CN108046808B - A kind of Si3N4 gradient material and preparation method thereof - Google Patents

Abstract

The invention provides Si₃N₄The preparation method of the gradient material comprises the following steps: a) providing mixed powder A and mixed powder B; the mixed powder A comprises Si powder and TiO powder₂Powder and sintering aid, wherein the sintering aid is prepared from Al with the molar ratio of less than or equal to 1₂O₃And Re₂O₃Composition is carried out; the mixed powder B comprises Si and TiO₂And a sintering aid, wherein the sintering aid is prepared from Al with a molar ratio of more than 1₂O₃And Re₂O₃Composition is carried out; the Re is selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu; b) alternately laying the mixed powder A and the mixed powder B to form a multilayer structure, and performing compression molding to obtain a blank; c) nitriding and sintering the blank obtained in the step b) to obtain Si₃N₄A gradient material. The invention controls Al in the sintering aid₂O₃And Re₂O₃Proportioning, controlling β -silicon nitride/α -silicon nitride in nitriding stage to obtain Si₃N₄The gradient material has strong binding force between gradient layers and excellent mechanical properties of hard surface and hard core.

Description

A kind of Si3N4 gradient material and preparation method thereof

technical field

The invention relates to the technical field of Si ₃ N ₄ ceramic materials, and more particularly, to a Si ₃ N ₄ gradient material and a preparation method thereof.

Background technique

As a structural material, Si ₃ N ₄ ceramic material has excellent mechanical properties, such as high hardness, high strength, wear resistance, high temperature resistance and other excellent properties, and can be widely used in bearings, high-speed cutting tools, armor, etc.; Under harsh conditions such as high temperature and high-speed cutting, it is still easy to wear and has a limited life. Therefore, it is necessary to further strengthen the surface to enhance its reliability. For Si ₃ N ₄ ceramic materials, gradient materials can usually be prepared or PVD and CVD technology can be used for their performance. make further improvements.

For PVD and CVD technology, there is often a defect that the coating is too thin and the protective effect is not good; in addition, PVD and CVD technology also has the problem of insufficient bonding force between the substrate and the coating, while the use of PVD and CVD technology for non-conductive materials When it is necessary to cover the surface of the material with a conductive layer, and then carry out coating treatment, there is a problem of insufficient bonding force between the substrate and the conductive layer. Therefore, for Si ₃ N ₄ ceramic materials, more gradient materials are used to further improve their properties.

At present, the preparation of Si ₃ N ₄ gradient materials is mainly by sintering the raw materials and even the materials with very different compositions into one, so that the surface layer and hardness have different properties; however, due to the difference in composition and structure between the surface layer and the core material , which makes the bonding force between the two weak, and some even have the separation of the surface layer and the core during the sintering process, which greatly weakens the application of Si ₃ N ₄ gradient materials.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a Si ₃ N ₄ gradient material and a preparation method thereof. The Si ₃ N ₄ gradient material obtained by the preparation method provided by the present invention has extremely strong binding force and improved mechanical properties .

The invention provides a preparation method of Si ₃ N ₄ gradient material, comprising the following steps:

a) Provide mixed powder A and mixed powder B;

The mixed powder A includes Si powder, TiO ₂ powder and a sintering aid, wherein the sintering aid is composed of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio of less than or equal to 1; the mixed powder B includes Si, TiO ₂ and a sintering aid, wherein the sintering aid is composed of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio greater than 1;

The Re is selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu;

b) alternately laying the mixed powder A and the mixed powder B to form a multi-layer structure, and pressing and molding to obtain a green body;

c) Nitriding and sintering the green body obtained in step b) to obtain a Si ₃ N ₄ gradient material.

Preferably, in step a), the purity of the Si powder is greater than or equal to 95%, and the particle size is less than or equal to 100 μm; the purity of the TiO ₂ powder is greater than or equal to 98%, and the particle size is less than or equal to 10 μm.

Preferably, the mass fraction ratio of Si powder and TiO ₂ powder in the mixed powder A in step a) is (60%-99%): (1%-40%), and the ratio of Si ₃ N ₄ to sintering aid is The molar ratio is (80%～95%): (5%～20%);

The mass fraction ratio of Si powder and _TiO2 powder in the mixed powder B is (60%～99%): (1%～40%), and the molar ratio _of Si3N4 and sintering aid is (80%～ ₄₀ %) 95%): (5%～20%).

Preferably, the sintering aid in the mixed powder A in step a) is composed of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio of 1:1;

The sintering aid in the mixed powder B is composed of Al ₂ O ₃ and Re ₂ O ₃ in a molar ratio of (2-3):1.

Preferably, the multi-layer structure in step b) is a three-layer structure; the three-layer structure is composed of the arrangement of mixed powder B-mixed powder A-mixed powder B.

Preferably, the pressing method in step b) is cold isostatic pressing; the pressure of the cold isostatic pressing is 100 MPa to 300 MPa, and the time is 1 min to 10 min.

Preferably, the nitriding temperature in step c) is 1250°C to 1600°C, and the time is 0.5h to 24h.

Preferably, the sintering method in step c) is pressureless sintering, gas pressure sintering at 10 MPa to 50 MPa, or SPS sintering at 10 MPa to 50 MPa.

Preferably, the sintering temperature in step c) is 1600°C to 2000°C, and the time is 0.5h to 24h.

The present invention also provides a Si ₃ N ₄ gradient material, which is prepared by the preparation method described in the above technical solution.

The present invention provides a preparation method of Si ₃ N ₄ gradient material, comprising the following steps: a) providing mixed powder A and mixed powder B; the mixed powder A includes Si powder, TiO ₂ powder and sintering aid , wherein the sintering aid consists of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio of less than or equal to 1; the mixed powder B includes Si, TiO ₂ and a sintering aid, wherein the sintering aid consists of a molar ratio greater than 1 composed of Al ₂ O ₃ and Re ₂ O ₃ ; the Re is selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu b) alternately laying the mixed powder body A and the mixed powder body B to form a multi-layer structure, and pressing and molding to obtain a green body; c) nitriding and sintering the green body obtained in step b) to obtain Si ₃ N ₄ Gradient material. Compared with the prior art, the present invention realizes the preparation of Si ₃ N ₄ gradient material through phase transformation, and specifically by controlling the ratio of Al ₂ O ₃ and Re ₂ O ₃ in the sintering aid, β-nitrogen is realized in the nitriding stage. With the control of silicon oxide/α-silicon nitride, the obtained gradient layer has strong binding force, so that the obtained Si ₃ N ₄ gradient material has extremely strong binding force and improved mechanical properties.

In addition, the preparation method provided by the present invention can control the thickness of the gradient layer according to requirements; the process is simple and the cost is low.

Description of drawings

Fig. 1 is the XRD pattern of the surface layer of the material after nitridation in Example 1 of the present invention;

Fig. 2 is the XRD pattern of the inner intermediate layer of the material after nitridation in Example 1 of the present invention;

FIG. 3 is a cross-sectional SEM photo of the surface layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention;

Fig. 4 is the SEM photograph of the polished corrosion surface of the surface layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention;

5 is a cross-sectional SEM photograph of the inner intermediate layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention;

FIG. 6 is a SEM photograph of the polished and corroded surface of the inner intermediate layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The invention provides a preparation method of Si ₃ N ₄ gradient material, comprising the following steps:

a) Provide mixed powder A and mixed powder B;

The mixed powder A includes Si powder, TiO ₂ powder and a sintering aid, wherein the sintering aid is composed of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio of less than or equal to 1; the mixed powder B includes Si, TiO ₂ and a sintering aid, wherein the sintering aid is composed of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio greater than 1;

The Re is selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu;

b) alternately laying the mixed powder A and the mixed powder B to form a multi-layer structure, and pressing and molding to obtain a green body;

c) Nitriding and sintering the green body obtained in step b) to obtain a Si ₃ N ₄ gradient material.

The present invention first provides mixed powder A and mixed powder B. In the present invention, the mixed powder A includes Si powder, TiO ₂ powder and a sintering aid, wherein the sintering aid is composed of Al 2 O 3 and Re 2 O 3 with a molar ratio of less than or equal to 1, preferably a molar ratio of Al ₂ O ₃ and Re ₂ O ₃ It is composed of Al ₂ O ₃ and Re ₂ O ₃ in a ratio of 1:1; the mixed powder B includes Si, TiO ₂ and a sintering aid, wherein the sintering aid consists of Al ₂ O ₃ and Re ₂ with a molar ratio greater than 1 The composition of O ₃ is preferably composed of Al ₂ O ₃ and Re ₂ O ₃ in a molar ratio of (2-3):1.

In the present invention, the purity of the Si powder is preferably greater than or equal to 95%, more preferably 95% to 100%; the particle size of the Si powder is preferably less than or equal to 100 μm, more preferably <100 μm. In the present invention, the purity of the TiO ₂ powder is preferably greater than or equal to 98%, more preferably 98%-100%; the particle size of the TiO ₂ powder is preferably less than or equal to 10 μm, more preferably <10 μm. In the present invention, there is no special restriction on the sources of the Si powder and TiO ₂ powder, and commercially available products well known to those skilled in the art can be used.

In the present invention, the mass fraction ratio of Si powder and TiO ₂ powder in the mixed powder A is preferably (60%-99%): (1%-40%), more preferably (85%-95%) : (5% to 15%). In the present invention, the mass fraction ratio of Si powder and TiO ₂ powder in the mixed powder B is preferably (60%-99%): (1%-40%), more preferably (85%-95%) : (5% to 15%). In a preferred embodiment of the present invention, the mass fraction ratio of Si powder and TiO ₂ powder in the mixed powder A and the mixed powder B is the same.

In the present invention, the sintering aid is composed of Al ₂ O ₃ and Re ₂ O ₃ ; wherein, the Re is selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb , Dy, Ho, Er, Tm, Yb or Lu, preferably Y, La, Yb or Lu. In the present invention, there is no special limitation on the source of the sintering aid, which is obtained by mixing commercially available Re ₂ O ₃ powder and Al ₂ O ₃ powder well known to those skilled in the art. In the present invention, the purity of the Re ₂ O ₃ powder is preferably greater than or equal to 99.9%; the purity of the Al ₂ O ₃ powder is preferably greater than or equal to 95%, more preferably 95% to 100%.

In the present invention, the molar ratio of Si ₃ N ₄ and sintering aid in the mixed powder A is preferably (80%-95%): (5%-20%), more preferably (90%-93%) ): (7%～10%). In the present invention, the molar ratio of Si ₃ N ₄ and sintering aid in the mixed powder B is preferably (80%-95%): (5%-20%), more preferably (90%-93%) ): (7%～10%). In a preferred embodiment of the present invention, the molar ratio of Si ₃ N ₄ and sintering aid in the mixed powder A and the mixed powder B is the same. In the present invention, Si ₃ N ₄ is calculated based on the complete nitridation of Si powder.

In the present invention, both the mixed powder A and the mixed powder B belong to the Si-TiO ₂ -Al ₂ O ₃ -Re ₂ O ₃ mixed powder. In the present invention, the preparation process of the Si-TiO ₂ -Al ₂ O ₃ -Re ₂ O ₃ mixed powder is preferably as follows:

The Si powder, TiO ₂ powder and sintering aid are mixed with ethanol as the solvent and Si ₃ N ₄ balls as the ball milling medium, mixed on a planetary ball mill for 6h to 10h, and dried to obtain Si-TiO ₂ -Al ₂ O ₃ -Re ₂ O ₃ mixed powder. According to the different molar ratios of Al ₂ O ₃ and Re ₂ O ₃ in the sintering aid, mixed powder A and mixed powder B are obtained respectively; wherein, in the mixed powder A, the molar ratio of the sintering aid is less than or equal to 1 It is composed of Al ₂ O ₃ and Re ₂ O ₃ , preferably composed of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio of 1:1; in the mixed powder B, the sintering aid is composed of Al with a molar ratio greater than 1 It is composed of ₂ O ₃ and Re ₂ O ₃ , preferably Al ₂ O ₃ and Re ₂ O ₃ in a molar ratio of (2-3):1.

After the mixed powder A and the mixed powder B are obtained, the present invention lays the mixed powder A and the mixed powder B alternately to form a multi-layer structure, and then press-molded to obtain a green body. In the present invention, the alternate laying method preferably adopts the method known to those skilled in the art to sequentially lay mixed powder A-mixed powder B-mixed powder A in the forming mold, and so on; or sequentially laying mixed powder A in the forming mold Lay mixed powder B-mixed powder A-mixed powder B, and so on.

In the present invention, the multi-layer structure is preferably a three-layer structure; the three-layer structure is preferably composed of an arrangement of mixed powder B-mixed powder A-mixed powder B.

In the present invention, the press forming method is preferably cold isostatic pressing; the pressure of the cold isostatic pressing is preferably 100MPa-300MPa, more preferably 200MPa; the time of the cold isostatic pressing is preferably 1 min to 10 min, more preferably 5 min.

After the green body is obtained, in the present invention, the obtained green body is nitrided and then sintered to obtain a Si ₃ N ₄ gradient material. The present invention does not have a special limitation on the nitriding method, and the technical solution of carrying out the reaction in nitrogen gas well known to those skilled in the art can be adopted. In the present invention, the nitriding temperature is preferably 1250°C-1600°C, more preferably 1300°C-1450°C; the nitriding time is preferably 0.5h-24h, more preferably 2h-4h. The invention realizes the control of β-silicon nitride/α-silicon nitride in the nitriding stage by controlling the ratio of Al ₂ O ₃ and Re ₂ O ₃ in Al ₂ O ₃ -Re ₂ O ₃ , When it is β-silicon nitride, equiaxed silicon nitride is obtained by sintering; when α-silicon nitride and β-silicon nitride coexist in two phases after nitridation, sintering obtains long columnar silicon nitride.

In the present invention, the sintering method is preferably pressureless sintering, pressure sintering at 10 MPa to 50 MPa, or SPS sintering at 10 MPa to 50 MPa, more preferably pressureless sintering, pressure sintering at 10 MPa, pressure sintering at 30 MPa, and pressure at 50 MPa Sintering or 50MPa SPS sintering. In the present invention, the sintering is preferably carried out in a nitrogen atmosphere, and the pressure of the nitrogen is preferably 0.5 atm to 1.5 atm, more preferably 1 atm.

In the present invention, the sintering temperature is preferably 1600°C-2000°C, more preferably 1600°C-1900°C; the sintering time is preferably 0.5h-24h, more preferably 2h-4h.

The present invention also provides a Si ₃ N ₄ gradient material, which is prepared by the preparation method described in the above technical solution. The gradient layer in the Si ₃ N ₄ gradient material provided by the present invention has strong binding force, and the thickness of the gradient layer can be controlled according to requirements. At the same time, the mechanical properties of the Si ₃ N ₄ gradient material are improved, the relative density is greater than 98%, the hardness is 19GPa-25GPa, the fracture toughness is 12MPa·m ^1/2 ～14MPa·m ^1/2 , and the flexural strength is 1200MPa ~1400MPa.

The present invention provides a preparation method of Si ₃ N ₄ gradient material, comprising the following steps: a) providing mixed powder A and mixed powder B; the mixed powder A includes Si powder, TiO ₂ powder and sintering aid , wherein the sintering aid consists of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio of less than or equal to 1; the mixed powder B includes Si, TiO ₂ and a sintering aid, wherein the sintering aid consists of a molar ratio greater than 1 composed of Al ₂ O ₃ and Re ₂ O ₃ ; the Re is selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu b) alternately laying the mixed powder body A and the mixed powder body B to form a multi-layer structure, and pressing and molding to obtain a green body; c) nitriding and sintering the green body obtained in step b) to obtain Si ₃ N ₄ Gradient material. Compared with the prior art, the present invention realizes the preparation of Si ₃ N ₄ gradient material through phase transformation, and specifically by controlling the ratio of Al ₂ O ₃ and Re ₂ O ₃ in the sintering aid, β-nitrogen is realized in the nitriding stage. With the control of silicon oxide/α-silicon nitride, the obtained gradient layer has strong binding force, so that the obtained Si ₃ N ₄ gradient material has extremely strong binding force and improved mechanical properties.

In addition, the preparation method provided by the present invention can control the thickness of the gradient layer according to requirements; the process is simple and the cost is low.

In order to further illustrate the present invention, the following examples are used for detailed description. The Y ₂ O ₃ powder, Yb ₂ O ₃ powder, Gd ₂ O ₃ powder, La ₂ O ₃ powder and Lu ₂ O ₃ powder used in the following examples of the present invention are all provided by Beijing Fandechen Technology Co., Ltd. The raw materials are all commercially available products; among them, the purity of Y ₂ O ₃ powder, Yb ₂ O ₃ powder, Gd ₂ O ₃ powder, La ₂ O ₃ powder and Lu ₂ O ₃ powder are all 99.9%, Al ₂ O ₃ powder The purity of TiO2 powder is 95%~100%, the purity of Si powder is 95%~100%, the particle size is <100μm, the purity of _TiO2 powder is 98%~100%, and the particle size is <10μm.

Example 1

(1) The formula of mixed powder A: the mass fraction ratio of Si:TiO ₂ is 95%:5%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 93%: 7% of the ingredients, wherein Si ₃ N ₄ Calculated according to the complete nitridation of Si powder; the sintering aid is composed of Al ₂ O ₃ and Y ₂ O ₃ with a molar ratio of 1:1;

Mixed powder B formula: the mass fraction ratio of Si:TiO ₂ is 95%: 5%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 93%: 7 _{% .} Complete nitriding is calculated; the sintering aid consists of Al ₂ O ₃ and Y ₂ O ₃ in a molar ratio of 2.5:1;

Using Si powder and TiO ₂ powder as raw materials, using Al ₂ O ₃ powder and Y ₂ O ₃ powder as sintering aids, respectively according to the above formula, the Si powder, TiO ₂ powder and sintering aid are prepared, and ethanol is used as a solvent, Si ₃ N ₄ balls were used as the ball milling medium, mixed on a planetary ball mill for 8 hours, and dried to obtain a Si-TiO ₂ -Al ₂ O ₃ -Y ₂ O ₃ mixed powder.

(2) The Si-TiO ₂ -Al ₂ O ₃ -Y ₂ O ₃ mixed powder obtained in step (1) is formed into a three-layer structure according to the arrangement of mixed powder B-mixed powder A-mixed powder B. Cold isostatic pressing at 200MPa for 300s to obtain a green body.

(3) Nitriding the green body obtained in step (2) at 1400° C. for 2 hours, and then performing pressureless sintering, the sintering atmosphere is 1 atm nitrogen, and maintaining the temperature at 1800° C. for 2 hours to obtain a Si ₃ N ₄ gradient material.

XRD analysis was performed on the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention, and the results are shown in FIGS. 1 to 2 ; wherein, FIG. 1 is the XRD pattern of the surface layer of the material after nitridation in Example 1 of the present invention, and FIG. 2 This is the XRD pattern of the inner intermediate layer of the material after nitridation in Example 1 of the present invention. It can be seen from Figures 1 to 2 that when the molar ratio of Al ₂ O ₃ : Y ₂ O ₃ is greater than 1, single-phase β-silicon nitride is obtained, and when the molar ratio of Al ₂ O ₃ : Y ₂ O ₃ is not greater than 1, the Two-phase coexistence of α-silicon nitride and β-silicon nitride.

Scanning electron microscope analysis was performed on the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention, and the results are shown in FIGS. 3 to 6 ; wherein, FIG. 3 is the surface layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention. SEM photo of the cross section, FIG. 4 is the SEM photo of the polished corrosion surface of the surface layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention, and FIG. 5 is the inner intermediate layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention Figure 6 is the SEM photo of the polished and corroded surface of the inner intermediate layer of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention. It can be seen from Figures 3-4 that since the surface layer of the Si ₃ N ₄ gradient material prepared in Example 1 only has single-phase β-silicon nitride, the morphology after sintering is all equiaxed crystals; it can be seen from Figures 5-6 , because the inner intermediate layer of the Si ₃ N ₄ gradient material prepared in Example 1 is α-silicon nitride and β-silicon nitride with two phases coexisting, so long columnar crystals with self-toughening are obtained after sintering.

In the above characterization process, the method of obtaining the cross section is: use a universal testing machine to test the strength of the bending sample, and after the universal testing machine breaks the sample, carry out SEM analysis on the surface section of the sample; the specific process of polishing corrosion is: the sample is removed from the middle. After incision, after polishing the middle layer, plasma etching equipment was used, and the power of 28W was used to corrode for 80s. After corrosion, the surface of the sample was analyzed by SEM.

After testing, the relative density of the Si ₃ N ₄ gradient material prepared in Example 1 of the present invention is 99%, the hardness is 19 GPa, the fracture toughness is 12 MPa·m ^1/2 , and the flexural strength is 1200 MPa.

Example 2

(1) The formula of mixed powder A: the mass fraction ratio of Si:TiO ₂ is 90%: 10%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10% ingredients, wherein, Si ₃ N ₄ Calculated according to the complete nitridation of Si powder; the sintering aid is composed of Al ₂ O ₃ and Yb ₂ O ₃ with a molar ratio of 1:1;

Mixed powder B formula: the mass fraction ratio of Si:TiO ₂ is 90%: 10%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10 _{% .} Complete nitriding is calculated; the sintering aid consists of Al ₂ O ₃ and Yb ₂ O ₃ in a molar ratio of 3:1;

Using Si powder and TiO ₂ powder as raw materials, using Al ₂ O ₃ powder and Yb ₂ O ₃ powder as sintering aids, respectively according to the above formula, the Si powder, TiO ₂ powder and sintering aid are prepared, and ethanol is used as a solvent, Si ₃ N ₄ balls were used as ball milling media, mixed on a planetary ball mill for 8 hours, and dried to obtain Si-TiO ₂ -Al ₂ O ₃ -Yb ₂ O ₃ mixed powder.

(2) The Si-TiO ₂ -Al ₂ O ₃ -Yb ₂ O ₃ mixed powder obtained in step (1) is formed into a three-layer structure according to the arrangement of mixed powder B-mixed powder A-mixed powder B. Cold isostatic pressing at 200MPa for 300s to obtain a green body.

(3) Nitriding the green body obtained in step (2) at 1375°C for 4h, and then performing gas pressure sintering at 10MPa, the sintering atmosphere is 1 atm nitrogen, and maintaining the temperature at 1900°C for 4h to obtain a Si ₃ N ₄ gradient material.

After testing, the relative density of the Si ₃ N ₄ gradient material prepared in Example 2 of the present invention is 99%, the hardness is 23GPa, the fracture toughness is 14MPa·m ^1/2 , and the flexural strength is 1400MPa.

Example 3

(1) The formula of mixed powder A: the mass fraction ratio of Si:TiO ₂ is 85%: 15%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10% of ingredients, in which, Si ₃ N ₄ Calculated according to the complete nitridation of Si powder; the sintering aid is composed of Al ₂ O ₃ and Yb ₂ O ₃ with a molar ratio of 1:1;

Mixed powder B formula: the mass fraction ratio of Si:TiO ₂ is 85%: 15%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10 _{% .} Complete nitriding is calculated; the sintering aid consists of Al ₂ O ₃ and Yb ₂ O ₃ in a molar ratio of 3:1;

Using Si powder and TiO ₂ powder as raw materials, and Al ₂ O ₃ powder Yb ₂ O ₃ powder as sintering aid, the Si powder, TiO ₂ powder and sintering aid were separately prepared according to the above formula, and ethanol was used as a solvent. Si ₃ N ₄ balls are ball milling media, mixed on a planetary ball mill for 8 hours, and dried to obtain Si-TiO ₂ -Al ₂ O ₃ -Yb ₂ O ₃ mixed powder.

(2) The Si-TiO ₂ -Al ₂ O ₃ -Yb ₂ O ₃ mixed powder obtained in step (1) is formed into a three-layer structure according to the arrangement of mixed powder B-mixed powder A-mixed powder B. Cold isostatic pressing at 200MPa for 300s to obtain a green body.

(3) Nitriding the green body obtained in step (2) at 1375°C for 4h, and then sintering at 50MPa with SPS, the sintering atmosphere is 1 atm nitrogen, and keeping at 1700°C for 4h to obtain a Si ₃ N ₄ gradient material.

After testing, the relative density of the Si ₃ N ₄ gradient material prepared in Example 3 of the present invention is 99%, the hardness is 25GPa, the fracture toughness is 14MPa·m ^1/2 , and the flexural strength is 1400MPa.

Example 4

(1) The formula of mixed powder A: the mass fraction ratio of Si:TiO ₂ is 90%: 10%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10% ingredients, wherein, Si ₃ N ₄ Calculated according to the complete nitridation of Si powder; the sintering aid is composed of Al ₂ O ₃ and Gd ₂ O ₃ with a molar ratio of 1:1;

Mixed powder B formula: the mass fraction ratio of Si:TiO ₂ is 90%: 10%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10 _{% .} Complete nitriding is calculated; the sintering aid consists of Al ₂ O ₃ and Gd ₂ O ₃ in a molar ratio of 3:1;

Using Si powder and TiO ₂ powder as raw materials, using Al ₂ O ₃ powder and Gd ₂ O ₃ powder as sintering aids, respectively according to the above formula, the Si powder, TiO ₂ powder and sintering aid are compounded, and ethanol is used as a solvent, Si ₃ N ₄ balls were used as ball milling media, mixed on a planetary ball mill for 8 hours, and dried to obtain Si-TiO ₂ -Al ₂ O ₃ -Gd ₂ O ₃ mixed powder.

(2) The Si-TiO ₂ -Al ₂ O ₃ -Gd ₂ O ₃ mixed powder obtained in step (1) is formed into a three-layer structure according to the arrangement of mixed powder B-mixed powder A-mixed powder B. Cold isostatic pressing at 200MPa for 300s to obtain a green body.

(3) Nitriding the green body obtained in step (2) at 1450°C for 2h, then performing gas pressure sintering at 30MPa, the sintering atmosphere is 1 atm nitrogen, and maintaining the temperature at 1800°C for 4h to obtain a Si ₃ N ₄ gradient material.

After testing, the relative density of the Si ₃ N ₄ gradient material prepared in Example 4 of the present invention is 99%, the hardness is 22GPa, the fracture toughness is 13MPa·m ^1/2 , and the flexural strength is 1300MPa.

Example 5

(1) The formula of mixed powder A: the mass fraction ratio of Si:TiO ₂ is 92%:8%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10% ingredients, wherein, Si ₃ N ₄ Calculated according to the complete nitridation of Si powder; the sintering aid is composed of Al ₂ O ₃ and La ₂ O ₃ with a molar ratio of 1:1;

Mixed powder B formula: the mass fraction ratio of Si:TiO ₂ is 92%: 8%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10 _{% .} Complete nitriding is calculated; the sintering aid consists of Al ₂ O ₃ and La ₂ O ₃ in a molar ratio of 2.5:1;

Using Si powder and TiO ₂ powder as raw materials, using Al ₂ O ₃ powder and La ₂ O ₃ powder as sintering aids, respectively according to the above formula, the Si powder, TiO ₂ powder and sintering aid are prepared, and ethanol is used as a solvent, Si ₃ N ₄ balls were used as the ball milling medium, mixed on a planetary ball mill for 8 hours, and dried to obtain a Si-TiO ₂ -Al ₂ O ₃ -La ₂ O ₃ mixed powder.

(2) The Si-TiO ₂ -Al ₂ O ₃ -La ₂ O ₃ mixed powder obtained in step (1) is formed into a three-layer structure according to the arrangement of mixed powder B-mixed powder A-mixed powder B. Cold isostatic pressing at 200MPa for 300s to obtain a green body.

(3) Nitriding the green body obtained in step (2) at 1400° C. for 2 hours, and then performing gas pressure sintering at 30 MPa, the sintering atmosphere is 1 atm nitrogen, and maintaining the temperature at 1700° C. for 4 hours to obtain a Si ₃ N ₄ gradient material.

After testing, the relative density of the Si ₃ N ₄ gradient material prepared in Example 5 of the present invention is 99%, the hardness is 23 GPa, the fracture toughness is 14 MPa·m ^1/2 , and the flexural strength is 1400 MPa.

Example 6

(1) The formula of mixed powder A: the mass fraction ratio of Si:TiO ₂ is 90%: 10%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10% ingredients, wherein, Si ₃ N ₄ Calculated according to the complete nitridation of Si powder; the sintering aid is composed of Al ₂ O ₃ and Lu ₂ O ₃ with a molar ratio of 1:1;

Mixed powder B formula: the mass fraction ratio of Si:TiO ₂ is 90%: 10%, and the molar ratio of Si ₃ N ₄ : sintering aid is controlled to be 90%: 10 _{% .} Complete nitriding is calculated; the sintering aid consists of Al ₂ O ₃ and Lu ₂ O ₃ in a molar ratio of 3:1;

Using Si powder and TiO ₂ powder as raw materials, using Al ₂ O ₃ powder and Lu ₂ O ₃ powder as sintering aids, respectively according to the above formula, the Si powder, TiO ₂ powder and sintering aid are prepared, and ethanol is used as a solvent, Si ₃ N ₄ balls were used as the ball milling medium, mixed on a planetary ball mill for 8 hours, and dried to obtain a Si-TiO ₂ -Al ₂ O ₃ -Lu ₂ O ₃ mixed powder.

(2) The Si-TiO ₂ -Al ₂ O ₃ -Lu ₂ O ₃ mixed powder obtained in step (1) is formed into a three-layer structure according to the arrangement of mixed powder B-mixed powder A-mixed powder B. Cold isostatic pressing at 200MPa for 300s to obtain a green body.

(3) Nitriding the green body obtained in step (2) at 1300°C for 4h, and then performing gas pressure sintering at 50MPa, the sintering atmosphere is 1 atm nitrogen, and maintaining the temperature at 1600°C for 4h to obtain a Si ₃ N ₄ gradient material.

After testing, the relative density of the Si ₃ N ₄ gradient material prepared in Example 6 of the present invention is 99%, the hardness is 25GPa, the fracture toughness is 12MPa·m ^1/2 , and the flexural strength is 1200MPa.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (8)

1. a preparation method of Si ₃ N ₄ gradient material, comprising the following steps: a) Provide mixed powder A and mixed powder B; The mixed powder A includes Si powder, TiO ₂ powder and sintering aid, wherein the mass fraction ratio of Si powder and TiO ₂ powder is (60%-99%): (1%-40%), Si ₃ N ₄ and the molar ratio of the sintering aid is 93%: 7% or 90%: 10%, and the sintering aid is composed of Al ₂ O ₃ and Re ₂ O ₃ with a molar ratio of 1: 1; the mixed powder B includes Si, TiO ₂ and sintering aid, wherein, the mass fraction ratio of Si powder and TiO ₂ powder is (60%-99%): (1%-40%), and the molar ratio of Si ₃ N ₄ and sintering aid is 93%: 7% or 90%: 10%, the sintering aid consists of Al ₂ O ₃ and Re ₂ O ₃ in a molar ratio of 2.5: 1 or 3: 1; The Re is selected from Y, La, Gd, Yb or Lu; b) alternately laying the mixed powder A and the mixed powder B to form a multi-layer structure, and pressing and molding to obtain a green body; c) Nitriding and sintering the green body obtained in step b) to obtain a Si ₃ N ₄ gradient material. 2. The preparation method according to claim 1, characterized in that, in step a), the purity of the Si powder is greater than or equal to 95%, and the particle size is less than or equal to 100 μm; the purity of the TiO ₂ powder is greater than or equal to 98%, and the particle The diameter is less than or equal to 10 μm. 3. preparation method according to claim 1, is characterized in that, the multilayer structure described in step b) is three-layer structure; Described three-layer structure is according to mixed powder B-mixed powder A-mixed powder B composition of the arrangement. 4. The preparation method according to claim 1, characterized in that, in step b), the press forming method is cold isostatic pressing; the pressure of cold isostatic pressing is 100MPa～300MPa, and the time is 1min ~10min. 5 . The preparation method according to claim 1 , wherein the nitriding temperature in step c) is 1250° C.˜1600° C. and the time is 0.5 h˜24 h. 6 . 6 . The preparation method according to claim 1 , wherein the sintering method in step c) is pressureless sintering, gas pressure sintering at 10 MPa to 50 MPa, or SPS sintering at 10 MPa to 50 MPa. 7 . 7 . The preparation method according to claim 1 , wherein the sintering temperature in step c) ranges from 1600° C. to 2000° C. and the time ranges from 0.5 h to 24 h. 8 . 8 . A Si ₃ N ₄ gradient material, characterized in that, it is prepared by the preparation method according to any one of claims 1 to 7 .

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