Silicon nitride ceramic tool and preparation method thereof

Abstract

The present invention belongs to the technical field of silicon nitride ceramics, and specifically relates to a silicon nitride ceramic tool and a preparation method thereof. The preparation method comprises the following steps: firstly weighing the following components by weight percentage: 75%-85% silicon nitride powder, 10%-16% pre-oxidized silicon nitride powder and ZrO 2 ‑Y 2 O 3 5%-10% of the powder is stirred with water and ethanol to prepare a ceramic slurry; the ceramic slurry is sprayed in a hot air flow, granulated, dried, ground, and sieved to obtain a ceramic powder; the ceramic powder is pressed into a shape to obtain a ceramic body; the ceramic body is sintered to obtain a silicon nitride ceramic tool. The silicon nitride ceramic tool obtained by the present invention has a Vickers hardness of 21.6-27.5GPa and a fracture toughness of 12.7-15.8MPa·m 1 / 2 , the flexural strength is 1053‑1290MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon nitride ceramics, and in particular relates to a silicon nitride ceramic cutting tool and a preparation method thereof. Background Art

[0002] Silicon nitride ceramics have become one of the ideal cutting tool materials for high-temperature alloys and bearing steel materials due to their high Vickers hardness, wear resistance, good high-temperature mechanical properties, oxidation resistance and thermal shock resistance. Usually, silicon nitride ceramics are made of high-purity Si3N4 powder, and sintering aids are added to promote densification. However, it was found in the study that although the addition of sintering aids can improve the mechanical properties of silicon nitride ceramics, this method is difficult to further improve the mechanical properties and is difficult to meet more demanding application scenarios.

[0003] In addition, the preparation of silicon nitride ceramic tools is usually carried out by grinding ceramic materials into the shape of the tool. However, this method is prone to cause microcracks on the surface and sub-surface, reducing the strength of the tool. There are also methods of forming the shape of the tool by dry pressing and cold isostatic pressing of ceramic powder, but the pressure of dry pressing is usually only tens of MPa, and it is difficult to further increase the pressure. The density of the formed body is low, and the mechanical properties of the obtained tool do not meet the requirements. Although the pressure of cold isostatic pressing can reach hundreds of MPa, the density of the formed body is high, and the obtained tool has high strength, but the shape of the ceramic body formed by cold isostatic pressing usually has a regular surface shape, which is difficult to press into a body with teeth or grooves, thereby limiting the application of cold isostatic pressing. Summary of the invention

[0004] The invention provides a method for preparing a silicon nitride ceramic tool. The obtained ceramic material has high density, Vickers hardness, fracture toughness and bending strength.

[0005] Based on the above purpose, the present invention provides a silicon nitride ceramic tool, which is mainly made of the following raw materials in weight percentage:

[0006] Silicon nitride powder 75%-85%, pre-oxidized silicon nitride powder 10%-16% and ZrO2-Y2O3 powder 5%-10%.

[0007] Optionally, the silicon nitride ceramic cutting tool comprises the following components in weight percentage:

[0008] Silicon nitride powder 79.5%, pre-oxidized silicon nitride powder 13%, ZrO2 powder 4.72%, Y2O3 powder 2.78%.

[0009] Optionally, the pre-oxidized silicon nitride powder has an oxygen content of 3.8-5.2 wt % and an oxide layer thickness of 0.02-0.06 μm.

[0010] Optionally, the particle size of the ceramic powder is 1-8 μm.

[0011] Optionally, the mass ratio of ZrO2 to Y2O3 in the ZrO2-Y2O3 powder is (1.5-2):1.

[0012] A method for preparing the silicon nitride ceramic tool comprises the following steps:

[0013] First, the following components are weighed in percentage by weight: silicon nitride powder, pre-oxidized silicon nitride powder, ZrO2 powder and Y2O3 powder are stirred with water and ethanol to prepare a ceramic slurry; the ceramic slurry is sprayed in a hot air flow, granulated, dried, ground and sieved to obtain a ceramic powder; the ceramic powder is pressed into a shape to obtain a ceramic green body; the ceramic green body is sintered to obtain a silicon nitride ceramic tool.

[0014] Optionally, the method for preparing the pre-oxidized silicon nitride powder comprises the following steps:

[0015] The silicon nitride powder is reacted at 750-900° C. in a high-pressure oxygen atmosphere, cooled, and sieved to obtain pre-oxidized silicon nitride powder.

[0016] Optionally, the compression molding method comprises the following steps:

[0017] The ceramic powder is loaded into a mold and dry-pressed by a profiled pressure head to obtain a dry-pressed green body, wherein the upper surface structure of the dry-pressed green body corresponds to the end face of the profiled pressure head and the upper surface of the dry-pressed green body is smooth; then, boron nitride powder or graphite powder is covered on the top of the dry-pressed green body to make the upper end face flat, and then a pressure head with a flat end is used for secondary dry pressing; and then, cold isostatic pressing is used to obtain a ceramic green body.

[0018] Optionally, in the ceramic green body forming method, the pressure of the two dry pressing processes is 16-20 MPa, and the pressure is maintained for 5-10 min; the pressure of the cold isostatic pressing process is 150-300 MPa, and the pressure is maintained for 1-5 min.

[0019] Optionally, the ceramic body is sintered under the following conditions: hot pressing sintering in an inert gas atmosphere, a sintering temperature of 1700-1900° C., a heat preservation time of 1-3 hours, and a sintering pressure not exceeding 20 MPa.

[0020] The beneficial effects of the present invention are as follows: the Vickers hardness of the silicon nitride ceramic tool obtained by the present invention is 21.6-27.5 GPa, and the fracture toughness is 12.7-15.8 MPa·m 1 / 2, the bending strength is 1053-1290MPa. With the increase of the content of pre-oxidized silicon nitride powder, the mechanical properties of ceramic tools first increase and then decrease. The mass ratio of ZrO2 to Y2O3 in ZrO2-Y2O3 powder should be controlled at (1.5-2):1. When the mass ratio of ZrO2 to Y2O3 is 1.7:1, the obtained silicon nitride ceramic tool has a significantly improved fracture toughness while the Vickers hardness and bending strength are not significantly reduced, thereby improving the overall performance.

[0021] The preparation method of silicon nitride ceramic cutting tools provided by the present invention comprises the following steps: dry pressing is performed by using a profiled surface pressing head to obtain a dry pressed green body, wherein the upper surface structure of the dry pressed green body corresponds to the end surface of the profiled surface pressing head, and the upper surface of the dry pressed green body is smooth; boron nitride powder or graphite powder is covered on the upper part of the dry pressed green body, the boron nitride powder or graphite powder fills the toothed grooves or grooves of the green body, and secondary dry pressing is performed by using a pressing head with a flat end portion to make the upper surface of the dry pressed green body flat and regular, and the other surfaces in contact with the mold are also flat and regular, so that the ceramic green body can be obtained by cold isostatic pressing, and the ceramic green body with teeth or grooves has a higher density, which is conducive to obtaining a profiled cutting tool with good mechanical properties. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0023] Example 1

[0024] A method for preparing a silicon nitride ceramic tool comprises the following steps:

[0025] S1. Weigh the following components by weight: 79.5% silicon nitride powder, 10% pre-oxidized silicon nitride powder, 5% ZrO2 powder, 2.5% Y2O3 powder, and mechanically stir with water and ethanol to prepare a ceramic slurry;

[0026] S2, spraying the ceramic slurry in a hot air flow at 100°C to granulate, drying at 100°C for 10 hours, grinding, sieving, and obtaining ceramic powder;

[0027] S3, loading the ceramic powder into a mold, using a profiled surface pressure head for dry pressing to obtain a dry pressed body, wherein the upper surface structure of the dry pressed body corresponds to the end face of the profiled surface pressure head, and the upper surface of the dry pressed body is smooth; then covering the upper part of the dry pressed body with boron nitride powder, and then using a pressure head with a flat end for secondary dry pressing to make the upper end face flat, the pressure of the two dry pressings is 16MPa, and the pressure is maintained for 6min; then cold isostatic pressing is used to obtain a ceramic body, the pressure of the cold isostatic pressing is 150-300MPa, and the pressure is maintained for 2min;

[0028] S4. Hot-pressing and sintering the ceramic body in a nitrogen atmosphere at a sintering temperature of 1800° C., a heat preservation time of 2 hours, and a sintering pressure of 15 MPa to obtain a silicon nitride ceramic tool.

[0029] Example 2

[0030] S1. Weigh the following components by weight: 79.5% silicon nitride powder, 13% pre-oxidized silicon nitride powder, 5% ZrO2 powder, 2.5% Y2O3 powder, and mechanically stir with water and ethanol to make a ceramic slurry; the remaining steps are the same as in Example 1.

[0031] Example 3

[0032] S1. Weigh the following components by weight: 79.5% silicon nitride powder, 16% pre-oxidized silicon nitride powder, 5% ZrO2 powder, 2.5% Y2O3 powder, and mechanically stir with water and ethanol to make a ceramic slurry; the remaining steps are the same as in Example 1.

[0033] Example 4

[0034] S1. Weigh the following components by weight: 79.5% silicon nitride powder, 13% pre-oxidized silicon nitride powder, 4.5% ZrO2 powder, 3% Y2O3 powder, and mechanically stir with water and ethanol to make a ceramic slurry; the remaining steps are the same as in Example 1.

[0035] Example 5

[0036] S1. Weigh the following components by weight: 79.5% silicon nitride powder, 13% pre-oxidized silicon nitride powder, 4.72% ZrO2 powder, 2.78% Y2O3 powder, and mechanically stir with water and ethanol to make a ceramic slurry; the remaining steps are the same as in Example 1.

[0037] Comparative Example 1

[0038] S1. Weigh the following components by weight: 92.5% silicon nitride powder, 4.5% ZrO2 powder, and 3% Y2O3 powder, and mechanically stir them with water and ethanol to make a ceramic slurry; the remaining steps are the same as in Example 1.

[0039] Comparative Example 2

[0040] S1. Weigh the following components by weight: 79.5% silicon nitride powder, 13% pre-oxidized silicon nitride powder, and 7.5% ZrO2 powder, and mechanically stir them with water and ethanol to make a ceramic slurry; the remaining steps are the same as in Example 1.

[0041] Comparative Example 3

[0042] S1. Weigh the following components by weight: 79.5% silicon nitride powder, 13% pre-oxidized silicon nitride powder, and 7.5% Y2O3 powder, and mechanically stir them with water and ethanol to prepare a ceramic slurry; the remaining steps are the same as in Example 1.

[0043] The mechanical properties of the silicon nitride ceramic cutting tools prepared in the above groups were tested. The test data of each sample are shown in Table 1 below:

[0044]

[0045]

[0046] Table 1

[0047] As shown in Table 1, the Vickers hardness of the silicon nitride ceramic tools prepared in Examples 1-5 of the present invention is 21.6-27.5 GPa, and the fracture toughness is 12.7-15.8 MPa·m 1 / 2 , the bending strength is 1053-1290MPa. It can be seen from Examples 1-3 that as the content of pre-oxidized silicon nitride powder increases, the mechanical properties of the ceramic tool first increase and then decrease. It can be seen from Examples 2, 4 and 5 that the mass ratio of ZrO2 to Y2O3 in ZrO2-Y2O3 powder should be controlled at (1.5-2):1. When the mass ratio of ZrO2 to Y2O3 is 1.7:1, the obtained silicon nitride ceramic tool has a significantly improved fracture toughness while the Vickers hardness and bending strength are not significantly reduced, thereby improving the overall performance.

[0048] In Comparative Example 1, no pre-oxidized silicon nitride powder was added, and the mechanical properties of the silicon nitride ceramic tools were significantly lower than those of the embodiments; in Comparative Example 2, no Y2O3 powder was added, and the mechanical properties of the silicon nitride ceramic tools were significantly lower than those of the embodiments; in Comparative Example 2, no ZrO2 powder was added, and the mechanical properties of the silicon nitride ceramic tools were significantly lower than those of the embodiments; and the mechanical properties of the ceramic tools obtained in Comparative Examples 1-3 were significantly reduced.

[0049] The preparation method of silicon nitride ceramic cutting tools provided by the present invention comprises the following steps: dry pressing is performed by using a profiled surface pressing head to obtain a dry pressed green body, wherein the upper surface structure of the dry pressed green body corresponds to the end surface of the profiled surface pressing head, and the upper surface of the dry pressed green body is smooth; boron nitride powder or graphite powder is covered on the upper part of the dry pressed green body, the boron nitride powder or graphite powder fills the toothed grooves or grooves of the green body, and secondary dry pressing is performed by using a pressing head with a flat end portion to make the upper surface of the dry pressed green body flat and regular, and the other surfaces in contact with the mold are also flat and regular, so that the ceramic green body can be obtained by cold isostatic pressing, and the ceramic green body with teeth or grooves has a higher density, which is conducive to obtaining a profiled cutting tool with good mechanical properties.

[0050] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0051] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a silicon nitride ceramic tool, characterized in that: The following steps are involved: First, the following components are weighed in percentage by weight: silicon nitride powder, pre-oxidized silicon nitride powder, ZrO2 powder and Y2O3 powder are mixed with water and ethanol to prepare a ceramic slurry; the ceramic slurry is sprayed in a hot air flow, granulated, dried, ground and sieved to obtain a ceramic powder; the ceramic powder is pressed into a shape to obtain a ceramic body; the ceramic body is sintered to obtain a silicon nitride ceramic tool; The compression molding method comprises the following steps: The ceramic powder is loaded into a mold, and dry pressed by a profiled pressing head to obtain a dry pressed green body, wherein the upper surface structure of the dry pressed green body corresponds to the end surface of the profiled pressing head, and the upper surface of the dry pressed green body is smooth; then, boron nitride powder or graphite powder is covered on the upper side of the dry pressed green body to make the upper end surface flat, and then dry pressed by a pressing head with a flat end for a second time; and then cold isostatic pressing is performed to obtain a ceramic green body; The mass ratio of ZrO2 to Y2O3 in the ZrO2-Y2O3 powder is (1.5-2):1; the Vickers hardness of the silicon nitride ceramic tool is 21.6-27.5 GPa, and the fracture toughness is 12.7-15.8 MPa·m 1 / 2 , flexural strength is 1053-1290MPa; The composition includes the following weight percentages: Silicon nitride powder 79.5%, pre-oxidized silicon nitride powder 13%, ZrO2 powder 4.72%, Y2O3 powder 2.78%; The pre-oxidized silicon nitride powder has an oxygen content of 3.8-5.2 wt % and an oxide layer thickness of 0.02-0.06 μm; The particle size of the ceramic powder is 1-8 μm; The method for preparing the pre-oxidized silicon nitride powder comprises the following steps: The silicon nitride powder is reacted in a high pressure oxygen atmosphere at 750-900° C., cooled, and sieved to obtain pre-oxidized silicon nitride powder; In the ceramic green body forming method, the pressure of the two dry pressing processes is 16-20 MPa, and the pressure is maintained for 5-10 minutes; the pressure of the cold isostatic pressing process is 150-300 MPa, and the pressure is maintained for 1-5 minutes; The sintering conditions of the ceramic body are: hot pressing sintering in an inert gas atmosphere, a sintering temperature of 1700-1900° C., a heat preservation time of 1-3 hours, and a sintering pressure not exceeding 20 MPa.

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