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CN-121974706-A - Silicon nitride ceramic with low thermal conductivity and high hardness and preparation method thereof

CN121974706ACN 121974706 ACN121974706 ACN 121974706ACN-121974706-A

Abstract

The invention relates to a silicon nitride ceramic with low thermal conductivity and high hardness and a preparation method thereof. The method comprises the steps of mixing raw materials of low-heat-conductivity high-hardness silicon nitride ceramics, adding a solvent, ball milling to obtain slurry, drying the slurry, sieving the slurry, wherein the raw materials comprise silicon nitride, aluminum nitride, silicon oxide, a precursor of metal ion A and a precursor of metal ion B, the metal ion A is ytterbium or lutetium, the metal ion B is selected from one or more than two of calcium, strontium, sodium and barium, and SPS sintering, cold isostatic pressing, air pressure sintering or hot press sintering are carried out on powder obtained through sieving to obtain the silicon nitride ceramics. The invention realizes the combination of low thermal conductivity and high mechanical property in the SN ceramic through the design of coexistence of submicron-micron isometric crystal and columnar crystal.

Inventors

  • ZHANG SHIJIA
  • LIU GUANGHUA
  • CHEN KEXIN

Assignees

  • 清华大学

Dates

Publication Date
20260505
Application Date
20251225

Claims (10)

  1. 1. A preparation method of a low-thermal conductivity high-hardness silicon nitride ceramic comprises the following steps: (1) Mixing raw materials of low-heat-conductivity high-hardness silicon nitride ceramics, adding a solvent, ball-milling to obtain slurry, drying the slurry, and sieving, wherein the raw materials of the low-heat-conductivity high-hardness silicon nitride ceramics comprise silicon nitride, aluminum nitride, silicon oxide, a precursor of metal ion A and a precursor of metal ion B, the metal ion A is ytterbium or lutetium, and the metal ion B is selected from one or more than two of calcium, strontium, sodium and barium; (2) Placing the sieved powder into SPS sintering mould, heating under vacuum and mechanical pressure to make SPS sintering, then cooling so as to obtain silicon nitride ceramic, or making the sieved powder undergo the processes of tabletting machine, initially forming, cold isostatic pressing, placing into crucible, air-pressure sintering under the nitrogen atmosphere, then cooling so as to obtain silicon nitride ceramic, or directly placing the sieved powder into hot-press mould or tabletting and cold isostatic pressing, then placing into hot-press mould, hot-press sintering under the nitrogen atmosphere, then cooling so as to obtain the silicon nitride ceramic.
  2. 2. The preparation method according to claim 1, wherein the mass ratio of the raw materials of the grinding ball and the low thermal conductivity high hardness silicon nitride ceramic in the ball milling process is 3:1 to 2:1; the ball milling time is 0.5-24 h.
  3. 3. The method of claim 1, wherein the SPS sintering has a maximum temperature of 1400-1900 ℃, a mechanical pressure of 50-200 MPa, and a holding time at the maximum temperature of 3-30 min; The temperature of the air pressure sintering is 1800-2000 ℃, the nitrogen pressure is 0.5-4 MPa, and the heat preservation time is 0.5-4 h; the hot-pressed sintering temperature is 1700-2000 ℃, the nitrogen pressure is 0.5-4 MPa, the mechanical pressure is 0-100 MPa, and the heat preservation time is 0.5-4 h.
  4. 4. The preparation method according to claim 1, wherein the molar ratio of the metal ion A to the metal ion B is 0.01:1-1:0.01.
  5. 5. The preparation method according to claim 1, wherein the metal ion A is ytterbium, the metal ion B is calcium, and the atomic ratio of ytterbium and calcium in silicon nitride is 2-7%.
  6. 6. The preparation method of claim 1, wherein the precursor of the metal ion A is ytterbium oxide and the precursor of the metal ion B is calcium carbonate.
  7. 7. The preparation method according to claim 1 or 6, wherein the molar ratio of the raw materials of the low-thermal-conductivity high-hardness silicon nitride ceramic is as follows: Si 3 N 4 : AlN : SiO 2 : Yb 2 O 3 : CaCO 3 = (16-x-2y) : (4x+4y) : (2y-x) : 4a : 4b; wherein the value range of x and y satisfies 0.8< x <3.6,0.5< y <2; a and b satisfy 6a+2b=x and a≥0, b≥0.
  8. 8. A low thermal conductivity high hardness silicon nitride ceramic, wherein it is prepared by the method of any one of claims 1-7.
  9. 9. The low thermal conductivity high hardness silicon nitride ceramic according to claim 8, wherein the silicon nitride ceramic has a morphology in which equiaxed crystals and columnar crystals coexist, and a grain size of 100 nm to 5 μm.
  10. 10. The low thermal conductivity high hardness silicon nitride ceramic according to claim 8, wherein the atomic ratio of Al in si+al is 12 to 40%.

Description

Silicon nitride ceramic with low thermal conductivity and high hardness and preparation method thereof Technical Field The invention relates to a silicon nitride ceramic with low thermal conductivity and high hardness and a preparation method thereof, belonging to the technical field of ceramic materials. Background In high temperature insulation applications, such as thermal barrier coatings for aircraft engine turbine blades, thermal engine inner cabins, and components that require reduced heat loss or thermal protection, stringent requirements are placed on the heat resistance, oxidation resistance, and thermal insulation capabilities of the material. Since metallic materials generally rely on free electron conduction, their thermal conductivity is generally high (e.g., steel is more than 40W/(mK)), resulting in poor self-insulation properties, and it is difficult to meet the above requirements. In contrast, many ceramic materials have a greater resistance to heat, oxidation and lower thermal conductivity and are therefore widely used in the field of thermal protection. In particular, ceramic materials having a thermal conductivity of less than 5W/(mK) are considered critical for achieving effective thermal insulation. However, in practical application, the material only has low thermal conductivity and is required to have good comprehensive performance so as to improve the application value and service reliability. Higher hardness means that the material has stronger wear resistance, higher toughness (typically measured as fracture toughness KIC) means that the material has better crack propagation resistance, contributing to longer working life, and lower density is beneficial to achieving device weight reduction, which is critical for weight sensitive applications such as aerospace. Currently, low thermal conductivity ceramic materials commonly used in the industry mainly include 8wt% yttria stabilized zirconia (8 YSZ), lanthanum Zirconate (LZO), and the like. For example, 8YSZ ceramics have a room temperature thermal conductivity of about 3.1W/(m.K) and meet low thermal conductivity requirements, but have a hardness (about 13 GPa) and toughness (about 4.4 MPa.m 1/2) at only moderate levels, and a relatively high density (about 6.0 g/cm 3), similar to many metallic materials. LZO ceramics have a room temperature thermal conductivity of about 3.2W/(mK), but have lower hardness (about 10 GPa) and toughness (about 2.0 MPa m 1/2) and also have higher density (about 6.1 g/cm 3). Thus, although 8YSZ and LZO ceramics are widely used due to their low thermal conductivity, their properties in terms of hardness, toughness and density (weight reduction) are relatively general, limiting their further use in certain high performance, weight reduction requirements. Among ceramic material systems, silicon nitride (Si 3N4, abbreviated as SN) ceramics are known for their excellent overall mechanical properties. The hardness can be as high as 19 GPa, fracture toughness is generally higher than 5 MPa m 1/2, and the density is only about 3.2 g/cm 3, which is significantly better than 8YSZ and LZO materials, exhibiting the desirable combination of properties of high hardness, high toughness and low density. However, silicon nitride ceramics have high phonon propagation rate and high intrinsic thermal conductivity due to the strong covalent bonds in their crystal structure. Even the alpha-phase silicon nitride ceramics with more impurities and defects and relatively low thermal conductivity have the thermal conductivity higher than 20W/(mK), and the thermal conductivity experimental value of the high-purity beta-phase silicon nitride ceramics can even exceed 170W/(mK). Therefore, silicon nitride ceramics are generally regarded as high thermal conductivity materials, and are used in applications requiring heat dissipation or heat conduction rather than heat insulation, and their excellent mechanical and lightweight properties are difficult to be directly applied to fields requiring strict requirements for heat insulation. In summary, the prior art has the problems that the low thermal conductivity ceramic materials (such as 8YSZ and LZO) widely used at present have the heat insulation performance meeting the requirements, but the hardness, toughness and lightweight (low density) performance are required to be improved, while the silicon nitride ceramic with excellent mechanical properties and low density characteristics cannot meet the requirements of the low thermal conductivity heat insulation application due to the inherent high intrinsic thermal conductivity. Therefore, the development of a novel ceramic material with low thermal conductivity (for example, less than or equal to 5W/(m.K)), high hardness, high toughness and low density has important practical significance and urgent need for promoting the development of high-performance heat insulation technology, especially in the high-technology fields of aerospace and