Method for improving density and mechanical property of ceramic

Abstract

The invention provides a method for improving density and mechanical properties of ceramics, and belongs to the technical field of ceramics. Ceramic is heated, a preset constant electric field is applied, and flash burning treatment is carried out until the flash burning phenomenon occurs; the flash burning phenomenon is that a power supply is converted from a constant voltage state to a constant current state, and the current density of the constant current state is controlled to be 3-25 mA / mm < 2 >. The preset constant electric field is applied to perform flash burning treatment on the ceramic, so that the density and mechanical property of the ceramic can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of ceramics, and in particular to a method for improving the density and mechanical properties of ceramics, specifically: utilizing flash firing technology to improve the mechanical properties of ceramics. Background Art

[0002] 3D printing technology is also known as additive manufacturing technology. It has the advantages of flexible structural design, integrated processing and molding, high preparation precision, and short preparation cycle. It is regarded as a revolution in the manufacturing industry and has been widely used in the fields of polymers, metals, ceramics and other materials. Alumina ceramics have many excellent properties such as high strength, high temperature resistance, oxidation resistance, and corrosion resistance. They are widely used in industrial-related fields such as aerospace. Therefore, alumina is a more mature ceramic system carried out in ceramic 3D printing research. Most of the current ceramic 3D printing technologies require the use of binders to complete ceramic printing and molding, and obtain ceramic parts after high-temperature sintering. During the degreasing and sintering process, due to reasons such as the volatilization of the binder, the density and mechanical properties of 3D printed ceramics are not as good as those prepared by traditional powder sintering technology. In particular, there are gaps between the printed layers, which affects the overall performance.

[0003] To address this problem, most researchers currently choose to add additives to the original slurry to reduce the impact of the degreasing process on the density and mechanical properties of 3D printed alumina. Up to now, the density and mechanical properties of 3D printed alumina ceramics are still insufficient. This technology addresses the above-mentioned deficiencies of 3D printed alumina that has completed the sintering process. Through the critical electric field assisted flash firing technology, a secondary sintering process can be performed, which can significantly improve the density and mechanical properties of the ceramics. Summary of the invention

[0004] In view of this, in order to solve the technical problem of poor density and mechanical properties of ceramics in the prior art, the present invention provides a method for improving the density and mechanical properties of ceramics, which can effectively improve the density and mechanical properties of ceramics by applying a preset constant electric field to flash-sinter the ceramics.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for improving the density and mechanical properties of ceramics, heating the ceramics and applying a preset constant electric field to perform a flash treatment until a flash phenomenon occurs;

[0007] The flash phenomenon is that the power supply changes from a constant voltage state to a constant current state, and the current density of the constant current state is controlled to be 3mA / mm 2 -25mA / mm 2 .

[0008] Preferably, the flash burning process is specifically:

[0009] Connect the ceramic in series to the circuit, heat it to a preset constant temperature, apply a preset constant electric field to the ceramic until the flash sintering phenomenon occurs, control the current density in the constant current state, maintain it at this current density for a period of time, disconnect the electric field, and let the sample cool down.

[0010] Preferably, the flash sintering treatment is specifically as follows:

[0011] Apply a preset constant electric field to the green body while heating, and continuously raise the temperature until the flash sintering phenomenon occurs.

[0012] Preferably, the preset heating temperature is 1000 - 1500 °C.

[0013] Preferably, the holding time in the constant current state is 10 - 600 s.

[0014] Preferably, the cooling method is furnace cooling or programmed cooling.

[0015] Preferably, the electric field strength of the preset constant electric field is 1000 V / cm - 5000 V / cm.

[0016] Preferably, the ceramic is a 3D printed alumina ceramic.

[0017] The present invention has the following beneficial effects compared with the prior art:

[0018] The method for improving the density and mechanical properties of ceramics provided by the present invention, based on the characteristics of rapid mass transfer of substances under flash sintering treatment, can effectively repair the gaps in the ceramics and improve the density and mechanical properties of the ceramics by applying a preset constant electric field to the ceramics and performing flash sintering treatment on the ceramics, thus solving the problem of insufficient mechanical properties of current ceramics.

[0019] The ceramics treated by this method can be used in high-end fields such as aerospace and biomedicine, providing ceramic materials with excellent mechanical properties for this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Scanning electron micrographs of the 3D printed alumina sample before and after flash sintering treatment in Example 1;

[0021] Figure 2 Scanning electron micrographs of the 3D printed alumina sample before and after flash sintering treatment in Example 2;

[0022] Figure 3 Scanning electron micrographs of the 3D printed alumina sample before and after flash sintering treatment in Example 3;

[0023] Among them, Figures 1 - 3 in the, the left photo is before the flash sintering treatment, and the right photo is after the flash sintering treatment. DETAILED DESCRIPTION OF THE INVENTION

[0024] The technical solution of the present invention will be clearly and detailedly described below in conjunction with specific embodiments.

[0025] Example 1

[0026] Strengthening 3D printed alumina ceramics using flash sintering technology, the process is as follows:

[0027] Connect the 3D printed alumina sample in series to the circuit, place it in a heating furnace and heat it to 1200 °C, apply an electric field strength of 3000 V / cm to the sample, wait for about 25 seconds for the flash sintering phenomenon to occur, and the power supply switches from the constant voltage mode to the constant current mode, with a current density of 7 mA / mm 2 , after maintaining for 60 s, disconnect the power supply, and the sample cools down with the furnace. After flash sintering treatment, the density of the sample increases from 3.70 g / cm 3 to 3.86 g / cm 3 , and the hardness increases from 9.73 GPa to 14.37 GPa.

[0028] Figure 1 The left picture is a scanning electron micrograph of 3D printed alumina before flash sintering treatment, and the right picture is a scanning electron micrograph of the sample after flash sintering treatment. It can be seen that there are significant gaps between layers in the sample before flash sintering treatment, with a lower density. After flash sintering treatment, the continuous gaps between layers in the sample are repaired, so both the density and hardness increase significantly.

[0029] Example 2

[0030] Strengthening 3D printed alumina ceramics using flash sintering technology, the process is as follows:

[0031] Connect the 3D printed alumina sample in series to the circuit, place it in a heating furnace and heat it to 1500 °C, apply an electric field strength of 1000 V / cm to the sample, wait for about 18 seconds for the flash sintering phenomenon to occur, and the power supply switches from the constant voltage mode to the constant current mode, with a current density of 15 mA / mm 2 , after maintaining for 10 s, disconnect the power supply, and the sample cools down with the furnace at a rate of 10 °C / min. After flash sintering treatment, the density of the sample increases from 3.70 g / cm 3 to 3.85 g / cm 3 , and the hardness increases from 9.73 GPa to 13.68 GPa.

[0032] Figure 2 The left picture is a scanning electron micrograph of 3D printed alumina before flash sintering treatment, and the right picture is a scanning electron micrograph of the sample after flash sintering treatment. It can be seen that there are significant gaps between layers in the sample before flash sintering treatment, with a lower density. After flash sintering treatment, the continuous gaps between layers in the sample are repaired, so both the density and hardness increase significantly.

[0033] Example 3

[0034] Strengthening 3D printed alumina ceramics using flash sintering technology, the process is as follows:

[0035] Connect the 3D printed alumina sample in series to the circuit, place it in a heating furnace, apply an electric field strength of 5000 V / cm, heat the sample while maintaining the continuous application of the electric field. When the temperature rises to about 1000 °C, the flash sintering phenomenon occurs, and the power supply switches from the constant voltage mode to the constant current mode, with a current density of 9 mA / mm 2 , disconnect the power supply after maintaining for 60 s, and the sample cools down with the furnace. The density of the sample after flash sintering treatment increases from 3.68 g / cm 3 to 3.79 g / cm 3 , and the hardness increases from 8.82 GPa to 12.74 GPa.

[0036] Example 4

[0037] Same as Example 1, except that the electric field strength is selected as 2000 V / cm. Wait for about 40 seconds for the flash sintering phenomenon to occur. The density of the sample after flash sintering treatment increases from 3.70 g / cm 3 to 3.85 g / cm 3 , and the hardness increases from 9.70 GPa to 13.95 GPa.

[0038] Example 5

[0039] Same as Example 1, except that the electric field strength is selected as 4000 V / cm. Wait for about 10 seconds for the flash sintering phenomenon to occur. The density of the sample after flash sintering treatment increases from 3.70 g / cm 3 to 3.82 g / cm 3 , and the hardness increases from 9.66 GPa to 13.47 GPa.

[0040] Example 6

[0041] Same as Example 1, except that the electric field strength is selected as 5000 V / cm. Wait for about 3 seconds for the flash sintering phenomenon to occur. The density of the sample after flash sintering treatment increases from 3.70 g / cm 3 to 3.83 g / cm 3 , and the hardness increases from 9.67 GPa to 13.28 GPa.

[0042] Example 7

[0043] Same as Example 1, except that the current density is 3 mA / mm 2 . Wait for about 23 seconds for the flash sintering phenomenon to occur. The density of the sample after flash sintering treatment increases from 3.70 g / cm 3 to 3.77 g / cm 3 , and the hardness increases from 9.68 GPa to 11.97 GPa.

[0044] Example 8

[0045] Same as Example 1, except that the current density is 20 mA / mm 2 . Wait for about 27 seconds for the flash sintering phenomenon to occur. After flash sintering treatment, the density of the sample increases from 3.69 g / cm 3 to 3.84 g / cm 3 , and the hardness increases from 9.71 GPa to 14.02 GPa.

[0046] Example 9

[0047] Same as Example 1, except that the current density is 25 mA / mm 2 . Wait for about 31 seconds for the flash sintering phenomenon to occur. After flash sintering treatment, the density of the sample increases from 3.69 g / cm 3 to 3.83 g / cm 3 , and the hardness increases from 9.70 GPa to 14.14 GPa.

[0048] Comparative Example 1

[0049] Same as Example 2, except that the electric field strength is selected as 900 V / cm. No flash sintering phenomenon occurs. After cooling, the sample has no significant change, and the density changes from 3.69 g / cm 3 to 3.70 g / cm 3 , and the hardness changes from 9.72 GPa to 9.92 GPa.

[0050] Comparative Example 2

[0051] Same as Example 2, except that the electric field strength is selected as 500 V / cm. No flash sintering phenomenon occurs.

[0052] Comparative Example 3

[0053] Same as Example 2, except that the electric field strength is selected as 100 V / cm. No flash sintering phenomenon occurs.

[0054] Comparative Example 4

[0055] Same as Example 2, except that the electric field strength is selected as 50 V / cm. No flash sintering phenomenon occurs.

[0056] Comparative Example 5

[0057] Same as Example 1, except that the current density is 2 mA / mm 2 . Wait for about 25 seconds for the flash sintering phenomenon to occur. After flash sintering treatment, the density of the sample changes from 3.69 g / cm 3 to 3.71 g / cm 3 , and the hardness changes from 9.71 GPa to 9.98 GPa.

[0058] Comparative Example 6

[0059] Same as Example 1, except that the current density is 2 mA / mm 2 . It took about 23 seconds for flash sintering to occur, and the density of the sample after flash sintering did not change (3.69 g / cm 3 ), and the hardness changed from 9.72 GPa to 9.92 GPa.

[0060] Comparative Example 7

[0061] Same as Example 1, except that the current density is 1 mA / mm 2 . It took about 24 seconds for flash sintering to occur, and the density of the sample after flash sintering did not change (3.69 g / cm 3 ), and the hardness changed from 9.69 GPa to 9.71 GPa.

[0062] Comparative Example 8

[0063] Same as Example 2, except that no electric field is applied. The density of the sample did not change (3.70 g / cm 3 ), and the hardness changed little (from 9.73 GPa to 9.80 GPa).

[0064] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for improving the density and mechanical properties of ceramics, characterized in that: Heating the ceramic and applying a preset constant electric field to perform a flash burning process until a flash burning phenomenon occurs; The flash phenomenon is that the power supply changes from a constant voltage state to a constant current state, and the current density of the constant current state is controlled to be 3mA / mm 2 -25mA / mm 2 .

2. A method for improving ceramic density and mechanical properties according to claim 1, characterized in that: The flash burning process is specifically: The ceramic is connected in series to the circuit and heated to a preset constant temperature. A preset constant electric field is applied to the ceramic until flash burning occurs. The current density in the constant current state is controlled and maintained for a period of time. The electric field is disconnected and the sample is cooled.

3. A method for improving ceramic density and mechanical properties according to claim 1, characterized in that: The flash burning process is specifically: While heating, a preset constant electric field is applied to the green body, and the temperature is continuously raised until flash burning occurs.

4. A method for improving ceramic density and mechanical properties according to claim 1, characterized in that: The preset temperature for heating is 1000-1500°C.

5. A method for improving ceramic density and mechanical properties according to claim 1, characterized in that: The constant current state is maintained for 10-600s.

6. A method for improving ceramic density and mechanical properties according to claim 2, characterized in that: The cooling method is furnace cooling or program cooling.

7. A method for improving density and mechanical properties of ceramics according to claim 1, characterized in that: The electric field strength of the preset constant electric field is 1000V / cm-5000V / cm.

8. A method for improving density and mechanical properties of ceramics according to any one of claims 1 to 7, characterized in that: The ceramic is 3D printed alumina ceramic.

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