JPH08259341A - Ceramic-metal joined body and its production - Google Patents

Abstract

PURPOSE: To obtain a joined body controlled in deforming amount of ceramic and free from occurrence of crack by relaxing heat stress by each carrying out specific treatment after or before joining in providing a joined body of ceramic with an iron-based metal body. CONSTITUTION: This joined body of ceramic (e.g. silicon nitride) with an iron- based metal body (e.g. carbon steel S20C) is obtained by carburizing the surface of the iron-based metal body before joining and cooling the metal body at 1-100 deg.C/sec under conditions preventing transformation of pearlite of the iron- based metal body after joining, preferably in the neighborhood of starting temperature of pearlite transformation and constituting the iron-based metal body so as to have one or more structures comprising martensite structure produced from supercooled austenite and/or other supercooled structure and relaxing heat stress generated in ceramic and the iron-based metal body by volume expansion in transformation.

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 / iron-based metal bodies and a manufacturing method thereof, and is used for various brazed joint parts including sliding parts such as tappets and rocker arms of internal combustion engines. It

[0002]

2. Description of the Related Art Engineering ceramics such as silicon nitride are desired to be applied to mechanical parts such as automobiles because of their excellent strength, heat resistance and wear resistance. However, in general, ceramics are difficult to process because they have high hardness and brittleness. Therefore, when they are used for sliding parts and the like, it is often the case that only the portions that require abrasion resistance are replaced with ceramics to improve the performance. At this time, it is necessary to firmly bond and fix the ceramics and other parts (mostly metal represented by iron), and a brazing joining method is generally used. However, ceramics such as silicon nitride and silicon carbide have a coefficient of thermal expansion of about 1/4 that of iron, and when cooling after brazing and bonding, extremely large thermal stress is generated due to the difference in contraction rate, and the ceramics side of the bonded body is affected. May cause cracks.
In addition, the bonded body that has accumulated such thermal stress may cause cracks due to processing after cooling, and it is difficult to give a desired shape after bonding.

As a means for solving such a problem, conventionally, as in Japanese Unexamined Patent Publication No. 62-171970, stress is relieved through a soft metal buffer plate between ceramics and metal,
I was getting a zygote. However, this method requires a buffer plate in addition to ceramics and metal, resulting in high cost, and it is difficult to join the three members of ceramics, metal, and buffer plate with high precision, and the work becomes complicated. was there.

As a method for solving these problems, Japanese Patent Application Laid-Open No. 2-199073 discloses a direct bonding method of ceramics and metal. In this method, it is not necessary to use a buffer plate because the thermal stress generated during cooling is relaxed by the hysteresis due to the transformation expansion of the metal body, and therefore,
Although problems with accuracy and work can be avoided, it is necessary to obtain a martensitic structure or other supercooled structure by gas cooling, and therefore applicable steel materials are limited to some alloy steels, and gas is used as a refrigerant. There has been a problem that a special device is required to obtain a sufficient cooling rate.

[0005]

In the above-mentioned conventional bonded body, there is a problem of accuracy when a buffer plate is used, there is a problem of limitation of applicable steel materials in the direct bonding method, and both of them have a problem of material or equipment. Therefore, there is a drawback that the cost becomes high.
On the other hand, iron-based materials often used for engine parts and the like have a C content of 0.2 to 0.4% as represented by low carbon steel.
It is relatively low in degree, and it is difficult to prevent the pearlite transformation during cooling using this type of steel material and obtain a transformation structure from supercooled austenite, so it is possible to relax thermal stress like the above-mentioned direct joining method. It is difficult.

An object of the present invention is to cool a joined body of ceramics and an iron-based metal body, even if any steel material that can be carburized and quenched by carburizing the iron-based metal body before joining is used. It is an object of the present invention to provide a bonded body in which the thermal stress generated in the subsequent ceramics and the iron-based metal body is relaxed, a bonded body in which a desired gentle gradient is provided by the stress relaxation, and a manufacturing method thereof.

[0007]

According to a first aspect of the present invention, there is provided a ceramic / metal joined body in which a surface of an iron-based metal body is carburized before joining in a joined body of a ceramic and an iron-based metal body, and the iron-based body is cooled after cooling. By preventing the pearlite transformation (Ar ₁ ) of the metal body, the iron-based metal body is constituted by at least one of a martensite structure generated from supercooled austenite or another supercooled structure, and the transformation (Ar ′).
And Ar ″), the thermal stress generated in the ceramic and the iron-based metal body is relaxed.

The ceramic-metal bonded body according to claim 2 is
The bonded body of claim 1 relaxes the thermal stress generated in the ceramic and the iron-based metal body to give the ceramic a desired gentle gradient.

According to a third aspect of the present invention, there is provided a method for manufacturing a ceramic / metal joined body, wherein the surface of an iron-based metal body is carburized before joining by the joined body according to the first or second aspect, and the temperature is equal to or higher than the melting point of the brazing filler metal. After joining at the body's austenitizing temperature (Ac ₁ ) or higher,
A cooling rate of 1 to 100 ° C./sec near the pearlite transformation (Ar ₁ ) start temperature during cooling. The pearlite transformation is prevented by cooling so as to become the above, and the thermal stress is relaxed by reducing the displacement difference between the shrinkage of the ceramics and the iron-based metal body due to the volume expansion due to the transformation (Ar 'and Ar ") of supercooled austenite. A desired gentle gradient is provided by relaxing the bonded body and thermal stress.

The present invention will be described in detail below.

In the present invention, low thermal expansion silicon nitride and silicon carbide are particularly preferable as the ceramics, but other ceramics having a lower thermal expansion coefficient than iron-based metal bodies such as zirconia and alumina are also preferable.

As the brazing material, any brazing material containing an active metal such as Ti, Zr or Hf can be used. However, considering the heat resistance of the iron-based metal body, an active metal-added silver brazing material is preferable. The composition of the brazing material suitable for the Ti-added silver brazing material is as follows.

Ag: 72% Cu: 23-27% Ti: 1-5% When a brazing material containing no active metal is used, the joint surface of the ceramics may be metallized before brazing.

The brazing temperature is 50 higher than the melting point of the brazing filler metal.
A temperature as high as about -100 ° C is suitable, and in the case of the brazing material having the above composition range, 800-950 ° C is suitable. As the iron-based metal body, any steel material that can be carburized and hardened such as carbon steel and alloy steel can be used. The carburizing depth of the iron-based metal body can be changed depending on the shape of the ceramic to be brazed and the shape desired to be applied after the joining, but is preferably about 0.3 to 1 mm. The C concentration on the surface after carburizing is preferably about 0.6 to 1.0%. During brazing, it is preferable to maintain the temperature at the melting point of the brazing material or higher for 10 to 60 minutes, and at the time of cooling, 1 to 100 ° C./sec. Around the pearlite transformation start temperature of the iron-based metal body. It is preferable to cool rapidly.

[0015]

OPERATION FIG. 1 shows the change in the shrinkage curve of the carburized S20C carbon steel depending on the cooling method during cooling. In the cooling process after brazing this steel material and ceramics at about 850 ° C., thermal stress due to shrinkage difference does not occur at the interface between the steel material and the ceramics up to about 600 ° C. due to plastic deformation of the steel material and the brazing material. Does not depend on cooling rate. But,
Below 600 ° C., when the steel material has already completed the normal pearlite transformation, the thermal stress in the bonded body continues to increase in accordance with the difference in thermal expansion coefficient from this temperature range to room temperature,
As a result, extremely large thermal stress is stored in the bonded body cooled to room temperature.

According to the present invention, as shown in FIG. 2, pearlite transformation of a steel material is prevented, and volume expansion occurs when a martensite structure or other supercooled structure is generated from supercooled austenite. The thermal stress is alleviated. Further, it is possible to adjust the thermal stress generated due to the change in the expansion amount obtained by controlling the carburizing depth and control the shape of the ceramics after cooling. Note that FIG. 3 is a conceptual diagram of deformation that occurs in ceramics when a ceramic disk and a cylindrical iron-based metal body are joined and cooled.

[0017]

【Example】

Example 1 Carbon steel S20C having a diameter of 30 mm and a length of 50 mm (composition
C: 0.21%, Si: 0.25%, Mn: 0.42
%, P: 0.030% or less, S: 0.035% or less) a surface used for carburizing and brazing (30 mm
Polishing of 0.1 mm was performed to remove the carburized skin on one end face of φ). Next, silicon nitride having a diameter of 30 mm and a thickness of 1.5 mm was bonded to this end face through a Ti-added silver brazing material. The composition of the brazing material was Ag: 72%, Cu: 26%, T
i: 2%, and the thickness of the brazing material was 50 μm. The temperature rising curve shown in Fig. 4 was used for joining and 850 ° C after joining.
More quenched in oil. As a result, the amount of deformation d of the ceramic shown in FIG. 3 was 40 μm.

Example 2 The surface used for joining the carbon steel used in Example 1 was 0.3 m.
m was polished, and joined and rapidly cooled under the same conditions to obtain a joined body. The amount of deformation d of the ceramic of this bonded body was 60 μm. As can be seen from FIG. 5, the C concentration on the joint surface of the carbon steel at this time is about 0.6%.

Comparative Example 3 The carbon steel used in Example 1 had a surface of 1.0 m used for joining.
m was polished, and joined and rapidly cooled under the same conditions to obtain a joined body. The amount of deformation d of the ceramic of this bonded body was 75 μm. The carbon concentration at the joining surface of the carbon steel at this time was about 0.2%, and the carburized layer had been removed.

As is clear from these Examples and Comparative Examples, the thermal stress generated by controlling the C concentration on the surface of the steel material can be relaxed and the amount of deformation of the ceramics can be adjusted.

[0021]

As described above, according to the present invention, it is possible to manufacture a bonded body of a ceramic and an iron-based metal body in which thermal stress is relaxed and the amount of deformation of the ceramic is controlled.

[Brief description of drawings]

FIG. 1 is a graph showing the coefficient of thermal expansion of steel materials and ceramics.

FIG. 2 is a sectional view showing a crowning amount.

FIG. 3 is a cross-sectional view showing a joined body.

FIG. 4 is a temperature pattern diagram of heat treatment.

FIG. 5 is a carbon concentration distribution map by carburization.

[Explanation of symbols] 1 Steel 2 Ceramics

Claims (3)

[Claims] 1. In a joined body of a ceramic and an iron-based metal body, by carburizing the surface of the iron-based metal body before joining and preventing pearlite transformation (Ar ₁ ) of the iron-based metal body in cooling after joining, The iron-based metal body is composed of at least one of a martensite structure generated from supercooled austenite or other supercooled structure, and a volume expansion occurs during its transformation (Ar 'and Ar ") into a ceramic and an iron-based metal body. A bonded body that relaxes the generated thermal stress. 2. The joined body according to claim 1, wherein the ceramic is provided with a desired gentle gradient by relaxing the thermal stress generated in the ceramic and the iron-based metal body. 3. The joined body according to claim 1, wherein the surface of the iron-based metal body is carburized before joining, and the joining is performed at the melting point of the brazing material or more and the austenitizing temperature (Ac ₁ ) of the iron-based metal body or more. After that, the cooling rate is 1 to 100 ° C./sec near the pearlite transformation (Ar ₁ ) start temperature during cooling. The pearlite transformation is prevented by cooling so as to become the above, and the thermal stress is relaxed by reducing the displacement difference between the shrinkage of the ceramics and the iron-based metal body due to the volume expansion due to the transformation (Ar 'and Ar ") of supercooled austenite. A method for manufacturing a bonded body and a bonded body in which a desired gentle gradient is provided by relaxing thermal stress.