JPH04272451A - Ring coupling of gradient functional material and its manufacture - Google Patents

Abstract

PURPOSE:To provide a ring coupling of a gradient functional material formed from a plurality of rings being joined together which have different coefficients of thermal expansion, and also provide a manufacturing method for such a ring coupling. CONSTITUTION:A ring coupling 7 is composed of an inner ring 6 and an outer ring 5 made of a gradient functional material, which assumes inversion of the coefficient of thermal expansion between normal temp. and the joining temp., wherein the inner ring 6 bears the tensile residual stress while the outer ring 5 does the compressive residual stress. The actual amounts of thermal expansion are adjusted in accordance with the temp. rising condition during operation, i.e., the actually expanding amount of the inner ring 6 generated according to the coefficient of thermal expansion dependent upon the physical property of its material is lessened while that of the outer ring 5 generated according to the coefficient of thermal expansion dependent upon the physical property of its material is enlarged. Thus the gradient function is increased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring assembly made of functionally graded materials having different coefficients of thermal expansion and a method for manufacturing the same.

0002

2. Description of the Related Art Conventionally, there is a ceramic-integrated piston disclosed in Japanese Utility Model Application Publication No. 141446/1983. The ceramic-embedded piston disclosed in this publication has a ceramic member built into a recess on the combustion chamber side of a piston body made of an aluminum alloy, and the outer periphery of the ceramic member has a thermal expansion coefficient of 10 to 23 x 10- 1
/°C heat-resistant and corrosion-resistant metal ring having a protruding part with a plurality of fastening holes on the head part, the protruding end is made to protrude from the upper end surface of the ceramic member, and the piston is attached to the outer periphery of the metal ring. This is an assembly in which a male threaded part is screwed into a female threaded part provided in a recessed part of the main body, and after this assembly is fastened to the piston main body, the protruding part including the fastening hole is removed. .

Further, as a piston for an internal combustion engine, there is one disclosed in Japanese Utility Model Application Publication No. 58-98455. The internal combustion engine piston has a piston base made of a metal material such as aluminum or cast iron, and a ceramic bonded to it via a metal body such as Kovar or 42 alloy having a coefficient of thermal expansion of 3 to 9 x 10-6/°C. It is.

0004

[Problems to be Solved by the Invention] In the combustion chamber of a reentrant piston, if the tip of the lip of the combustion chamber inlet, that is, the opening of the combustion chamber, is formed to have a sharp point,
The turbulence of the squish flow and the reverse squish flow increases, the mixture of fuel and air becomes more uniform, and the combustion condition improves.

However, in conventional pistons made of aluminum or ceramic fiber-reinforced aluminum, if the tip of the lip forming the combustion chamber is formed into a sharp point, the temperature at the tip of the lip becomes high. The heat load, that is, thermal stress applied to the lip portion causes damage such as melting and cracking of the lip portion, and there is a limit to the ability to sharpen the tip of the lip portion. A similar phenomenon also occurs when the tip of the lip is made of a non-aluminum material with excellent heat resistance, such as Niresist, steel, Fc, ceramics, etc.
There was a problem in that there was a large difference in coefficient of thermal expansion between the piston head and the aluminum material that made up the piston head body, and peeling occurred at the interface or joint surface.

[0006] Therefore, when assembling the lip portion to the piston head body, when bonding or bonding ceramics with significantly different coefficients of thermal expansion and metal materials such as aluminum, the operating temperature range is expanded to prevent cracks, melting damage, etc. of the ceramics. In order to prevent breakage, etc., a method has been adopted in which a ring assembly made of functionally graded materials with different thermal expansion coefficients is bonded and interposed between the ceramic lip portion and the metallic piston head body. There is.

By the way, as a method for manufacturing a ring assembly made of a functionally graded material, a method as shown in FIGS. 5 and 6 has been used. As shown in FIG. 5, the method for manufacturing the ring assembly made of the functionally graded material is to form rings 12, 13, and 14 with different coefficients of thermal expansion on both sides with tapered surfaces larger than the coefficient of thermal expansion of each material, and to cool them at room temperature. The intermediate ring 13 is supported by the tapered surface of the outer ring 14 and the inner ring 12 is supported by the tapered surface of the intermediate ring 13. 12. A brazing material 15 is placed between the rings 12 and 13 and between the rings 13 and 14. At this time, the coefficient of thermal expansion of the outer ring 14 is large (for example, α=15×10−6/℃), and the coefficient of thermal expansion of the inner ring 12 is small (for example, α=5×1
0-6/°C), and the intermediate ring 13 has an intermediate coefficient of thermal expansion (for example, α=15×10-6/°C). Next, when each ring 12, 13, 14 is placed in a furnace and heated to a brazing temperature (for example, 1100°C), the outer ring 14 has the largest thermal expansion, so as shown in FIG. The intermediate ring 13 is fitted into the ring 14, and the inner ring 12 is fitted into the intermediate ring 13 and joined together. In this method, the rings 12, 13, and 14 are joined so that the clearance between them becomes zero at the brazing temperature. Next, when the temperature is returned from the brazing temperature to room temperature, a compressive residual stress is applied to the inner ring 12, and a tensile residual stress is applied to the outer ring 14.

[0008] When producing functionally graded materials with different coefficients of thermal expansion as in each of the above manufacturing methods, residual stress is imparted to the inner ring 12 and the outer ring 14 if each ring is brazed. . Therefore, for example, when this functionally graded material is assembled into the structure of a combustion chamber, when the temperature of the combustion chamber rises during engine operation and rises above normal temperature, the material of the inner ring 12 may change. The thermal expansion displacement is the sum of the thermal expansion amount and the expansion displacement amount that expands the inner diameter due to the release of residual compressive stress, and the thermal expansion is larger than the material property value of the inner ring 12. In addition, for the outer ring 14, the thermal expansion displacement is the amount of thermal expansion of the material of the outer ring 14 minus the amount of contraction displacement that reduces the outer diameter due to the release of residual tensile stress, and the thermal expansion is smaller than the physical property value of the material of the outer ring 14. It will cause expansion. That is,
In conventional functionally graded materials, the actual amount of thermal expansion of the inner ring 12 is larger than the amount of thermal expansion generated by the coefficient of thermal expansion determined by the physical properties of the material due to the influence of residual stress, and the actual amount of thermal expansion of the outer ring 14 is The amount of thermal expansion is smaller than the amount of thermal expansion generated by the coefficient of thermal expansion determined by the physical properties of the material due to the influence of residual stress. Therefore, the gradient function with respect to the coefficient of thermal expansion of the functionally gradient material becomes small.

[0009] The above-mentioned problem can be solved by
The ceramic built-in piston disclosed in Japanese Patent No. 41446 also has a similar problem. That is, the ceramic built-in piston has a metal ring screwed onto a piston body made of an aluminum alloy, and the metal ring is joined to a ceramic member, but metals and ceramics have different coefficients of thermal expansion. In a piston head that is subjected to thermal stress, cracks or fissures occur in the ceramic member, resulting in the problem of damage to the ceramic member.

An object of the present invention is to solve the above-mentioned problems, and includes, for example, a heat-resistant piston head body that extends radially inward in the shape of a pointed ring and forms a combustion chamber opening in the center. In a ring assembly made of a functionally graded material with a different coefficient of thermal expansion, which is interposed between the lip part made of a ceramic rich in A tensile residual stress is applied to the inner ring and a compressive residual stress is applied to the outer ring in the ring assembly, and the actual amount of thermal expansion is determined according to the thermal expansion coefficient determined by the physical properties of the material. An object of the present invention is to provide a ring assembly made of a functionally graded material that reduces the amount of thermal expansion generated and increases the functionally graded material, and a method for manufacturing the same.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention is constructed as follows. That is,
The present invention provides a ring assembly made of functionally graded materials having different coefficients of thermal expansion, which are manufactured from an inner ring and an outer ring joined to the outer peripheral surface of the inner ring, in which the coefficient of thermal expansion of the inner ring is The coefficient of thermal expansion of the inner ring is smaller than the coefficient of thermal expansion of the outer ring, and the coefficient of thermal expansion of the inner ring is larger than the coefficient of thermal expansion of the outer ring at the bonding temperature, and there is a tensile residual stress in the inner ring at room temperature (usage temperature), and in the outer ring. The present invention relates to a ring assembly made of a functionally graded material to which compressive residual stress is applied.

The present invention also provides a method for manufacturing a ring assembly consisting of functionally graded materials having different coefficients of thermal expansion, which are made from an inner ring and an outer ring bonded to the outer peripheral surface of the inner ring. The inner ring is made of a material whose coefficient of thermal expansion is larger than that of the outer ring, and whose coefficient of thermal expansion is reversed between room temperature and bonding temperature such that the coefficient of thermal expansion of the outer ring is larger than the coefficient of thermal expansion of the inner ring at room temperature. and the outer ring, and then the inner ring and the outer ring are bonded to each other by brazing or diffusion bonding.

Alternatively, the present invention provides a method for manufacturing a ring assembly consisting of functionally graded materials having different coefficients of thermal expansion manufactured from an inner ring and an outer ring bonded to the outer peripheral surface of the inner ring. Select a material whose coefficient of thermal expansion is greater than that of the outer ring, and whose coefficient of thermal expansion is reversed between room temperature and sintering temperature, such that at room temperature the coefficient of thermal expansion of the outer ring is greater than the coefficient of thermal expansion of the inner ring. Then, the material is molded into a ring molded body having an integral structure in a mold for molding an inner ring molded body and an outer ring molded body, and the ring molded body is fired to produce a sintered body having an integral structure, and the inner ring molded body is The present invention relates to a method for manufacturing a ring assembly made of a functionally graded material, characterized in that a tensile residual stress is applied to the outer ring and a compressive residual stress is applied to the outer ring.

[0014]

[Operation] The ring assembly made of functionally graded material and the method for manufacturing the same according to the present invention are constructed as described above, and operate as follows. That is, in the ring assembly made of this functionally graded material, the inner ring and the outer ring are made of a material whose coefficient of thermal expansion is reversed at room temperature (usage temperature) and bonding temperature, and the inner ring is Since a tensile residual stress is applied and a compressive residual stress is applied to the outer ring joined to the inner ring, when the temperature rises in use, the inner ring shrinks in inner diameter due to the release of residual stress, and its thermal expansion becomes smaller. , the outer ring expands in outer diameter due to release of residual stress, resulting in increased thermal expansion and increased tilting function. Therefore, when the ring assembly is assembled into a combustion chamber in which a lip portion made of a material with a low coefficient of thermal expansion is joined to the inner ring and a piston head body made of a material with a high coefficient of thermal expansion is joined to the outer ring, the ring assembly is attached to the combustion chamber. It is possible to cause thermal expansion matching that of the lip portion and provide a good buffering function to the lip portion.

[0015] Furthermore, in this method of manufacturing a ring assembly made of a functionally graded material, when an inner ring and an outer peripheral ring are joined to each other by brazing or diffusion bonding, tensile residual stress is applied to the inner ring and the outer ring is A ring assembly to which compressive residual stress is applied can be easily manufactured.

Alternatively, this method for manufacturing a ring assembly made of a functionally graded material involves using a material that will become the inner ring and a material that will become the outer ring in order to produce a ring assembly that joins the inner ring and the outer ring. A ring sintered body can be easily produced by placing the ring in a mold, molding a composite ring molded body in which an inner ring molded body and an outer ring molded body have an integral structure, and then firing the composite ring molded body. Can be manufactured. In this ring assembly, a tensile residual stress can be applied to the inner ring and a compressive residual stress can be applied to the outer ring.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a ring assembly made of functionally graded material and a method for manufacturing the same according to the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing one embodiment of the method for manufacturing a ring assembly made of functionally graded material according to the present invention, FIG. 2 is a graph showing an example of the coefficient of thermal expansion determined by the physical properties of the material, and FIG. 1 is a schematic view showing an embodiment in which a ring assembly made of a functionally graded material according to the present invention is applied to a combustion chamber formed in a piston head body.

FIG. 3 shows a combustion chamber opening 3 extending radially inward in a pointed shape so as to cover the upper part of a cavity 10 forming a combustion chamber 1 formed in a piston head body 2.
A reentrant piston is shown having a looped lip 8 with . This reentrant type piston consists of a piston head body 2 made of a metal material such as aluminum, which has a cast-molded piston skirt and a cavity 10 that is fixed to the piston skirt and constitutes a combustion chamber 1. It has a combustion chamber opening 3 on the upper surface thereof and a bottom surface 4 of a cavity 10 having a larger area than the combustion chamber opening 3.

The structure of this combustion chamber includes a cavity wall surface formed in a cavity 10 formed in the piston head body 2, a ring assembly 7 joined to the cavity wall surface, and a ring assembly 7 joined to the ring assembly 7 and connected to the piston head body 2. It has a lip portion 8 which extends inward in the radial direction in a loop shape with a tapered surface and forms a combustion chamber opening 3 in the central portion. The ring assembly 7 is constructed by joining together a plurality of concentrically arranged rings, ie, an outer ring 5 and an inner ring 6, made of functionally functional materials having different coefficients of thermal expansion α.

[0020] In this combustion chamber structure, the lip portion 8 is made of a ceramic material with high heat resistance and high temperature strength and a low coefficient of thermal expansion, such as silicon nitride (Si3 N4), silicon carbide (SiC), etc. There is. This lip part 8
The tip forming the combustion chamber opening 3 is a tapered surface that extends radially inward, and is formed in an extremely acute rounded shape, and the upper and lower portions of the outer peripheral surface are tapered radially inward with the center as the boundary. It is manufactured in a shape with a surface.

As shown in FIG. 1 or 3, the ring assembly 7 includes outer rings 5 arranged concentrically and joined to each other.
and an inner ring 6, the thermal expansion coefficient α of the inner ring 6 is
The outer ring 5 and the outer ring 5 have different coefficients of thermal expansion α, and the ring assembly 7 is manufactured as a functionally graded material having different coefficients of thermal expansion α. That is, the inner ring 6 is made of material A, and the outer ring 5 is made of material B. As shown in FIG. 2, at room temperature or the actual operating temperature (for example, 400 to 500°C in an engine combustion chamber), the coefficient of thermal expansion α of the material A of the inner ring 6 is equal to the thermal expansion of the material B of the outer ring 5. The bonding temperature TH such as brazing temperature, diffusion bonding temperature or sintering temperature (for example, 1000~
1100°C), the coefficient of thermal expansion α of the material A of the inner ring 6 is
is larger than the coefficient of thermal expansion α of the material B of the outer ring 5. That is, the coefficient of thermal expansion α of material A and material B is higher than the temperature TR at which the ring assembly 7 is used.
Reversal occurs at a reversal temperature TX (Curi point) lower than the junction temperature TH. If the inner ring 6 and outer ring 5 are manufactured by selecting materials A and B as described above, tensile residual stress will be applied to the inner ring 6 at room temperature, and compressive residual stress will be applied to the outer ring 5. The ring assembly 7 can be manufactured in the following state.

Materials A and B as described above are incoloy,
Various combinations can be considered from materials such as Kovar, manganese steel, Invar, iron-nickel alloy, iron-nickel-cobalt alloy, SUS, and Hastelloy. Figure 4 shows
It is a graph showing the relationship between temperature T and thermal expansion coefficient (linear expansion coefficient) α of these materials. In FIG. 4, the right end of the graph is about 900° C., and it can be seen that the coefficient of thermal expansion α is reversed at a temperature equal to or higher than the operating temperature TR. In FIG. 4, symbol A is SUS, symbol B is iron-nickel alloy, symbol C is Hastelloy, symbol D is iron-nickel alloy, symbol E is Incoloy, symbol F is molybdenum steel, symbol G is nickel-manganese. Invar is an iron-based alloy, and the symbol H indicates an example of superinvar. For example, if Kovar is selected as the material A for the inner ring 6, the outer ring 5
It is sufficient to select material B that is compatible with the above conditions.

If the ring assembly 7 is manufactured by joining the outer ring 5 and the inner ring 6 as described above, for example,
When the ring assembly 7 is assembled and used in the combustion chamber 1 formed in the piston head, the operating temperature T during engine operation
R (for example, 450°C), the inner ring 6 has a small displacement amount, which is the displacement amount due to thermal expansion that occurs according to the coefficient of thermal expansion determined by the physical properties of the material minus the amount of displacement that shrinks the inner diameter due to the release of tensile residual stress. Further, the outer ring 5 has a large displacement amount, which is the sum of the displacement amount due to thermal expansion that occurs according to the thermal expansion coefficient determined by the physical properties of the material, and the displacement amount that expands the outer diameter due to the release of compressive residual stress. Therefore,
For example, when a lip portion 8 made of highly heat-resistant ceramics is attached to an aluminum piston head body 2 via a ring assembly 7, the thermal expansion of the lip portion 8 is small, and the thermal expansion of the piston head body 2 is small. becomes larger, so the inner ring 6 on the lip portion 8 side can match the thermal expansion of the lip portion 8, and the outer ring 5 on the piston head body 2 side can match the thermal expansion of the piston head body 2, The tilting function of the ring assembly 7 relative to the lip portion 8 and the piston head body 2 is increased.

Next, an embodiment of a method for manufacturing a ring assembly made of a functionally graded material according to the present invention will be described. For the inner ring 6 and outer ring 5 that constitute the ring assembly 7, materials A and B shown in FIG. 2 are used. That is, the coefficient of thermal expansion α of the material A of the inner ring 6 is equal to the bonding temperature TH (for example, 11
00℃), the thermal expansion coefficient α of the outer ring 5 is larger than that of the material B of the outer ring 5, and the thermal expansion coefficient α of the outer ring 5 is larger than the inner ring 6 at room temperature.
is larger than the coefficient of thermal expansion α. That is, the inner ring 6 and the outer ring 5 are each made of a material whose coefficient of thermal expansion is reversed between room temperature and bonding temperature. Next, the inner ring 6 and the outer ring 5 are placed adjacent to each other in a furnace, a brazing material is placed on the interface, the temperature is raised to the joining temperature, and the outer ring 5 and the inner ring 6 are brazed together. join each other. In some cases, the inner ring 6 and the outer ring 5 may be bonded to each other by diffusion bonding to produce the ring assembly 7.

Another embodiment of the method for manufacturing a ring assembly made of functionally graded material according to the present invention will be described. In the manufacturing method of this embodiment as well, the materials A and B shown in FIG. 2 are used for the inner ring 6 and outer ring 5 constituting the ring assembly 7, as in the manufacturing method of the above embodiment. For example, by placing a partition wall in the radial center of a ring-shaped mold,
A raw material powder or slurry of material A is charged radially inside the partition wall of the mold, and a raw material powder or slurry of material B is charged radially outside the partition wall of the mold. Next, the partition wall is removed from the mold, and each raw material powder or slurry is simultaneously pressed and molded using a press to form a composite ring molded body having an integral structure consisting of an inner ring molded body and an outer ring molded body. After the composite ring molded body is hardened and dried, the composite ring molded body is fired to produce a ring sintered body having an integral structure. This ring sintered body has material A on the inside in the radial direction.
An inner ring 6 made of material B and an outer ring 5 made of material B radially outward are joined in one piece. This ring assembly 7 is configured such that the inner ring 6 is loaded with a tensile residual stress and the outer ring 5 is loaded with a compressive residual stress at room temperature.

When the ring assembly made of the functionally graded material according to the present invention is incorporated into a combustion chamber, it functions as follows. That is, even if a large thermal stress is generated due to a difference in thermal expansion between the lip portion 8 and the piston head main body 2 due to a temperature difference when the engine is operated, the ring assembly 7 made of a functionally gradient material maintains a large gradient function. It functions as a buffer material and absorbs the difference in thermal expansion caused by the temperature difference between the lip portion 8 and the piston head body 2. Therefore, combustion chamber 1
Even if a temperature change occurs and a thermal expansion difference occurs between the lip portion 8 and the piston head body 2, no cracks or cracks will occur in the lip portion 8 and the combustion chamber 1 will be destroyed. There is no. In addition, the lip portion 8 has a pointed, acute-angled shape that allows a large amount of heat to flow in from the combustion gas, but the heat that has flowed into the lip portion 8 is blocked in the direction of the piston head body 2 through the ring combination body 7 and the metal ring body 6. It flows through the piston skirt, piston ring, etc. to the cylinder liner side. Therefore, the temperature rise is suppressed without maintaining the temperature of the lip portion 8 at a high temperature, so even if the edge of the lip portion 8 is configured to have an acute pointed shape, the edge is made with heat resistance. will not melt or break.

Furthermore, since the lip portion 8 is made of a material such as ceramics that has a low coefficient of thermal expansion and is highly heat resistant, the edge of the lip portion 8 that forms the combustion chamber opening 3 is formed at an extremely acute angle and the shape is can be maintained even at high temperatures. Therefore, it is possible to increase the squish flow that occurs during the compression stroke of the piston's upward movement and the reverse squish flow that occurs during the piston's downward explosion stroke, promoting the mixing of air and fuel, suppressing the amount of carbon generated, and reducing the amount of fuel. It is possible to perform combustion that reduces consumption and improve combustion conditions.

[0028]

[Effects of the Invention] The ring assembly made of functionally graded material and the method for manufacturing the same according to the present invention, constructed as described above, have the following effects. That is, the ring assembly made of this functionally graded material has an inner ring and an outer ring such that the coefficient of thermal expansion of the inner ring is smaller than the coefficient of thermal expansion of the outer ring at room temperature, and the coefficient of thermal expansion of the inner ring is smaller than that of the outer ring at the bonding temperature. Since the ring is made of a material whose coefficient of thermal expansion is larger than that of the outer ring, tensile residual stress can be applied to the inner ring and compressive residual stress can be applied to the outer ring at room temperature. Therefore, when the temperature rises during use, the actual amount of thermal expansion of the inner ring will be smaller than the thermal expansion that occurs according to the coefficient of thermal expansion determined by the physical properties of the material, and the actual amount of thermal expansion of the outer ring will depend on the physical properties of the material. It is larger than the thermal expansion that occurs according to the determined coefficient of thermal expansion. Therefore, when this ring assembly is installed, for example, between the aluminum piston head body of the combustion chamber formed in the piston head and the lip portion made of ceramics with a low coefficient of thermal expansion,
In order to absorb the difference in thermal expansion between the lip portion and the piston head main body, closely matching thermal expansion occurs as a tilting function, and the tilting function becomes large.

Furthermore, when the ring assembly made of the functionally graded material according to the present invention is assembled into the combustion chamber formed in the piston head, the ring assembly absorbs the difference in thermal expansion between the lip portion and the piston head body. In particular, the outer circumferential ring can be deformed by a thermal expansion larger than the thermal expansion that occurs at a coefficient of thermal expansion determined from the physical properties of the outer circumferential ring when the temperature rises during engine operation. On the other hand, the inner ring can be deformed so that the thermal expansion is smaller than the thermal expansion that occurs at a thermal expansion coefficient determined from the physical properties of the inner ring when the temperature rises. Therefore, when the lip portion is made of ceramics with a low coefficient of thermal expansion and the piston head body is made of a metal material with a high coefficient of thermal expansion, the gradient function that absorbs the difference in thermal expansion caused by the difference in coefficient of thermal expansion is greatly exhibited. It is possible to provide a slope function that closely matches the structure.

[0030] Furthermore, the lip portion can be formed of highly heat-resistant ceramics because the effect of thermal expansion from the piston head body is alleviated by the functionally graded material of the ring assembly, and the tip of the lip portion The portion can be formed to have an acutely pointed point with a radially inward tapered surface. Moreover, by forming the edges of the lip portion at an acute angle, the squish flow that flows into the combustion chamber during the compression stroke of the piston's upward movement and the reverse squish flow that flows out from the combustion chamber that occurs during the explosion stroke of the piston's downward movement are suppressed. can increase,
The squish flow and the reverse squish flow can achieve better mixing of the atomized fuel and air, and compared to conventional reentrant pistons, the amount of carbon generated is suppressed, fuel consumption is reduced, and combustion is improved. can do.

[0031] Furthermore, by closely assembling the lip part to the piston head main body via the ring assembly of the functionally graded material, each part is connected from the lip part at the tip of the combustion chamber to the piston head at the outer peripheral part. The heat flow at the boundary is not hindered, and the heat is conducted well, and the heat at the tip of the lip is transferred to the outside through the piston head body, piston ring, cylinder liner, etc., and the combustion gas causes the heat to be transferred to the outside of the lip Even if the tip reaches a high temperature, the heat is immediately transferred to avoid being maintained at a high temperature, thereby preventing melting and damage of the lip tip due to high temperatures.

[0032] Furthermore, in order to manufacture a ring assembly made of a functionally graded material according to the present invention, an inner ring and an outer ring are manufactured using the above-mentioned material, and then the inner ring and the outer ring are joined by brazing or diffusion bonding. By joining them together, it is possible to easily manufacture a ring assembly in which the inner ring is loaded with tensile residual stress and the outer ring is loaded with compressive residual stress.

Alternatively, in order to produce a ring assembly made of a functionally graded material according to the present invention, an inner ring molded body and an outer ring molded body are molded from a raw material having the characteristics of the material described above, and a composite ring of integral structure is formed with a mold. A ring in which a tensile residual stress is applied to the inner ring and a compressive residual stress is applied to the outer ring by molding a molded body and firing the composite ring molded body to produce a sintered body having an integral structure. Conjugates can be easily produced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the method for manufacturing a ring assembly made of functionally graded material according to the present invention.

FIG. 2 is a graph showing an example of a thermal expansion coefficient determined by the physical properties of a material.

FIG. 3 is a sectional view showing a combustion chamber constructed by assembling a ring assembly made of functionally graded material according to the present invention to a piston head body.

FIG. 4 is a graph showing the relationship between temperature and coefficient of thermal expansion of various materials for manufacturing the ring assembly.

FIG. 5 is an explanatory diagram showing an example of a manufacturing method of joining a plurality of rings to form a ring assembly.

6 is an explanatory diagram showing a ring assembly formed by the manufacturing method shown in FIG. 5. FIG.

[Explanation of symbols]

1 Combustion chamber 2 Piston head body 3 Combustion chamber opening 5 Outer ring 6 Inner ring 7 Ring combination 8 Lip part 10 Cavity

Claims (3)

[Claims] 1. A ring assembly comprising functionally graded materials having different coefficients of thermal expansion manufactured from an inner ring and an outer ring joined to the outer peripheral surface of the inner ring, wherein the coefficient of thermal expansion of the inner ring is equal to that of the outer ring at room temperature. and the coefficient of thermal expansion of the inner ring is greater than the coefficient of thermal expansion of the outer ring at the bonding temperature, and a tensile residual stress is applied to the inner ring and a compressive residual stress is applied to the outer ring at room temperature. A ring assembly made of a functionally graded material characterized by the following. 2. A method for manufacturing a ring assembly consisting of functionally graded materials having different coefficients of thermal expansion manufactured from an inner ring and an outer ring bonded to the outer circumferential surface of the inner ring, wherein the coefficient of thermal expansion of the inner ring at the bonding temperature is The inner ring and the outer ring are made of a material whose coefficient of thermal expansion is larger than that of the outer ring, and whose coefficient of thermal expansion is reversed between normal temperature and bonding temperature such that the coefficient of thermal expansion of the outer ring is larger than the coefficient of thermal expansion of the inner ring at room temperature. 1. A method for manufacturing a ring assembly made of a functionally graded material, characterized in that the inner ring and the outer ring are bonded to each other by brazing or diffusion bonding. 3. A method for manufacturing a ring assembly comprising functionally gradient materials having different coefficients of thermal expansion manufactured from an inner ring and an outer ring bonded to the outer peripheral surface of the inner ring, wherein the coefficient of thermal expansion of the inner ring at the sintering temperature is is larger than the coefficient of thermal expansion of the outer ring, and the coefficient of thermal expansion of the outer ring is larger than the coefficient of thermal expansion of the inner ring at room temperature. A ring molded body with an integral structure is molded using a mold for molding an inner ring molded body and an outer ring molded body, and the ring molded body is fired to produce a sintered body with an integral structure, and the tensile residual stress is applied to the inner ring. and a compressive residual stress is applied to the outer ring.