Ceramic component

Abstract

Provided is a ceramic component comprising alumina (Al2O3) and tungsten carbide (WC). In this ceramic component, there is an atomic layer of zirconium (Zr) present at crystal grain boundaries between crystal grains of alumina and crystal grains of tungsten carbide. In any section of this ceramic component, the proportion of pores is 0.3% or less.

Description

Ceramic parts

[0001] The present invention relates to ceramic components.

[0002] Alumina (Al ２ O ３ In order to improve the properties of ceramic parts mainly composed of alumina (Al ２ O ３ ) and a technique of including tungsten carbide (WC) in the alloy.

[0003] For example, Patent Document 1 discloses alumina (Al ２ O ３ and tungsten carbide (WC); wherein the atomic layer formed by at least one element selected from transition metals belonging to groups 4 to 6 of the periodic table, yttrium (Y), scandium (Sc) and lanthanides is alumina (Al ２ O ３ A ceramic component is disclosed that is characterized by the presence of crystalline grain boundaries between tungsten carbide (WC) grains and tungsten carbide (WC) grains.

[0004] Patent No. 6491363

[0005] As mentioned above, alumina (Al ２ O ３ Various approaches have been proposed to improve the properties of ceramic components containing tungsten carbide (WC).

[0006] One aspect of the present invention is to further improve the environmental performance of ceramic components containing alumina and tungsten carbide.

[0007] [1] A ceramic part according to one aspect of the present invention is made of alumina (Al ２ O ３ ) and tungsten carbide (WC), ２ O ３ An atomic layer formed by zirconium (Zr) is present at the grain boundary between the crystal grains of the ceramic component and the crystal grains of the tungsten carbide (WC), and the ratio of pores in any one cross section of the ceramic component is 0.3% or less.

[0008] [2] In the ceramic part according to one aspect of the present invention described in [1], the atomic layer is formed by the alumina (Al ２ O ３ The crystal grains may be formed along the arrangement period of at least one of the crystal grains of the tungsten carbide (WC) and the crystal grains of the tungsten carbide (WC).

[0009] [3] In the ceramic part according to one aspect of the present invention described in [2], the atomic layers may be formed at the grain boundaries along an arrangement period of (100) planes of the tungsten carbide (WC) crystal grains.

[0010] [4] In the ceramic part according to one aspect of the present invention described in [3], the atomic layer may be formed at the grain boundary with a thickness corresponding to one arrangement of (100) planes of the tungsten carbide (WC) crystal grains.

[0011] [5] The ceramic part according to one aspect of the present invention described in any one of [1] to [4] may be used in a high-temperature environment of 1400°C or higher.

[0012] [6] The ceramic part according to one aspect of the present invention described in any one of [1] to [5] may be used in any one of a gas turbine component, a jet nozzle for an artificial satellite, a mold for a lens, an aircraft engine component, and a sealing material.

[0013] According to one aspect of the present invention, a ceramic part can be obtained that has improved ductility and bending strength properties in high temperature environments.

[0014] FIG. 1 is a perspective view showing the appearance of a ceramic part according to an embodiment. FIG. 2 is a view showing a TEM image of the A-A cross section of a ceramic part according to an embodiment. FIG. 3 is a view showing a HAADF-STEM image of the vicinity of a grain boundary of a ceramic part according to an embodiment. FIG. 4 is a view showing SEM images of a cross section of three samples of a ceramic part according to an embodiment, with each component color-coded. FIG. 5 is a view showing a TEM image of a cross section of a ceramic part after stress has been applied. FIG. 6 is a flowchart showing the flow of a method for manufacturing a ceramic part according to an embodiment.

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a ceramic component 10, which is an example of a ceramic component, will be described as an example. The ceramic component 10 is suitable for use as a ceramic component included in equipment used in high-temperature environments of 1400°C or higher. Specifically, the ceramic component 10 is used, for example, in any of gas turbine components, satellite jet nozzles, lens molds, aircraft engine components, and sealing materials.

[0016] (Configuration of Ceramic Component) Fig. 1 is a perspective view showing the appearance of a ceramic component 10. The ceramic component 10 is made of alumina (Al ２ O ３ ) and tungsten carbide (WC). In this ceramic component 10, alumina (Al ２ O ３ At the grain boundaries between the crystal grains of tungsten carbide (WC) and the crystal grains of silicon dioxide (SiO2), there are atomic layers formed by zirconium (Zr).

[0017] The atomic layer formed by zirconium (Zr) is, for example, zirconia (ZrO ２ ) as a raw material when manufacturing the ceramic component 10.

[0018] Fig. 2 shows an example of a TEM image of the ceramic part 10 shown in Fig. 1. The TEM image shown in Fig. 2 can be obtained by observing a sample prepared by the following procedure with a transmission electron microscope.

[0019] First, the ceramic composition was cut into a φ3 mm disk plate in a predetermined position and direction using a diamond cutter and an ultrasonic disk cutter, and then the thickness was adjusted to less than 100 μm using 30 μm diamond polishing paper and thinned. Next, a dimple was applied to the center of the disk using a dimpler, and the disk was then processed using a precision ion polishing system (PIPS). The TEM image shown in Figure 2 was obtained by observing a sample obtained by ion polishing under the following conditions: Ar ions, acceleration voltage 4.0 kV, beam irradiation angle ±4°, and damage layer removal treatment at 1.0 kV for 2 minutes after penetration of the sample.

[0020] FIG. 3 shows an example of a HAADF-STEM image of the vicinity of a grain boundary in the ceramic component 10 shown in FIG. 1. HAADF-STEM (High-Angle Annular Dark Field Scanning Transmission Electron Microscopy) is a high-angle scattering annular dark field scanning transmission microscope. In the HAADF-STEM image, heavy elements appear bright. When compared with a structural model, it can be seen that the bright white dots correspond to tungsten (W) atomic columns.

[0021] 3 is a HAADF-STEM image of the vicinity of the grain boundary between an alumina crystal grain and a tungsten carbide crystal grain, in which the atomic layer of the alumina crystal grain is an alumina layer 20, the atomic layer of the tungsten carbide crystal grain is a WC layer 30, and the atomic layer derived from the zirconium compound is a Zr layer 40.

[0022] As shown in FIG. 3, in the ceramic part 10, a Zr layer 40 exists between an alumina layer 20 and a WC layer 30. In other words, the ceramic part 10 is made of alumina (Al ２ O ３ An atomic layer formed by zirconium (Zr) exists at the grain boundary between the crystal grains of silicon dioxide (SiO2) and the crystal grains of tungsten carbide (WC). The Zr layer 40 includes a segregated layer of zirconium atoms (one layer of zirconium atomic arrangement).

[0023] The Zr layer 40 is formed at the grain boundaries in accordance with the arrangement period of at least one of alumina crystal grains and tungsten carbide crystal grains. More specifically, the Zr layer 40 is formed in accordance with the atomic arrangement of the WC layer 30. That is, the Zr layer 40 is formed at the grain boundaries in accordance with the arrangement period of the (100) planes of tungsten carbide (WC) crystal grains.

[0024] As shown in FIG. 3, the Zr layer 40 is preferably formed at the grain boundaries with a thickness equivalent to one arrangement of the (100) planes of the tungsten carbide (WC) crystal grains.

[0025] As described above, the presence of the Zr layer 40 at the grain boundaries between the alumina crystal grains and the tungsten carbide crystal grains can improve the adhesion strength between the alumina crystal grains and the tungsten carbide crystal grains.

[0026] In the ceramic part according to this embodiment, the pore ratio in any one cross section is 0.3% or less, which allows a ceramic part to be obtained that is excellent in ductility in high-temperature environments (e.g., 1400°C or higher).

[0027] (Regarding Pores in Ceramic Component) Next, the pores contained in the ceramic component 10 will be described in more detail. Here, pores refer to voids contained within the solid ceramic component 10. The pores contained in the ceramic component obtained after molding and processing the ceramic component 10 are also called cavities.

[0028] For example, when a ceramic component is placed in a high-temperature environment of 1400° C. or higher and subjected to stress, the ratio of pores or cavities contained in the structure of the ceramic component tends to increase. This ratio tends to increase over time.

[0029] It is known that fracture of ceramic parts under high temperature environments is caused by the formation, growth, and connection of pores or cavities in the ceramic parts. Furthermore, when ceramic parts are processed into a predetermined shape, the proportion of pores or cavities tends to increase when stress is applied to the ceramic parts by bending or the like.

[0030] Therefore, by keeping the ratio of pores contained in ceramic parts as low as possible, it is expected that ceramic parts with higher performance (specifically, ceramic parts with excellent high-temperature ductility) can be obtained.

[0031] In the ceramic component 10 according to this embodiment, the pore ratio in any one cross section is 0.3% or less. This results in a ceramic component with excellent high-temperature ductility. The ceramic component 10 having such properties can be manufactured by the method described below.

[0032] The pore ratio can be determined by taking multiple samples from the target ceramic part and calculating the pores of each sample based on the pore measurement method described below. If the pore ratio of the sample with the largest pore ratio among the multiple samples is 0.3% or less, it can be determined that the pore ratio is 0.3% or less.

[0033] In the ceramic component 10 according to this embodiment, the lower limit of the pore ratio is not particularly limited. In a typical ceramic component containing alumina and tungsten carbide, it is difficult to achieve zero pores (no pores at all). Therefore, the pore ratio in the ceramic component 10 according to this embodiment is greater than 0%.

[0034] In the ceramic part 10 according to this embodiment, an increase in the pore ratio can be suppressed to some extent even after stress application (for example, bending) (see FIG. 5 ). FIG. 5 shows the results of observing a cross section of the ceramic part 10 after stress application (after a bending test) in this example.

[0035] (Method of Measuring Pore Ratio) Here, an example of a method of measuring the ratio of pores contained in the ceramic component 10 will be described.

[0036] First, the solid ceramic component 10 is broken into small pieces, and any cross section is polished to the order of several microns. Next, a cross-section perpendicular to the cross section is processed using a shielding plate in a depth direction of 50 μm or more from the polished surface to form an ion-milled cross section with polishing damage removed, which serves as the observation surface. For example, an Ar ion milling device with an acceleration voltage of 5 to 6 kV is used as the processing device. An area of ​​300 μm x 300 μm or more is secured as the observation surface.

[0037] Next, an SEM image of the observation surface is taken. For example, an electron microscope with a voltage variable between 0.1 kV and 20 kV is used to photograph the observation surface and obtain image data. The resolution and magnification of the obtained image data are adjusted so that the resolution (number of pixels) is at least 10 times that of the smallest grain in the ceramic structure, and the image data is saved in a data format that does not require irreversible processing (for example, tiff or bmp).

[0038] Thereafter, the obtained image data is subjected to image analysis. Specifically, the obtained image data is ternarized using a region-classification function of image analysis software (for example, Avizo software for materials research (Thermo Fisher Scientific Inc.)). Specifically, the image data is ternarized for each of the following three regions: A: alumina (Al ２ O ３ A: Region formed by tungsten carbide (WC) C: Pore region

[0039] When converting to three values ​​as described above, grain boundary layers are not taken into consideration, regardless of whether the material is the same or different from the other material. In the case of the same material, it is extracted as a continuous region. Note that SEM images contain overlapping information in the depth direction, so regions are divided based on the observed top surface information. The area and occupancy rate of each region are calculated using pixel spacing and the software's 2D calculation function for digitization.

[0040] An example of an image obtained by performing ternary processing on an SEM image of an arbitrary cross section of the ceramic part 10 using the above method is shown in Figure 4. Figure 4 shows images of three samples (samples 1 to 3) taken from one ceramic part 10. Also, below the images in Figure 4, the results of calculating the area proportions of each of the above regions A to C are shown.

[0041] 4, it was confirmed that the pore ratio in any one cross section of the ceramic component 10 according to this embodiment was 0.3% or less. It was also confirmed that the average pore ratio was 0.2%.

[0042] The above-described method for measuring the pore ratio can also be used to calculate the proportions (volume %) of the alumina component and the tungsten carbide component contained in the ceramic component 10 .

[0043] Specifically, the area of ​​each region is calculated for the ternary-valued image data for each of the three regions A to C. Then, A / (A+B+C) and B / (A+B+C) are calculated based on the calculated values.

[0044] This gives the percentage (volume %) of each component in the ceramic part 10. ２ O ３ The table shows the proportions of the alumina (A) component and the tungsten carbide (WC) component. Note that the zirconium (Zr) component is not considered here because it is present in a trace amount. The proportion (volume %) of the zirconium component can be, for example, 2% to 5% when the total of the main components (alumina component and tungsten carbide component) is taken as 100%.

[0045] (Method for Manufacturing Ceramic Component) Next, a description will be given of a method for manufacturing the ceramic component 10. Fig. 6 shows an example of a method for manufacturing the ceramic component 10.

[0046] First, alumina, tungsten carbide, and a zirconium compound, which are raw materials for the ceramic part, are prepared (step S11). Each raw material is prepared in the form of powder. Specifically, alumina (Al２ O ３ ) powder, tungsten carbide (WC) powder with an average particle size of about 0.7 μm, zirconia (ZrO ２ ) powder is used.

[0047] The average particle size of the zirconia powder described here is an example. In order to more uniformly disperse the zirconia powder at the interfaces between the alumina crystal particles and the tungsten carbide crystal particles, it is preferable that the zirconia powder be a finer powder. The average particle size of the powder can be measured using a laser diffraction particle size distribution analyzer.

[0048] Next, the prepared raw materials are weighed and mixed in a predetermined ratio (step S12). The mixing ratio of the raw materials can be determined based on the desired ratio (e.g., volume %) of each component in the resulting ceramic component 10. For example, if the raw material powders are mixed and then fired to produce the ceramic component 10, the raw material powders can be mixed so that the mixing ratio of each raw material powder is the desired volume %. The volume % of each raw material powder can be determined based on the mass of each raw material powder used in the mixture and the specific gravity of each raw material.

[0049] Because the raw materials hardly react with each other during the manufacturing process, the volume percentages of the respective components in the ceramic component 10 can be adjusted to the desired values ​​by adjusting the volume percentages of the respective raw materials used in the mixing. The proportions (volume percentages) of the respective components in the manufactured ceramic component 10 can be determined by the method described above.

[0050] Then, pre-mixing and pulverization is carried out (step S13). At this time, it is preferable to carry out a dispersion and mixing process in which only the zirconia powder is pulverized first. Specifically, the zirconia powder is pre-pulverized for about 40 hours using a solvent and a ball mill. Alternatively, the zirconia powder particles may be pulverized using a bead mill or other method.

[0051] In the pre-mixing and grinding step, the alumina powder and the tungsten carbide powder are mixed together with a solvent (e.g., ethanol) using a ball mill, while the particles of each powder are ground. The processing time here may be shorter than 20 hours or longer than 20 hours.

[0052] Next, a slurry is obtained by mixing and pulverizing (step S14). Specifically, the pre-pulverized zirconia powder and a solvent (e.g., ethanol) are added to the mixture of alumina powder and tungsten carbide powder in the ball mill, and further mixing and pulverization are performed.

[0053] This results in a slurry containing dispersed alumina, tungsten carbide, and zirconia particles. In this embodiment, the time for adding zirconia to the mixture of alumina and tungsten carbide and further mixing and grinding can be approximately 20 hours. However, this is not limiting, and in other embodiments, the time may be less than 20 hours or greater than 20 hours.

[0054] Next, the slurry is dried to produce a mixed powder (step S15). For example, a method for obtaining the mixed powder from the slurry includes drying the slurry in a hot water bath to remove the solvent from the slurry, and then passing the obtained powder through a sieve.

[0055] Finally, the mixed powder is sintered by hot pressing to obtain a ceramic part (step S16). In this embodiment, the mixed powder is filled into a carbon mold and heated while being uniaxially pressed. This results in a sintered ceramic part 10, which is a sintered body of the mixed powder.

[0056] The hot pressing conditions in this embodiment are, for example, as follows: the firing temperature is 1700°C or higher and 1900°C or lower (preferably 1800°C or higher and 1900°C or lower, more preferably 1850°C), the firing time is 1 hour or higher and 3 hours or lower (preferably 2 hours), the pressure is 25 MPa or higher and 35 MPa or lower (preferably 30 MPa), and the atmospheric gas is argon (Ar). The firing temperature during firing is preferably set near the liquid phase formation temperature of alumina and zirconia. This can promote the movement (diffusion) of specific elements.

[0057] The above manufacturing method provides a solid ceramic part 10. In the ceramic part 10 manufactured by this manufacturing method, alumina (Al ２ O ３ A zirconium segregation layer (i.e., Zr layer 40) is formed at the grain boundary (i.e., interface) between the alumina crystal grains (i.e., alumina layer 20) and the tungsten carbide (WC) crystal grains (i.e., WC layer 30) (see FIG. 3, etc.). This is thought to strengthen the adhesion at the interface and allow the ceramic component 10 to exhibit high-temperature ductility.

[0058] That is, it is possible to obtain a ceramic component 10 that maintains high ductility even in a high-temperature environment of about 1400° C. and has a bending strength exceeding 400 MPa. Furthermore, the ceramic component 10 according to this embodiment can keep the pore ratio in the composition low (for example, 0.1% or less) even after stress is applied.

[0059] (Uses of Ceramic Component) The ceramic component 10 according to this embodiment can maintain its performance even in high-temperature environments of, for example, 1400°C or higher. Therefore, the ceramic component 10 according to this embodiment is suitable for use as a component for devices used in high-temperature environments. Specific uses of the ceramic component 10 include, for example, gas turbine components, spray nozzles for artificial satellites, lens molds, aircraft engine components, and sealing materials.

[0060] When the ceramic part 10 is used for the above-mentioned purposes, for example, the rectangular parallelepiped ceramic part 10 shown in FIG. 1 is deformed (for example, by cutting, grinding, polishing, etc.) into a predetermined shape.

[0061] Summary of the Embodiments The ceramic component 10 according to the present embodiment has improved heat resistance compared to conventional heat-resistant alloy members used in high-temperature environments. Furthermore, the ceramic component 10 according to the present embodiment has improved reliability because it is less susceptible to brittle fracture compared to conventional ceramic components used in high-temperature environments. These characteristics make the ceramic component 10 according to the present embodiment applicable to components of devices and systems used in high-temperature environments, such as those in the aerospace and power generation industries.

[0062] Furthermore, the ceramic component 10 according to this embodiment can maintain its strength during deformation processing, making it possible to perform superplastic deformation processing and joining, improving the formability and sealing properties of complex shapes. These characteristics also enable applications such as curved lens molds and sealing materials.

[0063] As described above, the ceramic component 10 according to this embodiment is excellent in strength and ductility in high-temperature environments, and is expected to exhibit a wide range of effects, such as improved life and workability.

[0064] Examples The present invention will be described below with reference to examples, but the present invention is not limited to the examples below.

[0065] In this example, the ceramic component 10 was manufactured based on the above-described manufacturing method, and the high-temperature ductility of the ceramic component 10 was evaluated. As a comparative example, a ceramic component not including the Zr layer 40 was manufactured, and the high-temperature ductility of the ceramic component 10 was similarly evaluated.

[0066] (Raw Materials for Ceramic Parts) The raw materials and their blending ratios (volume %) for the ceramic parts according to the examples and comparative examples were as follows.

[0067] <Example> 1. Alumina (Al) with an average particle size of 0.5 μm ２ O ３) powder: 55% 2. Tungsten carbide (WC) powder with an average particle size of 0.7 μm: 45% 3. Zirconia (ZrO ２ ) Powder: 5% (blending ratio (volume %) when the total of the main components 1 and 2 above is taken as 100%)

[0068] <Comparative Example> 1. Alumina (Al) with an average particle size of 0.5 μm ２ O ３ 1. ) powder: 55% 2. Tungsten carbide (WC) powder with an average particle size of 0.7 μm: 45%

[0069] (Hot Press Conditions) In both the Examples and Comparative Examples, the hot press conditions during production were as follows: Firing temperature: 1850° C. Firing time: 2 hours Pressure: 30 MPa Atmospheric gas: argon (Ar)

[0070] (Evaluation of High-Temperature Ductility) The ceramic parts according to the examples and comparative examples were subjected to a bending strength test under the following method and conditions to evaluate high-temperature ductility.

[0071] <Testing method for bending strength> Bending strength was measured using a test piece having a total length of 35 mm, a width of 4 mm, and a thickness of 3 mm. The tester determined the three-point bending strength of each sample of the examples and comparative examples in accordance with Japanese Industrial Standard JIS R1601 under the following conditions: Temperature: 1400°C Atmospheric gas: Argon (Ar) Deflection rate: 0.5 mm / min Bending span distance: 30 mm Testing machine: MST808 type ultra-high temperature material testing machine Jig material: SiC

[0072] <Results> It was confirmed that the ceramic parts according to the examples had a bending strength of more than 400 MPa under a temperature condition of 1400° C. In contrast, it was confirmed that the ceramic parts according to the comparative examples broke when a bending stress of about 300 MPa was applied under a temperature condition of 1400° C.

[0073] (HAADF-STEM Image of Ceramic Part) A HAADF-STEM image of a cross section of the ceramic part according to this example before the bending test is shown in FIG. 3. As shown in FIG. 3, alumina (Al ２ O３ It was confirmed that an atomic layer formed by zirconium (Zr) exists at the grain boundary between crystal grains of tungsten carbide (WC) and crystal grains of tungsten carbide (WC). It was also confirmed that the atomic layer formed by zirconium has a thickness equivalent to one arrangement of the (100) plane of the tungsten carbide (WC) crystal grains.

[0074] It was confirmed that no zirconium atomic layer was formed at the grain boundaries in the ceramic parts according to the comparative examples.

[0075] (TEM Image of Ceramic Part) A TEM image of a cross section of the ceramic part according to this example before the bending test is shown in Fig. 2. A TEM image of a cross section of the ceramic part according to this example after the bending test is shown in Fig. 5. The TEM image shown in Fig. 5 was obtained by observing a sample prepared in the same manner as the TEM image shown in Fig. 2.

[0076] As shown in Figure 2, it was confirmed that there were almost no pores in the structure of the ceramic part before the bending test. After the bending test, it was confirmed that some pores (cavities) were generated in the structure of the ceramic part, such as at the locations indicated by the arrows in Figure 5.

[0077] (Pore Ratio of Ceramic Component) FIG. 4 shows the measurement results of the pore ratio of one cross section of the ceramic component according to this example before the bending test.

[0078] As shown in FIG. 4, it was confirmed that the pore ratio was 0.3% or less in the three samples (samples 1 to 3) taken from the ceramic part according to this example.

[0079] (Summary of Examples) From the above results, it was confirmed that the ceramic part according to the present example has ductility (the property of not breaking brittle) even in an ultra-high temperature environment of 1400°C or more, and can maintain a high bending strength of 400 MPa or more.

[0080] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. Furthermore, configurations obtained by combining the configurations of different embodiments described in this specification are also included in the scope of the present invention.

[0081] 10: Ceramic part 20: Alumina layer (alumina crystal grains) 30: WC layer (tungsten carbide crystal grains) 40: Zr layer (atomic layer formed by zirconium)

Claims

1. Alumina (Al ２ O ３ A ceramic part containing alumina (Al) and tungsten carbide (WC), ２ O ３ a zirconium (Zr) atomic layer is present at the grain boundary between a crystal grain of the ceramic component and a crystal grain of the tungsten carbide (WC), and a pore ratio in any one cross section of the ceramic component is 0.3% or less.

2. The atomic layer is formed by the alumina (Al ２ O ３ 2. The ceramic part according to claim 1, wherein the crystal grains are formed along the arrangement period of at least one of the crystal grains of the tungsten carbide (WC) and the crystal grains of the tungsten carbide (WC).

3. The ceramic part according to claim 2, wherein the atomic layers are formed at the grain boundaries along the arrangement period of the (100) planes of the tungsten carbide (WC) crystal grains.

4. The ceramic part according to claim 3, wherein the atomic layer is formed at the grain boundary with a thickness corresponding to one arrangement of the (100) planes of the tungsten carbide (WC) crystal grains.

5. The ceramic part according to any one of claims 1 to 4, which is used in a high-temperature environment of 1400°C or higher.

6. The ceramic part according to any one of claims 1 to 4, which is used in any one of gas turbine components, satellite jet nozzles, lens molds, aircraft engine components, and seal materials.

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