JP7684535B2 - Ceramic bonding material - Google Patents

Description

The present invention provides a material for joining ceramics or ceramics and metals, a method for joining ceramics or ceramics and metals using the joining material, and a joined member obtained by the joining method.

Materials that can withstand high temperatures are required in various situations, such as in the development of low fuel consumption and new energy sources, and ceramics and high-melting-point metals are expected to be candidates for such materials. Among them, ceramics have the advantage of being lighter, cheaper, and easier to process than high-melting-point metal materials, but on the other hand, they have the disadvantage that, unlike metals, they cannot be welded, making it difficult to create complex shapes such as turbines. In order to combine two ceramic members or a ceramic member and a metal member, there are joining techniques and metallization methods that use insert materials such as brazing materials instead of welding (for example, Patent Documents 1 to 4), but all of these methods have problems such as the brazing material remaining, which has lower heat resistance and oxidation resistance than ceramics, causing the joint to melt when used under high-temperature conditions, or the joint to crack due to oxidation in air, and the need for long-term heating at high temperatures to join them.

Therefore, attempts have been made to join ceramics using silicon, which has a high melting point (Non-Patent Documents 1 to 3). For example, Non-Patent Document 1 provides a method for joining ceramics, in which a paste of Si-based Al mixed powder is applied, and heated at 800 to 1300°C for 60 minutes under reduced pressure conditions of about 20 Pa to evaporate the Al, forming a Si-based paste joining layer.

JP 2017-52673 A JP 2016-216352 A JP 2007-119313 A JP 2015-20927 A

Summary of Lectures at the National Convention of the Japan Welding Society, Vol. 99 (2016-9) Japan Welding Society National Convention Lecture Summary No. 100 (2017-4) Summary of Lectures at the National Convention of the Japan Welding Society, Vol. 101 (2018-9)

The problem to be solved by the present invention is to bond ceramics or ceramics and metals so that they can withstand use under high-temperature conditions, and in particular to reduce the heating temperature and heating time of the bonding material. The bonding methods using Si-based Al mixed powders presented in Non-Patent Documents 1 to 3 do not provide sufficient bonding at about 800°C, and require heating up to 1300°C even under reduced pressure conditions. In addition, the heating time is long, which places a great burden on the furnace, requires a high-grade furnace with high heat resistance, and increases manufacturing costs. Therefore, we have searched for a bonding material that can be worked with a simple electric furnace that does not require a high-temperature heater or a furnace wall cooling mechanism and can be heated for a short time at 1200°C or less, preferably 1100°C or less, and more preferably 1000°C or less.

In a first aspect, the present invention provides a bonding material for bonding between ceramics or between ceramics and metals, characterized in that it contains silicon and a metal having a vapor pressure of 0.1 Pa or more at 1000°C (hereinafter, the bonding material of the present invention). The bonding material of the present invention forms a eutectic liquid phase of silicon and metal by short-term heating at a temperature lower than the melting point of silicon alone, for example, 1200°C or less, preferably 1100°C or less, more preferably 1000°C or less, by eutectic reaction, and further evaporates the metal from the obtained eutectic liquid phase to become a bonding member of silicon alone. Since silicon alone has a melting point of 1414°C and is known to have oxidation resistance, the bonding member obtained from the bonding material of the present invention is a bonding material having heat resistance and oxidation resistance.

A high vapor pressure at a certain temperature means that the metal is more easily evaporated, and therefore in a preferred embodiment, the metal contained in the bonding material of the present invention preferably has a vapor pressure at 1000° C. of 1 Pa or more, more preferably 10 Pa or more, even more preferably 1×10 ² Pa or more, and most preferably 1×10 ⁴ Pa or more. Examples of such metals include magnesium, lithium, calcium, and sodium, and magnesium is particularly preferred in terms of ease of handling of the metal compound and ease of availability.

In a preferred embodiment, all or a part of the silicon and the metal having a vapor pressure of 0.1 Pa or more at 1000°C in the bonding material of the present invention are contained as metal silicide. When metal silicide is used, it is possible to prevent the metal from evaporating before the silicon is sufficiently liquefied, making it easier to obtain a eutectic liquid phase and facilitating control of the bonding process. In order to further facilitate the bonding process, the mixture ratio of silicon and metal in the bonding material of the present invention may be adjusted. In a preferred embodiment, for example, the metal having a vapor pressure of 0.1 Pa or more at 1000°C is contained in an amount of 1/4 or more, preferably 1/3 or more, more preferably 1/2 or more, as atoms, relative to the silicon.

In a further preferred embodiment, the bonding material of the present invention may be dispersed in a suitable carrier for ease of handling.

When the thus obtained joining material of the present invention was applied between ceramic members to be joined and heated to form a joining member, it was surprisingly found that not only was a layer of simple silicon formed, but the metal reacted with the ceramic component to form a metal compound layer, resulting in a stronger bond. Therefore, in a second aspect, the present invention provides a joining member between ceramics or between ceramics and a metal, which includes a metal compound layer of the ceramic component and a layer of simple silicon, and is characterized in that the metal in the metal compound layer of the ceramic component has a vapor pressure of 0.1 Pa or more at 1000°C (hereinafter, the joining member of the present invention).

Furthermore, in a third aspect, the present invention provides a method for joining two ceramic members or a ceramic member and a metal member, comprising:
1) applying the joining material of the present invention between both components;
2) heating both members to which the bonding material has been applied to obtain a eutectic liquid phase of silicon and metal, and 3) further heating to evaporate the metal and obtain a layer of silicon alone (hereinafter, the bonding method of the present invention). Preferably, steps 2) and 3) are performed under reduced pressure conditions of ^1x102 Pa or less.

The joining material of the present invention is capable of providing joining members primarily made of silicon that have excellent heat resistance and oxidation resistance, and can be worked on at lower temperatures and in shorter times than conventional joining materials or joining materials, making it superior in both performance and cost.

The phase diagram of silicon and magnesium is shown. The horizontal axis shows the atomic percentage (at%) of magnesium, and the vertical axis shows temperature (°C). 13 shows SEM photographs of bonded members in which both of the bonded members are made of alumina and the bonding material is a mixture of elemental silicon and magnesium silicide (47 at % Mg). The figure shows an EPMA photograph (silicon) of bonded members in which the bonded members are all alumina and the bonding material is a mixture of elemental silicon and magnesium silicide (47 at % Mg). 1 shows an EPMA photograph (magnesium) of bonded members in which both of the bonded members are alumina and the bonding material is a mixture of elemental silicon and magnesium silicide (47 at % Mg). The graph shows the tensile strength at room temperature of the bonded members when the bonded members are all alumina and a bonding material containing silicon and magnesium is used. The horizontal axis shows the atomic percentage (at%) of magnesium, and the vertical axis shows the tensile breaking strength (MPa). The graph shows the three-point bending strength at high temperatures of the bonded members when the bonded members are all alumina and the bonding material contains silicon and magnesium. The horizontal axis shows the atomic percentage (at%) of magnesium, and the vertical axis shows the bending fracture strength (MPa). 1 shows SEM photographs of bonded members in which the bonded members are all made of silicon nitride and the bonding material is a mixture of simple silicon and magnesium silicide (47 at % Mg). 1 shows an EDX photograph (silicon) of bonded members in which the bonded members are all silicon nitride and the bonding material is a mixture of elemental silicon and magnesium silicide (47 at % Mg). 1 shows an EDX photograph (magnesium) of bonded members in which both bonded members are silicon nitride and the bonding material is a mixture of elemental silicon and magnesium silicide (47 at % Mg). The graph shows the tensile strength at room temperature of the bonded members when the bonded members are all silicon nitride and a bonding material containing silicon and magnesium is used. The horizontal axis shows the atomic percentage (at%) of magnesium, and the vertical axis shows the tensile breaking strength (MPa). The graph shows the three-point bending strength at high temperatures of bonded members when the bonded members are all silicon nitride and a bonding material containing silicon and magnesium is used. The horizontal axis shows the atomic percentage (at%) of magnesium, and the vertical axis shows the bending fracture strength (MPa). The graph shows the tensile strength at room temperature of bonded members when the bonded members are all silicon carbide and a bonding material containing silicon and magnesium is used. The horizontal axis shows the atomic percentage (at%) of magnesium, and the vertical axis shows the tensile breaking strength (MPa).

The present invention provides a bonding material for bonding between ceramics or between ceramics and metals, characterized in that it contains silicon and a metal having a vapor pressure of 0.1 Pa or more at 1000°C. Here, "containing" silicon or a metal means that each is contained as an element, regardless of whether it is a simple substance or a compound, or one type of compound or multiple compounds. Thus, the bonding material of the present invention may contain only one type of metal silicide, or the silicon and the metal may each be a simple substance or one or more types of compounds.

In this invention, ceramics refers to ceramics in the broad sense of the word, which means sintered bodies of inorganic materials, and includes not only classic ceramics made from natural raw materials, but also so-called fine ceramics such as aluminum oxide (alumina), silicon carbide, silicon nitride, and zirconia.

In the present invention, the ceramics to be joined may be ceramics made of the same components or ceramics made of different components. For example, the ceramics to be joined may be a first joined member made of alumina ceramics and a second joined member made of alumina ceramics, or a first joined member made of alumina ceramics and a second joined member made of silicon carbide ceramics. The ceramics may have any shape including the joining surfaces. The metal joined member to be joined to the ceramic joined member may be any metal joined member that is commonly used by those skilled in the art in terms of composition, shape, etc.

In the present invention, a joining material means a material used to join two members to be joined, and does not need to have exactly the same composition after the joining is completed. In other words, after the joining material is applied between the two members to be joined, the composition of the material changes chemically or physically by performing a joining operation such as heating, and a joining member that joins the two members is obtained. Therefore, in the present invention, a joining member means a layered member that actually achieves the joining between the members to be joined, and is distinguished from a joining material that should be applied between the members to be joined before the joining is actually achieved.

In the present invention, a metal having a vapor pressure of 0.1 Pa or more at 1000°C means a metal element of Groups 1 to 12 of the periodic table, excluding hydrogen, whose simple metal has a boiling point of 1000°C or less at 0.1 Pa or whose vapor pressure at 1000°C is 0.1 Pa or more, as measured by a normal vapor pressure measurement method such as the effusion method, evaporation method, or flow method. The metal may be one type or more, but from the viewpoint of ease of reaction management and necessity, it is preferable to use one type. Since the vapor pressure curves of simple metals are known, the metal may be selected by referring to those documents. Typically, metals having a vapor pressure of 0.1 Pa or more at 1000°C include, but are not limited to, magnesium, lithium, calcium, sodium, etc.

In a preferred embodiment of the present invention, in order to enable the joining operation to be performed at a lower temperature or under conditions closer to atmospheric pressure, the metal contained in the joining material of the present invention preferably has a vapor pressure at 1000°C of 1 Pa or more, more preferably ¹⁰ Pa or more, even more preferably 1x102 Pa or more, and most preferably ^1x104 Pa or more. Furthermore, the metal element may be selected in consideration of the ease of handling and availability of the metal element or metal compound used. Taking these points into consideration comprehensively, a particularly preferred metal having a vapor pressure of 0.1 Pa or more at 1000°C is magnesium, which is known to have a vapor pressure of about ^3x104 Pa at 1000°C.

The silicon contained in the bonding material of the present invention may be silicon alone as long as it contains silicon as an element, but is also preferably a silicide. Examples of silicides include, but are not limited to, nickel silicide, lithium silicide, calcium silicide, sodium silicide, and magnesium silicide. As described above, the bonding material of the present invention contains silicon as an element and a metal whose vapor pressure at 1000 ° C is 0.1 Pa or more, so it is understood that the material is sufficient if it contains a silicide of the metal, i.e., a metal silicide, such as calcium silicide, sodium silicide, or magnesium silicide. When a metal silicide is used, it is possible to prevent the metal from evaporating before the silicon is sufficiently liquefied, making it easier to obtain the eutectic liquid phase described below, and it is expected to have the advantage of making it easier to control the bonding process. Furthermore, in order to enable bonding under desired bonding conditions, the bonding material of the present invention may contain, in addition to a silicide of a metal whose vapor pressure at 1000 ° C is 0.1 Pa or more, a silicon alone, a further silicide, a metal alone, or a further metal compound.

It is known that the melting point of silicon is 1414°C, but in a mixture of silicon and a metal silicide, the melting point is lower than that of silicon due to a eutectic reaction. A similar eutectic reaction can also occur in a mixture of silicon and/or a silicide and a metal and/or a metal silicide. In a mixture of silicon and a metal in which such a eutectic reaction occurs, a part or all of the mixture will be in a eutectic liquid phase even at a temperature lower than the melting point of silicon alone, as long as it is above the eutectic temperature. Many metal silicides also have melting points lower than 1414°C; for example, calcium silicide has a melting point of about 1020°C, and magnesium silicide has a melting point of about 1100°C. In this way, a joining member of silicon alone can be obtained by melting the joining material of the present invention to obtain a eutectic liquid phase of silicon and metal, and then evaporating the metal.

When the joining material of the present invention is used for joining, the metal and the components of the ceramic members to be joined may react to form a layer of a metal compound of the ceramic components, but such a layer of a metal compound of the ceramic components is expected to improve the joining surface of the ceramic members to be joined and contribute to stronger joining, and is rather a preferable by-product. For example, when alumina (Al ₂ O ₃ ) is used as the ceramic and magnesium is used as the metal, alumina reacts with magnesium and silicon forms a dense layer, resulting in a joining member including a MgAl ₂ O ₄ layer, a Si layer, and a MgAl ₂ O ₄ layer. Since the melting point of MgAl ₂ O ₄ is 2130°C and the melting point of Si is 1414°C, the joining member of the present invention has excellent heat resistance. Magnesium, lithium, calcium, and sodium, which are given above as examples of metals having a vapor pressure of 0.1 Pa or more at 1000°C, are preferred metals because they have good reactivity with ceramics and can easily modify the joining surfaces of the ceramic members to be joined, thereby obtaining a strong joined state.

Therefore, as a further aspect of the present invention, there is provided a joining member between ceramics or between ceramics and a metal, comprising a metal compound layer of a ceramic component and a layer of simple silicon, wherein the metal in the metal compound layer of the ceramic component has a vapor pressure of 0.1 Pa or more at 1000°C.

The above eutectic temperature varies depending on the type of metal element combined with silicon, but can be easily obtained by showing the relationship of the liquidus (a line indicating the lowest temperature at which the entire mixture can exist in a liquid phase) and solidus (eutectic isotherm) (a line indicating the highest temperature at which the entire mixture can exist in a solid phase) to the composition (atomic percentage, also at%) of the metal element in the mixture of silicon and metal in a phase diagram. The triple point where two liquidus lines and one solidus line intersect is the eutectic point, and the temperature and composition corresponding to that point are the eutectic temperature and eutectic composition, respectively. The atomic percentage of the metal element in the mixture of silicon and metal means that only the simple substance of silicon is present at 0 at%, and that only the simple substance of metal is present at 100 at%. In the range of more than 0 at% and less than 100 at%, it means a state in which silicon and metal are mixed as elements, but the form may include any of simple substance of silicon, silicide, simple substance of metal, and metal silicide. Examples of such combinations may be metal silicide alone, silicon and metal silicide, silicon and metal, silicide and metal silicide, silicide and metal, silicon and metal, silicide and metal, silicon and metal, silicide and metal, silicide and metal, silicide and metal, metal, silicide, metal silicide and metal, or silicon and metal. For example, when the metal element is magnesium, 66.7 at% Mg means a mixture of silicon and magnesium containing 66.7 at% magnesium (including magnesium silicide (Mg ₂ Si) alone). 0 to 66.6 at% Mg means a mixture of silicon and magnesium (which may be magnesium silicide (Mg ₂ Si)) containing 66.6 at% or less magnesium. The eutectic point of magnesium and silicon is a eutectic composition of 47 at% Mg and a eutectic temperature of 945.6 °C.

The important point here is that silicon is sufficiently liquefied under the desired joining conditions (temperature, pressure, and heating time). If silicon is not sufficiently liquefied, powder of the material silicon will remain in the joining components, which may cause cracks and voids. The atomic percentage of metal required to achieve such a melting point drop can be easily obtained from the phase diagram for obtaining the above eutectic point, and is, for example, 20 at% or more (1/4 or more of the metal atoms relative to the silicon), preferably 25 at% or more (1/3 or more of the metal atoms relative to the silicon), and more preferably 33.3 at% or more (1/2 or more of the metal atoms relative to the silicon).

Since both the silicon element and the metal silicide are solids such as powders, the solids may be dispersed in a suitable carrier when applied to the members to be joined. For example, when the joining material of the present invention is made into a paste, the carrier is preferably a liquid that can be applied to ceramic or metal surfaces and that easily evaporates at 1000°C or less, for example, 600°C or less, and typically includes, but is not limited to, polyethylene glycol, water, ethanol, isopropyl alcohol, etc. Alternatively, when the joining material of the present invention is made into a foil, the carrier is preferably a liquid that easily evaporates at 1000°C or less, for example, 600°C or less, and that can be processed into a foil, and typically includes, but is not limited to, polyacetal resin, acrylic resin, polyethylene, paraffin, etc. Silicon dispersed in a carrier and a metal whose vapor pressure at 1000°C is 0.1 Pa or more are also included in the joining material of the present invention.

The bonding material of the present invention may further contain additives that are commonly used in the art for various purposes, such as improving the wettability of the bonding material, adjusting the thermal expansion coefficient, improving adhesion to the bonded members, improving the strength of the bonded members, or improving the heat resistance of the bonded members. Examples of such additives include, but are not limited to, carbon simple substance (so-called carbon powder), silicon carbide (SiC) particles, alumina (Al ₂ O ₃ ) particles, etc. For example, by adding carbon powder, silicon and carbon react to obtain a bonded member containing silicon carbide with high heat resistance.

In another aspect, the present invention provides a method of using the joining material of the present invention, i.e., a method of joining two ceramic members or a ceramic member and a metal member. Specifically, the present invention provides a method of joining two ceramic members or a ceramic member and a metal member, comprising the steps of:
1) applying the joining material of the present invention between both components;
2) heating both members with the joining material applied to them to obtain a eutectic liquid phase of silicon and metal; and 3) further heating to evaporate the metal and obtain a layer of elemental silicon.

The bonding material of the present invention used in the bonding method of the present invention is as described above, and the bonding materials that are particularly preferred above can be used. All detailed descriptions of the preferred bonding materials of the present invention, etc., apply mutatis mutandis to the bonding method of the present invention.

Step 1) in the joining method of the present invention is a step of applying the joining material of the present invention between the joining surfaces of the first and second members to be joined. Here, application means that the powder is placed directly on the joining surfaces, or that the joining material of the present invention in foil form is sandwiched, or, if the joining material of the present invention cannot be placed on the joining surfaces as powder, the powder may be dispersed in a carrier to prepare, for example, a paste, paste, or liquid joining material of the present invention and then applied. The amount of the joining material of the present invention to be applied is an amount that is usually understood to be an appropriate amount in the field of ceramic joining, and is not particularly limited.

Step 2) in the bonding method of the present invention is a step of melting the bonding material of the present invention by heating. The heating temperature varies depending on the composition of the bonding material of the present invention actually used, but can be easily determined by preparing the melting points of each component and their phase diagrams. For example, when the bonding material of the present invention is a mixture of silicon and magnesium silicide, it is heated at least to their eutectic temperature of 945.6°C or higher, for example, about 1000°C to about 1100°C. When the bonding material of the present invention contains a carrier, it is desirable that the carrier evaporates during this step. For example, polyethylene glycol has a boiling point of about 250°C, so it can be sufficiently evaporated by heating it to about 400°C. Typically, the heating can be performed in a commercially available electric furnace or a spark plasma sintering device, but is not limited thereto.

In step 2), the heating time is preferably as short as possible from the viewpoint of manufacturing costs, but the heating time can be easily determined depending on the composition of the joining material of the present invention and the heating temperature, and is, for example, 30 minutes or less, preferably 20 minutes or less, and more preferably 10 minutes or less. In the present invention, when obtaining a eutectic liquid phase of silicon and metal, heating may be performed in an inert atmosphere, for example, an argon atmosphere, or in a vacuum, for example using a vacuum pump, so that the metal is not oxidized by oxygen in the air.

Step 3) in the bonding method of the present invention is a step of further heating the eutectic liquid phase of silicon and metal obtained in step 2) to evaporate the metal component. Steps 2) and 3) have different purposes, but since they are both heating steps, steps 2) and 3) may be treated as one step without being differentiated, or may be treated as separate steps differentiated by conditions such as temperature and reduced pressure. The conditions for evaporating the metal can be easily understood from the vapor pressure of the metal itself. For example, when the metal is magnesium, the vapor pressure is about 3x10 ⁴ Pa at 1000°C and about 1x10 ⁵ Pa at 1100°C, so heating may be performed, for example, at 1100°C without reducing the pressure, or heating may be performed at 1100°C after reducing the pressure to 3x10 ⁴ Pa or less, for example 1x10 ⁴ Pa or ^less , for example 1x10 2 Pa or less, preferably ¹⁰ Pa or less, or heating may be performed at 1000°C after reducing the pressure to 3x10 ⁴ Pa or less, for example 1x10 ⁴ Pa or less, for example 1x10 2 Pa or less, preferably 10 Pa or less. When the pressure is not reduced sufficiently, heating may be performed in an inert atmosphere, for example an argon atmosphere, in order to avoid a reaction between oxygen in the air and the metal.

By evaporating the metal in step 3), the eutectic liquid phase becomes silicon-rich, the melting point rises, and the silicon solidifies by isothermal solidification. In other words, as the metal evaporates, the melting point approaches silicon's natural melting point of 1414°C, and the silicon solidifies as it is no longer able to maintain the liquid phase. Due to this property, the preferred joining member of the present invention has the characteristic that it does not melt even when reheated to the joining temperature.

The thus obtained bonded member of the present invention may be subjected to a strength test that is normally performed in the technical field in order to confirm whether the bond strength is sufficient. Such a test is not particularly limited, but may be, for example, a tensile test in which the bonded members of the bonded body are fixed and pulled to measure the strength at which they break, or a shear test in which one of the bonded members of the bonded body is fixed and a load is applied horizontally (parallel to the bonded surface) to the other bonded member to measure the shear fracture stress. Alternatively, a strength test in accordance with a standard such as JIS may be performed, for example, in accordance with JIS R1624 or JIS R1606-1995. Or, more simply, the bonded members may be fixed and pulled at room temperature, and if only the joint breaks, the bond strength is insufficient, and if any of the ceramic bonded members breaks, the bond strength is sufficient. For example, when the ceramic members to be joined are blocks of alumina, silicon nitride or silicon carbide, a tensile breaking stress of, for example, about 5 MPa, preferably 10 MPa, more preferably 15 MPa, and even more preferably 20 MPa at room temperature can be said to be a sufficiently strong bond.

In addition to the above aspects, the present invention can be embodied in the following examples. However, the examples are merely illustrative and should not be construed as limiting the scope of the present invention.

A rectangular parallelepiped with a bottom surface (joint surface) of 4 _mm x 8 mm was cut out from a plate material of sintered alumina ( _Al2O3 ) (purity 99.6%, plate thickness 5 mm). The joint surface was in the as-received state (about 0.5 μm Ra) and was only washed with acetone.

Mixtures of magnesium silicide and silicon were prepared at 20 at% Mg (Example 1), 43 at% Mg (Example 2), 47 at% Mg (Example 3), 53 at% Mg (Example 4) and 59 at% Mg (Example 5). In addition to the mixtures of Examples 1 to 5, magnesium silicide alone (Example 6) and silicon alone (Comparative Example 1) were each dispersed in polyethylene glycol (PEG) to prepare pastes. The pastes of Examples 1 to 6 and the Comparative Example were applied to the joining surfaces of alumina sintered bodies, and the alumina sintered bodies were butted together.

The above butted samples were joined by pulsed current heating using a spark plasma sintering (SPS) device. Specifically, the samples were inserted into a graphite die and sandwiched between graphite punches on both ends, then sandwiched from above and below by electrodes in the SPS device, with a constant pressure (10 MPa) applied to the joining surfaces. The chamber was evacuated to approximately 10 Pa, and pulsed current heating was performed at a holding temperature of 1100°C for 10 minutes. The PEG evaporated and decomposed at around 250°C during the temperature rise, and was removed into the vacuum.

When any of the pastes in Examples 1 to 6 and Comparative Example 1 was used, the alumina could be joined without cracking or deformation. The joint structure was observed and evaluated by SEM, electron probe microanalyzer (EPMA), and X-ray diffraction (XRD). Figure 2 shows an SEM image of the joint structure in the 47 at% Mg paste (Example 3), and Figures 3 and 4 show EPMA images. A thin Si layer with almost no voids was observed in the joint. In addition, Mg was segregated at the interface between the Si layer and the Al ₂ O ₃ layer. When the results of XRD were also taken into account, it was found that a part of the Mg reacted with Al ₂ O ₃ to form a layer of MgAl ₂ O ₄ .

The tensile strength of the bonded bodies was tested at room temperature. Specifically, each bonded member was fixed and one of the bonded members was pulled, and the fracture location and tensile strength were measured at the time of fracture. The relationship between the room temperature tensile strength of the bonded bodies and the initial Mg composition of the paste is shown in Figure 5. In both cases, fracture occurred near the joint. While the tensile strength was 5 MPa or less for 0 at% Mg (comparative example), the tensile strength increased to about 10 MPa for 20 at% Mg (Example 1), exceeded 20 MPa for 43 at% Mg (Example 2), and significantly increased to an average of about 30 MPa for 53 at% Mg (Example 4). The paste containing only magnesium silicide (Example 6) also showed a high tensile strength of about 30 MPa on average.

Furthermore, three-point bending strength tests at high temperatures were also conducted for Examples 2, 3, and 4. Specifically, two rectangular parallelepipeds measuring 8 mm x 21 mm were cut out from a 5 mm thick plate of sintered alumina, and the 5 mm x 8 mm faces of each rectangular parallelepiped were used as the bonding surfaces to prepare bonded bodies in the same manner as in Examples 1 to 6 above using the pastes of Examples 2, 3, and 4. The bonded bodies were cut out to 4 mm x 5 mm x 42 mm, polished, and heated in air at a heating rate of 5°C/min for 4 hours until they reached 1200°C, and then held at 1200°C for another 30 minutes. Each bonded body was pressurized from above the bonded area with a support distance of 30 mm and a pressure rate of 0.5 mm/min, and the maximum bending stress until breakage was measured. The results are shown in Figure 6. All of the specimens showed a bending strength of approximately 65 MPa, indicating that the bonding material of the Examples maintained a strong bonded state even when heated to the bonding temperature or higher after bonding. Furthermore, even though the joints made with the joining materials of Examples 2 to 4 were not subjected to any anti-oxidation coating or the like, no cracks occurred even when they were heated to and held at 1200°C in air. This demonstrates the high oxidation resistance of the joining materials of the Examples and the small difference in thermal expansion coefficient between the joining materials and alumina.

The sintered body was silicon nitride (Si ₃ N ₄ ), and the mixtures were prepared as 20 at% Mg (Example 7), 37 at% Mg (Example 8), 43 at% Mg (Example 9), 47 at% Mg (Example 10), 53 at% Mg (Example 11), and 59 at% Mg (Example 12). In addition to the mixtures of Examples 7 to 12, silicon alone (Comparative Example 2) or magnesium silicide alone (Example 13) was dispersed in polyethylene glycol (PEG) to prepare each paste. Each paste was applied to a silicon nitride sample piece, and bonding was performed in the same manner as above. In any case where any paste was used, bonding was possible without causing cracks or deformation in the Si ₃ N _4. The joint structure was observed and evaluated by SEM, energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). The SEM image of the joint structure in the 47 at% Mg paste (Example 10) is shown in Figure 7, and the EDX images are shown in Figures 8 and 9. A thin Si layer with almost no voids was observed at the joint. Mg was also segregated at the interface between the Si layer and _{the Si3N4} layer. Combined with the results of _XRD , it was found that some of the Mg reacted with _Si3N4 to form _MgSiN2 layers.

The tensile strength of the bonded bodies at room temperature was tested for Examples 7 to 13 and Comparative Example 1 in the same manner as above. The results are shown in Figure 10. With 37 at% Mg (Example 8), the tensile strength increased to approximately 12 to 25 MPa, and with 43 to 59 at% Mg (Examples 9 to 12), the tensile strength exceeded 25 MPa in most cases, and even exceeded 40 MPa in some cases. Magnesium silicide alone (Example 13) showed a tensile strength of approximately 10 to 20 MPa.

Furthermore, a three-point bending strength test was also conducted at high temperatures for the joints of Examples 10, 11, and 12. The method of the three-point bending strength test was as described above. The results are shown in FIG. 11. All of the joints showed bending strengths of 100 to 200 MPa, which revealed that the joints of the examples maintained a strong bond even when heated to a temperature higher than the joining temperature after joining. Furthermore, although the joints of Examples 10 to 12 were not coated with any oxidation prevention coating, no cracks were observed even when heated to 1200°C in air. This revealed the high oxidation resistance of the joints of the examples and the small difference in thermal expansion coefficient between the joints and Si ₃ N ₄ .

The sintered body was silicon carbide (SiC), and the mixtures were prepared as 37 at% Mg (Example 14), 43 at% Mg (Example 15), 47 at% Mg (Example 16), 53 at% Mg (Example 17), and 59 at% Mg (Example 18). In addition to the mixtures of Examples 14 to 18, only magnesium silicide (Example 19) was dispersed in polyethylene glycol (PEG) to prepare each paste. Each paste was applied to a silicon carbide sample piece, and bonding was performed in the same manner as above. The results of testing the tensile strength of the bonded body at room temperature in the same manner as above are shown in FIG. 12. The tensile strength increased to about 10 MPa for 37 to 47 at% Mg (Examples 14 to 16), and increased to about 15 MPa for 53 at% Mg (Example 17).

Claims (12)

A bonding material for bonding between ceramics or between a ceramic and a metal, the bonding material comprising silicon and a metal having a vapor pressure of 0.1 Pa or more at 1000°C as main components, and containing all or a part of the silicon and the metal having a vapor pressure of 0.1 Pa or more at 1000°C as metal silicides . A bonding material for bonding between ceramics or between ceramics and metals, comprising silicon and a metal having a vapor pressure of 0.1 Pa or more at 1000°C as main components, and containing at least 1/4 of the atoms of the metal having a vapor pressure of 0.1 Pa or more at 1000°C relative to the silicon. 3. The bonding material according to claim 2, wherein the silicon and the metal having a vapor pressure of 0.1 Pa or more at 1000[deg.] C. are all or partly contained as metal silicide. 4. The bonding material according to claim 1 , wherein the metal having a vapor pressure of 0.1 Pa or more at 1000° C. has a vapor pressure of 1×10 ⁴ Pa or more at 1000° C. The bonding material according to any one of claims 1 to 3, characterized in that the metal having a vapor pressure of 0.1 Pa or more at 1000°C is one or more metals selected from the group consisting of magnesium, lithium, calcium, and sodium. The bonding material according to any one of claims 1 to 3 , wherein the metal having a vapor pressure of 0.1 Pa or more at 1000°C is magnesium. 7. The bonding material according to claim 1 , wherein the metal having a vapor pressure of 0.1 Pa or more at 1000° C. relative to the silicon is contained in an amount of 1/2 or more atoms. The joining material according to any one of claims 1 to 7, characterized in that it is substantially free of metals whose vapor pressure at 1000°C is 0.1 Pa or less. The joining material according to any one of claims 1 to 8, characterized in that it is dispersed in a carrier. A joining member between ceramics or between ceramics and metals, comprising a metal compound layer of a ceramic component and a layer of simple silicon, characterized in that the metal in the metal compound layer of the ceramic component has a vapor pressure of 0.1 Pa or more at 1000°C. A method for joining two ceramic members or a ceramic member and a metal member, comprising the steps of:
1) applying the joining material according to any one of claims 1 to 9 between both members;
2) heating both members to which the joining material has been applied at 1200°C or less to obtain a eutectic liquid phase of silicon and metal; and 3) further heating at 1200°C or less to evaporate the metal , thereby making the eutectic liquid phase silicon-rich in composition and solidifying silicon as an elemental substance to obtain a layer of elemental silicon. The method according to claim 11, wherein steps 2) and 3) are carried out under reduced pressure conditions of 1×10 ² Pa or less.

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