JPH04356344A - Cast-in composite body of ceramics and metal - Google Patents

Abstract

PURPOSE:To obtain the ceramics-metal composite body in which a stress generat ed in ceramics is low in the normal temperature, the work process is small since it can be manufactured without executing a machine work of a coupling part of ceramics and a metal and the cost is low, and also, which has sufficient coupling strength between the ceramics and the metal even at a high tempera ture. CONSTITUTION:A cavity 1 of a piston combustion chamber is constituted of a silicon nitride member whose resistance of heat transfer per weight is large, and this cast-in composite body of ceramics and a metal is formed by casting in this member by low expansion cast iron 3 for constituting a piston main body. Also, it is possible to obtain a cast-in composite body formed by casting in furthermore the low expansion cast iron 3 side by an aluminum alloy.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a cast composite of ceramics and metal, and more specifically, it has high bonding strength between ceramics and metals even at high temperatures, and has low stress generated in ceramics even at low temperatures. This invention relates to a ceramic-metal casting composite that has low strength and high reliability, and has a simple manufacturing process and low cost.

0002

BACKGROUND OF THE INVENTION In recent years, research and development has been actively conducted on mechanical structural parts that take advantage of the excellent heat resistance, abrasion resistance, light weight, heat insulation properties, etc. of ceramics. Many ceramic materials are brittle compared to metals, so it is often difficult to use ceramic materials alone as mechanical structural parts.
Therefore, it is generally known to be used in the form of a composite with a metal. However, many of the ceramic materials that have the above-mentioned excellent properties have a smaller coefficient of thermal expansion than ordinary metal materials for mechanical structures, so they cannot be used in parts that are used at varying temperatures, especially parts that are used at high temperatures. Sometimes there is a problem that the holding force between the metal and the ceramic decreases or a gap occurs. On the other hand, when trying to obtain sufficient holding power at high temperatures, excessive stress is generated in the ceramics at room temperature, causing the ceramics to break.

As a countermeasure to these problems, a method has been proposed in which a low thermal expansion metal such as titanium or Kovar, which has a coefficient of thermal expansion similar to that of the ceramic, is provided as an intermediate layer between the ceramic and a cast metal such as cast iron or aluminum alloy.
These intermediate layer members need to be joined to ceramics by shrink fitting, press fitting, brazing, etc., and there is a problem that the machining of ceramics, brazing, etc. requires many steps and high costs. Furthermore, methods using ceramic wool, a low-density ceramic calcined layer, or a low-rigidity material such as copper as an intermediate layer have also been proposed, but there is a problem in that sufficient strength cannot be obtained. Particularly in moving parts that require weight reduction, it is advantageous to use aluminum alloy as the metal material from the viewpoint of weight reduction, but since aluminum alloy has a higher coefficient of thermal expansion than iron-based materials, the above-mentioned The problem caused by the difference in thermal expansion coefficient with ceramics was even more serious than when iron-based materials were used.

0004

[Problems to be Solved by the Invention] Therefore, the present invention solves the above-mentioned conventional problems, and provides a method in which the stress of ceramics at room temperature is low, and the joining part of ceramics with metal does not require machining. It is an object of the present invention to provide a cast composite of ceramics and metal that can be produced in a number of steps, requires few manufacturing steps, is low cost, and has sufficient strength.

[0005]

[Means for Solving the Problems] According to the present invention, the object can be achieved by a ceramic-metal cast composite body, which is made by casting ceramics with low expansion cast iron. Further, the present invention provides a ceramic-metal cast composite in which the above-described low expansion cast iron side is further cast with an aluminum alloy. Furthermore, the cast-in composite of the present invention uses ceramic only in areas subject to severe heat load, such as the opening lip of the combustion chamber, the center of the combustion chamber, etc., and the ceramic is cast in low-expansion cast iron to create a ceramic-cast piston. It is preferable to apply it as

The present invention will be explained in detail below. The ceramic-metal casting composite of the present invention preferably has a thermal expansion coefficient of 3.5 x 10-6/°C to 9.0 x 10-6/°C from room temperature to 400°C in its composite structure. It is characterized by having a part in which ceramics are cast with low expansion cast iron in the range of ℃. The low expansion cast iron used in the present invention has, for example, a weight ratio of C 0.3 to 2.0%.
, Ni 25-32%, Co 12-20%, Si
0.3 to 2.0%, Nb 0.2 to 0.8%, Mg or Ca 0.01 to 0.2%, Mn 1.0% or less, the balance being Fe containing impurities, and at room temperature ~400
Thermal expansion coefficient in °C is 3.5 x 10-6 to 5.5 x 10-6
/℃ cast iron, or C 0.8-3.
0%, Ni 30-34%, Co 4.0-6.0
%, Si 1.0-3.0%, Mn 2.0% or less, Sulfur 1.0% or less, Phosphorus 1.5% or less, Mg
1.0% or less, the remainder has a composition of Fe containing impurities,
The coefficient of thermal expansion from room temperature to 400°C is approximately 9 x 10-6/°C or less, and the coefficient of thermal expansion from room temperature to 200°C is approximately 2 x 10-6 to 3 x
Cast iron or the like having a temperature of 10-6/°C is preferable.

The reason why it is desirable to use cast iron with the above composition is as follows.
These cast irons contain graphite (density approximately 2g/cm3) during solidification.
) is precipitated from the liquid metal (density approximately 8 g/cm3) and solidification shrinkage is reduced, and the total shrinkage up to room temperature is smaller than that of low thermal expansion alloys such as Invar alloy and Kovar. This is because metals other than low-expansion cast iron do not have the preferable characteristics of low-expansion cast iron of the above composition, such as having a coefficient of thermal expansion closer to that of ceramics than ordinary iron-based materials, and being able to be cast. Furthermore, the ceramics mentioned here include silicon nitride and sialon, which are superior to metals in terms of heat resistance, thermal shock resistance, abrasion resistance, lightness, heat insulation, etc., and also have the strength necessary for mechanical structural members. , silicon carbide, alumina, aluminum titanate, etc.

In the present invention, as for the relationship between the thickness of the ceramic member and the thickness of the surrounding low expansion cast iron, it is desirable that the average thickness of the cast iron is thinner than the average thickness of the ceramic member. The reason why such a thickness relationship is desirable is that even though it is a low-expansion cast iron, the average value of the coefficient of thermal expansion over a wide temperature range is still larger than the coefficient of thermal expansion of ceramics. This is because stress is generated due to the difference in thermal expansion coefficient between ceramic and metal, and if the ceramic is too thin, this stress becomes too large and the ceramic breaks. For the same reason, it is more preferable to understand the stress generated in the ceramic member and the cast iron member by FEM analysis or the like, and to design such that the stress is sufficiently reduced.

When casting ceramics with low-expansion cast iron, the ceramic member is preheated in consideration of the thermal shock resistance temperature of the ceramic member to prevent the ceramic from being destroyed by thermal shock during pouring. It is preferable to keep the temperature difference between the For this reason, it is desirable to preheat the ceramic member to about 600°C or higher, and more preferably to about 800°C or higher. When preheating a ceramic member, it is preferable to preheat the ceramic together with the mold while it is set in the mold, in terms of work efficiency and to prevent the ceramic from cooling down. Preferably, a mold is used.

Furthermore, in castings, in order to improve the adhesion between ceramics and cast iron, it is preferable to pressurize the molten metal immediately after pouring it into the mold, or to vacuum or reduce the pressure inside the mold. After casting, it is effective to slowly cool the casting in an annealing furnace and to hold it for a long time, especially at 400°C to 600°C, to relieve stress from the casting. Cooling too quickly can cause the ceramic to break or peel due to stress due to differential thermal expansion. From the perspective of reducing the weight of parts, ceramics
It is desirable to construct as many of the metal parts of a metal composite as possible with a material with a high (strength/weight) ratio, such as an aluminum alloy, so the ceramic is cast in low expansion cast iron and the outside is further covered with an aluminum alloy, etc. It is desirable to have a structure in which the material is cast inside.

[0011] When casting the outside of low expansion cast iron with an aluminum alloy, if the surface of the low expansion cast iron is subjected to Alphine treatment or alumel treatment, the cast iron and aluminum alloy will chemically bond, creating a gap at the interface. This is effective in achieving strong connections where there is no When casting a ceramic-low-expansion cast iron composite with aluminum alloy, use gas pressure or hydraulic pressure of 2 to 50 kg/cm to prevent sink marks, etc.
It is desirable to perform pressure casting as shown in step 2.

0012

EXAMPLES The present invention will be explained in more detail below based on the illustrated embodiments, but the present invention is not limited to these embodiments. (Example 1) Fig. 1 shows an example in which the ceramic-metal casting composite of the present invention is applied to the crown portion of a two-part piston of a direct injection diesel engine. As shown in Figure 1,
The cavity 1 of the piston combustion chamber is made of a thick silicon nitride member with a high heat transfer resistance per weight, and this is surrounded by the low expansion cast iron 3 that makes up the piston body. It is possible to reduce heat transfer loss from the combustion gas to the combustion chamber wall, and the heat resistance of the combustion chamber opening is improved, preventing problems such as burnout and cracking of the opening, which are problems with metal pistons. This is an example of use for the purpose of By adopting such a structure, a component with high strength and reliability was obtained, in which the stress of the ceramic was low over the entire operating temperature range, and the bonding strength between the metal and the ceramic was high.

FIG. 2 shows an example of a casting method for the embodiment shown in FIG. After setting the piston cavity member 1 made of silicon nitride, whose outer circumferential surface remains the fired surface and has not been machined, into the ceramic mold 2, the ceramic mold 2 is heated together, and after preheating to approximately 900°C. , C 1.2% by weight, Si 1.
2%, Mn 0.3% or less, Ni 28%, Co
A 1400° C. molten metal of low expansion cast iron 3 having a chemical composition of 14% Mg, 0.03% Mg, and 0.3% Nb was poured into a mold. At this time, in order to improve the adhesion between the silicon nitride piston cavity member 1 and the low expansion cast iron 3, the inside of the mold 2 was vacuumed and depressurized through the lower chamber 4. When the temperature of the molten metal has decreased to approximately 800°C, the mold 2 is transferred to an electric furnace, and after being gradually cooled to room temperature, the mold 2 is released to obtain a ceramic-low expansion cast iron composite, and then a low expansion cast iron 3
The outer periphery was machined.

(Embodiment 2) FIG. 3 shows an example in which the ceramic-metal casting composite of the present invention is applied to a cylinder liner of a diesel engine. That is, the inner surface of the cylinder liner 5 is made of silicon nitride 6, which has excellent wear resistance and has a small coefficient of friction with the metal piston ring, and the outer surface is filled with low expansion cast iron 3. This is an example of use aimed at reducing wear and engine friction loss. FIG. 4 shows a method for manufacturing the parts of the embodiment shown in FIG. An insert mold (core) in which a cylindrical silicon nitride member 6, which is not machined and has both the inner and outer fired surfaces, is set in a mold 7, and the surface is coated with carbon, zircon, etc. 8, preheated to about 400℃, and heated to 2.0% C and S by weight.
i 2.3%, Mn 0.3% or less, Ni 32.5
%, Co 5.4%, Mg 0.03% molten low expansion cast iron 3 at about 1300°C was immediately pressurized from above with a piston 9 at a hydraulic pressure of about 40 kg/cm2. did. Thereafter, the mold 7 was slowly cooled to room temperature in an electric furnace and then released from the mold 7 to obtain a ceramic-metal cast composite. The cast iron outer periphery and upper and lower surfaces of this composite were machined, and the ceramic inner surface was ground to obtain a cylinder liner 5.

(Embodiment 3) FIG. 5 shows an example in which the ceramic-metal casting composite of the present invention is applied to a piston of a small direct injection diesel engine. By using silicon nitride, which has excellent heat resistance, for the lip part 11 provided at the opening of the piston combustion chamber, the lip part 11 is prevented from burning out, cracking, etc., which are problems with metal pistons, and the piston body 12 is This is an example of the use of the present invention for the purpose of suppressing an increase in the weight of the entire component while taking measures against local heat load by constructing the component using a lightweight aluminum alloy. After obtaining a composite ring-shaped member of a silicon nitride ring (lip portion) 11 and a low expansion cast iron ring 3 by the same method as in Example 1 or Example 2, the surface of the low expansion cast iron 3 was subjected to alumel treatment, After setting this composite ring-shaped member in a metal mold and preheating it, approximately 600
A molten aluminum alloy of ~700°C was poured. At this time, pressure casting was carried out at approximately 5 kg/cm2 in order to prevent the occurrence of sink marks. Thereafter, it was cooled down to room temperature, then released from the mold, and the outer circumference, piston ring groove, and piston pin hole were machined to obtain a piston.

(Example 4) FIG. 6 shows an example in which a ceramic-metal casting composite of the present invention made of silicon nitride, low expansion cast iron, and aluminum alloy was produced in the same process as in Example 3. In other words, the aluminum alloy piston 12 is designed to improve the heat resistance of the upper part of the piston and reduce heat loss by utilizing the heat resistance and heat insulation properties of silicon nitride.
This is an example in which the upper part of the cylinder is covered with silicon nitride 18 and is applied to a piston of a small direct injection diesel engine.

(Embodiments 5 to 7) FIGS. 7 to 9 show examples in which ceramics are used only in areas subject to severe heat load, and are applied to a two-part piston of a direct injection diesel engine. FIG. 7 shows an example in which silicon nitride with excellent heat resistance is used for the lip portion 11 provided at the opening of the piston combustion chamber, and the lip portion 11 is cast with low expansion cast iron 3. Note that 21 indicates an aluminum skirt portion. FIG. 8 shows an example in which silicon nitride, which has excellent heat resistance and heat insulation properties, is used in a relatively wide portion 20 of the entire lower part including the center of the piston combustion chamber. With this configuration, it is possible to improve the heat insulation of the combustion chamber, increase the gas temperature in the combustion chamber, and improve fuel efficiency and purify exhaust gas while taking measures against melting damage and cracks caused by heat load. FIG. 9 shows an example in which the measures against heat load and the degree of insulation of the combustion chamber are further improved by combining the examples shown in FIGS. 7 and 8. Also, as in the example of FIG.
Although it was difficult to construct a combustion chamber with a plurality of ceramic members using conventional shrink fitting methods, it has become possible to easily construct the combustion chamber with the cast body of the present invention. In this way, since the ceramic is used in parts, it is possible to avoid destruction of individual ceramic members.

(Embodiment 8) FIG. 10 shows that the inner surface 14 of the exhaust port provided in the cylinder head body 13 of a diesel engine is made of a tubular aluminum titanate member, and the valve guide 15 is made of a silicon nitride member. In addition, the valve seat 16 is made of silicon nitride, and the cylinder head plate 17, which is the contact surface, is made of a disc-shaped member made of silicon nitride, thereby reducing heat loss at the exhaust port and improving the valve guide. This is an application example of the ceramic-metal cast composite member of the present invention, which aims to reduce wear of valve seats 15 and 16 and reduce heat loss to the ignition surface.

[0019]

[Effects of the Invention] As explained above, according to the ceramic-metal cast composite of the present invention, the stress generated in the ceramic at room temperature is low, and the joint between the ceramic and the metal does not require machining. Since it can be produced, it is possible to obtain a ceramic-metal composite that requires few work steps and is low cost, and has sufficient ceramic-metal bond strength even at high temperatures. In addition, in the present invention, ceramics, which are brittle and unreliable when used alone, can be easily used as mechanical structural members in a composite structure with metal, and the heat resistance, wear resistance,
In order to make it possible to put it into practical use as mechanical structural parts that take advantage of its light weight and heat insulation properties, especially ceramic cast pistons,
It is extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of a ceramic-metal casting composite according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of the casting method of the embodiment shown in FIG. 1;

FIG. 3 is a schematic cross-sectional view showing another embodiment of the casting composite of the present invention.

FIG. 4 is a schematic cross-sectional view showing a method for manufacturing a component according to the embodiment of FIG. 3;

FIG. 5 is a schematic cross-sectional view showing another embodiment of the casting composite of the present invention.

FIG. 6 is a schematic cross-sectional view showing another embodiment of the casting composite of the present invention.

FIG. 7 is a schematic cross-sectional view showing an example in which ceramics are applied only to areas subject to severe heat load.

FIG. 8 is a schematic cross-sectional view showing another example in which ceramics are applied only to areas subject to severe heat load.

FIG. 9 is a schematic cross-sectional view showing another example in which ceramics are applied only to areas subject to severe heat load.

FIG. 10 is a schematic cross-sectional view showing another embodiment of the casting composite of the present invention.

[Explanation of symbols]

1 Piston cavity, 2 Ceramic mold, 3 Low expansion cast iron, 4 Lower chamber, 5 Cylinder liner, 6 Silicon nitride, 7
Mold, 8 insert mold, 9 piston, 11 lip part, 12 piston body, 13 cylinder head body, 14 exhaust port inner surface, 15 valve guide, 16 valve seat, 17 cylinder head plate, 18 silicon nitride, 20 combustion chamber Lower part, 21 Aluminum skirt part

Claims (8)

[Claims] 1. A cast composite of ceramics and metal, characterized in that ceramics are cast in low expansion cast iron. 2. The ceramic-metal cast composite according to claim 1, wherein the low expansion cast iron side is further cast with an aluminum alloy. 3. As low expansion cast iron, the coefficient of thermal expansion from room temperature to 400°C is 3.5 x 10-6/°C to 9.0 x 10-6.
2. The ceramic-metal casting composite according to claim 1, wherein the ceramic-metal casting composite is made of a material having a temperature within the range of /°C. 4. The low expansion cast iron has a weight ratio of C 0.
3-2.0%, Ni 25-32%, Co 12-
20%, Si 0.3~2.0%, Nb 0.2~
0.8%, Mg or Ca 0.01-0.2%, Mn
1.0% or less, the remainder has a composition of Fe containing impurities, and the thermal expansion coefficient from room temperature to 400°C is 3.5 × 10-6 ~
The ceramic-metal casting composite according to claim 1, which has a temperature of 5.5 x 10-6/°C. [Claim 5] The low expansion cast iron has a weight ratio of C 0.8.
~3.0%, Ni 30-34%, Co 4.0~
6.0%, Si 1.0-3.0%, Mn 2.0
% or less, sulfur 1.0% or less, phosphorus 1.5% or less, M
g 1.0% or less, the remainder has a composition of Fe containing impurities, and the coefficient of thermal expansion from room temperature to 400°C is approximately 9 x 10-6 /
℃ or less, the coefficient of thermal expansion from room temperature to 200℃ is approximately 2 x 10-6
The ceramic-metal casting composite according to claim 1, which has a temperature of ~3 x 10-6/°C. 6. The ceramic-metal cast composite according to claim 1, wherein the average thickness of the cast iron casting is smaller than the average thickness of the ceramic member. 7. The ceramic-metal cast composite according to claim 1, which is used as a ceramic cast piston. 8. The ceramic-metal casting composite according to claim 7, wherein ceramic is used for the opening lip of the combustion chamber and/or the center of the combustion chamber.