Preparation method of carburized ZTA ceramic material

Abstract

The present application belongs to the technical field of ZTA ceramic, and particularly relates to a preparation method of carburized ZTA ceramic material. The method comprises the following steps: 1) preparation of ZTA ceramic blank; 2) carburizing heat treatment; and 3) hot isostatic pressing treatment. Compared with the prior art, the technical advantages of the present application are as follows: the carburized ZTA ceramic material of the present application is a product pre-sintered at 1200 DEG C, which retains porosity and gives the blank certain strength. The present application realizes the carburization of carbon atoms by the migration of carbon atoms in the pre-sintered ceramic. A part of the carbon atoms acts in the zirconia lattice, which plays a stabilizing role on the high-temperature phase of zirconia, so that the stable tetragonal phase can be better retained to room temperature, avoiding the transformation to monoclinic phase, increasing the volume change, and further avoiding the generation of defects such as cracks in the ceramic. Another part of the carbon atoms stays at the grain boundaries of the ceramic particles, which can avoid the generation of abnormal phenomena such as the expansion of ceramic cracks.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ZTA ceramic materials, and particularly relates to a preparation method of carburized ZTA ceramic materials. BACKGROUND

[0002] The ZTA ceramic has good high-temperature mechanical strength, high hardness, high elastic modulus, high bending strength, high fracture toughness, heat shock resistance, wear resistance, oxidation resistance and corrosion resistance, and can be used as structural ceramics such as high-efficiency gas turbine, aerospace automobile parts, corrosion-resistant coating, ceramic pipe plug, cutting blade, sealing valve, armor, mold and metal linking part; has low thermal conductivity, high insulation, good thermal expansion coefficient, special optical properties and good biocompatibility, and can be used in the fields of functional ceramics such as electrical insulator, prosthesis, piezoelectric ceramic, dental ceramic, ceramic film, high-efficiency filtration, reverse osmosis, gas separation and catalysis.

[0003] In the conventional preparation process, the ZTA ceramic is usually sintered in a muffle furnace under an air atmosphere. However, the phase transformation toughening effect of zirconia is affected by the addition amount of stabilizers. When the yttrium content of yttrium stabilized zirconia is increased to more than 5%, c-ZrO2 is easily generated in the preparation process, which leads to poor stability of zirconia. Therefore, the stabilizing effect of yttrium on zirconia is also limited.

[0004] Carburizing technology is a heat treatment process of surface treatment. The method is to place the workpiece into an active carburizing medium, heat to a certain temperature and keep for a sufficient time, so that the active carbon atoms dispersed in the carburizing medium penetrate into the surface layer of the steel part, so as to obtain a high-carbon surface layer and maintain the original composition in the core. According to the different carbon-containing medium, carburizing can be divided into gas carburizing, solid carburizing, liquid carburizing and carbonitriding. The commonly used one is solid carburizing.

[0005] The existing patent application 201410026240.9 about ceramic carburizing discloses a zirconia-based ceramic and metal connecting piece and a connecting method thereof, which describes the corresponding carburizing process, but it focuses on the penetration of carbon vapor into the unit cell and the intercellular gap. However, the present application is to realize the penetration of carbon atoms by the migration of carbon atoms in the pre-sintered ceramic. A part of the carbon atoms acts in the zirconia lattice, which stabilizes the high-temperature phase of zirconia, so that the stable tetragonal phase can be better preserved at room temperature, avoiding the transformation to monoclinic phase, increasing the volume change, and further avoiding the generation of defects such as cracks in the ceramic. Another part of the carbon atoms stays at the grain boundary of the ceramic particles, which can avoid the generation of abnormal phenomena such as crack propagation of the ceramic. Moreover, the patent does not involve preheating treatment of the carburized workpiece, which is only to improve the wettability of the ceramic connecting piece and the nickel-based alloy, while the present application is to improve the fracture strength and wear resistance of the ceramic material. SUMMARY

[0006] The technical problem solved by the present application is that the fracture strength of ceramic materials cannot be greatly improved under the preparation conditions of the prior art, and a preparation method of carburized ZTA ceramic material is provided, and the fracture strength of the ZTA ceramic material prepared by the method is high.

[0007] The technical solution adopted by the present application to solve its technical problem is as follows: a preparation method of carburized ZTA ceramic material, comprising the following preparation steps:

[0008] 1) Preparation of ZTA ceramic blank

[0009] Powder mixing: the alumina powder, yttrium stabilized zirconia powder, dispersant and water are uniformly mixed by using acoustic resonance technology to obtain mixed slurry;

[0010] The acoustic resonance technology has an acceleration of 80G and a mixing time of 10-15min, and uses zirconia balls with a particle size of 0.3-1.4mm as auxiliary mixing medium;

[0011] Powder granulation: the dispersed mixed slurry is filtered by a screen, and then a binder and a release agent are sequentially added and granulated by a granulation tower.

[0012] Dry pressing: the prepared granulated powder is dry pressed to obtain a ceramic green body;

[0013] Pre-burning: the ceramic green body is placed in a muffle furnace for pre-burning to obtain a ZTA ceramic blank;

[0014] 2) Carburizing heat treatment

[0015] A layer of graphite is laid on the bottom of an alumina crucible, then the ZTA ceramic blank pre-burned in step 1) is placed in the graphite-padded crucible, and then another layer of graphite is placed to cover the ZTA ceramic blank, the crucible cover is covered, and the heat treatment is carried out in the furnace to obtain a ZTA ceramic piece; the heat treatment has a sintering temperature of 1450-1550℃, a holding time of 4-6h, and a heating rate of 2-18℃ / min;

[0016] 3) Hot isostatic pressing treatment

[0017] The ZTA ceramic piece after carburizing in step 2) is ultrasonically cleaned, dried and then placed in a Hip sintering furnace for hot isostatic pressing treatment;

[0018] The alumina powder is 70-96 parts by weight, the yttrium stabilized zirconia powder is 4-30 parts by weight, the dispersant is 1-10 parts, the mass ratio of the sum of the weight of the alumina powder and the yttrium stabilized zirconia powder to water is 1:(1-2), the binder is 2-3 parts, and the release agent is 0.5-1 part.

[0019] Preferably, the alumina powder has a particle size of 100-400 nm and a purity of 99.99%, and the yttrium stabilized zirconia powder has a particle size of 30-40 nm and a purity of 99.9%.

[0020] Preferably, the screen mesh has a mesh number of 200-325 mesh, the dry pressing forming has a dry pressing pressure of 1.1-2.3 MPa, and the pre-sintering has a pre-sintering temperature of 800-1300 ℃, a heating rate of 1.5-15 ℃ / min, and a holding time of 30-60 min.

[0021] Preferably, the hot isostatic pressing treatment has a heating rate of 5-10 ℃ / min, a holding pressure of 100-200 MPa, a maximum temperature of 1350-1400 ℃, and a holding time of 1-3 h.

[0022] Preferably, the ZTA ceramic blank has a diameter of 2.8 mm and a length of 12 mm.

[0023] Preferably, the graphite is high-purity graphite powder with a mass percentage of 99.9% and a mesh number of 100 mesh.

[0024] Compared with the prior art, the technical advantage of the present application lies in that:

[0025] 1) The average fracture strength of the conventional color ZTA ceramic material is 1091.4 MPa, and the average fracture strength of the ceramic material after using the method of the present application is 1349.8 MPa, which is increased by about 20%, and the advantage is also more obvious in the actual wear test.

[0026] 2) The carburized ZTA ceramic material of the present application is a product pre-sintered at 1200 ℃, which retains the porosity and gives the blank a certain strength. In principle, the present application is the migration of carbon atoms in the pre-sintered ceramic to realize the infiltration of carbon atoms, part of which acts in the zirconia lattice, which plays a stabilizing role for the high-temperature phase of zirconia, so that the stable tetragonal phase can be better retained at room temperature, avoiding the transformation to monoclinic phase, increasing the volume change, and further avoiding the generation of defects such as cracks in the ceramic. The other part stays at the grain boundary of the ceramic particles, which can avoid the generation of abnormal phenomena such as crack propagation of the ceramic. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Microstructure of ZTA ceramic part material prepared for Example 1 of the present application.

[0028] Figure 2 Microstructure of ZTA ceramic part material prepared for Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0029] The present application will be further described below in conjunction with examples. Example 1

[0030] Preparation of ZTA ceramic blank

[0031] Powder mixing: 85 parts of alumina powder with a particle size of 300 nm and a purity of 99.99%; 20 parts of yttrium stabilized zirconia powder with a particle size of 30-40 nm and a purity of 99.9%; 5 parts of ammonium polyacrylate; and 210 parts of water were mixed using acoustic resonance technology (80G acceleration, mixing for 10 min, using zirconia balls with a particle size of 1 mm as auxiliary mixing medium) to prepare a mixed slurry.

[0032] Powder granulation: the mixed slurry after dispersion was filtered through a 300-mesh sieve to remove the zirconia balls, and 3 parts of ammonium polyacrylate emulsion and 1 part of vegetable oil were added in sequence and granulated through a granulation tower.

[0033] Dry pressing: the prepared powder was dry-pressed at 2.0 MPa to prepare a ceramic green body.

[0034] Pre-sintering: the ceramic green body was pre-sintered in a muffle furnace to prepare a ZTA ceramic blank, the diameter of the ceramic blank was 2.8 mm, the length was 12 mm, the pre-sintering temperature was 1200℃, the heating rate was 10℃ / min, and the holding time was 40 min.

[0035] 2) Carburizing heat treatment

[0036] A first graphite with a thickness of 80 mm was laid on the bottom of an alumina crucible, the graphite was high-purity graphite powder with a mass percentage of 99.9% and a mesh size of 100 mesh, and then the pre-sintered ZTA ceramic blank was gently placed in the graphite-lined crucible (to avoid direct contact of the ceramic blank with the bottom through the graphite pad, resulting in poor carburizing effect), and then a second graphite with a thickness of 80 mm was placed to cover the ZTA ceramic blank, the crucible cover was covered, and the ZTA ceramic blank was placed in the furnace for heat treatment, to prepare a ZTA ceramic part, the sintering temperature was 1500℃, the holding time was 5 h, and the heating rate was 10℃ / min.

[0037] 3) Hot isostatic pressing treatment

[0038] The ZTA ceramic piece after the carburizing of step 2) is ultrasonically cleaned, dried and then put into a Hip sintering furnace for hot isostatic pressing, with a heating rate of 8°C / min, a holding pressure of 150 MPa, a maximum temperature of 1380°C and a holding time of 2h.

[0039] The ZTA ceramic piece prepared in Example 1 has a microstructure of the material as shown in Figure 1 The product has the following properties:

[0040] The fracture strength of 6pcs products is measured as 1439.8 MPa, 1257.8 MPa, 1455.6 MPa, 1444.6 MPa, 1151.3 MPa, and the average is 1349.8 MPa.

[0041] The hardness of 6pcs products is measured as 1834HV5, 1862HV5, 1819HV5, 1889HV5, 1885HV5, 1854HV5.

[0042] The average wear volume of 3pcs products is measured as 0.052mm 3 .

[0043] The life of 3pcs products is determined by wire bonding, and the wear resistance is determined by the number of bonding times. The number of bonding times is 10 million to 15 million. Comparative Example 1

[0044] The ceramic green body is not pre-sintered, but is directly degreased after dry pressing, and the rest is the same as in Example 1. The degreasing conditions are as follows: a heating rate of 0.33-0.67°C / min, a maximum temperature of 650°C and a holding time of 90 min. After degreasing, the ceramic green body is directly picked up with tweezers and put into a graphite crucible. It is found that the green body is easily broken during the picking and moving process. The product after degreasing has basically no strength, and therefore, pre-sintering is needed to make the ceramic piece have certain strength to avoid easy breaking in subsequent operations. Comparative Example 2

[0045] The conventional ZTA ceramic piece product is not carburized, and the product has the following properties:

[0046] The fracture strength of 6pcs products is measured as 1007.4 MPa, 1207.9 MPa, 1241.3 MPa, 1129.4 MPa, 870.9 MPa, and the average is 1091.4 MPa.

[0047] The hardness of 6pcs products is measured as 1774HV5, 1793HV5, 1796HV5, 1772HV5, 1760HV5, 1779HV5.

[0048] Test 3pcs products, the average wear volume of wear resistance test is 0.080mm 3 ;

[0049] Test 3pcs products, the bonding times: 6 million times ~ 9 million times. Comparative Example 3

[0050] The same as Example 1, the difference is that 3 parts of chromium oxide powder are added to the raw materials. Because the conventional ZTA ceramic can improve the bonding times after adding 3 parts of chromium oxide powder to the raw materials, the rest is the same as Example 1. The microstructure of the ZTA ceramic material prepared in Comparative Example 3 is shown in Figure 2 It can be seen that the surface cavity defects increase.

[0051] The product performance of the ZTA ceramic piece of Comparative Example 3:

[0052] Test 6pcs products, the breaking strength measurement data: 926.4MPa, 961.4MPa, 1135.1MPa, 1148.7MPa, 1176.7MPa, the average is 1069.7MPa, which is decreased by 20.75% compared with the optimal condition of Example 1.

[0053] Test 6pcs products, the hardness data: 1699HV5, 1575HV5, 1661HV5, 1640HV5, 1581HV5, 1638HV5, which is decreased by 11.21% compared with the optimal condition.

[0054] Test 3pcs products, the average wear volume of wear resistance test is 0.078mm 3 .

[0055] Test 3pcs products, the bonding times: 6 million times ~ 9 million times.

Claims

1. A method for preparing a ZTA carburized ceramic material, characterized in that: The preparation steps are as follows: 1) Preparation of ZTA ceramic blanks Powder mixing: Alumina powder, yttrium-stabilized zirconia powder, dispersant and water are mixed evenly using acoustic resonance technology to obtain a mixed slurry; the acoustic resonance technology has an acceleration of 80G, a mixing time of 10 to 15 minutes, and uses zirconia balls with a particle size of 0.3 to 1.4 mm as an auxiliary mixing medium. Powder granulation: The dispersed slurry is filtered through a sieve, and then the binder and release agent are added in sequence, and granulated through a granulation tower; Dry pressing: The granulated powder obtained is dry pressed to obtain a ceramic blank; Pre-firing: The ceramic blank is placed in a muffle furnace for pre-firing to obtain ZTA ceramic blanks; 2) Carburizing heat treatment A layer of graphite is laid at the bottom of an alumina crucible. Then, the ZTA ceramic blank pre-fired in step 1) is placed in the crucible with the graphite layer. Another layer of graphite is then placed on top to cover the ZTA ceramic blank. The crucible is then covered and placed in a furnace for heat treatment to obtain the ZTA ceramic blank. The heat treatment is carried out at a sintering temperature of 1450-1550℃, a holding time of 4-6 hours, and a heating rate of 2-18℃ / min. 3) Hot isostatic pressing treatment After the ZTA ceramic parts in step 2) have been carburized, they are ultrasonically cleaned, dried, and then placed in a Hip sintering furnace for hot isostatic pressing. The composition, by weight, comprises 70-96 parts alumina powder, 4-30 parts yttrium-stabilized zirconia powder, 1-10 parts dispersant, with the sum of the weights of alumina powder and yttrium-stabilized zirconia powder and water having a mass ratio of 1:(1-2); 2-3 parts binder and 0.5-1 part release agent; wherein the dispersant is ammonium polyacrylate or ammonium polymethacrylate, the binder is ammonium acrylate or ammonium acrylate salt, and the release agent is vegetable oil.

2. The method according to claim 1, characterized in that: The alumina powder has a particle size of 100-400 nm and a purity of 99.99%; the yttrium-stabilized zirconium oxide powder has a particle size of 30-40 nm and a purity of 99.9%.

3. The method according to claim 1, characterized in that: The screen has a mesh size of 200-325; the dry pressing is performed at a pressure of 1.1-2.3 MPa; the pre-firing is performed at a temperature of 1100-1300℃, a heating rate of 1.5-15℃ / min, and a holding time of 30-60 min.

4. The method according to claim 1, characterized in that: The hot isostatic pressing process is as follows: the heating rate is 5-10℃ / min, the holding pressure is 100-200MPa, the maximum temperature is 1350℃-1400℃, and the holding time is 1-3h.

5. The method according to claim 1, characterized in that: The ZTA ceramic blank has a diameter of 2.8 mm and a length of 12 mm.

6. The method according to claim 1, characterized in that: The graphite is high-purity graphite powder with a mass percentage of 99.9% and a mesh size of 100.

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