasma sintering device after prepressing, the inner wall of the graphite mold, a pressure head and the powder are separated by graphite paper, argon is filled in the discharge plasma sintering device under the high vacuum state that the vacuum degree is less than 100Pa, axial pressurization with the pressure intensity of 50-100 MPa is carried out, and pulse current is applied to carry out in-situ reaction sintering.

7. Diamond-B according to claim 2₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized in that the cooling process in the step S2 is constant-speed cooling.

8. Diamond-B according to claim 2₄The two-step sintering method of the C-SiC three-phase composite ceramic is characterized in that the furnace cooling in the step S2 further comprises a post-treatment process, which specifically comprises the following steps: and removing the graphite paper on the surface of the block sample, and grinding and polishing the surface of the block sample.