Ceramic component

Abstract

To further improve the characteristics in a high environment, of a ceramic component containing alumina and tungsten carbide.SOLUTION: A ceramic component contains alumina (Al2O3) and tungsten carbide (WC). In the ceramic component, an atomic layer made from zirconium (Zr) exists in a crystal particle boundary between the crystal particles of the alumina and the crystal particles of the tungsten carbide. A ratio of pores on one arbitrary cross section of the ceramic component is 0.3% or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to ceramic components. [Background technology]

[0002] A technique has been disclosed in which tungsten carbide (WC) is added to alumina (Al2O3) in order to improve the properties of ceramic parts whose main component is alumina (Al2O3).

[0003] For example, Patent Document 1 discloses a ceramic part containing alumina (Al2O3) and tungsten carbide (WC), characterized in that an 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 lanthanoids is present at the grain boundaries between alumina (Al2O3) crystal grains and tungsten carbide (WC) crystal grains. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6491363 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, various approaches have been proposed to improve the properties of ceramic components containing alumina (Al2O3) and 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. [Means for solving the problem]

[0007] [1] A ceramic part according to one aspect of the present invention is a ceramic part containing alumina (Al2O3) and tungsten carbide (WC), in which an atomic layer formed by zirconium (Zr) is present at the grain boundaries between crystal grains of the alumina (Al2O3) and crystal grains of the tungsten carbide (WC), and the ratio of pores in any one cross section of the ceramic part is 0.3% or less.

[0008] [2] In the ceramic part according to one aspect of the present invention described in [1], the atomic layers may be formed at the grain boundaries along the arrangement period of at least one of the alumina (Al2O3) crystal grains and the tungsten carbide (WC) crystal grains.

[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 the arrangement period of the (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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing an appearance of a ceramic part according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a TEM image of the AA cross section of the ceramic part according to one example. [Figure 3] FIG. 2 is a diagram showing an HAADF-STEM image of the vicinity of a grain boundary of a ceramic part according to an example. [Figure 4] FIG. 1 is a diagram showing SEM images of cross sections of three samples of a ceramic part according to an example, with each component color-coded. [Figure 5] FIG. 1 shows a TEM image of a cross section of a ceramic component after stress application. [Figure 6] 1 is a flowchart showing the flow of a method for manufacturing a ceramic component according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0016] (Ceramic component structure) 1 is a perspective view showing the appearance of a ceramic part 10. The ceramic part 10 contains alumina (Al2O3) and tungsten carbide (WC). In this ceramic part 10, an atomic layer formed by zirconium (Zr) exists at the grain boundaries between the alumina (Al2O3) crystal grains and the tungsten carbide (WC) crystal grains.

[0017] The atomic layer formed by zirconium (Zr) can be obtained by adding a zirconium compound such as 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 according to the following procedure with a transmission electron microscope.

[0019] First, the ceramic composition was cut into a 3mm diameter disk in the desired position and orientation using a diamond cutter and an ultrasonic disk cutter. The thickness was then adjusted to less than 100µm using 30µm diamond polishing paper and thinned. Next, a dimple was created in the center of the disk using a dimpler, and the disk was then polished using a precision ion polishing system (PIPS). The TEM image shown in Figure 2 was obtained by ion polishing using Ar ions, an acceleration voltage of 4.0kV, and a beam irradiation angle of ±4°. After penetration of the sample, the damaged layer was removed at 1.0kV for 2 minutes.

[0020] Figure 3 shows an example of a HAADF-STEM image near the grain boundary of the ceramic part 10 shown in Figure 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. Comparing with the structural model reveals that the bright white dots correspond to tungsten (W) atomic columns.

[0021] Figure 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 Figure 3, the atomic layer of the alumina crystal grain is the alumina layer 20, the atomic layer of the tungsten carbide crystal grain is the WC layer 30, and the atomic layer derived from the zirconium compound is the Zr layer 40.

[0022] 3, in the ceramic component 10, a Zr layer 40 exists between the alumina layer 20 and the WC layer 30. In other words, in the ceramic component 10, an atomic layer formed of zirconium (Zr) exists at the grain boundaries between alumina (Al2O3) crystal grains and tungsten carbide (WC) crystal grains. 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 the ceramic part to have excellent ductility in high-temperature environments (e.g., 1400°C or higher).

[0027] (Pores in ceramic parts) Next, we will explain in more detail the pores contained in the ceramic component 10. Here, pores refer to air gaps 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 part 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 part 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, the pore ratio can be determined to be 0.3% or less.

[0033] In the ceramic component 10 according to this embodiment, there is no particular lower limit for the pore ratio. 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 in this example after stress application (after a bending test).

[0035] (Method for measuring pore ratio) Here, an example of a method for measuring the ratio of pores contained in the ceramic part 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 vertical ion milling method using a shielding plate is used to process the polished surface in a depth direction of 50 μm or more, forming 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 particle in the ceramic structure, and the data is saved in a data format that does not require irreversible processing (for example, tiff or bmp).

[0038] The obtained image data is then subjected to image analysis. Specifically, the obtained image data is ternarized using the region segmentation function of image analysis software (e.g., Avizo software for materials research (Thermo Fisher Scientific Inc.)). Specifically, the image data is ternarized into the following three regions: A: Area formed by alumina (Al2O3) B: Area 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 surface information. Numerical conversion uses pixel spacing and the software's 2D calculation function to calculate the area and occupancy rate of each region.

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

[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, and 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 image data for 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 component 10. FIG. 4 shows the percentages of the alumina (Al2O3) component and the tungsten carbide (WC) component contained in the ceramic component 10. Note that the zirconium (Zr) component is not considered here because it is present in a trace amount. The percentage (volume %) of the zirconium component can be, for example, 2% to 5% of the total of the main components (alumina and tungsten carbide) described above, taken as 100%.

[0045] (Method of manufacturing ceramic parts) 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, the raw materials for the ceramic part, alumina, tungsten carbide, and zirconium compound, are prepared (Step S11). Each raw material is prepared in powder form. Specifically, alumina (Al2O3) powder with an average particle size of approximately 0.5 μm, tungsten carbide (WC) powder with an average particle size of approximately 0.7 μm, and zirconia (ZrO2) powder with an average particle size of approximately 0.4 μm are 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 here 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 percentage of each component in the ceramic component 10 can be adjusted to a desired value by adjusting the volume percentage of each raw material used in mixing. The proportion (volume percentage) of each component in the manufactured ceramic component 10 can be determined using 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 technique such as bead mill pulverization.

[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 less than 20 hours or may be 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 carried out.

[0053] This results in a slurry containing dispersed alumina, tungsten carbide, and zirconia particles. In this embodiment, the time for adding zirconia to the alumina and tungsten carbide mixture 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 longer 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 to obtain a powder, and then passing the obtained powder through a sieve.

[0055] Finally, the mixed powder is sintered by hot pressing to obtain a ceramic part from the mixed powder (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 the specific elements.

[0057] The above manufacturing method produces a solid ceramic part 10. In the ceramic part 10 manufactured by this manufacturing method, a zirconium segregation layer (i.e., Zr layer 40) is formed at the grain boundary (i.e., interface) between alumina (Al2O3) crystal grains (i.e., alumina layer 20) and 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 enable the ceramic part 10 to exhibit high-temperature ductility.

[0058] That is, it is possible to obtain a ceramic part 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 part 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] (Use of ceramic parts) The ceramic part 10 according to this embodiment can maintain its performance even in high-temperature environments, for example, at 1400°C or higher. Therefore, the ceramic part 10 according to this embodiment is suitable for use as a component for devices used in high-temperature environments. Specific applications of the ceramic part 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 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 embodiment) The ceramic component 10 according to this embodiment has improved heat resistance compared to conventional heat-resistant alloy members used in high-temperature environments. Furthermore, the ceramic component 10 according to this embodiment has a reduced risk of brittle fracture compared to conventional ceramic components used in high-temperature environments, improving reliability. These characteristics make the ceramic component 10 according to this embodiment applicable to components for devices and systems used in high-temperature environments, such as those in aerospace and power generation.

[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 its use as a mold for a curved lens or a sealing material.

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

[0064] [Example] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[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 material for ceramic parts) The raw materials and their blending ratios (volume %) of the ceramic parts according to the examples and comparative examples were as follows:

[0067] <Example> 1. Alumina (Al2O3) powder with an average particle size of 0.5 μm: 55% 2. Tungsten carbide (WC) powder with an average particle size of 0.7 μm: 45% 3. Zirconia (ZrO2) powder with an average particle size of approximately 0.4 μm: 5% (volume %) when the total of the main components 1 and 2 above is taken as 100%)

[0068] <Comparative Example> 1. Alumina (Al2O3) powder with an average particle size of 0.5 μm: 55% 2. Tungsten carbide (WC) powder with an average particle size of 0.7 μm: 45%

[0069] (Hot pressing conditions) In both the examples and comparative examples, the hot pressing conditions during production were as follows. Firing temperature: 1850℃ Baking 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] <Bending strength test method> The 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℃ Atmospheric gas: Argon (Ar) Deflection speed: 0.5mm / min Bending span distance: 30mm Testing machine: MST808 type ultra-high temperature material testing machine Jig material: SiC

[0072] <Result> It was confirmed that the ceramic parts according to the examples had a bending strength of more than 400 MPa at a temperature 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 at a temperature of 1400°C.

[0073] (HAADF-STEM image of ceramic part) Figure 3 shows an HAADF-STEM image of a cross section of the ceramic part according to this example before the bending test. As shown in Figure 3, it was confirmed that an atomic layer formed by zirconium (Zr) was present at the grain boundary between alumina (Al2O3) crystal grains and tungsten carbide (WC) crystal grains. It was also confirmed that the atomic layer formed by zirconium was formed with 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 several pores (cavities) had appeared in the structure of the ceramic part, such as in the locations indicated by the arrows in Figure 5.

[0077] (pore ratio of ceramic parts) FIG. 4 shows the measurement results of the pore ratio in one cross section of the ceramic part 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 of this example has ductility (the property of not breaking due to brittleness) 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. [Explanation of symbols]

[0081] 10: Ceramic parts 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 ) and tungsten carbide (WC), The alumina (Al ２ O ３ an atomic layer formed by zirconium (Zr) is present at the grain boundary between the crystal grains of the tungsten carbide (WC) and the crystal grains of the tungsten carbide (WC), The pore ratio in any one cross section of the ceramic component is 0.3% or less. Ceramic parts.

2. The atomic layer is formed by the alumina (Al ２ O ３ 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). The ceramic part of claim 1 .

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

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

5. It is used in high temperature environments of 1400°C or higher. The ceramic part according to any one of claims 1 to 4.

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

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