A thermal expansion gradient type composite ceramic body and a preparation method of the composite ceramic body

Abstract

The application discloses a thermal expansion gradient type composite ceramic body and a preparation method of the composite ceramic body, relates to the technical field of ceramic materials, and realizes the protection of a yttrium-magnesium composite ceramic window base material by preparing yttrium-magnesium composite ceramics with different components and by the different thermal expansion coefficients caused by the different components, so that the purpose of preventing thermal shock cracking is achieved. The thermal expansion gradient type composite ceramic body takes yttria-magnesium oxide with a volume ratio of 1:1 as the base of an infrared window, a yttria-magnesium oxide composite surface layer with a thickness of 0.5-1.0 mm and a lower thermal expansion coefficient is arranged on the surface of the base, the surface layer exerts a compressive stress on the base in the heating process by using the thermal expansion difference, the generation and expansion of surface cracks are inhibited, and the stability and service life of the ceramic structure are improved.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, and in particular to a thermally expanded gradient type multiphase ceramic body and a method for preparing the multiphase ceramic body. Background Technology

[0002] Multiphase ceramics generally refer to ceramic bodies or materials composed of two or more phases with different chemical compositions or crystal structures. Currently, high-performance infrared optical core materials possessing both high infrared transmittance and excellent mechanical properties mainly include Y₂O₃-MgO multiphase ceramics, mullite multiphase ceramics, silicon nitride-boron nitride multiphase ceramics, MgAl₂O₄-based multiphase ceramics, and AlON. In particular, Y₂O₃-MgO multiphase ceramic materials are used in the aerospace field as infrared windows and radomes, capable of withstanding high temperatures and high-speed airflow erosion, ensuring stable operation of infrared detection and guidance systems. In the field of infrared optoelectronics, for example, Y₂O₃-MgO multiphase ceramics are suitable for infrared thermal imagers, detectors, and infrared temperature measurement windows, exhibiting high transmittance, clear imaging, and high sensitivity in the 3-5 micrometer mid-infrared band. Furthermore, Y2O3-MgO composite ceramic materials, with their high thermal conductivity and low phonon energy characteristics, can be used as mid-infrared laser matrix materials and applied to high-power laser devices, playing an irreplaceable role in high-end equipment such as military, industrial inspection, and medical detection.

[0003] These types of multiphase ceramic materials, such as existing Y2O3-MgO multiphase ceramics, are produced by uniformly mixing Y2O3 nanoparticles and MgO nanoparticles in a molar ratio of 1:5, followed by sintering to obtain a Y2O3-MgO multiphase ceramic body with a volume ratio of 1:1. While these multiphase ceramics achieve the best overall performance in terms of infrared transmittance and mechanical properties, the uniform or identical ceramic material composition of the ceramic body makes them more susceptible to thermal shock cracking and damage under extremely high-temperature environments, resulting in lower safety assurance for aerospace components. Summary of the Invention

[0004] The purpose of this invention is to address the problem that existing multiphase ceramic materials, due to their uniform composition, pose a significant risk of thermal shock cracking and damage in the face of rapidly increasing temperatures. This invention provides a thermally expanding gradient multiphase ceramic body and a method for preparing the multiphase ceramic body.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A thermally expanded gradient type multiphase ceramic body includes a substrate and a surface layer; the surface layer is thermally bonded to the outside of the substrate; the substrate is a first ceramic layer; the surface layer is a second ceramic layer; the coefficient of thermal expansion of the first ceramic layer is greater than the coefficient of thermal expansion of the second ceramic layer.

[0007] The thermal expansion gradient type multiphase ceramic body described in this invention, by setting the surface layer thermally bonded to the outside of the substrate, and setting the thermal expansion coefficient of the first ceramic layer of the substrate to be greater than that of the second ceramic layer, forms a multiphase ceramic body with two thermal expansion gradients for the surface layer and the substrate. When facing a rapidly heating environment, the surface of the ceramic body heats up faster, and the smaller expansion coefficient of the surface layer reduces the volume sensitivity to temperature. The interior of the ceramic body heats up slower, and the larger thermal expansion coefficient of the substrate increases the sensitivity to temperature. The surface layer generates compressive stress on the substrate inward, which significantly inhibits the generation of surface cracks, reduces the possibility of expansion fracture between crystals, and improves the thermal shock resistance and fracture toughness of the multiphase ceramic. While taking into account infrared transmittance and mechanical properties, it reduces the risk of thermal shock cracking and damage to the ceramic body or device, and improves the safety and robustness of such materials as devices.

[0008] Preferably, in the thermal expansion gradient type multiphase ceramic body of the present invention, the first ceramic layer comprises a first proportion of multiphase ceramic material; the second ceramic layer comprises a second proportion of the multiphase ceramic material.

[0009] As a preferred embodiment of the present invention, by setting the second ceramic layer to include the same type of multiphase ceramic material as the first ceramic layer, the difference is that the first ceramic layer uses a first ratio of multiphase ceramic material and the second ceramic layer uses a second ratio, so that the substances of the multiphase materials are the same but the proportions are different. On the basis of enhancing the consistency of infrared transmittance and mechanical properties of the multiphase ceramic body, the thermal shock resistance and fracture toughness of the multiphase ceramic are improved, and the applicability and functional reliability of the multiphase ceramic body are further improved.

[0010] Preferably, in the thermal expansion gradient type multiphase ceramic body of the present invention, the multiphase ceramic material is Y2O3-MgO multiphase ceramic; the first ratio is a first target volume ratio of Y2O3:MgO; the second ratio is a second target volume ratio of Y2O3:MgO; the value of the first target volume ratio is less than the value of the second target volume ratio.

[0011] As a preferred embodiment of the present invention, by setting the multiphase ceramic material to Y2O3-MgO multiphase ceramic, which has better optical properties, it is preferable that the target volume ratio of Y2O3:MgO in the Y2O3-MgO multiphase ceramic has a high correlation with the coefficient of thermal expansion. Furthermore, by setting the value of the first target volume ratio to be less than the value of the second target volume ratio, the difference in volume expansion between the ceramic body surface and the outside can be further reduced, thereby improving the thermal shock resistance and fracture toughness of the multiphase ceramic.

[0012] Preferably, in the thermal expansion gradient type multiphase ceramic body of the present invention, the first target volume ratio is 1:1; and the second target volume ratio is 6:4 to 9:1.

[0013] As a preferred embodiment of the present invention, based on setting the multiphase ceramic material as Y2O3-MgO multiphase ceramic, the ratio range of the second target volume ratio and the first target volume ratio is further optimized, thereby further improving the infrared transmittance and mechanical properties, while further improving the thermal shock resistance and fracture toughness of the multiphase ceramic.

[0014] Preferably, in the thermal expansion gradient type multiphase ceramic body of the present invention, the thickness of the substrate perpendicular to the surface direction is 3 to 10 times the thickness of the surface layer.

[0015] As a preferred embodiment of the present invention, by controlling the thickness of the substrate, the possibility of interface delamination and peeling caused by excessive thermal expansion difference can be reduced.

[0016] Preferably, in the thermal expansion gradient type multiphase ceramic body of the present invention, the thickness of the substrate perpendicular to the surface direction is 3.0~5.0mm; and the thickness of the surface layer is 0.5~1.0mm.

[0017] As a preferred embodiment of the present invention, by matching the thickness range of the substrate and the thickness range of the surface layer, the possibility of interface delamination and peeling caused by excessive thermal expansion difference can be reduced, while possessing adaptability as a device and improving the applicability of the multiphase ceramic body.

[0018] To achieve the objectives of this invention, another technical solution is provided:

[0019] A method for preparing a multiphase ceramic body, capable of preparing the thermal expansion gradient type multiphase ceramic body of the present invention, includes the following steps:

[0020] S1. Prepare a first powder according to the first raw material ratio of the first ceramic layer; prepare a second powder according to the second raw material ratio of the second ceramic layer; and perform powder processing on each powder.

[0021] S2. The first powder and the second powder are respectively subjected to molding or cold isostatic pressing to obtain the first ceramic blank and the second ceramic blank;

[0022] S3. The first ceramic blank and the second ceramic blank are respectively debinded in an air environment of 600-800°C, and then sintered, kept warm and cooled in sequence to obtain the first ceramic layer and the second ceramic layer.

[0023] S4. Polish the bonding surfaces of the first ceramic layer and the second ceramic layer respectively;

[0024] S5. The bonding surfaces of the first ceramic layer and the second ceramic layer are brought together and subjected to thermal bonding under pressure and temperature conditions to obtain a thermally expanded gradient type multiphase ceramic body.

[0025] The method for preparing the multiphase ceramic body described in this invention can prepare a multiphase ceramic body with two thermal expansion gradients that are thermally bonded to the substrate. By proportioning the first raw material of the first ceramic layer and the second raw material of the second ceramic layer, the thermal expansion coefficient of the first ceramic layer of the substrate can be made greater than that of the second ceramic layer, thus preparing a multiphase ceramic body with stronger thermal shock resistance and fracture toughness, as well as superior infrared transmittance and mechanical properties.

[0026] Preferably, in the method for preparing the multiphase ceramic body of the present invention, the pressure condition is 1~3MPa; the temperature condition is 500-800℃; and the thermal bonding treatment time is 100~500 hours.

[0027] As a preferred embodiment of the present invention, by setting the above-mentioned thermal bonding treatment conditions, the thermal bonding effect of the first ceramic layer and the second ceramic layer can be further optimized, the crystal form can be improved, and the overall crack resistance of the multiphase ceramic body can be further enhanced, thereby improving the overall performance of the multiphase ceramic body.

[0028] Preferably, in the method for preparing the multiphase ceramic body of the present invention, the polishing achieves a surface finish of ≤5nm on the bonding surface.

[0029] As a preferred embodiment of the present invention, by controlling the surface finish of the surfaces to be bonded, the interaction between the surfaces to be bonded during thermal bonding can be further improved, and the possibility of interface delamination and peeling due to excessive thermal expansion difference can be further reduced.

[0030] Preferably, in the method for preparing the multiphase ceramic body of the present invention, the heating rate for debinding is 2~5℃ / min; and the heating rate for sintering is 5~10℃ / min.

[0031] As a preferred embodiment of the present invention, by controlling the heating rate of the debinding and sintering, the grain size and crystal morphology of the multiphase ceramic body can be further optimized, thereby further improving the thermal shock resistance and fracture toughness of the multiphase ceramic body.

[0032] Preferably, in the method for preparing the multiphase ceramic body of the present invention, the molding pressure is 20~50 MPa; the cold isostatic pressing is 100~200 MPa.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] 1. The aforementioned thermal expansion gradient type multiphase ceramic body exhibits rapid surface heating in the face of extremely rapid heating environments. The smaller coefficient of thermal expansion at the surface reduces the volume's sensitivity to temperature, while the slower heating inside the ceramic body increases its sensitivity to temperature due to the larger coefficient of thermal expansion at the substrate. This generates compressive stress from the surface layer into the substrate, significantly inhibiting surface crack formation and reducing the likelihood of expansion fracture between crystals. This enhances the thermal shock resistance and fracture toughness of the multiphase ceramic body. By balancing infrared transmittance and mechanical properties, it reduces the risk of thermal shock cracking and damage to the ceramic body or device, thereby improving the safety and robustness of devices made from this material.

[0035] 2. The method for preparing the composite ceramic body can prepare a composite ceramic body with two thermal expansion gradients that are thermally bonded to the substrate by the surface layer. By proportioning the first raw material of the first ceramic layer and the second raw material of the second ceramic layer, the thermal expansion coefficient of the first ceramic layer of the substrate can be made greater than that of the second ceramic layer, thus preparing a composite ceramic body with stronger thermal shock resistance and fracture toughness, as well as superior infrared transmittance and mechanical properties. Moreover, the preparation steps are not complicated, and the properties of the substrate and the surface layer are highly controllable and stable. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the cross-sectional structure of the thermal expansion gradient type multiphase ceramic body of the present invention;

[0037] Figure 2 This is a process flow diagram of the preparation method of the multiphase ceramic body of the present invention;

[0038] Icons: 1. Base; 2. Surface. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings.

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] Example 1:

[0042] refer to Figure 1 As shown, the present invention discloses a thermal expansion gradient type multiphase ceramic body, including a substrate 1 and a surface layer 2; the surface layer 2 is thermally bonded to the outside of the substrate 1; the substrate 1 is a first ceramic layer; the surface layer 2 is a second ceramic layer; the thermal expansion coefficient of the first ceramic layer is greater than that of the second ceramic layer.

[0043] The term "multiphase" as used in this invention is understood to refer to ceramic bodies or ceramic materials with two or more different chemical compositions or different crystal structures. This can be understood as including a composite of two-phase crystal structures. For example, the multiphase ceramic body of this invention includes a two-phase crystal structure composed of a first ceramic material and a second ceramic material. Alternatively, it can be understood as a composite of two materials. For example, the first ceramic material is a Y2O3-MgO multiphase ceramic crystal composed of Y2O3 and MgO; the second ceramic material is also a Y2O3-MgO multiphase ceramic composed of Y2O3 and MgO, but the ratio of Y2O3 to MgO in the first ceramic material is different from that in the second ceramic material, resulting in different crystal structures for the first and second ceramic materials.

[0044] It should be noted that the first target volume ratio or the second target volume ratio mentioned in this invention is understood as the volume ratio of the multiphase ceramic in the final sintered green or formed ceramic body. In the preparation process, the proportion of raw material powders can be calculated by the density of each material to determine the required mass fraction of raw materials, thereby achieving the target volume ratio requirement. For example, if the first ceramic crystal needs to achieve a first target volume ratio of Y2O3:MgO of 1:1, the initial mass of Y2O3 powder and MgO powder to be prepared can be calculated based on the density of Y2O3 powder and MgO powder, thereby achieving the Y2O3 powder and MgO powder proportion in the preparation of the first ceramic crystal.

[0045] In a preferred embodiment, the first ceramic layer of the thermal expansion gradient type multiphase ceramic body of the present invention comprises a first proportion of multiphase ceramic material; the second ceramic layer comprises a second proportion of the multiphase ceramic material. Specifically, the multiphase ceramic material is Y2O3-MgO multiphase ceramic; the first proportion is a first target volume ratio of Y2O3:MgO; the second proportion is a second target volume ratio of Y2O3:MgO; the value of the first target volume ratio is less than the value of the second target volume ratio. More specifically, the first target volume ratio is 1:1; the second target volume ratio is 6:4 to 9:1.

[0046] Specifically, in this embodiment, for example, the substrate 1 is a multiphase ceramic window material uniformly mixed with yttrium oxide and magnesium oxide in a volume ratio of 1:1; the surface layer 2 is a yttrium oxide-magnesium oxide multiphase ceramic, with the volume of yttrium oxide being larger than that of magnesium oxide, and a specific thickness of 0.5~1.0 mm, and its coefficient of thermal expansion is lower than that of the substrate 1. When this ceramic body is used as a device, facing a rapidly heating environment, because the thermal expansion of the surface layer 2 is less than that of the substrate 1, the surface layer 2 forms in-plane compressive stress on the substrate 1, achieving self-compressive stress reinforcement. The volume fraction of yttrium oxide in the surface layer 2 is higher than that of the substrate 1, and the volume fraction of magnesium oxide is lower than that of the substrate 1, thereby achieving a lower coefficient of thermal expansion of the surface layer 2 than that of the substrate 1. The volume ratio of yttrium oxide to magnesium oxide in the surface layer 2 is (6~9):(1~4). The thickness of the substrate 1 is 3.0~5.0 mm, and the thickness of the surface layer 2 is strictly controlled to be 0.5~1.0 mm to ensure a moderate stress gradient and stable interface bonding.

[0047] Example 2:

[0048] Based on Example 1, and referring to Figure 1 As shown, in the thermal expansion gradient type multiphase ceramic body disclosed in this embodiment, the thickness of the substrate 1 perpendicular to the surface direction is 3 to 10 times the thickness of the surface layer 2.

[0049] Specifically, the thickness of the substrate 1 perpendicular to the surface direction is 3.0~5.0mm; the thickness of the surface layer 2 is 0.5~1.0mm.

[0050] It should be noted that the "direction perpendicular to the surface" mentioned in this invention is understood as the direction perpendicular to the surface of the surface layer 2. For example, if the thermal expansion gradient type multiphase ceramic body is prepared as a sheet, then the direction perpendicular to the surface is the normal direction of the plane of the sheet. Similarly, the thickness of the surface layer 2 is still understood as the thickness taken in the direction perpendicular to the surface.

[0051] Example 3:

[0052] refer to Figure 2 As shown, this embodiment discloses a method for preparing a multiphase ceramic body, used to prepare a thermally expanded gradient type multiphase ceramic body as described in Example 1 or Example 3, including the following steps:

[0053] S1. Prepare a first powder according to the first raw material ratio of the first ceramic layer; prepare a second powder according to the second raw material ratio of the second ceramic layer; and perform powder processing on each powder.

[0054] S2. The first powder and the second powder are respectively subjected to molding or cold isostatic pressing to obtain the first ceramic blank and the second ceramic blank;

[0055] S3. The first ceramic blank and the second ceramic blank are respectively debinded in an air environment of 600-800°C, and then sintered, kept warm and cooled in sequence to obtain the first ceramic layer and the second ceramic layer.

[0056] S4. Polish the bonding surfaces of the first ceramic layer and the second ceramic layer respectively;

[0057] S5. The bonding surfaces of the first ceramic layer and the second ceramic layer are brought together and subjected to thermal bonding under pressure and temperature conditions to obtain a thermally expanded gradient type multiphase ceramic body.

[0058] The powder processing technology described in this embodiment is understood as a powder processing technology that can mix the powder evenly and meet the requirements of the blanking process. In this embodiment, the preferred powder processing technology is ball milling, drying, and sieving. The powder processing can be controlled to meet the requirements by controlling the ball milling mixing conditions, drying temperature, and sieving aperture.

[0059] The first raw material described in this invention can be Y2O3 powder and MgO powder. Similarly, the second raw material liquid can be Y2O3 powder and MgO powder. It should be noted that the first powder and the second powder in this invention can be understood as two powders with different proportions but the same composition. For example, the first powder is a mixed powder with a mass ratio of Y2O3:MgO = 1:5, and the second powder is a mixed powder with a mass ratio of Y2O3:MgO > 1:5. The mass ratio of the second powder only needs to achieve the second target volume ratio.

[0060] Specifically, in the preparation method of the multiphase ceramic body of the present invention, the pressure condition is 1~3MPa; the temperature condition is 500-800℃; and the thermal bonding treatment time is 100~500 hours.

[0061] In this preferred embodiment, the polishing achieves a surface finish of ≤5nm on the surfaces to be bonded.

[0062] In this preferred embodiment, the heating rate for debinding is 2~5℃ / min; the heating rate for sintering is 5~10℃ / min.

[0063] For example, the first step: prepare base 1 powder and surface 2 powder according to the volume ratio, and add them after ball milling, drying and sieving;

[0064] Step 2: First, press the ceramic blank into a ceramic body using molding or cold isostatic pressing.

[0065] Step 3: Remove the binder in air at 600-800℃, then sinter at 1200-1650℃ without pressure, hold for 2-4 hours, and cool with the furnace to obtain yttrium oxide-magnesium oxide multiphase ceramic (substrate 1) with a volume ratio of 1:1 and yttrium oxide-magnesium oxide ceramic (surface layer 2) with a volume ratio of (6-9):(1-4).

[0066] Step 4: Polish the surfaces of the yttrium oxide-magnesium oxide composite ceramic substrate 1 and surface layer 2 that are to be bonded at high temperature, respectively, and the surface finish is less than or equal to 5nm.

[0067] Step 5: Polish the surfaces of substrate 1 and surface layer 2 together, and perform thermal bonding at 1-3 MPa pressure and 500-800℃ for 100-500 hours to finally obtain a thermally expanded gradient type yttrium oxide-magnesium oxide multiphase ceramic.

[0068] Example 4:

[0069] Based on Example 3, this example discloses a method for preparing Y2O3-MgO multiphase ceramic body, wherein the substrate 1 is made of yttrium oxide and magnesium oxide powder with a volume ratio of 1:1, and the surface layer 2 is made of yttrium oxide and magnesium oxide with a volume ratio of 6:4.

[0070] The first step is to make a base layer 1 with a thickness of 4.0 mm and a surface layer 2 with a thickness of 0.5 mm.

[0071] The second step involves ball milling, mixing, drying, and sieving the powders of substrate 1 and surface layer 2 separately. The powders of substrate 1 and surface layer 2 are then molded separately, debinded at 650℃, and sintered without pressure at 1500℃ for 3 hours.

[0072] The third step involves polishing the bonding surfaces of the substrate 1 and the surface layer 2 yttrium-magnesium composite ceramics to a roughness of ≤5nm. After docking, they are thermally bonded at 600℃ and 2MPa for 200h to obtain thermally expanded gradient yttrium oxide-magnesium oxide composite ceramics.

[0073] Example 5:

[0074] Based on Example 3, this example discloses a method for preparing a Y2O3-MgO multiphase ceramic body. The substrate 1 is made of yttrium oxide to magnesium oxide powder with a volume ratio of 1:1, and the surface layer 2 is made of yttrium oxide to magnesium oxide with a volume ratio of 7:3. The thickness of the substrate 1 is 3.5 mm, and the thickness of the surface layer 2 is 0.6 mm.

[0075] The first step is to ball-mill, mix, dry, and sieve the powders of base 1 and surface 2 respectively.

[0076] The second step involves molding the base 1 and surface 2 powders separately, removing the binder at 700℃, sintering at 1550℃, and holding at that temperature for 3 hours.

[0077] The third step involves polishing the bonding surfaces of the substrate 1 and the surface layer 2 yttrium magnesium composite ceramics to a roughness of ≤5nm, and then thermally bonding them at 650℃ and 2MPa for 250h to obtain a gradient structure composite ceramic.

[0078] Example 6:

[0079] Based on Example 3, this example discloses a method for preparing a Y2O3-MgO multiphase ceramic body. The substrate 1 is made of yttrium oxide to magnesium oxide powder with a volume ratio of 1:1, and the surface layer 2 is made of yttrium oxide to magnesium oxide with a volume ratio of 8:2. The thickness of the substrate 1 is 4.5 mm, and the thickness of the surface layer 2 is 0.7 mm.

[0080] The first step is to ball-mill, mix, dry, and sieve the powders of base 1 and surface 2 respectively.

[0081] The second step involves molding the base 1 and surface 2 powders separately, removing the binder at 750°C, sintering at 1600°C, and holding at that temperature for 2.5 hours.

[0082] The third step involves polishing the bonding surfaces of the substrate 1 and the surface layer 2 yttrium magnesium composite ceramics to a roughness of ≤5nm. After polishing, the surfaces are thermally bonded at 700℃ and 1.5MPa for 300h to obtain a thermal expansion gradient ceramic.

[0083] Example 7:

[0084] Based on Example 3, this example discloses a method for preparing a Y2O3-MgO multiphase ceramic body. The substrate 1 is made of yttrium oxide to magnesium oxide powder with a volume ratio of 1:1, and the surface layer 2 is made of yttrium oxide to magnesium oxide with a volume ratio of 8.5:1.5. The thickness of the substrate 1 is 3.0 mm, and the thickness of the surface layer 2 is 0.8 mm.

[0085] The first step is to ball-mill, mix, dry, and sieve the powders of base 1 and surface 2 respectively.

[0086] The second step involves molding the base 1 and surface 2 powders separately, removing the binder at 700℃, sintering at 1620℃, and holding at that temperature for 2 hours.

[0087] The third step involves polishing the bonding surfaces of the substrate 1 and the surface layer 2 yttrium magnesium composite ceramics to a roughness of ≤5nm. After polishing, the bonding surfaces are thermally bonded at 750℃ and 2MPa for 350h to obtain gradient composite ceramics.

[0088] Example 8:

[0089] Based on Example 3, this example discloses a method for preparing a Y2O3-MgO multiphase ceramic body. The substrate 1 is made of yttrium oxide to magnesium oxide powder with a volume ratio of 1:1, and the surface layer 2 is made of yttrium oxide to magnesium oxide with a volume ratio of 9:1. The thickness of the substrate 1 is 5.0 mm, and the thickness of the surface layer 2 is 1.0 mm.

[0090] The first step is to ball-mill, mix, dry, and sieve the powders of base 1 and surface 2 respectively.

[0091] The second step involves molding the base 1 and surface 2 powders separately, removing the binder at 800℃, sintering at 1650℃, and holding at that temperature for 2 hours.

[0092] The third step involves polishing the bonding surfaces of the substrate 1 and the surface layer 2 yttrium-magnesium composite ceramics to a roughness of ≤5nm. After polishing, the bonding surfaces are thermally bonded at 800℃ and 3MPa for 400h to obtain thermally expanded gradient yttrium oxide-magnesium oxide composite ceramics.

[0093] The thermal expansion gradient type yttrium oxide-magnesium oxide multiphase ceramics prepared in Examples 3 to 8 above were tested for thermal expansion properties, mechanical properties, thermal shock resistance and infrared transmittance.

[0094] The results show that as the volume fraction of yttrium oxide in the surface layer 2 increases, the coefficient of thermal expansion of the surface layer 2 gradually decreases, forming a significant gradient in the coefficient of thermal expansion between the surface layer 2 and the substrate 1. During the heating process, because the expansion of the surface layer 2 is less than that of the substrate 1, it generates a stable in-plane compressive stress on the substrate 1, which can effectively inhibit the initiation and propagation of microcracks on the surface of the substrate 1.

[0095] Compared with traditional 1:1 homogeneous yttrium oxide-magnesium oxide multiphase ceramics, the thermal expansion gradient yttrium oxide-magnesium oxide multiphase ceramic of this invention exhibits an increased thermal shock resistance temperature of 80–150°C and a 15%–30% improvement in fracture toughness. It does not crack, delamination, or peeling under rapid heating and cooling cycles. Furthermore, the substrate 1 maintains the optimal 1:1 optical ratio, and the 0.5–1.0 mm thin surface layer 2 has minimal impact on infrared transmittance; the average transmittance in the mid-infrared band at a thickness of 3–5 μm still reaches over 70%, achieving a balance of excellent optical, mechanical, and thermal shock resistance properties. Comprehensive comparison shows that Examples 6 and 7 demonstrate the best performance in terms of interfacial bonding strength, stress gradient matching, and overall performance, meeting the stringent requirements for use in demanding applications such as infrared windows and high-temperature optical detection devices.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermally expanded gradient type multiphase ceramic body, characterized in that, It includes a substrate (1) and a surface layer (2); the surface layer (2) is thermally bonded to the outside of the substrate (1); the substrate (1) is a first ceramic layer; the surface layer (2) is a second ceramic layer; the coefficient of thermal expansion of the first ceramic layer is greater than that of the second ceramic layer.

2. The thermal expansion gradient type multiphase ceramic body according to claim 1, characterized in that, The first ceramic layer comprises a first proportion of multiphase ceramic material; the second ceramic layer comprises a second proportion of the multiphase ceramic material.

3. The thermal expansion gradient type multiphase ceramic body according to claim 2, characterized in that, The multiphase ceramic material is Y2O3-MgO multiphase ceramic; the first ratio is a first target volume ratio of Y2O3:MgO; the second ratio is a second target volume ratio of Y2O3:MgO; the value of the first target volume ratio is less than the value of the second target volume ratio.

4. The thermal expansion gradient type multiphase ceramic body according to claim 3, characterized in that, The first target volume ratio is 1:1; the second target volume ratio is 6:4 to 9:

1.

5. The thermal expansion gradient type multiphase ceramic body according to any one of claims 1-4, characterized in that, The thickness of the substrate (1) perpendicular to the surface direction is 3 to 10 times the thickness of the surface layer (2).

6. The thermal expansion gradient type multiphase ceramic body according to claim 5, characterized in that, The thickness of the substrate (1) perpendicular to the surface direction is 3.0~5.0mm; the thickness of the surface layer (2) is 0.5~1.0mm.

7. A method for preparing a multiphase ceramic body, characterized in that, The method for preparing the thermally expanding gradient type multiphase ceramic body as described in any one of claims 1-6 includes the following steps: S1. Prepare a first powder according to the first raw material ratio of the first ceramic layer; prepare a second powder according to the second raw material ratio of the second ceramic layer; and perform powder processing on each powder. S2. The first powder and the second powder are respectively subjected to molding or cold isostatic pressing to obtain the first ceramic blank and the second ceramic blank; S3. The first ceramic blank and the second ceramic blank are respectively debinded in an air environment of 600-800°C, and then sintered, kept warm and cooled in sequence to obtain the first ceramic layer and the second ceramic layer. S4. Polish the bonding surfaces of the first ceramic layer and the second ceramic layer respectively; S5. The bonding surfaces of the first ceramic layer and the second ceramic layer are brought together and subjected to thermal bonding under pressure and temperature conditions to obtain a thermally expanded gradient type multiphase ceramic body.

8. The method for preparing a multiphase ceramic body according to claim 7, characterized in that, The pressure conditions are 1~3MPa; the temperature conditions are 500-800℃; and the heat bonding treatment time is 100~500 hours.

9. The method for preparing a multiphase ceramic body according to claim 7, characterized in that, The polishing process achieves a surface finish of ≤5nm on the surfaces to be bonded.

10. The method for preparing a multiphase ceramic body according to claim 7, characterized in that, The heating rate for debinding is 2~5℃ / min; the heating rate for sintering is 5~10℃ / min.

Images