JPH0419182B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a novel ceramic sintered body,
In particular, the present invention relates to a ceramic sintered body having a thermal expansion coefficient equivalent to that of metal materials, particularly stainless steel, from room temperature to high temperature. [Prior Art] In recent years, the use of ceramics, which have excellent thermal properties, has been expanding because they can be used at higher temperatures than metal materials. However, ceramics have poor workability, toughness, thermal shock resistance, etc.
There is still a problem. Therefore, for example, various research and developments have been carried out regarding low thermal expansion ceramics in order to improve thermal shock resistance. On the other hand, in electronic parts and structural parts such as magnetic heads, they are increasingly being used in combination with metal materials. For this purpose, a composite design of ceramics and metal materials is important.
However, the crystal structure itself is different between ceramics made of ionic crystals and Iari crystals and metal materials made of metal crystals, and the thermal expansion caused by this is usually about 2 to 3 times different. The occurrence of cracks (eventually leading to breakage) in the joints due to this has become a problem. Therefore,
Various methods have been considered in the past to alleviate thermal stress caused by differences in thermal expansion, but it is thought that the most useful method would be to develop ceramics that have thermal expansion equal to or close to that of the metal material used. For example, various ceramics for magnetic heads have been developed that are matched to the coefficient of thermal expansion of the core of the magnetic head. In Japanese Patent Publication No. 60-29668, by using TiO as the main component and adding BaO, SiO ₂ , Nb ₂ O ₅ and ZnO, the thermal expansion coefficient value was increased from 6 to 12 ×
It can be freely selected within the range of 10 ^-6 /℃, has no color unevenness due to changes in the firing atmosphere, has high mechanical strength, good pore distribution, has wear resistance comparable to ferrite, and , provides ceramics characterized by good thermal shock properties. Other examples of high thermal expansion ceramics related to magnetic heads include patents 1986-31210, JP-A 50-5506, and
52-57218, JP 52-135318, JP 60-29669
and so on. Regarding high thermal expansion ceramics for structural parts,
For engine parts, Japanese Patent Publication No. 60-18621 provides high-strength partially stabilized zirconia with a coefficient of thermal expansion (10.3 x 10 ^-6 /°C) almost equivalent to that of cast iron. Excellent heat insulation and mechanical strength (bending strength
598Mpa), and the temperature characteristics of the coefficient of thermal expansion are almost the same as those of metal parts. Among the above conventional examples, the thermal expansion coefficient of ceramics related to magnetic heads of Japanese Patent Publication No. 60-29668 is 12×
10 ^-6 /℃ or less, which is sufficient for combination with ferrite, but carbon steel (its coefficient of thermal expansion is 13 to 14
×10 ^-6 /℃), alloy steel (thermal expansion coefficient is ~20 ×
10 ^-6 /℃), stainless steel (coefficient of thermal expansion is 15~
20×10 ^-6 /°C), the coefficient of thermal expansion is too small when considering expanded use as structural parts. Furthermore, the bending strength is less than 160 MPa, which is insufficient in terms of strength when used as a structural component. In addition, the ceramics for structural parts of the Japanese Patent Publication No. 60-18621 have higher strength, but because it is difficult to freely select the value of the thermal expansion coefficient, it is difficult to select the value of the thermal expansion coefficient freely, so it is difficult to select specific metal materials, such as cast iron, There was a problem in that it could only be combined with other methods, and its uses were limited. In addition, since the coefficient of thermal expansion is 10.3×10 ^-6 /℃, similar to the above-mentioned Japanese Patent Publication No. 60-29668,
The coefficient of thermal expansion is too low, making it difficult to use in combination with carbon steel, alloy steel, stainless steel alloy, etc. [Problems to be solved by the invention] As described above, when ceramics and metal materials are bonded together, it is useful to increase the coefficient of thermal expansion of the ceramics so that it approaches that of the metal materials. The high thermal expansion ceramics developed in , however, have a coefficient of thermal expansion of no more than 12×10 ^-6 /°C, making them difficult to use for electronic components.
Furthermore, there has been a strong demand for the development of ceramics for structural parts that have a coefficient of thermal expansion equivalent to that of alloys, carbon steel, alloy steel, stainless steel, and the like. An object of the present invention is to provide a ceramic sintered body having excellent oxidation resistance and strength. Another object of the present invention is to use metal materials such as cast iron, cast steel, carbon steel alloy steel, steel such as stainless steel, nickel and its alloys, copper and its alloys, Co-based alloys, and alloys such as aluminum alloys. The object of the present invention is to provide a ceramic sintered body having thermal expansion equal to or close to the same. [Means for Solving the Problems] The present invention is characterized in that the composition before sintering is Al ₂ O ₃ , ZrO ₂ , and
At least one oxide of BaTiO ₃ ;
It is composed of at least one fluoride of CaF ₂ , MgF ₂ , AlF ₃ , ScF ₃ , YF ₃ , and LaF ₃ and contains 10 to 90% by volume of fluoride as a volume percentage after sintering. The feature lies in the ceramic sintered body. Thermal expansion is closely related to thermal properties such as melting point, content, heat of formation, crystal structure, and strength of chemical bonds, and is generally said to be as follows. (1) Substances with low melting point, low heat of formation, and large heat capacity have large thermal expansion. (2) Thermal expansion increases in the order of covalent crystals, ionic crystals, and metal crystals. (3) In ionic crystals, the bond strength is small;
In other words, the smaller the valence of the cation and the larger the coordination number, the larger the thermal expansion. In view of the above, among oxides and halides that have fairly large crystals with ionic bonding properties, oxides with an 8- or 6-acid structure and a relatively large thermal expansion CaF ₂ type structure, perovskite Among oxides that have any of the type structure, NaCl type structure, ReO ₃ type structure, etc., they have excellent water resistance and oxidation resistance, can be sintered at relatively low temperatures (below 1400℃), and have a coefficient of thermal expansion of 7× 10 ^-6 /℃ (room temperature to 500℃)
ZrO ₂ has the above properties and also has excellent mechanical properties.
BaTiO ₃ and Al ₂ O ₃ having a corundum structure, which is industrially highly versatile, are preferred. At least one of these has relatively low mechanical properties, but a coefficient of thermal expansion of 15
Among fluorides that exhibit a value of ×10 ^-6 /℃ or higher, which is equivalent to or higher than that of metal materials, CaF ₂ , MgF ₂ , which have excellent chemical stability and a melting point of 1000℃ or higher,
At least one type of rare superelement fluoride such as AlF ₃ , ScF ₃ , YF ₃ , and LaF ₃ is preferred, and these were added to create a mixed powder. After pressure-molding this, a ceramic sintered body with sufficient strength was developed by holding it at 900-1400°C for 0.5-3 hours. In addition, the metal oxide used is partially stabilized.
It is most desirable to use ZrO ₂ , and a ceramic sintered body with particularly high strength can be obtained in this gap. Furthermore, the smaller the grain size of the sintered body, the higher the strength and the better the heat cycle resistance, and for practical purposes, the grain size is preferably 2 μm or less. By adjusting the amount of fluoride, this ceramic sintered body can have an arbitrary coefficient of thermal expansion as shown in Figure 3, and as shown in Table 4, the type of fluoride can be adjusted. Depending on the selection, the thermal expansion coefficient can be varied while maintaining the same strength. For example, when CaF ₂ is added at a volume ratio of 75 to Al ₂ O ₃ , the thermal expansion coefficient becomes 17×10 ⁶ /℃ (from room temperature to 500
℃), and the coefficient of thermal expansion is 17.0×10 ^-6 / SUS308L.
℃ (room temperature to 500℃).
Furthermore, since fluorides have a lower specific gravity than oxides, they are also useful for reducing the weight of ceramics. Furthermore,
It is also useful as a sintering aid to lower the sintering temperature. By using the ceramic sintered body of the present invention and joining it to carbon steel, alloy steel, stainless steel, etc. by a well-known method, it is possible to reduce the occurrence of thermal stress caused by differences in thermal expansion. Furthermore, joining is easier than in the past, and highly reliable ceramic and metal composite structural parts can be obtained.
In addition, since metal fluoride acts as a brazing agent when joining metal, the strength of the joints between high thermal expansion ceramic and metal composite structural parts is significantly improved and more reliable than before. It enhances sexuality. Further, when ceramics are fitted to the ring-shaped metal, by using the ceramics of the present invention, there is less risk of the ceramics being damaged by hot pressing. [Examples of the Invention] The present invention will be described below based on Examples. The coefficient of thermal expansion, bending strength, oxidation resistance, alkali resistance, and water resistance of the ceramics obtained in the following examples were examined by the following methods. Thermal expansion coefficient...The measurement temperature range is room temperature to
The average coefficient of thermal expansion is determined as 500℃. Bending strength: 4-point bending strength test at room temperature. Oxidation resistance...Weight change per unit area after being left in the air at 1000℃ for 24 hours. Alkali resistance...70℃, 3% NaOH aqueous solution, 12
Weight change after time immersion. Water resistance…Weight change after 12 hours immersion in pure water at 70℃. Al ₂ O ₃ , ZrO ₂ , BaTiO ₃ and CaF ₂ , MgF ₃ ,
First, raw material powder selected from AlF ₃ , YF ₃ , and LaF ₃
The samples were weighed to have the chemical compositions of Examples 1 to 33 shown in Tables 2 and 4. The reason why the combined amount of fluoride was set at a volume ratio of 10 to 90 is because if the volume ratio is less than 10, the effect of increasing thermal expansion and the effect as a soldering agent for bonding will be small.
On the other hand, if the volume ratio is 90 or more, practical strength of the sintered body cannot be obtained. A solvent was added to the mixed powder of oxide and fluoride in a ball mill, the mixture was mixed in a powder frame for more than several tens of hours, and then sufficiently dried to prepare a raw material powder. In this way, the particle size of one or both of the oxide and fluoride was reduced to 0.5 μm or less, thereby lowering the sintering temperature and achieving densification. This raw material powder is pressure-molded, and the molded body is pressurized in a temperature range of 900 to 1400℃.
Apply 300Kg/ ^mm2 , hold for 0.5 to 3 hours, and reduce the particle size to 2μm.
The following sintered body was obtained. Each test piece was obtained from this sintered body. In addition, the ZrO ₂ raw material powder is
Although a material containing 4 mol % of Y ₂ O ₃ was used, a material containing 1 to 8 mol % of Y ₂ O ₃ to ZrO ₂ may be used.

【table】

【table】

[Table] Table 1 shows examples 1 to 15 of high thermal expansion ceramics obtained by the above manufacturing method. Ceramics that have been put into practical use and have comparatively large thermal expansion coefficients of 1 to 5 are shown below. Examples 1 to 15 are
It showed a larger coefficient of thermal expansion than any of Comparative Examples 1-5. In particular, Examples 9 to 15 have a thermal expansion coefficient of 13×
Carbon steels showing large values of 10 ^-6 /℃ to 15×10 ^-6 /℃ and shown in Reference Examples 1 to 3 and Reference Examples 4 to 6
The coefficient of thermal expansion was equivalent to that of alloy steel shown in . Furthermore, in Examples 1 to 8, the coefficient of thermal expansion is 15×
It showed a value of 10 ^-6 /°C or more, and a value equivalent to the coefficient of thermal expansion of stainless steel shown in Reference Examples 7 to 10.
Furthermore, in Examples 1 to 4, the coefficient of thermal expansion is 17.5×
It showed a value of 10 ^-6 /°C or more, which was equivalent to the coefficient of thermal expansion of the alloys shown in Reference Examples 11 to 13. From this, the high thermal expansion ceramics of the present invention can be selected according to the respective thermal expansion coefficients of alloys such as carbon steel, alloy steel, and stainless steel.

【table】

[Table] Examples 16 to 23 show the oxidation resistance, alkali resistance, and water resistance of the ceramics of the present invention. These are comparable to those of the oxides of Comparative Examples 6-8. In particular, those using CaF ₂ as the fluoride exhibit excellent properties.

〔Effect of the invention〕

The ceramics of the present invention have excellent oxidation resistance and strength. In particular, since it exhibits a coefficient of thermal expansion equivalent to that of two types of metals, such as carbon steel, alloy steel, and stainless steel, it is possible to provide an integrated structure of ceramics and metals that is less prone to cracking due to thermal stress. The reliability of composite structures can be greatly increased.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a cylinder liner made of a ceramic/metal composite which is an embodiment of the present invention, and Figs. 2 and 5 are an exhaust liner made of a ceramic/metal composite which is an embodiment of the present invention. The perspective view of the bulb, FIGS. 3 and 4, are curve diagrams showing the relationship between the characteristics of the ceramics of the embodiment of the present invention and the CaF ₂ content. 21... Ceramic cylinder liner, 2
2...Metal sleeve, 31...Ceramic valve seat, 32...Metal, valve stem.

Claims (1)

[Claims] 1. The composition before sintering is Al ₂ O ₃ , ZrO ₂ , and
At least one oxide of BaTiO ₃ ;
It is composed of at least one kind of fluoride among CaF ₂ , MgF ₂ , AlF ₃ , ScF ₃ , YF ₃ , and LaF ₃ and contains 10 to 90% by volume of fluoride as a volume percentage after sintering. Characteristic ceramic sintered body. 2 In claim 1 or 2, the coefficient of thermal expansion between room temperature and 500°C is 15×10 ^-6 /
A ceramic sintered body characterized by a temperature of ℃ or higher. 3. The ceramic sintered body according to claim 1, characterized in that the average crystal grain size of the sintered body is 2 μm or less.