CN104926345A - Alumina fiber-reinforced silicon carbide-aluminum silicate ceramic and preparation method thereof - Google Patents

Abstract

An alumina fiber-reinforced silicon carbide-aluminosilicate ceramic, which uses an alumina fiber fabric as a reinforcement, and uses silicon carbide ceramics and aluminum silicate ceramics as a matrix. The silicon carbide ceramics are mainly formed by chemical vapor infiltration. Aluminum silicate ceramics are introduced through a sol-gel process; the preparation method includes the following steps: using alumina fiber fabrics, trichloromethylsilane, hydrogen, and argon as raw materials, and using chemical vapor infiltration to prepare Al ₂ O _3f / SiC ceramic body; surface processing of the prepared ceramic body to change a large number of closed cells on the surface into open pores; use silicon-aluminum composite sol to vacuum impregnate the ceramic body, and transform it into an intermediate after gelation and high-temperature ceramicization product; repeat at least 4 times to finally obtain alumina fiber-reinforced silicon carbide-aluminosilicate ceramics. The product of the invention has excellent mechanical properties, high temperature resistance and oxidation resistance, and has short preparation period, low cost and can be molded to a near-net size.

Description

A kind of alumina fiber reinforced silicon carbide-aluminum silicate ceramic and its preparation method

technical field

The invention relates to the field of fiber-reinforced ceramic materials, in particular to a fiber-reinforced silicon carbide-aluminum silicate ceramic and a preparation method thereof.

Background technique

Oxide fiber reinforced silicon carbide ceramics have excellent mechanical properties, dielectric properties, oxidation resistance and environmental resistance, and are an important class of high-temperature structural functional materials. However, silicon carbide has poor high-temperature environmental resistance, such as easy oxidation and failure in a high-temperature aerobic water vapor environment, which greatly limits its application.

At present, the preparation techniques of oxide fiber reinforced silicon carbide ceramics mainly include precursor transformation method (PIP) and chemical vapor infiltration method (CVI). The PIP method has low sintering temperature, strong designability of the matrix, and near-net size molding, but the material prepared by PIP has high porosity, large fiber damage, and strong fiber/matrix interface bonding. In addition, SiC ceramics prepared by PIP usually contain impurities such as free carbon and glass phase SiO _x C _y , and their oxidation resistance is inferior to that of pure SiC ceramics. The preparation temperature of the CVI method is low, the purity of the obtained SiC matrix is high, and it can also be formed into a near-net size. However, during the preparation of CVI, the oxidation resistance of CVI will be greatly reduced due to the generation of defects and the cracks in the matrix caused by thermal mismatch. Through matrix modification and post-densification treatment, further increasing the density of the composite material can improve the oxidation resistance of the SiC matrix to a certain extent.

In the early stage, we used the PIP process to prepare alumina fiber reinforced silicon carbide (Al ₂ O _3f /SiC) ceramic matrix composites, and studied its mechanical properties and microscopic morphology. The results showed that: Al ₂ O without interface modification The fiber/matrix interface in the _3f /SiC composite is strongly bonded, showing brittle fracture behavior, and the bending strength is only 42.8MPa. In addition, the Al ₂ O _3f /SiC composite material was prepared by CVI process. The research results showed that a thin layer of carbon coating could be formed in situ between the alumina fiber and the SiC matrix, thus weakening the interfacial bonding and improving the mechanical properties of the composite material. Better, the bending strength reaches 92.1MPa. However, due to the existence of many pores and cracks in the matrix, the oxidation resistance of the composite is not ideal.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, provide an alumina fiber reinforced silicon carbide-aluminosilicate ceramic with excellent mechanical properties, high temperature resistance and oxidation resistance, and provide correspondingly The invention discloses a preparation method of the alumina fiber reinforced silicon carbide-aluminosilicate ceramics which has short preparation period, low cost and can be molded in near net size.

In order to solve the above technical problems, the technical solution proposed by the present invention is an alumina fiber reinforced silicon carbide-aluminum silicate ceramic (referred to as Al ₂ O _3f /SiC-AS), the ceramic is made of alumina fiber fabric (Al ₂ O _3f ) as a reinforcement, with silicon carbide ceramics (SiC) and aluminum silicate ceramics (AS) as substrates, the silicon carbide ceramics are mainly formed by chemical vapor infiltration, and the aluminum silicate ceramics are formed by sol- The gel process is introduced.

The above-mentioned alumina fiber reinforced silicon carbide-aluminum silicate ceramics, preferably: the matrix contains 20% to 40% volume fraction (accounting for the volume fraction of the entire alumina fiber reinforced silicon carbide-aluminum silicate ceramics, the same below) Silicon carbide ceramics and aluminum silicate ceramics with a volume fraction of 10% to 20% (the rest of the volume space is mainly pores).

The above alumina fiber reinforced silicon carbide-aluminosilicate ceramics, preferably: the bending strength of the ceramic is above 125MPa, and the bending strength after high temperature oxidation at 1000°C for 100h is above 110MPa; the elastic modulus of the ceramic It is above 70GPa, and the elastic modulus after high temperature oxidation at 1000°C for 100h is above 60GPa.

As a general technical concept, the present invention also provides a method for preparing the above-mentioned alumina fiber reinforced silicon carbide-aluminosilicate ceramics, comprising the following process steps:

(1) Preparation of Al ₂ O _3f /SiC ceramic body: Al ₂ O _3f /SiC ceramics were prepared by chemical vapor infiltration (CVI) using alumina fiber fabric, trichloromethylsilane, hydrogen, and argon as raw materials Body;

(2) Processing of Al ₂ O _3f /SiC ceramic body: Surface processing is carried out on the Al ₂ O _3f /SiC ceramic body prepared in the above step (1), and a large number of closed pores on the surface are changed into open pores for easy processing. subsequent densification;

(3) Subsequent densification of AS ceramics: the Al ₂ O _3f /SiC ceramic body after the above step (2) is vacuum impregnated with silicon-aluminum composite sol, and transformed into an intermediate product after gelation and high-temperature ceramicization;

(4) Repeat the process of the above step (3) at least 4 times (preferably 4-8 times), and finally obtain alumina fiber reinforced silicon carbide-aluminosilicate ceramics.

In the above preparation method, preferably, in the step (1), the alumina fiber fabric is a 2.5D structure, a three-dimensional four-way structure, a three-dimensional five-way structure, a three-dimensional six-way structure or a three-dimensional orthogonal structure; The fiber volume fraction in the aluminum fiber fabric is 35% to 45%.

In the above-mentioned preparation method, preferably, in the step (1), the process parameter conditions of the chemical vapor infiltration method include: the deposition temperature is 1000°C to 1200°C, the deposition pressure is 1kPa to 5kPa, and the flow rate ratio of hydrogen and argon is It is 3:1～1:1, and the deposition time is 6h～10h.

In the above-mentioned preparation method, preferably, in the step (3), the vacuum impregnation process includes: vacuum impregnating the Al ₂ O _3f /SiC ceramic body with a silicon-aluminum composite sol for 4h to 8h, and then taking it out in the The solid content of the silicon-aluminum composite sol is 18.2wt%-25.3wt%.

In the above-mentioned preparation method, preferably, in the step (3), the gelation is completed by drying, and the drying process includes: putting the vacuum-impregnated ceramic body into an oven at 2°C /min～3℃/min heating rate to 150℃～200℃, dry for 4h～6h, then cool naturally to room temperature and take out.

In the above preparation method, preferably, in the step (3), the high-temperature ceramization is completed by high-temperature cracking, and its specific process includes: putting the gelled ceramic body into cracking In the furnace, raise the temperature to 900°C-1100°C at a rate of 5°C/min-10°C/min in the air, keep it warm for 0.5h-1.5h, cool naturally to below 100°C and take it out.

The present invention mainly follows the following technical ideas: on the premise of not changing the properties of the Al ₂ O _3f /SiC composite material prepared by the CVI process, the matrix is modified and subsequently densified to further bridge the crack defects in the matrix, and then Improve the mechanical properties and oxidation resistance of composite materials. In the specific preparation process, we firstly prepared the Al ₂ O _3f /SiC ceramic body by the CVI process, and then used the silicon-aluminum composite sol as the precursor, and used the sol-gel process to prepare the Al ₂ O _3f /SiC ceramic body. After post-densification treatment, alumina fiber reinforced silicon carbide-aluminosilicate ceramics with excellent mechanical properties and oxidation resistance were obtained.

Compared with the prior art, the present invention has the advantages of:

1. The preparation method of the Al ₂ O _3f /SiC-AS ceramics of the present invention is a gas phase method combined with a liquid phase method, and the SiC-AS ceramic substrate can be prepared by pressureless sintering at a relatively low temperature, and the preparation cycle is short;

2. The method of the present invention can prepare components with complex structures through fiber weaving, and the external dimensions of the products can be precisely controlled by CNC machine tools; the selected raw materials are widely available and can be widely used in industrial production.

The Al ₂ O _3f /SiC-AS ceramic of the present invention has common advantages of general ceramic matrix composite materials, such as high specific strength and specific modulus, excellent thermal shock resistance and the like. In addition, compared with C _f /SiC, SiC _f /SiC and Al ₂ O _3f /SiC ceramic matrix composites, the Al ₂ O _3f /SiC-AS ceramics of the present invention have more excellent oxidation resistance and environmental resistance.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are For some embodiments of the present invention, those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is an optical photograph of Al ₂ O _3f /SiC-AS ceramics prepared in Example 1 of the present invention.

Fig. 2 is an energy spectrum analysis of the matrix in Al ₂ O _3f /SiC-AS ceramics prepared in Example 1 of the present invention.

Fig. 3 is a microscopic morphology diagram of Al ₂ O _3f /SiC-AS ceramics prepared in Example 1 of the present invention.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described in more detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

Example 1:

A kind of aluminum oxide fiber reinforced silicon carbide-aluminosilicate ceramics (abbreviated as Al ₂ O _3f /SiC-AS) of the present invention as shown in Figure 1, comprises the alumina fiber of about 41% volume fraction, about 33% volume Fraction of SiC ceramics and about 12% volume fraction of AS ceramics.

A method for preparing the above-mentioned Al ₂ O _3f /SiC-AS ceramics in this embodiment, specifically comprising the following steps:

(1) Preparation of Al ₂ O _3f /SiC ceramic body: Using three-dimensional orthogonal alumina fiber fabric as reinforcement and trichloromethylsilane-hydrogen-argon as raw material, Al ₂ O _3f /SiC ceramics were prepared by CVI Green body; CVI process parameters are: deposition temperature is 1100°C, deposition pressure is 1.5kPa, hydrogen and argon gas flow ratio is 1.5:1, deposition time is 10h;

(2) Processing of Al ₂ O _3f /SiC ceramic body: Surface processing is carried out on the Al ₂ O _3f /SiC ceramic body prepared in the above step (1), and a large number of closed pores on the surface are changed into open pores for easy processing. subsequent densification;

(3) Subsequent densification of AS ceramics: first, the Al ₂ O _3f /SiC ceramic green body prepared in the above step (2) was vacuum impregnated for 6 hours with the silicon-alumina composite sol with a solid content of 19.5 wt% as the precursor, Take it out and leave it in the air for 2 hours; then, put the vacuum-impregnated ceramic body into an oven for gelation treatment, heat up to 200°C at a heating rate of 2°C/min, dry for 5h, and cool naturally to room temperature. ; Finally, put the gelled ceramic body into the cracking furnace, raise the temperature to 1000°C in the air at a rate of 8°C/min, keep it warm for 1 hour, and cool it naturally to below 100°C to take it out;

(4) Repeat the above step (3) four times to prepare Al ₂ O _3f /SiC-AS ceramics.

The optical photo of the Al ₂ O _3f /SiC-AS ceramics of this example prepared through the above steps is shown in Figure 1, and its matrix energy spectrum analysis is shown in Figure 2. It can be seen from Figure 2 that the Al 2 O 3f/SiC-AS ceramics prepared in this example The ₂ O _3f /SiC-AS ceramic matrix contains C, Si, Al and O elements, which are consistent with those contained in SiC and AS.

The cross-sectional morphology of the Al ₂ O _3f /SiC-AS ceramics prepared in this example is shown in Figure 3. It can be seen from Figure 3 that there are a small amount of micropores inside the bundles of the Al ₂ O _3f /SiC-AS ceramic composites. The pores between the bundles are larger; in addition, the interface between the fiber and the matrix is clearer, indicating that the compatibility of the fiber and the matrix is better.

Referring to the above-mentioned process parameter conditions of this example, Al ₂ O _3f /SiC ceramics were prepared by CVI process as control sample 1; at the same time, Al ₂ O _3f /AS ceramics were prepared by densifying alumina fiber fabrics with silicon-aluminum composite sol. 2 as usual. The comparative test of the mechanical properties of the Al ₂ O _3f /SiC-AS ceramic obtained in the above-mentioned embodiment and the control sample was carried out, and the main performance parameters shown in Table 1 below were obtained.

Table 1: The main performance parameters of the three composite materials obtained by comparative testing in Example 1

Example 2:

An alumina fiber reinforced silicon carbide-aluminosilicate ceramic (abbreviated as Al ₂ O _3f /SiC-AS) of the present invention comprises about 43% volume fraction of alumina fiber, about 25% volume fraction of SiC ceramic and about 18% volume fraction of AS ceramics.

A method for preparing the above-mentioned Al ₂ O _3f /SiC-AS ceramics in this embodiment, specifically comprising the following steps:

(1) Preparation of Al ₂ O _3f /SiC ceramic body: Using three-dimensional orthogonal alumina fiber fabric as reinforcement and trichloromethylsilane-hydrogen-argon as raw material, Al ₂ O _3f /SiC ceramics were prepared by CVI Green body; CVI process parameters are: deposition temperature is 1050°C, deposition pressure is 2kPa, hydrogen and argon flow ratio is 2:1, deposition time is 8h;

(2) Processing of Al ₂ O _3f /SiC ceramic body: Surface processing is carried out on the Al ₂ O _3f /SiC ceramic body prepared in the above step (1), and a large number of closed pores on the surface are changed into open pores for easy processing. subsequent densification;

(3) Subsequent densification of AS ceramics: first, the Al ₂ O _3f /SiC ceramic green body prepared in the above step (2) was vacuum impregnated for 7 hours using the silicon-alumina composite sol with a solid content of 21.2 wt% as a precursor, Take it out and let it dry in the air for 1.5h; then, put the vacuum-impregnated ceramic body into an oven for gelation treatment, raise the temperature to 180°C at a heating rate of 2.5°C/min, dry for 6h, and naturally cool to room temperature Take it out; finally, put the gelled ceramic body into the cracking furnace, raise the temperature to 1050°C in the air at a rate of 10°C/min, keep it warm for 0.5h, cool naturally to below 100°C and take it out;

(4) Repeat the above step (3) 6 times to prepare Al ₂ O _3f /SiC-AS ceramics.

Referring to the above-mentioned process parameter conditions of this example, Al ₂ O _3f /SiC ceramics were prepared by CVI process as control sample 1; at the same time, Al ₂ O _3f /AS ceramics were prepared by densifying alumina fiber fabrics with silicon-aluminum composite sol. 2 as usual. The comparative test of the mechanical properties of the Al ₂ O _3f /SiC-AS ceramic obtained in the above-mentioned embodiment and the control sample was carried out, and the main performance parameters shown in Table 2 below were obtained.

Table 2: The main performance parameters of the three composite materials obtained by comparative testing in Example 2

It can be seen from the above that the bending strength of the aluminum oxide fiber reinforced silicon carbide-aluminosilicate ceramics prepared by the present invention is above 129MPa, and the bending strength after high temperature oxidation at 1000°C for 100h is still above 115MPa; the elastic modulus of ceramics It is above 72GPa, and the elastic modulus after high temperature oxidation at 1000°C for 100h is still above 61GPa.

Claims (9)

1. An alumina fiber reinforced silicon carbide-aluminosilicate ceramic, characterized in that: the ceramic is an alumina fiber fabric as a reinforcement, with silicon carbide ceramics and aluminum silicate ceramics as a matrix, and the silicon carbide ceramic It is mainly formed by chemical vapor infiltration, and the aluminum silicate ceramics are introduced through a sol-gel process. 2. Alumina fiber reinforced silicon carbide-aluminosilicate ceramics according to claim 1, characterized in that: the matrix contains 20% to 40% volume fraction of silicon carbide ceramics and 10% to 20% volume fraction of silicon acid aluminum ceramics. 3. The alumina fiber reinforced silicon carbide-aluminosilicate ceramic according to claim 1 or 2, characterized in that: the bending strength of the ceramic is above 125 MPa, and the bending strength after high temperature oxidation at 1000°C for 100 hours is Above 110MPa; the elastic modulus of the ceramic is above 70GPa, and the elastic modulus after high temperature oxidation at 1000°C for 100h is above 60GPa. 4. A method for preparing alumina fiber reinforced silicon carbide-aluminosilicate ceramics as claimed in claim 1 or 2 or 3, comprising the following processing steps: (1) Preparation of Al ₂ O _3f /SiC ceramic body: Al ₂ O _3f /SiC ceramic body was prepared by chemical vapor infiltration method with alumina fiber fabric, trichloromethylsilane, hydrogen and argon as raw materials; (2) Processing of Al ₂ O _3f /SiC ceramic body: Surface processing is carried out on the Al ₂ O _3f /SiC ceramic body prepared in the above step (1), and a large number of closed pores on the surface are changed into open pores for easy processing. subsequent densification; (3) Subsequent densification of AS ceramics: the Al ₂ O _3f /SiC ceramic body after the above step (2) is vacuum impregnated with silicon-aluminum composite sol, and transformed into an intermediate product after gelation and high-temperature ceramicization; (4) Repeat the process of the above step (3) at least 4 times to finally obtain alumina fiber reinforced silicon carbide-aluminosilicate ceramics. 5. The preparation method according to claim 4, characterized in that, in the step (1), the alumina fiber fabric is a 2.5D structure, a three-dimensional four-way structure, a three-dimensional five-way structure, a three-dimensional six-way structure or Three-dimensional orthogonal structure; the fiber volume fraction in the alumina fiber fabric is 35%-45%. 6. The preparation method according to claim 4 or 5, characterized in that, in the step (1), the process parameter conditions of the chemical vapor infiltration method include: the deposition temperature is 1000°C to 1200°C, and the deposition pressure is 1kPa～5kPa, the flow rate ratio of hydrogen and argon is 3:1～1:1, and the deposition time is 6h～10h. 7. The preparation method according to claim 4, characterized in that, in the step (3), the vacuum impregnation process comprises: vacuum impregnating the Al ₂ O _3f /SiC ceramic blank with a silicon-aluminum composite sol The solid content of the silicon-aluminum composite sol is 18.2wt%-25.3wt%. 8. The preparation method according to claim 4 or 7, characterized in that, in the step (3), the gelation is completed by drying, and the drying process comprises: vacuum-impregnated ceramics Put the green body into an oven, raise the temperature to 150-200°C at a rate of 2°C/min-3°C/min, dry for 4h-6h, then cool naturally to room temperature and take it out. 9. The preparation method according to claim 4 or 7, characterized in that, in the step (3), the high-temperature ceramization is completed by high-temperature cracking, and its specific process includes: Put the gelled ceramic body into the cracking furnace, raise the temperature in the air to 900-1100°C at a rate of 5°C/min-10°C/min, keep it warm for 0.5h-1.5h, and cool naturally to below 100°C take out.