JPH0292875A - Formation of thermal stress relaxing layer in bonding between ceramic and metal - Google Patents

Abstract

PURPOSE:To bond ceramic to metal readily and firmly by flame spraying copper on the surface of a metal to be bonded to ceramic to form a coating film, heating the coating film in a hydrogen gas atmosphere and forming fine voids in the coating film to form a thermal stress relaxing layer. CONSTITUTION:The surface of a metal 1 to be bonded to ceramic is flame sprayed with copper or a mixture of copper and ceramic to form a coating film of flame spraying containing copper 2, voids 3 and copper oxide 4. Then the coating film is heated in a hydrogen gas atmosphere, the copper oxide 4 in the coating film of flame spraying is reduced, ductility of the coating film is improved and fine voids 5 are formed to form a nonrigid, porous thermal stress relaxing layer having the voids 3 and the voids 5. Then the metal 1 is bonded to ceramic 7 through a brazing material 6 (e.g., titanium-containing silver braze). Consequently, the metal is readily bonded to the ceramic even if a bond interface has a curved face.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a thermal stress relaxation layer using thermal spraying when joining ceramics and metals.

[Prior art] Although ceramics have excellent heat resistance, wear resistance, and corrosion resistance, they have the disadvantage of being brittle and susceptible to impact. Therefore, when used as structural materials, it is appropriate to use them in conjunction with metal materials with high toughness. It is. As a bonding method, solid phase diffusion bonding using high temperature heating and brazing including liquid phase diffusion are used.

At this time, the biggest issue is the high thermal stress generated due to the difference in thermal expansion coefficient between the metal and ceramics as they cool down from the high temperature during bonding, and this can reduce the bonding strength and cause peeling at the bonding interface. It is the cause that causes it.

For this reason, methods to suppress the generation of thermal stress include choosing a combination of ceramic and metal bonding with a small difference in thermal expansion coefficients, and installing a thermal stress relaxation layer between the ceramic and metal. ing.

The method of installing a thermal stress relaxation layer is to insert a soft material such as a copper plate or an aluminum plate into the joint interface, but the thermal stress relaxation capacity is still low and the joint strength is low. Development is desired.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for forming a thermal stress relaxation layer having a high thermal stress relaxation ability at a joint portion when ceramics and metal are joined.

[Means for solving the problem] As a method for increasing the thermal stress relaxation ability of the thermal stress relaxation layer,
First, the difference in thermal expansion coefficient between the ceramic and metal can be reduced by setting the thermal expansion coefficient of this relaxation layer to an intermediate expansion coefficient between the ceramic and metal to be joined, or by changing the thermal expansion coefficient in stages. This is the way to do it.

The second method is to use a soft metal or porous material that is easily deformed and has a so-called small Young's modulus as the thermal stress relaxation layer.

Therefore, in the present invention, a thermal stress relaxation layer is formed by combining the first and second methods.

In this method, a soft material such as copper or a mixed material of copper and ceramics is thermally sprayed onto the metals to be joined, and then this thermally sprayed coating is heated to approximately 300°C in a hydrogen gas atmosphere to eliminate the oxidation in the thermally sprayed coating. Copper is reduced to generate pores, which together with the fine pores scattered throughout the coating during thermal spraying, create a high-performance thermal stress relaxation layer. Furthermore, as the coefficient of thermal expansion decreases in the case of mixing copper and ceramics, thermal stress relaxation is further facilitated.

It should be noted that thermal spraying can be used to create thin layers not only on flat surfaces, but also on metal products with curved surfaces, and can be applied more evenly and easily than other methods. Therefore, it is far superior as a thermal stress relaxation layer.

[Function] When copper is used as the thermal spraying material, the structure of the thermal stress relaxation layer has both pores formed in the copper base during thermal spraying and fine pores formed by hydrogen reduction of copper oxide generated during thermal spraying. It is a soft porous material with high deformability.

Therefore, it exhibits high thermal stress relaxation ability during bonding and increases the bonding strength between ceramic and metal.

In addition, when a mixed material of copper and ceramics is used as the thermal spraying material, the thermal stress relaxation layer will have pores dispersed in the copper base as in the case of ceramics and copper above, but if ceramics is mixed. Therefore, although the plastic deformability is somewhat lower than that of copper only, the coefficient of thermal expansion is smaller, so it has an extremely high thermal stress relaxation ability.

In this way, the thermal stress relaxation layer of the present invention can be used to reduce bonding strength due to a large tensile residual stress exerted on ceramics with a low coefficient of thermal expansion due to contraction by the metal part with a large coefficient of thermal expansion during cooling from a high temperature. It is clear that the presence of this has a far superior effect on improving the bonding strength compared to relaxation layers created by other methods.

[Example] A joining example in which the ceramic to be joined is alumina and the metal is cast iron will be described with reference to the drawings.

As shown in Figure 1, copper is plasma sprayed onto cast iron (1) to be joined to form a sprayed coating consisting of copper (2), voids (3), and copper oxide (4).

Next, as shown in Figure 2, the sprayed cast iron is heated to 300°C in a hydrogen gas atmosphere to reduce the copper oxide in the sprayed coating, improve the ductility of the coating, and reduce the fine particles formed thereby. A soft and porous thermal stress relaxation layer is formed by the pores (5) and the pores (3) formed during thermal spraying.

As shown in Figure 3, a titanium-containing silver solder (6) was inserted between the alumina (7) to be joined, and the temperature was maintained at 840°C for 20 minutes in a vacuum (1 O'Torr). Brazing was performed under these conditions.

The shape and dimensions of the bonded test piece are 27ml in diameter for alumina111
Disc-shaped, 8ff1m thick, cast iron 16mm in diameter.

It has a rod shape with a length of 40 mm, and these are butt-jointed as shown in FIG.

The joint tensile strength showed a relatively low value of 3.4 kgf/mm'', but this was due to the influence of the notch coefficient based on the shape of the tensile test piece, so by adding the actually measured notch coefficient of 7, The actual bonding tensile strength is approximately 23.8 kg/+nm, which is high strength.

Furthermore, the condition of the tensile fracture part shows that the fracture occurs at the brazing material, there is almost no peeling of the ceramic, and the joint is in a high-strength state with almost no residual thermal stress.

[Effects of the invention Coceramics are highly functional materials that surpass metal materials.
Although it is expected to be a new material with an extremely wide range of applications, it has drawbacks such as poor toughness and difficulty in processing, and it is necessary to compensate for these drawbacks.

This invention is one way to compensate for this drawback. Being able to easily and firmly join ceramics and metals will have a great impact on expanding the fields of application of ceramics.

Moreover, the shape of the bonded interface according to the present invention was difficult to form on surfaces other than flat surfaces using conventional methods, but due to the characteristics of thermal spraying, it is easy to form curved surfaces, and it is clear that the range of application will further expand.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a thermally sprayed copper coating formed on metal, Figure 2 is a schematic diagram of a thermal stress relaxation layer formed by reducing copper oxide in the sprayed coating with hydrogen, and Figure 3 is a diagram of ceramics and thermal stress relaxation. A schematic diagram of vacuum brazing with a brazing material inserted between the layers. l...Metal to be joined, 2...Copper base of thermal spray coating, 3...Vacancies formed during thermal spraying, 4...
- Copper oxide formed during thermal spraying, 5... Vacancies formed as a result of reduction of copper oxide in the thermal sprayed coating. 6... Brazing metal, 7... Ceramics to be joined,

Claims (1)

[Claims] 1. Copper or a mixed material of copper and ceramics is thermally sprayed onto the surface of the metal to be bonded to the ceramic to form a thermally sprayed coating, and then heated in a hydrogen gas atmosphere to generate fine pores in the coating. 1. A method for forming a thermal stress relaxation layer in bonding ceramics and metal, characterized in that the thermal stress relaxation layer is retained.