CN108794033A - A kind of self toughening fibrous monolithic ceramic structural ceramics and preparation method thereof - Google Patents

Abstract

The invention discloses a self-toughening fiber monolithic ceramic, which is composed of ceramic fiber cell bodies arranged in a one-dimensional orientation and a relatively thin interface separation layer between the cell bodies, wherein the interface separation layer and the fiber cell body are of the same type A ceramic material, and the crystal grain size of the interfacial separation layer ceramic is larger than that of the fiber cell body. The invention also discloses a preparation method of the monolithic structure ceramic. The interface separation layer with larger crystal grains of the present invention can not only induce the deflection, bifurcation and lateral expansion of cracks, but also prevent the interface layer from being oxidized or peeled off due to thermal mismatch in a high temperature environment, thereby improving the performance of the material at high temperature. Reliability for long-term service in the environment.

Description

A self-toughening fiber monolithic ceramic and its preparation method

technical field

The invention relates to a self-toughening fiber monolithic structural ceramic and a preparation method thereof, belonging to the field of structural materials, in particular to the field of bionic structural materials.

Background technique

Ceramic materials have excellent properties that many metal materials and polymer materials do not have, such as high melting point, high hardness, wear resistance, oxidation resistance, light weight and high strength, and have broad application prospects as structural materials in high temperature environments. However, the inherent brittleness of ceramic materials seriously reduces the reliability and stability of materials. After years of hard work, researchers in this field have developed a variety of toughening methods for ceramics, such as phase transformation toughening, whisker toughening, particle dispersion toughening, and bionic structure toughening.

In the 1980s, Coblenz et al. (US Patent 4772524[P]) proposed a fiber monolithic structure by imitating the structure of bamboo and wood. The fibrous cell bodies are arranged in a certain way, separated by relatively thin cell interfaces and assembled into one blocks. This special structure can make the cracks deflect, proliferate, and expand laterally when the material is broken, and then passivate the cracks, thereby improving the fracture toughness and fracture work of the material. Baskaran and Wang Changan of Tsinghua University et al. (J. Am. Ceram.Soc., 1993, 76(9): 2209-2216; "High Performance Multiphase Composite Ceramics" Tsinghua University Press, pp: 285-351, 2008) In-depth study of the preparation methods and fracture behavior of fiber monolithic ceramics in multiple systems, involving SiC/C, Si ₃ N ₄ /BN, Al ₂ O ₃ /Ni, TZP/Al ₂ O ₃ , Ce-TZP/Ce- TZP-Al ₂ O ₃ and other systems show that this structure can significantly improve the fracture resistance and thermal shock resistance of ceramic materials.

However, after long-term service in a high-temperature environment, this kind of fiber monolithic ceramics has the problem of oxidation of the interfacial separation layer between heterogeneous phases or the loss of the interfacial layer due to thermal mismatch between the fiber cell body and the interfacial separation layer, which affects the long-term stability of the component under high temperature conditions. service reliability.

Contents of the invention

In order to overcome the above defects, the technical problem to be solved by the present invention is to provide a self-toughening fiber monolithic ceramic with long-term high temperature resistance and oxidation resistance and a preparation method thereof.

A self-toughening fiber monolithic structure ceramic, the ceramic is composed of ceramic fiber cells arranged in a one-dimensional orientation and a relatively thin interface separation layer between the cell bodies, as shown in Figure 1, characterized in that the interface separation layer The same ceramic material as the fiber cell body forms a single-component fiber monolithic ceramic, and the grain size of the interfacial separation layer ceramics is larger than that of the fiber cell body, forming a single-component fiber through the difference in grain size Monolithic ceramics. Since the entire material is composed of the same ceramic with a single component, it has excellent oxidation resistance under high temperature conditions, and can avoid the problem of poor reliability caused by thermal mismatch, thereby achieving long-term stability in high temperature environments Reliable service.

The composition of the fiber monolithic ceramics may be ceramic materials such as Al ₂ O ₃ , SiC, Si ₃ N ₄ and ZrO ₂ .

The difference between the ceramic grain size of the fiber cell body and the interface separation layer is the key to the formation of the self-toughening fiber monolithic structure. The larger the difference is, the more beneficial the interface is to induce crack propagation. Therefore, the grain size of the ceramic material of the interface separation layer is preferably more than one order of magnitude larger than the grain size of the fiber cell body ceramics.

As another preferred solution of the present invention, the diameter of the fiber cell body is 100-1200 μm, and the thickness of the interface separation layer is 10-50 μm.

The present invention also provides a method for preparing self-toughening fiber monolithic ceramics as described above, comprising the following steps:

1) Preparation of ceramic fiber cell bodies: Add fine-grained ceramic powder to PVA (polyvinyl alcohol) (polymerization degree 1750±50) aqueous solution to form a ceramic slurry, in which PVA is used as an adhesive. Then the homogeneously mixed ceramic slurry is extruded to form ceramic fiber cells, and the diameter of the obtained fiber cells can be controlled by the inner diameter of the extrusion port, and the extruded fiber cells can be used in the next step after drying.

2) Preparation of the interfacial separation layer: The coarse-grained ceramic powder with the same phase as step 1) was used to disperse in the PVA aqueous solution to obtain the interfacial separation layer slurry, in which the mass ratio of ceramic powder to PVA was 99:1. Then, the ceramic fiber cell body is attached with an interface separation layer of the same phase on the surface of the ceramic fiber cell body by a dipping method. The thickness of the interfacial separation layer can be controlled by the solid phase content of the slurry and the dipping times.

3) Forming of the green body: Arrange the dried ceramic fiber cells containing the interfacial separation layer in a one-dimensional orientation in a steel mold, then press 180-250 MPa to form, hold the pressure for 3-10 minutes, and get a self- Green body of toughened fiber monolithic structure ceramics.

4) Debinding and sintering: After debinding the obtained green body at 500 ℃ for 1 hour in a vacuum furnace, sintering with SPS (spark plasma sintering) for 5-10 minutes at a pressure of 25-30 MPa, cooling and demoulding to obtain the prepared Self-toughening fiber monolithic ceramics. The sintering temperature is determined by the selected ceramic densification temperature.

In the step 1), the mass concentration of the PVA aqueous solution is preferably 2%, and the mass fraction of the solid phase content of the slurry is 50%.

The ceramic grain size in step 2) is larger than the ceramic grain size in step 1) by more than one order of magnitude, and the ceramic grain size in step 1) is less than 500 nm.

The advantages of the present invention are:

In the self-toughening fiber monolithic ceramics of the present invention, the fiber cell body and the interface separation layer are made of the same ceramic material, and the difference is only in the grain size. Therefore, while the interface can induce the crack to expand laterally, it can also avoid the oxidation of the interface layer in a high-temperature environment or the peeling caused by thermal mismatch, thereby improving the reliability of the material in service in a high-temperature environment.

Description of drawings

Fig. 1 is a schematic diagram of self-toughening fiber monolithic ceramics according to the present invention.

Figure 2 is a photomicrograph of Example 1 of the present invention.

Fig. 3 A partially enlarged photomicrograph of the interfacial separation layer and fiber cell body in Example 1 of the present invention.

In the figure: 1, ceramic fiber cell body; 2, ceramic interface separation layer.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below, obviously, the described embodiments are only some 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 persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

Nano-Al ₂ O ₃ powder (80-200 nm) was added to PVA aqueous solution with a mass concentration of 2% to form Al ₂ O ₃ slurry, in which PVA was used as an adhesive, and the solid phase content of the slurry was 50%. Then the uniformly mixed Al ₂ O ₃ slurry was extruded into Al ₂ O ₃ fiber cells with a diameter of 800 μm by extrusion. Disperse micron Al ₂ O ₃ powder (1~3 μm) in water, add PVA as a binder, and then attach nanometer Al ₂ O ₃ fiber cells to the surface of Al ₂ O ₃ fiber cells by dipping. _{Al2O3 interfacial} layer. The green body of the material was obtained through one-dimensional directional arrangement and dry pressing, and the forming pressure was 180 MPa. After debinding, the SPS sintering method was used to sinter at 1250°C for 5 min at a pressure of 25 MPa, and self-toughened fiber monolithic Al ₂ O ₃ ceramics were successfully prepared.

Although there is a phenomenon of grain growth in the ceramic sintering process, the difference in grain size after sintering can be realized by controlling the initial particle size of the powder, thereby forming a pre-designed fiber monolithic structure. The microscopic morphology of the prepared self-toughening fiber monolithic structure Al ₂ O ₃ ceramics is shown in Fig. 2 in the section perpendicular to the fiber axis. Further, the partially enlarged microstructure photos of the interfacial separation layer and the fibroblast body are shown in Fig. 3 . The fracture toughness of this material can reach 8.0 MPa m ^1/2 , more than twice that of single-phase Al ₂ O ₃ , and it has excellent oxidation resistance for a long time in a high-temperature aerobic environment, which greatly improves the reliability of high-temperature service .

Example 2

Based on the same design ideas and preparation methods, different types of self-toughening fiber monolithic ceramics with different structural parameters were successfully prepared using SiC, Si ₃ N ₄ and ZrO ₂ as raw materials. Self-toughening fiber monolithic ceramics were prepared by selecting fiber cell bodies with diameters of 100 μm, 300 μm, 500 μm and 1200 μm, and interfacial separation layers with thicknesses of 10 μm, 30 μm and 50 μm. Since the interfacial separation layer and the fiber cell body of this kind of self-toughening fiber monolithic ceramics are the same ceramic material, the coarse-grained interfacial separation layer is used to achieve the deflection, proliferation and lateral expansion of induced cracks to improve the fracture resistance of the material. , the fracture toughness can reach more than 10 MPa·m ^1/2 . It can also solve the problem of the oxidation of the interfacial separation layer between heterogeneous phases or the detachment of the interfacial layer due to thermal mismatch between the fiber cell body and the interfacial separation layer, thereby improving the service reliability of the material under high temperature conditions. After heat treatment in an aerobic environment at 1000 °C for 5 hours, there is no cracking phenomenon in the interface layer of the material, and the retention rate of fracture toughness can reach more than 90%.

Claims (10)

1. a kind of self toughening fibrous monolithic ceramic structural ceramics, the ceramics are by the ceramic fibre cell space arranged by one-dimensional oriented approach and born of the same parents Relatively thin interface separate layer composition between body, it is characterised in that the interface separate layer and fiber cell space are ceramic material of the same race Material, and the crystallite dimension of interface separate layer ceramics is more than the crystallite dimension of fiber cell space.

2. self toughening fibrous monolithic ceramic structural ceramics as described in claim 1, it is characterised in that the fiber cell space and interface point Interlayer is Al₂O₃、SiC、Si₃N₄And ZrO₂In one kind.

3. self toughening fibrous monolithic ceramic structural ceramics as described in claim 1, it is characterised in that the interface separate layer ceramics Crystallite dimension is greater than fiber cell space ceramic crystalline grain size an order of magnitude or more.

4. self toughening fibrous monolithic ceramic structural ceramics as described in claim 1, it is characterised in that the fiber cell space it is a diameter of 100 ~ 1200 μm, the thickness of interface separate layer is 10 ~ 50 μm.

5. a kind of method preparing Claims 1-4 any one of them self toughening fibrous monolithic ceramic structural ceramics, including following step Suddenly：

1）The preparation of ceramic fibre cell space：Superfine ceramics powder is added in PVA aqueous solutions and forms ceramic slurry, it then will mixing Uniform ceramic slurry forms ceramic fibre cell space by the method extruded；

2）The preparation of interface separate layer：Using with step 1）The coarse-grain ceramic powder of phase jljl phase is dispersed in PVA aqueous solutions, is obtained Interface separate layer slurry, then ceramic fibre cell space is adhered into phase jljl phase by the method dipped on ceramic fibre cell space surface Interface separate layer；

3）The molding of green body：Ceramic fibre cell space containing interface separate layer after drying is arranged in steel mold by one-dimensional orientation Then cloth is press-formed, pressurize, and the green body of self toughening fibrous monolithic ceramic structural ceramics is obtained after demoulding；

4）Dumping and sintering：It by gained green body dumping, is sintered using SPS, the self toughening fibrous monolithic ceramic is obtained after cooling and demolding Structural ceramics.

6. method as claimed in claim 5, it is characterised in that the degree of polymerization of the PVA is 1750 ± 50.

7. method as claimed in claim 5, it is characterised in that the step 1）A concentration of the 2% of middle PVA aqueous solutions, slurry is solid Phase content mass fraction is 50%；Step 2）Described in ceramic powder and PVA mass ratioes be 99:1.

8. method as claimed in claim 5, it is characterised in that the step 2）Middle ceramic crystalline grain size ratio step 1）Middle ceramics More than crystallite dimension is order of magnitude greater, and step 1）Ceramic crystalline grain size is less than 500 nm.

9. method as claimed in claim 5, it is characterised in that step 3）Described in the pressure pressurizeed be 180 ~ 250 MPa, protect Press 3 ~ 10 min.

10. method as claimed in claim 5, it is characterised in that step 4）Described in dumping condition：500 DEG C, 1 h；It is described The condition of sintering：5-10 min, 25 ~ 30 Mpa.