JPS6354666B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of joining a metal member and a ceramic member, and particularly to a method suitable for joining a metal member and a ceramic member that have a large difference in coefficient of thermal expansion.

In recent years, non-oxide ceramics such as silicon nitride, silicon carbide, and sialon, as well as aluminum oxide and zirconium oxide, have been used as high-temperature, high-strength structural materials.
So-called new ceramics are rapidly gaining attention, and much research and development is being carried out. These ceramics are used in many applications such as gas turbine rotors, diesel engine cylinders, and other high-temperature machine parts, but all of them have strict requirements for shape and dimensional accuracy, making it difficult to mold and manufacture them as one piece from the beginning. Often. For this reason, it is necessary to join partial products together to create products with complex shapes, and there is a desire to develop a method for firmly joining ceramics and metals.

A brazing method is one of such joining methods with high joining strength. However, in the case of parts joined by conventional brazing methods, if there is a large difference in the coefficient of thermal expansion of the joined members, excessive thermal stress will be generated in the brazed metal, which may cause the joint to break. There is.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for joining a metal member and a ceramic member, which has extremely high joint strength and strong resistance to thermal stress.

In order to achieve this object, the joining method of the present invention is a method for joining a metal member and a ceramic member. The gist of the present invention is a method for joining a metal member and a ceramic member, characterized in that the ceramic members are joined together.

That is, the present invention utilizes intergranular corrosion to make the surface of a metal member porous, and makes this porous surface layer effectively act as a stress buffer zone, thereby alleviating thermal stress due to the difference in coefficient of thermal expansion. This is what I did. Furthermore, in the present invention, the surface roughness of the metal member is further increased, thereby providing a sufficient anchoring effect and increasing the bonding strength.

Although the ceramic member used in the present invention is not limited in any way, the present invention is particularly suitable for joining ceramic members that have a large difference in coefficient of thermal expansion from metal members. Furthermore, if the surface of the ceramic member is previously subjected to a metallization process in which a thin metal film is coated, the bonding strength with the metal member can be increased. Methods for such metallization include Telefunkel method, thermal spraying method,
Various already known methods such as CVD method and PVD method can be employed.

Moreover, various metals or alloy members can be joined as the metal members.

Various methods can be employed to elute substances existing along the grain boundaries and the vicinity thereof of the metal member. For example, when the metal member is stainless steel, the stainless steel is sensitized and then immersed in a high-temperature acid solution containing an oxidizing agent for a predetermined period of time. substances that are present can be eluted.

Further, a layer where intergranular corrosion is likely to occur and has a certain depth may be formed on the entire surface of the metal member or at a desired location in the following manner. That is, effective methods include (1) changing the structure of the metal, (2) changing the alloying element, (3) changing the heat treatment, and (4) changing the crystal grain size. Next, we will explain these four methods in detail.

() Method of changing the structure of metals In the case of austenitic stainless steel, materials with a single austenite phase are more difficult to dissolve in a mixed solution of 10% copper sulfate and 10% sulfuric acid than materials with a mixed phase of austenite and ferrite or martensite. When immersed in water (hereinafter referred to as treatment), the rate of progress of intergranular corrosion is significantly higher. Therefore, for a material that has a single phase of austenite from the surface to a certain depth and a mixed phase of austenite and ferrite or martensite beyond a certain depth from the surface, the thickness of the treated layer after the above treatment is applied for a certain period of time is This is the apparent depth from the surface to the boundary between the two phases. Therefore, an intergranular corrosion layer of a constant depth can be obtained regardless of the treatment time and the treated material.

() Method of changing alloying elements (a) Stabilizing elements such as Ti and Nb are added from the back side of the material, and after a stabilizing heat treatment is performed, the above treatment is performed. In the case of cast steel, Ti and Nb are added to the surface of the mold.
When casting after applying a compound of Ti, Nb
penetrates inside. In addition, in the case of rolled steel, Ti,
It is preferable to perform the above treatment after diffusing Nb by a known method and performing solution treatment and stabilization treatment.

(b) C is added to the surface of the material by a known dipping method and the above treatment is performed.

(c) Joining together different materials that are prone to intergranular corrosion by physical means such as diffusion bonding.

() Method of changing heat treatment (a) While cooling the back side of the material, heat the front side with a suitable firearm to sensitize only the front side. In this case, it is more effective if the surface is processed in advance.

(b) The stabilized steel material is subjected to solution treatment and sensitization treatment only in the vicinity of its surface, and then subjected to the above treatment. Further, after the stabilization treatment is performed on the back surface, the above treatment may be performed on the front surface.

(c) Spot welding is performed on the surface of the material to make the surface sensitized and to generate internal stress near the surface, making intergranular corrosion more likely to occur.

(d) By maintaining the surface of the material at 450 to 700℃ and the back surface at 700 to 900℃, carbide is continuously precipitated near the surface and discontinuously precipitated near the back surface. , the above treatment is performed to apparently stop intergranular corrosion in the vicinity of the discontinuous precipitation area.

() Method of changing grain size (a) For cast steel, a chilled metal is used in a part of the mold, and the crystal grains are made smaller only in the vicinity of the chilled metal.

(b) For rolled steel, only the surface is subjected to appropriate pressure, such as rolling, and then subjected to appropriate hot treatment.

(c) Crystal grains are made smaller by the method described in (a) above. If the crystal grains are made smaller in this way, the area where intergranular corrosion occurs increases.

Note that the metal member may be uniform, but
It may also be a clad material in which a metal plate that is susceptible to intergranular corrosion is laminated on the surface.

When joining a metal member whose surface has been subjected to intergranular corrosion in this manner to a ceramic member, various joining methods can be employed, such as a brazing method using a brazing filler metal. Various types of brazing materials can be used as the brazing material, including copper solder, silver solder, nickel solder, zirconium solder, titanium solder, gold solder, palladium solder, and brass solder. Further, the brazing method using this brazing material is the same as a normal brazing method. In addition to brazing, other joining methods such as friction welding and pressure welding can be used if the surface of the ceramic material is metallized.

Examples will be described below.

Example A steel plate (SUS304) and an aluminum oxide plate (commercially available with a density of 88%) were joined according to the method of the present invention. First, the surface of the SUS304 steel plate was shot peened using a steel ball with a diameter of 2 mm. After cooling the back surface with water, the surface was heated with an acetylene burner, and the vicinity of the surface was held at 650° C. for 10 minutes. As a result, it was confirmed that the strength was sensitized to a depth of 250 μm from the surface. Next, the SUS304 material was immersed in a boiling solution of 10% copper sulfate and 10% sulfuric acid for 2 to 3 hours. As a result, the surface of the SUS304 material was corroded along its grain boundaries.

On the other hand, an aluminum oxide plate was metallized based on the Telefunkel method. That is, after applying metallic molybdenum powder to an aluminum oxide plate, it is heated to 1300℃.
The metallization process was carried out in a humid air stream. Next, this surface was nickel plated, and then brazed to the SUS304 material that had undergone the above treatment using silver solder.

On the other hand, as a comparative example, an aluminum oxide plate,
Brazed with SUS304 material using silver solder.

(In the Examples and Comparative Examples, the composition of the silver solder is the same as 60% by weight of silver and 40% by weight of copper. Also, the brazing temperature is 69.0°C.)
After heating it to 100℃, it was put into water at 0℃.
No peeling occurred between the members in both the examples and the comparative examples. However, brazed parts
When heated to 300°C and then placed in water at 0°C, the brazing member according to the example did not peel off, but the brazing member according to the comparative example peeled off, and the joining method according to the example of the present invention It was confirmed that the bonding method was able to perform bonding with extremely excellent thermal shock resistance.

It was also found that the brazing strength of the parts joined by the method according to the embodiment of the present invention was extremely high.

As described above, according to the present invention, there is provided a joining method that can extremely firmly join a metal member and a ceramic member, and also has strong resistance to thermal stress.

Claims (1)

[Claims] 1. In a method of joining a metal member and a ceramic member using a brazing filler metal, after eluting substances existing along the grain boundaries and the vicinity of the grain boundaries on the surface of the metal member to be joined, the ceramic member is bonded to the ceramic member. A method for joining metal members and ceramic members, characterized by joining the members. 2. The joining method according to claim 1, wherein the surfaces of the ceramic members to be joined are coated with a thin metal film in advance.