A silicon nitride ceramic formula and a silicon nitride ceramic preparation method that can be used in a 3D printing process

Abstract

The application relates to a silicon nitride ceramic formula and a silicon nitride ceramic preparation method which can be used in a 3D printing process. The ceramic formula is as follows: 75-85% of silicon nitride powder, 3-6% of boron oxide powder or 3-6% of boric acid, 3-5% of silicon oxide powder, 3-6% of aluminum oxide powder, 3-6% of yttrium oxide powder and 3-5% of boron nitride powder. The preparation method adopts the following preparation method: powder weighing and mixing, liquid phase ball milling with a water-material ratio of 1-2, drying, crushing and 100-mesh screening; the preparation process comprises the following steps: after a silicon nitride blank is prepared through photosensitive solidification molding or fused deposition molding, the blank is sintered, wherein the temperature rising rate is 0.5-2 DEG C / min at 400-800 DEG C, the temperature rising rate is 3-6 DEG C / min at 800-1300 DEG C, the temperature rising rate is 5-10 DEG C / min at 1300-1750 DEG C, the final sintering temperature is 1700-1800 DEG C, and the holding time is 1-2 h. The silicon nitride ceramic prepared through the above formula and preparation method has a density of 70-94%, a bending strength of 200-300 MPa, and can be used in the field of aerospace.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a silicon nitride ceramic formula that can be used in a 3D printing process and a method for preparing the silicon nitride ceramic. Background Art

[0002] Additive manufacturing technology, originating in the 1980s, enables the fabrication of complex structures through the layer-by-layer accumulation of materials. This includes additive manufacturing of polymers, metals, ceramics, and biomaterials. Its process involves two steps: 3D design and layer-by-layer printing. It offers unparalleled advantages over subtractive manufacturing in fields such as aerospace and mold making.

[0003] Additive manufacturing technology is developing rapidly in the field of ceramic preparation, with significant achievements in alumina ceramics, silica ceramics, and zirconia ceramics. Alumina ceramics prepared using additive manufacturing technology, after sintering, achieve a density of 99% and a flexural strength of 400 MPa, with overall performance comparable to alumina ceramics prepared using conventional molding technology. Silica ceramics prepared using additive manufacturing technology have an adjustable porosity between 65% and 99%, encompassing porous ceramics and high-density glass-ceramics, with a wider range of applications. Zirconia ceramics prepared using additive manufacturing technology achieve a density of 97%, a ceramic hardness of 13 GPa, and a flexural strength of 1000 MPa. Ceramic products prepared using additive manufacturing technology demonstrate superior performance in terms of precision, structural complexity, production cycle, environmental friendliness, and overall performance.

[0004] In recent years, there have been many attempts to use additive manufacturing technology in the preparation of silicon nitride ceramics, but the results have not been good. The main problem is that cracks occur between printed layers during the sintering process, and the specific reason is unknown. The invention team of this patent conducted an in-depth analysis and concluded that the stress release between silicon nitride printed layers is concentrated during the low-temperature (~1000°C) sintering stage, but there is no high-temperature viscous material between the layers to absorb the stress, resulting in interlayer cracking. This patent optimizes the silicon nitride ceramic formula. By doping with a variety of high-temperature "binders", the interlayer stress during the sintering shrinkage process can be absorbed in each temperature rising zone, thereby realizing the preparation of structurally controllable silicon nitride ceramics. Summary of the Invention

[0005] (1) Technical issues to be resolved

[0006] To address the current problem of preparing silicon nitride ceramics using 3D printing technology, namely interlayer cracking during the sintering process, the present invention provides a set of silicon nitride ceramic formulas to achieve the release of interlayer stress during the high-temperature sintering stage, and ultimately the overall uniform shrinkage of the ceramic.

[0007] (2) Technical solution

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] In its first aspect, the present invention provides a silicon nitride ceramic formulation suitable for 3D printing, comprising the following ceramic powders in the following mass ratios: 75-85% silicon nitride powder, 3-6% boron oxide powder, 3-5% silicon oxide powder, 3-6% aluminum oxide powder, 3-6% yttrium oxide powder, and 3-5% boron nitride powder. Except for the silicon nitride powder, the remaining components are sintering aids.

[0010] Preferably, in the ceramic formula, the average particle size of silicon nitride powder, boron oxide powder, yttrium oxide powder, and boron nitride powder is 0.5-1 micron, and the particle size of silicon oxide powder and aluminum oxide powder is 0.1-0.3 micron.

[0011] It is worth noting that, in the ceramic formulation, as an alternative formulation, boron oxide can be replaced by boric acid, that is, 3-6% boron oxide powder or 3-6% boric acid.

[0012] The formula provided by the present invention can overcome the stress release of 3D printed components during the sintering process, providing technical support for the additive preparation of silicon nitride.

[0013] In a second aspect, the present invention provides a method for preparing silicon nitride ceramics using a 3D printing process, comprising the following steps:

[0014] Ceramic powder that can be used in 3D printing process is prepared according to the above silicon nitride ceramic formula;

[0015] Using the prepared ceramic powder, a silicon nitride blank is prepared by a 3D printing process;

[0016] The silicon nitride body is subjected to a sintering temperature increase program to obtain silicon nitride ceramics.

[0017] Preferably, the ceramic powder for 3D printing prepared according to the aforementioned silicon nitride ceramic formula comprises the following main steps: powder weighing and mixing, liquid-phase ball milling, drying, pulverization, and screening. It is worth noting that the liquid-phase ball milling medium is water, with a water-to-powder mass ratio of (1-2):1; the sieving sieve is 100 mesh.

[0018] Preferably, the 3D printing process includes photosensitive curing molding and fused deposition modeling.

[0019] Preferably, the green body sintering process has a specific sintering temperature rise program, so that each sintering aid can play a fluxing role within its temperature range, thereby reducing interlaminar stress and ensuring that the green body can shrink as a whole.

[0020] Preferably, the sintering temperature rise program includes: when the temperature rise range is 400-800°C, boron oxide will gradually melt, improve the adhesion between printed layers, and absorb interlayer stress; when the temperature rise range is 800-1300°C, silicon oxide will gradually melt to ensure that the ceramic component begins to shrink as a whole; when the temperature rise range is 1300-1750°C, aluminum oxide, yttrium oxide, and boron nitride will successively increase the strength and toughness of the ceramic component by increasing the grain boundary area between particles, and resist damage to the component caused by stress during shrinkage deformation.

[0021] Preferably, the sintering temperature program is as follows: the heating rate from 400 to 800°C is 0.5-2°C / min, the heating rate from 800 to 1300°C is 3-6°C / min, the heating rate from 1300 to 1750°C is 5-10°C / min, the final sintering temperature is 1700-1800°C, and the holding time is 1-2h.

[0022] In a third aspect, the present invention provides a silicon nitride ceramic prepared according to the above preparation method.

[0023] The silicon nitride ceramics prepared by the above-mentioned method for preparing the silicon nitride ceramics can have a density of 70-94% and a bending strength of 200-300 MPa.

[0024] (3) Beneficial effects

[0025] The above technical solution of the present invention has the following advantages:

[0026] (1) The silicon nitride ceramic formula proposed in the present invention can effectively overcome the stress concentration during the sintering process of silicon nitride ceramics and achieve uniform shrinkage of silicon nitride ceramics.

[0027] (2) The silicon nitride ceramics prepared by the present invention have performances that reach the level of conventional processes, with a ceramic density of 70-94% and a bending strength of 200-300 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flowchart of the steps of the method for preparing silicon nitride ceramics using a 3D printing process. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] The present invention provides a silicon nitride ceramic formula and a method for preparing silicon nitride ceramic that can be used in a 3D printing process. The preparation process includes the following steps:

[0031] First, a ceramic powder is prepared: 75-85% silicon nitride powder, 3-6% boron oxide powder or 3-6% boric acid, 3-5% silicon oxide powder, 3-6% aluminum oxide powder, 3-6% yttrium oxide powder, and 3-5% boron nitride powder; the average particle size of the silicon nitride powder, boron oxide powder, yttrium oxide powder, and boron nitride powder is 0.5-1 micron, and the particle size of the silicon oxide powder and aluminum oxide powder is 0.1-0.3 micron. Then, the above powders are weighed and mixed, liquid-phase ball milled at a water-to-material ratio of (1-2):1, dried, crushed, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride blank is prepared using photosensitive curing molding or fused deposition modeling. Finally, the following sintering temperature program is performed: 400-800°C at a heating rate of 0.5-2°C / min, 800-1300°C at a heating rate of 3-6°C / min, and 1300-1750°C at a heating rate of 5-10°C / min. The final sintering temperature is 1700-1800°C, and the holding time is 1-2 hours. The silicon nitride ceramic formula and application method described above can produce silicon nitride ceramics with a density of 70-94% and a flexural strength of 200-300 MPa, suitable for use in the aerospace industry.

[0032] Example 1

[0033] First, a ceramic powder was prepared: 80% silicon nitride powder, 5% boron oxide powder, 5% silicon oxide powder, 3% aluminum oxide powder, 3% yttrium oxide powder, and 4% boron nitride powder. The average particle size of the silicon nitride, boron oxide, yttrium oxide, and boron nitride powders was 1 micron, while the particle size of the silicon oxide and aluminum oxide powders was 0.2 micron. The powders were then weighed, mixed, liquid-phase ball milled at a 1:1 water-to-material ratio, dried, pulverized, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride green body was prepared using photopolymerization. Finally, the following sintering temperature program was followed: a heating rate of 2°C / min from 400-800°C, 6°C / min from 800-1300°C, and 10°C / min from 1300-1750°C. The final sintering temperature was 1700°C, and the hold time was 1 hour. The silicon nitride ceramics prepared by the above-mentioned silicon nitride ceramic formula and application method can achieve a density of 70% and a bending strength of 200 MPa.

[0034] Example 2

[0035] First, a ceramic powder was prepared: 85% silicon nitride powder, 3% boron oxide powder, 3% silicon oxide powder, 3% aluminum oxide powder, 3% yttrium oxide powder, and 3% boron nitride powder. The average particle size of the silicon nitride, boron oxide, yttrium oxide, and boron nitride powders was 1 micron, while the particle size of the silicon oxide and aluminum oxide powders was 0.2 micron. The powders were then weighed, mixed, liquid-phase ball milled at a 1:1 water-to-material ratio, dried, pulverized, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride green body was prepared using photopolymerization. Finally, the following sintering temperature program was followed: a heating rate of 2°C / min from 400°C to 800°C, 6°C / min from 800°C to 1300°C, and 10°C / min from 1300°C to 1750°C. The final sintering temperature was 1700°C, and the hold time was 1 hour. The silicon nitride ceramics prepared by the above-mentioned silicon nitride ceramic formula and application method can achieve a density of 80% and a bending strength of 240 MPa.

[0036] Example 3

[0037] First, a ceramic powder was prepared: 85% silicon nitride powder, 3% boron oxide powder, 3% silicon oxide powder, 3% aluminum oxide powder, 3% yttrium oxide powder, and 3% boron nitride powder. The average particle size of the silicon nitride, boron oxide, yttrium oxide, and boron nitride powders was 0.5 microns, while the particle size of the silicon oxide and aluminum oxide powders was 0.1 microns. The powders were then weighed, mixed, liquid-phase ball milled at a 1:1 water-to-material ratio, dried, pulverized, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride green body was prepared using photopolymerization. Finally, the following sintering temperature program was followed: a heating rate of 2°C / min from 400°C to 800°C, 6°C / min from 800°C to 1300°C, and 10°C / min from 1300°C to 1750°C. The final sintering temperature was 1700°C, and the hold time was 1 hour. The silicon nitride ceramics prepared by the above-mentioned silicon nitride ceramic formula and application method can achieve a density of 83% and a bending strength of 270 MPa.

[0038] Example 4

[0039] First, a ceramic powder was prepared: 85% silicon nitride powder, 3% boron oxide powder, 3% silicon oxide powder, 3% aluminum oxide powder, 3% yttrium oxide powder, and 3% boron nitride powder. The average particle size of the silicon nitride, boron oxide, yttrium oxide, and boron nitride powders was 0.5 microns, while the particle size of the silicon oxide and aluminum oxide powders was 0.1 microns. The powders were then weighed, mixed, liquid-phase ball milled at a 2:1 water-to-material ratio, dried, pulverized, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride green body was prepared using photopolymerization. Finally, the following sintering temperature program was followed: 400-800°C at a heating rate of 1°C / min, 800-1300°C at a heating rate of 4°C / min, and 1300-1750°C at a heating rate of 5°C / min. The final sintering temperature was 1700°C, and the holding time was 1 hour. The silicon nitride ceramics prepared by the above-mentioned silicon nitride ceramic formula and application method can achieve a density of 86% and a bending strength of 290 MPa.

[0040] Example 5

[0041] First, a ceramic powder was prepared: 85% silicon nitride powder, 3% boron oxide powder, 3% silicon oxide powder, 3% aluminum oxide powder, 3% yttrium oxide powder, and 3% boron nitride powder. The average particle size of the silicon nitride, boron oxide, yttrium oxide, and boron nitride powders was 0.5 microns, while the particle size of the silicon oxide and aluminum oxide powders was 0.1 microns. The powders were then weighed, mixed, liquid-phase ball milled at a water-to-material ratio of 2:1, dried, pulverized, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride green body was prepared using photopolymerization. Finally, the sintering temperature was ramped as follows: 400-800°C at a heating rate of 1°C / min, 800-1300°C at a heating rate of 4°C / min, and 1300-1750°C at a heating rate of 5°C / min. The final sintering temperature was 1750°C, and the holding time was 1 hour. The silicon nitride ceramics prepared by the above formula and application method can achieve a density of 90% and a bending strength of 300MPa.

[0042] Example 6

[0043] First, a ceramic powder was prepared: 85% silicon nitride powder, 3% boron oxide powder, 3% silicon oxide powder, 3% aluminum oxide powder, 3% yttrium oxide powder, and 3% boron nitride powder. The average particle size of the silicon nitride, boron oxide, yttrium oxide, and boron nitride powders was 0.5 microns, while the particle size of the silicon oxide and aluminum oxide powders was 0.1 microns. The powders were then weighed, mixed, liquid-phase ball milled at a 2:1 water-to-material ratio, dried, pulverized, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride green body was prepared using photopolymerization. Finally, the following sintering temperature program was followed: 400-800°C at a heating rate of 1°C / min, 800-1300°C at a heating rate of 4°C / min, and 1300-1750°C at a heating rate of 5°C / min. The final sintering temperature was 1800°C, and the holding time was 1 hour. The silicon nitride ceramics prepared by the above-mentioned silicon nitride ceramic formula and application method can achieve a density of 92% and a bending strength of 280 MPa.

[0044] Example 7

[0045] First, a ceramic powder was prepared: 85% silicon nitride powder, 3% boron oxide powder, 3% silicon oxide powder, 3% aluminum oxide powder, 3% yttrium oxide powder, and 3% boron nitride powder. The average particle size of the silicon nitride, boron oxide, yttrium oxide, and boron nitride powders was 0.5 microns, while the particle size of the silicon oxide and aluminum oxide powders was 0.1 microns. The powders were then weighed, mixed, liquid-phase ball milled at a water-to-material ratio of 2:1, dried, pulverized, and sieved through 100 mesh to obtain a ceramic powder suitable for 3D printing. Subsequently, a silicon nitride green body was prepared using photopolymerization. Finally, the following sintering temperature program was followed: a heating rate of 1°C / min from 400°C to 800°C, 4°C / min from 800°C to 1300°C, and 5°C / min from 1300°C to 1750°C. The final sintering temperature was 1800°C, and the hold time was 2 hours. The silicon nitride ceramics prepared by the above-mentioned silicon nitride ceramic formula and application method can achieve a density of 94% and a bending strength of 260 MPa.

[0046] The performance of the components prepared in the above embodiments was recorded, and the results are shown in Table 1.

[0047] Table 1

[0048]

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing silicon nitride ceramics using a 3D printing process, characterized in that: The following steps are involved: Ceramic powder for 3D printing is prepared according to a silicon nitride ceramic formula; the silicon nitride ceramic formula includes the following ceramic powders and mass ratios: 75-85% silicon nitride powder, 3-6% boron oxide powder, 3-5% silicon oxide powder, 3-6% aluminum oxide powder, 3-6% yttrium oxide powder, and 3-5% boron nitride powder; except for the silicon nitride powder, the rest are sintering aids; Using the prepared ceramic powder, a silicon nitride blank is prepared by a 3D printing process; performing a sintering temperature increase program on the silicon nitride blank to obtain silicon nitride ceramics; In the sintering temperature rise program, each sintering aid works in a different temperature range and principle: when the temperature rise range is 400-800°C, boron oxide gradually melts, improving the adhesion between printed layers and absorbing interlayer stress; when the temperature rise range is 800-1300°C, silicon oxide gradually melts, ensuring that the ceramic component begins to shrink as a whole; when the temperature rise range is 1300-1750°C, aluminum oxide, yttrium oxide, and boron nitride successively increase the grain boundary area between particles to improve the toughness of the ceramic component, resisting damage to the component caused by stress during shrinkage deformation; The sintering temperature program includes: 400-800°C heating rate of 0.5-2°C / min, 800-1300°C heating rate of 3-6°C / min, 1300-1750°C heating rate of 5-10°C / min, the final sintering temperature of 1700-1800°C, and the holding time of 1-2h.

2. The preparation method according to claim 1, characterized in that The average particle size of silicon nitride powder, boron oxide powder, yttrium oxide powder and boron nitride powder is 0.5-1 micron, and the particle size of silicon oxide powder and aluminum oxide powder is 0.1-0.3 micron.

3. The preparation method according to claim 1, characterized in that Boric acid is used to replace boron oxide, and the mass fraction of boric acid is 3-6%.

4. The preparation method according to claim 1, characterized in that The preparation of ceramic powder that can be used in a 3D printing process includes powder weighing and mixing, liquid-phase ball milling, drying, crushing, and screening; the medium used in the liquid-phase ball milling is water, and the mass ratio of water to powder is (1-2):1; the mesh size used for screening is 100 mesh.

5. The preparation method according to claim 1, characterized in that The 3D printing process includes photosensitive curing molding and fused deposition modeling.

6. Silicon nitride ceramics prepared according to the preparation method according to any one of claims 1 to 5.

7. The silicon nitride ceramic according to claim 6, characterized in that The silicon nitride ceramic has a density of 70-94% and a bending strength of 200-300 MPa.

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