JPH05163078A - Joint form made up of ceramic and metal - Google Patents

Abstract

PURPOSE:To easily improve the impact resistance of the subject joint form by incorporating a specified amount of ceramic fine powder in a brazing filler metal at the interface between a ceramic and metal constituting the joint form. CONSTITUTION:Firstly, active metal (e.g. Ag-Cu-Ti)-contg. metallic powder is incorporated with ceramic (e.g. alumina) fine powder so that the ceramic fine powder account for 5-20vol.% of the brazing filler metal at the interface of the final joint form, followed by kneading together with an organic binder into a pasty product (A). The component A is then applied on the surface of a ceramic (e.g. silicon nitride ceramic) (B) followed by heating under a vacuum to produce a metallized product (C). Thence, the component C and a metal (D) is mutually brazed with a Ag-Cu-based brazing filler metal powder through e.g. vacuum brazing technique, thus obtaining the objective joint form made up of the silicon nitride ceramic 1, the brazing filler metal 2, the alumina fine powder 3 and the metal 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joined body of ceramics and a metal with an active metal braze, and more particularly to a joined body excellent in impact resistance.

[0002]

2. Description of the Related Art Ceramics have excellent properties such as wear resistance and heat resistance and are actively used. However, while it has excellent properties, it has the drawback of poor toughness, so when used as a structural material,
It is often used by joining to a metal having high toughness. Many methods have been proposed as a method for joining the ceramics and the metal, but in practice, a brazing method, that is, a direct brazing method using an active metal braze or a method of brazing after active metal metallization is generally used. ..

Generally, ceramics and metals have large differences in thermal expansion coefficient. Therefore, when brazing ceramics and metals, the difference in thermal expansion coefficient between the ceramics and metal is caused in the cooling process after the brazing material is solidified and the joining is completed. Thermal stress is generated to destroy the ceramics, or large thermal strain is left in the ceramics in the vicinity of the bonding interface even if the ceramics are not destroyed, thereby lowering the bonding strength. Thus, the biggest problem in brazing ceramics and metals is the thermal stress problem that occurs at the joint interface between ceramics and metal. Among the ceramics, silicon nitride ceramics have a low expansion coefficient,
This problem is particularly noticeable.

The most general method for relaxing the stress generated in the brazing joint surface of ceramics and metal is to interpose one or more intermediate materials mainly made of metal between ceramics and metal. However, in this thermal stress relaxation method, the intermediate material for thermal stress relaxation and the brazing filler metal must be accurately placed between the ceramic and the metal. However, there were cases where ceramics were destroyed. Further, stacking multiple layers of the intermediate material has been a problem in terms of manufacturing cost.

In order to solve these problems, a method has been proposed in which the thermal stress is relaxed by controlling the coefficient of thermal expansion of the brazing material without using an intermediate material (JP-A-3-20).
5389 publication). This method is a method of bringing the thermal expansion coefficient of the brazing material close to that of the ceramic by mixing the active metal brazing material with the fine ceramic powder to be joined or the fine ceramic powder having a thermal expansion coefficient similar to that of the ceramic to be joined. However, since the brazing material layer can be regarded as a thin intermediate layer, it is conceptually within the scope of the method of interposing the intermediate material.

[0006]

The latter method of the preceding paragraph is a simple and efficient method for relaxing thermal stress, but the joint strength to be improved is static shear strength and dynamic strength such as impact resistance strength. The effect on bond strength is unknown. Further, the idea of thermal stress relaxation is the idea of reducing residual thermal stress instead of releasing it, as in the method of interposing an intermediate layer between ceramics and metal. Therefore, although reduced, thermal stress still exists, so that there is a defect that it is brittle with respect to an impact force in which stress is easily concentrated.

In the present invention, impact resistance is inversely proportional to residual thermal stress. That is, it is an object of the present invention to provide a joined body of ceramic and metal having excellent impact resistance under the idea that the smaller the residual thermal stress, the higher the impact resistance.

[0008]

SUMMARY OF THE INVENTION In order to provide a ceramic-metal joined body which has a minimal residual thermal stress and is excellent in impact resistance, the present invention provides a ceramic containing silver containing active metal.
After metallizing with a copper-based metal powder braze, the metal is brazed to the metal with a silver-copper-based metal braze, or a joined body in which ceramics and a metal are directly brazed with a silver-copper-based metal powder braze containing an active metal, The constituent requirement is that the fine metal powder is contained in the brazing metal at the interface of the bonded body in a volume ratio of 5 to 20%.

The present invention will be described in detail below. FIG. 1 is a sectional structural view showing the basic structure of the present invention, in which 1 is ceramics, 2 is a metal brazing layer, 3 is ceramic fine powder contained in the metal brazing layer, and 4 is metal. The method for achieving the joined body of the present invention shown in FIG. 1 includes a metallizing brazing method and a direct brazing method.

In the metallizing brazing method, fine ceramic powder is mixed with silver-copper-based metal powder solder (mixed metal powder solder or alloy powder solder) containing an active metal, and the ceramic is metallized by this, and then silver is added to the metal. Brazing is performed using a copper-based metal powder braze. As a metallizing method, an Ag-Cu-Ti-based metal brazing material such as Ag: 71 wt%, Cu: 27 wt%, Ti: 2 on the surface of the ceramic is used.
A fine powder of ceramics is mixed with a metal powder having a composition of wt%, and the mixture is kneaded with an organic binder to form a paste (hereinafter simply referred to as a paste), which is applied to the surface of the ceramic, and then a temperature range of 780 to 890 ° C. The metallization is performed by heating for a predetermined time in an atmosphere controlled to a vacuum of 10 ⁻⁴ Torr or more.

Next, the method of brazing to a metal with a silver-copper-based metal powder brazing material uses various brazing materials such as vacuum brazing, atmospheric brazing, and high-frequency brazing in the air, using a plate brazing material or a powder brazing material. You can choose the attachment method. During this final brazing, the metallized layer is redissolved and integrated with the final brazing material to form the metal brazing layer 2 of FIG.

Here, the compounding amount of the ceramic fine powder in the paste at the time of the metallization is such that the volume ratio in the metal brazing layer 2 in FIG. 1 becomes 5 to 20%, that is, the dilution amount by the final brazing is taken into consideration. Must be set in.

In the direct brazing method, the above-mentioned paste is inserted between ceramics and metal, and brazing is performed under the same heating conditions as for the metallization. The compounding amount of the ceramic fine powder in this paste is 5 to 20% by volume ratio with respect to the solid substance excluding the organic binder, that is, the total of the metal powder and the ceramic fine powder.

The idea of the present invention to provide a ceramic-metal joined body having excellent impact resistance is that the impact resistance is inversely proportional to the residual thermal stress. That is, with the recognition that the smaller the residual thermal stress is, the higher the impact resistance is, and the impact resistance of the joined body is improved by releasing the residual thermal stress by introducing minute defects in the joint. It is to let. Mixing fine ceramic powder into the metal brazing layer is an effective means for introducing fine defects.

FIG. 2 shows the result of experimental confirmation of the idea of the present invention.
Described in. FIG. 2 shows the influence of the alumina fine powder volume ratio in the metal brazing layer on the strength of the joined body of silicon nitride ceramics and steel produced by the metallizing brazing method. Ceramics and steel used for joining are plate-shaped, ceramics 20 mm on a side, thickness 4 mm, steel 25 x 30 mm,
The thickness was 12 mm.

The strength was determined by measuring the impact strength, which is the object of the present invention, and the shear strength for comparison. Impact strength measurement is
A jig having a blade-shaped contact surface with the ceramic was placed on the upper surface of the ceramic of the joined body, and a load of 4 kg was dropped on the jig while changing the height. Impact strength is indicated by the height at which ceramics break down.

As can be seen from FIG. 2, the shear strength, which is static strength, hardly changes at first as the volume ratio of the alumina fine powder increases, but gradually exceeds 5%, the strength gradually decreases. It is considered that this is because if the fine alumina powder, which is a foreign substance, enters the metal brazing layer, it has almost no effect up to about 5%, but it also reduces the strength of the metal brazing layer.

On the other hand, the impact strength, which is the dynamic strength indicated by the load drop height, behaves differently from the shear strength. The impact strength is remarkably improved with an increase in the volume ratio of the fine alumina powder, reaches a maximum strength at 11%, and then decreases.
Improving the impact strength by blending the fine alumina powder is due to the deviation between the fine alumina powder and other materials (metal brazing layer, ceramics and metal) during the cooling process after brazing, or the fine fracture in the fine alumina powder. It was judged that the above phenomenon occurred and the residual thermal stress was released, and the idea of the present invention was confirmed by experiments.

At the alumina fine powder volume ratio of 11%, the maximum strength was exhibited and then it started to decrease. At 11%, all of the residual thermal stress was released, and thereafter, the influence of the alumina fine powder which was a foreign substance caused the metal braze layer to be reduced. It is considered that the strength is reduced. From the experience, it is considered that the impact resistance strength is practically sufficient if the load drop height is 30 cm or more. Therefore, it is understood from FIG. 2 that the range of the optimum alumina fine powder volume ratio is 5 to 20%.

The addition of the ceramic fine powder to the metal brazing layer is effective in any of the so-called engineering ceramics-metal joints such as silicon nitride, sialon, silicon carbide, alumina and zirconia.
Above all, the joint strength of silicon nitride and sialon (hereinafter collectively referred to as silicon nitride ceramics) and metal is high in impact strength. Zirconia has the highest toughness among the ceramics and the highest impact strength was expected, but it was lower than that of silicon nitride ceramics. It is estimated that this is because the bonding strength itself is lower than that of the silicon nitride ceramics.

The optimum value of the particle size of the ceramic fine powder to be mixed into the metal brazing layer is affected by the thickness of the metal brazing layer, but normally, assuming that the thickness of the metal brazing layer is 50 μm, the particle size is preferably 50 μm or less. If the particle size is larger than this, the variation in impact strength becomes large, which is not practical. As for the types of ceramics fine powder, evaluation experiments were conducted on fine powders of silicon nitride, sialon, silicon carbide, alumina and zirconia, and it was confirmed that all were effective.

However, the magnitude of the effect depends on the type of the ceramic fine powder, and the effect is remarkable when the fine ceramic powder having a thermal expansion coefficient larger than that of the ceramic of the joined body is used as a whole. In the case of a joined body of silicon nitride ceramics and a metal, the highest impact strength can be obtained when alumina fine powder is used.

[0023]

According to the present invention, in the active metal brazing method of ceramics and metal, the fine metal powder is blended in the metal brazing layer and micro defects are introduced into the brazing joint to release the residual thermal stress. It provides a joined body of ceramics and metal that has impact resistance far superior to that of the active metal brazing method, and is used for diesel engines that require impact resistance and wear resistance as product applications. It has many uses such as tappets and guides for steel rolling.

[0024]

EXAMPLE An iron ore shoot liner was produced according to the present invention. A large number of ceramics plates are attached to a thick steel plate by brazing. Since iron ore falls into the chute liner and is loaded into the lower hopper, ceramics brazed to thick steel plates are required to have high impact resistance and wear resistance. Sialon is used as the ceramic, and the size of one sheet is 40 mm on a side and 7 mm in thickness.

Ag: 70 wt%, Cu: 26 wt%, Ti:
After applying a paste composed of a metal powder having a composition of 4 wt% and an alumina fine powder having a volume ratio of 16% to a sialon plate, 1
0 ^-4 Torr, 840 ℃ 30 minutes in a vacuum furnace of metallized heat treated to. This metallized sialon plate was applied to a thick steel plate (2 m x 1 m) with a plate-shaped silver solder (BAg-4).
High frequency brazed by. The shoot liner thus manufactured exhibited sufficient durability, and the effectiveness of the present invention in practical products was confirmed.

[0026]

EFFECTS OF THE INVENTION According to the present invention, a joined body having impact resistance far superior to that of the conventional active metal brazing joined body of ceramics and metals can be obtained by an extremely simple operation, and a new application of ceramics can be obtained. It has the effect of opening up.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a bonded body of ceramics and metal showing a basic configuration of the present invention.

FIG. 2 is a table showing a relationship between a load drop height (index of impact strength) and a shear strength of a bonded body of silicon nitride ceramics and steel, and a volume ratio of fine alumina powder in a metal brazing layer.

Claims (2)

[Claims] 1. A method of metallizing a ceramic with a silver-copper-based metal powder braze containing an active metal, and then silver-metalizing the metal.
In a joined body brazed with a copper-based metal braze or a joined body in which ceramics and a metal are directly brazed with a silver-copper-based metal powder braze containing an active metal, the fine ceramic powder is contained in the metal braze at the interface of the joined body. 5 to 5
A ceramic-metal joined body characterized by containing 20%. 2. The bonded body of ceramic and metal according to claim 1, wherein the ceramic is a silicon nitride ceramic and the fine ceramic powder in the brazing metal is fine alumina powder.