A fiber-reinforced silicon nitride green body and its preparation method

Abstract

The present invention discloses a fiber-reinforced silicon nitride green body and a preparation method thereof. It is characterized in that during the forming process of the silicon nitride green body, a pre-forming mold with the same size is added. The pre-forming mold has a circular small hole group through which fiber bundles can penetrate. Fiber bundles penetrate the pre-forming mold in the x, y, and z directions. Then, silicon nitride powder is added and slowly pre-formed to obtain a toughened silicon nitride green body. After taking out the green body and cutting off the fiber bundles, the green body is then put into a mold for formal forming to be formed.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and particularly relates to a fiber-reinforced silicon nitride green body and a preparation method thereof. Background Art

[0002] Silicon nitride ceramics have unique physical and chemical properties, making them an excellent choice for high-temperature structural materials, tool ceramic materials, wear-resistant materials, and corrosion-resistant materials. However, silicon nitride ceramics are polycrystalline sintered bodies composed of grains with ionic or covalent bonds. The directionality of these chemical bonds is extremely strong, resulting in a low grain dislocation density and few slip systems, making the energy for crack growth small. During the fracture process, there are almost no other mechanisms for dissipating energy except for increasing the new fracture surface energy, which leads to disadvantages such as insufficient toughness in silicon nitride ceramics.

[0003] The existing preparation method of silicon nitride components is a process of molding silicon nitride powder by die pressing and then sintering. The silicon nitride ceramics prepared by this technology have high strength but lack toughness. The present invention breaks through the above process limitations, adds fiber toughening technology, and overcomes the problem of insufficient toughness while ensuring the original characteristics of silicon nitride components. Summary of the Invention

[0004] The purpose of the present invention is to provide a fiber-reinforced silicon nitride green body and a preparation method thereof. Through the design of the mold, the present invention adds fiber bundles in the die pressing molding process to improve the toughness of silicon nitride.

[0005] A fiber-reinforced silicon nitride green body and a preparation method thereof, characterized in that:

[0006] S1. Prepare a perforated molding die A and a non-perforated molding die B;

[0007] S2. Add silicon nitride powder into the molding die A;

[0008] S3. Prepare a long needle, and the long needle perforates with a fiber bundle;

[0009] S4. Repeatedly perform die pressing and feeding to form;

[0010] S5. Open the mold to take out the green body, put it into the non-perforated molding die B for secondary molding to obtain a toughened green body.

[0011] Further, the outer surface of the molding die A is a cuboid. The molding die A has a hydraulic cover plate A. The cavity part of the molding die A has a group of circular small holes with the same size. The hydraulic cover plate A has a group of circular small holes, and the sizes of the circular small holes are all the same; the molding die B has the same shape as the molding die A. The molding die B has a hydraulic cover plate B. The hydraulic cover plate B has the same shape as the hydraulic cover plate A. The molding die B and the hydraulic cover plate B do not have a group of circular small holes.

[0012] Preferably, the circular small hole groups of the molding die A and the hydraulic cover plate A are symmetrical structures, and a single small hole and its symmetrical small hole are on the same straight line.

[0013] Furthermore, silicon nitride powder is added into the molding die A, wherein the silicon nitride powder comprises silicon nitride powder, a sintering additive, a dispersant, a binder, a pore former, and a solvent, so as to keep the silicon nitride powder loose.

[0014] Furthermore, the long needle is a long straight round needle, the diameter of the long needle is smaller than the diameter of the circular hole, the length of the long needle is greater than the thickness of the molding mold A, the length of the long needle is greater than the thickness of the hydraulic cover plate A, and the end of the long needle is flat with a circular hole.

[0015] Furthermore, the end of the long needle is inserted into the fiber filaments and tied tightly, the fiber filaments bind the fiber bundles, the long needle is inserted from the circular hole on the A side, and comes out from the circular hole on the same straight line on the B side, and is fixed at one point after passing out, the long needle turns back and inserts from the circular hole on the B side, and comes out from the circular hole on the A side, and is fixed at one point after passing out, and this reciprocating process is repeated until all the holes have fiber bundles; the circular holes in the three directions of the x-axis, y-axis, and z-axis are all processed in this way until all the circular holes have fiber bundles.

[0016] Preferably, the number of positions for fixing the fiber bundles on one side of the hydraulic cover plate A is the same as the number of circular holes on the hydraulic cover plate A, the positions correspond to each other, and the fiber bundles on one side of the hydraulic cover plate A are in a straight line.

[0017] Further, the hydraulic cover plate A is slowly started to compact the silicon nitride powder, the silicon nitride powder is slowly added during the compaction process, and the molding mold A is shaken during the compaction process.

[0018] Further, the green body is taken out, the external fiber bundles are cut off, the green body is polished to be smooth, and then placed in a forming mold B for secondary hydraulic forming. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation of the present invention or the technical solution in the prior art, the drawings required for use in the specific implementation or the description of the prior art are briefly introduced below.

[0020] Figure 1 This is a structural diagram of the molding die A after the fiber bundle is introduced. DETAILED DESCRIPTION

[0021] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0022] For ease of understanding, the blank component of this embodiment is a cube with dimensions of 50 mm×50 mm×50 mm.

[0023] Prepare 2 sets of identical rectangular parallelepiped molding molds, which are divided into cover plate molds and main body molds. Take a set of molding mold A, and punch holes in the effective parts of the 5 faces of the main body and 1 face of the cover plate. The holes are circular holes with a hole diameter of 1mm and a hole density of 2mm×2mm. The effective part refers to the position of each face corresponding to the shape of the cavity part in the mold component. The punching dot matrix of each face of molding mold A is 23*23, and the cavity section is a square. 1mm is required to be reserved at the four corners of the square, and the center of the circle must start from 3mm. The holes on the parallel faces can be penetrated by a straight line.

[0024] Silicon nitride powder is added into the molding mold A to keep the silicon nitride powder in a loose state.

[0025] Prepare a long needle, which must remain straight. The straightness of the long needle needs to be tested every 20 times it is used. The end of the long needle is flat, with a round hole in the flat part, and fiber filaments are tied to the round hole, which hold the fiber bundle. The length of the long needle is greater than the length of the mold, and it can directly penetrate the mold. The long needle is inserted into the round holes of the molding mold A in turn. The long needle is guided by a fixed guide on one side, and the long needle penetrates the corresponding round holes through the linearity of the long needle. After the long needle penetrates the molding mold A, it brings out the fiber bundle, which is composed of 4 strands of 3k carbon fiber bundles and does not need to be twisted. The carbon fiber bundle is fixed at a fixed point on one side of the bringing-out surface, and the long needle is inserted into the second round hole, penetrates the molding mold A, and brings out the carbon fiber bundle on the other side, and is fixed at a fixed point on the other side. During this period, the carbon fiber is kept in a taut state. Under reciprocating work, the carbon fiber bundle fully penetrates all the round holes of the molding mold A in the x direction. The same method is used to penetrate the round holes in the y and z directions.

[0026] The cover mold A in the z direction is a movable cover, so when the carbon fiber bundle passes through in the z direction, the position and number of the fixed points at one end of the cover mold correspond to the number of small circular holes in the cover mold A. During the activity of the cover mold A, it remains perpendicular to the carbon fiber bundle.

[0027] The cover plate mold A slowly presses the silicon nitride powder. Each time it is pressed, a little silicon nitride powder is added to the surface. This step is repeated 20 times. After pressing out a cube shape, the fiber bundles exposed outside are cut off, the mold is opened to take out the cube silicon nitride blank, and then the fiber bundles exposed outside are cut off.

[0028] The green body is placed into a forming mold B and hydraulically formed again to obtain a final toughened green body.

Claims

1. A method for preparing a fiber-reinforced silicon nitride blank, characterized in that: The steps are: S1. Prepare a forming mold A with holes and a forming mold B without holes; the outer surface of the forming mold A is a rectangular parallelepiped, the forming mold A has a hydraulic cover plate A, the cavity of the forming mold A has a group of circular small holes of the same size, the hydraulic cover plate A has a group of circular small holes, the holes on the two parallel surfaces can be penetrated by a straight line, and the sizes of the circular small holes are the same; the forming mold B has the same shape as the forming mold A, the forming mold B has a hydraulic cover plate B, the hydraulic cover plate B has the same shape as the hydraulic cover plate A, and the forming mold B and the hydraulic cover plate B do not have a group of circular small holes; S2. Add silicon nitride powder into the molding die A; the silicon nitride powder comprises silicon nitride powder, a sintering additive, a dispersant, a binder, a pore-forming agent, and a solvent, and the silicon nitride powder is in a loose state; S3, prepare a long needle, and pierce the hole with the fiber bundle; the end of the long needle is inserted into the fiber filament and tied tightly, and the fiber filament binds the fiber bundle, the long needle is inserted from the circular hole on the A side, and comes out from the circular hole on the same straight line on the B side, and is fixed at a point after passing out, the long needle turns back and inserts from the circular hole on the B side, and comes out from the circular hole on the A side, and is fixed at a point after passing out, and repeats until all the holes have fiber bundles; the circular holes in the three directions of the x-axis, y-axis, and z-axis are all in this way until all the circular holes have fiber bundles; the cover mold A in the z direction is a movable cover, and when the carbon fiber bundle is passed through in the z direction, the position and number of the fixed points at one end of the cover mold correspond to the number of small circular holes in the cover mold A; during the activity of the cover mold A, it is kept perpendicular to the carbon fiber bundle; S4, repeatedly molding and adding materials to form; slowly start the hydraulic cover plate A, compact the silicon nitride powder, slowly add silicon nitride powder during the compaction process, and shake the molding mold A during the compaction process; the number of positions of the fixed fiber bundles on one side of the hydraulic cover plate A is the same as the number of circular holes on the hydraulic cover plate A, and the positions correspond to each other, and the fiber bundles on one side of the hydraulic cover plate A are in a straight line; S5. Open the mold, take out the green body, and put it into a non-porous molding mold B for secondary molding to obtain a toughened green body.

2. The method for preparing a fiber-reinforced silicon nitride blank according to claim 1, characterized in that: The circular small hole groups of the molding die A and the hydraulic cover plate A are both symmetrical structures, and a single small hole is on the same straight line as its symmetrical small hole.

3. The method for preparing a fiber-reinforced silicon nitride blank according to claim 1, characterized in that: The long needle is a long straight round needle, the diameter of the long needle is slightly smaller than the diameter of the circular hole, the length of the long needle is greater than the thickness of the molding mold A, the length of the long needle is greater than the thickness of the hydraulic cover plate A, and the end of the long needle is flat with a round hole.

4. The method for preparing a fiber-reinforced silicon nitride blank according to claim 1, characterized in that: The blank is taken out, the external fiber bundles are cut off, the blank is polished until smooth, and then placed in the forming mold B for secondary hydraulic forming.

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