JPH03131579A - Production of metal-ceramic gradient composite material - Google Patents

Abstract

PURPOSE:To obtain the subject composite material having a dense gradient layer by using plural porous ceramic boards having different porosity an metallic powder, making a pre-composite material having porosities larger in an upper layer, setting in a main mold with a reversing top and bottom and injecting a molten metal from a lower part. CONSTITUTION:Plural porous ceramic boards having different porosity 1-1 and 1-2, etc., are laid in a pre-mold 20 in laminating with a charging metallic powder 2 in turn of having larger porosity from a lower layer to an upper layer. Then, inside of the pre-mold 20 is heated at a temperature higher than 80% of melting point of a metallic powder 2 to obtain a pre-composite material 4 of the porous ceramic boards and metal. Next, the pre-composite material 4 is set in a main mold 21 with a reversing top and bottom and a molten metal 5 is injected from injecting holes 22 installed in a lower part, then the molten metal 5 and the pre-composite material 4 are made to one body. By said method, the aimed metal-ceramic gradient composite material having ceramic-containing volume fractions unidirectionally varied in stepwise is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a metal-ceramic gradient composite material in which the ceramic content volume fraction changes stepwise in one direction, and in particular, relates to a method for manufacturing a metal-ceramic gradient composite material in which the ceramic content volume fraction changes stepwise in one direction. The present invention relates to a manufacturing method for manufacturing a metal-ceramic gradient composite material by casting.

[Prior Art] Ceramics have excellent properties such as oxidation resistance and high rigidity at high temperatures, but on the other hand, they also have the disadvantage of being weak against mechanical or thermal shock, tension and bending, etc. ing. In order to take advantage of the excellent properties of ceramics, metal-ceramic composite materials, which are composites of ceramics and metals, have been developed. As such a metal-ceramic composite material, a composite material made by dispersing ceramic particles or ceramic fibers in a metal, a composite material made by bonding a metal and a ceramic, etc. are known. In the case of the former composite material, the volumetric shear between the ceramic and the metal is approximately constant in the composite material, so in an environment where a steep exhaustion gradient occurs, thermal stress will be reduced in the same way as in the case of a single material. Destruction may occur due to

In addition, even in the case of the latter composite, it is a metal-ceramic composite material that can be used in high-temperature environments to alleviate the thermal stress that can occur at the bonding interface between metal and ceramics, causing peeling or cracking of the ceramic. The development of a so-called metal-ceramic gradient composite material, which is a composite material in which the volume fraction of ceramics on the exposed side is 100% and gradually decreases toward the inside, is underway.

There are four methods for producing a layer in which the ceramic volume ratio changes stepwise in one direction, that is, a layer in which the metal-ceramic composition is graded (hereinafter referred to as a graded layer): is known (Survey report on basic technology for function expression and thermal stress relaxation by dicomplexization, Science and Technology Public Relations Foundation, 1982).

■ Particle arrangement method ■ Method using physical vapor deposition (PVO) or chemical vapor deposition (CVD) ■ Plasma spraying method ■ Self-heating reaction method [Problem to be solved by the invention] Method (2) involves mixing ceramics and metal powder. This is a method of sintering a laminated body while gradually changing the ratio. Although relatively thick gradient layers can be produced using this method, it is difficult to obtain a dense gradient layer due to sintering.

Because the degree of shrinkage that occurs during sintering differs in the gradient layer due to the difference in the composition ratio between ceramic and metal, cracks may occur during sintering.

Method (2) has problems such as the formation speed of the gradient layer is extremely slow and it is difficult to obtain a thick gradient layer.

With method (2), it is difficult to produce a dense gradient layer as in method (2), and therefore, due to the thermal stress generated in the process of the high-temperature coating being adhered to the base metal one after another and being cooled, Cracks may occur in the sloped layer.

Method (2) utilizes a self-heating reaction between the raw materials and simultaneously performs sintering during the reaction. for example,
When manufacturing a TiBz-Cu-based gradient layer, the heat of reaction between Ti and B is utilized. If there is a large amount of metal that does not participate in the reaction (Cu in this example), the reaction progresses slowly, and if a high melting point metal such as Fe is used instead of a low melting point metal such as Cu, the gradient layer Formation is difficult. In addition, since sintering is performed in this method as well, it is difficult to obtain a dense gradient layer, similar to the methods (1) and (2) described above.

All of the three important issues when manufacturing a graded layer (the ability to form a thick graded layer, the ability to form a dense graded layer, and the absence of defects such as cracks during the formation of the graded layer) are all explained above. Traditional manufacturing methods are unsatisfactory. Further, it is desirable that the selection range of materials used for the gradient layer be wide.

The thickness of the gradient layer has a great effect on the temperature distribution or the generated thermal stress in the composite material, and for the reasons described below, the thicker the layer, the better.

If the graded layer is expected to have a heat shielding function, it is necessary to form a graded layer with low thermal conductivity, and the thicker the graded layer made of the same material, the higher the heat shielding efficiency.

Next, the influence of the thickness of the gradient layer on the generated thermal stress will be explained. For two examples in which gradient layers with a small coefficient of thermal expansion were created with different thicknesses in order to alleviate thermal stress, the stress at which free thermal expansion strain ε79 occurred was measured with respect to the temperature distribution as shown in FIG. FIG. 5 shows a case where the thickness of the gradient layer is thin, and FIG. 6 shows a case where the thickness of the gradient layer is thick. Figure 5(a) (Figure 6(a)) shows the thermal expansion coefficient α when the thickness of the gradient layer is thin (thick), and in the figure A and B are the thickness of the metal and the gradient layer. Figure 5 (b) shows the thickness of
) (Fig. 6(b)) represents the free thermal expansion strain ε when the thickness of the gradient layer is thin (thick), and Fig. 5(C) (Fig. 6(C)
)) represents the stress generated when the thickness of the gradient layer is thin (thick). For a gradient layer with a thin thickness, at a certain time (1=
If the material of the gradient layer is designed so that the stress change in the gradient layer is small with respect to the temperature distribution at 1υ, then at another time (t
= tz), a large gradient stress change occurs in the graded layer. This large gradient stress change causes bending deformation in the gradient layer, causing peeling or cracking of the gradient layer. However, in a thick gradient layer, the gradient of stress change is small, and the value of the generated stress itself can be reduced (FIG. 6(C)).

As described above, it is desirable to have a method for manufacturing a gradient layer that can form a thick gradient layer, but in conventional manufacturing methods, the thicker the gradient layer is, the more voids are generated in the gradient layer. There was a problem that it became porous and cracked.

The present invention has been made in view of the above circumstances, and provides a method for producing a metal-ceramic gradient composite material that can produce a metal-ceramic gradient composite material that satisfies all of the three items mentioned above, and in which the process is simple. The purpose is to

[Means to solve the problem]

The method for manufacturing a metal-ceramic gradient composite material according to the present invention is a method for manufacturing a metal-ceramic gradient composite material in which the ceramic content volume ratio changes stepwise in one direction, in which pores are formed from the lower layer to the upper layer. a step of stacking and placing a plurality of porous ceramic plates having different porosity in a pre-mold while filling metal powder in order of increasing porosity; heating the interior of the porous ceramic plate to create a preliminary composite of the porous ceramic plate and metal; placing the preliminary composite upside down in the preliminary mold; and a step of injecting molten metal from the injection hole to integrate the molten metal and the preliminary composite.

[Effect]

In the manufacturing method of the present invention, a plurality of porous ceramic plates having different porosities are prepared, and each of these porous ceramic plates is filled with metal powder in order from the porous ceramic plate with the lowest porosity. Stack and place in the mold. Next, the preliminary mold is heated to bring its internal temperature to 80% or more of the melting point of the filled metal powder, thereby creating a preliminary composite of the porous ceramic plate and the metal. Next, after placing the preliminary composite in the main mold upside down from when it was placed in the preliminary mold, molten metal is injected from the injection hole provided at the bottom of the main mold, and the molten metal and A metal-ceramic gradient composite material is manufactured by integrating the preliminary composite body.

In the present invention, by stacking a plurality of porous ceramic plates with different porosities in order of porosity, the volume fraction of the ceramics can be controlled and a stepwise change in the volume fraction in one direction can be realized. . In addition, since we decided to fill the pores of the porous ceramic with metal powder before sintering it, the molten metal can completely penetrate into the pores during the subsequent injection process of the molten metal. It is possible to produce composite materials with gradient layers that are thick and dense.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a schematic diagram showing the steps of the method for manufacturing a metal-ceramic gradient composite material according to the present invention.

First, a plurality of (n) porous ceramic plates made of, for example, AlzOi and having different porosities are prepared.

The thickness of the porous ceramic plate and the porosity of each porous ceramic plate may be set arbitrarily, but since it is used as a material for the graded layer, the plate thickness should be about 3 mm and the porosity should be about 15% to 8.
It is appropriate to vary the amount by at least 10% between 5% and 5%. Since porous ceramic plates having a porosity of 40% to 85% are commercially available, commercially available ones are used. For porous ceramic plates with a porosity of less than 40%, a slurry obtained by adding ceramic particles with a diameter of 0.2 mm to 1 mm, a ceramic powder with a diameter of 1 μm or less, and a small amount of a SiC-based binder and expanded polystyrene is used. It is created by mixing, forming into a plate shape, and then firing.

At this time, a porous ceramic plate having a desired porosity is obtained by adjusting the amount of styrene foam added to the slurry and the amount of ceramic particles added to the slurry.

A porous ceramic plate having the smallest porosity among the prepared porous ceramic plates is placed in the pre-mold 20, and a CO-based heat-resistant alloy (CO-based heat-resistant alloy ( A metal powder 2 having a melting point of 1400° C.) is filled (FIG. 1(a)). At this time, pore 3-1
In order to efficiently fill the inside with metal powder 2, the first
The preliminary mold 20 is vibrated in the direction of the arrow in Figure (a). Next, a porous ceramic plate 1-z having the second lowest porosity among the prepared porous ceramic plates is placed in the preliminary mold 20 in such a manner that it is laminated on the porous ceramic plate 1-3, Pores 3-2 of this porous ceramic plate 1-z
Similarly, the metal powder 2 is filled inside (FIG. 1(b)).

This operation is repeated for the remaining (n-
2) n porous ceramic plates IL whose pores are filled with metal powder 2 by performing the process on the porous ceramic plates
, 11-t+..., 11-, to obtain a laminate. The particle size of the metal powder 2 is appropriately selected depending on the diameter of the pores in the porous ceramic plates 1-I and 1-z, and the particle size is smaller than the diameter of the pores in the porous ceramic plates 1-+ and 1-t. Use metal powder with Next, the preliminary mold 20 is heated to bring its internal temperature to 8, which is the melting point of the metal powder 2.
Maintain at 0%. Then, by sintering the metal powders, the n porous ceramic plates are connected, and a preliminary composite 4 in which the ceramic volume fraction changes stepwise is created (FIG. 1(C)). In this state, the ceramic volume fraction of each layer (each porous ceramic plate) is set to V+ (i
=1.2. ...n), then V,>V2>...>
■It's nice.

It is preferable that the volume of the metal powder filled into the pores of each porous ceramic plate is close to the pore volume, but it is not necessary to completely fill the pores, and it is not necessary to fill up the pores completely;
It is sufficient if it is 0% or less. If this is done, sintering and injection of molten metal will be performed later, so there will be no problem in forming a gradient layer without voids. In the step of filling this metal powder 2, it is better to keep the volume of the metal powder at about 80% to 90% of the pore volume from the viewpoint of preventing the formation of a layer of only metal powder between the porous ceramic plates. , it can be said that it is rather preferable.

Also, the reason why porous ceramic plates are stacked in order of decreasing porosity is that if this order were reversed, the semi-molten metal powder during sintering would be more likely to move to the layer with higher porosity due to the difference in specific gravity. As a result, in a layer with a low porosity, metal powder may not be filled at all over a wide range of pores.

Further, the reason why the sintering temperature is set to 80% or more of the melting point of the metal powder is that when the temperature is below this temperature, sintering of the metal powders or adhesion of the metal powder to the ceramics does not occur.

Next, the prepared preliminary composite 4 is taken out from the preliminary mold 20, turned upside down, and placed into the main mold 21. The lower wall of the main mold 21 is provided with an injection hole 22 for injecting molten metal, and the earthen wall of the main mold 21 is provided with a deaeration hole 23 for discharging air. While maintaining the temperature inside the main mold 21 at 1200°C, molten metal 5 (for example, a Go-based heat-resistant alloy in a molten state), which is the same material as the metal powder 2, is injected into the main mold 21 through the injection hole 22. (Figure 1(d)). While pushing up the preliminary composite 4, the molten metal 5 is infiltrated into the pores remaining in the preliminary composite 4 to form the inclined layer 1.
4 and at the same time the metal layer 1 is 100% metal.
5 is formed on the lower surface of the gradient layer 14 (FIG. 1(e)). At this time, the air in the pores remaining in the preliminary composite 4 is removed from the deaeration hole 2.
3 and is discharged to the outside of the main mold 21. In this way, it is composed of the graded layer 14 and the metal layer 15, and the graded layer I
The ceramic volume fraction in 4 is from the surface to the metal layer 1
A metal-ceramic gradient composite material is manufactured in which the gradient gradually decreases toward the interface with 5.

If the molten metal 5 is injected from the upper part of the main mold 21, the preliminary composite 4 will float in the main mold 21 due to the difference in specific gravity between the ceramic and the metal, and a metal layer 15 will be formed above and below the inclined layer 14. Furthermore, the connected porous ceramic plates may separate due to the heat during casting, and the metal layer 15 may be formed in the gap between them. Therefore, in order to prevent these situations, in the example of the present invention, the molten metal 5 is injected from the lower part of the main mold 21.

By the way, when the molten metal 5 is directly cast into a laminate of porous ceramic plates without using the metal powder 2, the molten metal 5 does not penetrate into the portions where the porosity is small. Therefore, in the present invention, the metal powder 2 is filled in the pores of a porous ceramic plate in advance and then heated to sinter the metal powder 2 and coat the surface of the ceramic with the metal powder 2 in a semi-molten state. When the molten metal 5 is injected, the wetting between the ceramic and the molten metal 5 is improved to facilitate the penetration of the molten metal 5 into the remaining pores. Therefore, according to the present invention, it is possible to produce a dense metal-ceramic gradient composite material with no casting defects and whose pores are completely filled with metal.

Gradient layer manufactured by the manufacturing method of the present invention (layer thickness: 25 m
The properties of m) are shown in Table 1 below. Table 1 also shows the properties of a gradient layer manufactured by a method with a partial modification of the manufacturing method of the present invention as a comparative example of the present invention, and further manufactured using a conventional manufacturing method (the above-mentioned particle arrangement method). The properties of the gradient layer obtained are also shown in Table 1. The diameter of the pores of the ceramic plate used was about 500 μm to 41 μm, and the particle diameter of the metal powder was about 10 to 80 μm.

Table 1 Marked with * Outside the scope of the present invention As can be understood from the results in Table 1, the gradient layer produced by the present invention has superior density compared to that produced by the conventional method. No cracks occur.

In addition, a metal-ceramic gradient composite material produced by the production method of the present invention (total plate thickness: 33 mm, gradient layer thickness: 25 m
, metal layer thickness: 8 mm) was subjected to a thermal stress durability test using an apparatus as shown in FIG. A test piece 30 (metal-ceramic gradient composite material) equipped with a thermocouple 31 is fixed with a fixing jig 32, and high temperature gas is injected from a gas source 33 onto the surface of the test piece 30 on the gradient layer side to 1200°C. After heating the test piece 30 to
As a cycle, repeat this process over and over again.
The occurrence of cracks on the surface of the gradient layer and the presence or absence of peeling of the gradient layer were investigated.

FIG. 3 shows the temporal change in temperature of the test piece 30 in this test. When a similar test was conducted on a ceramic plate (thickness: 12 mm), many cracks were generated on the surface after one cycle. On the other hand, in the case of the metal-ceramic gradient composite material produced by the production method of the present invention, no cracks occurred on the surface and no peeling of the gradient layer was observed even after 100 cycles. There wasn't.

〔Effect of the invention〕

As detailed above, the manufacturing method of the present invention can produce a metal-ceramic gradient composite material that has a thick and dense gradient layer and does not cause cracking or peeling of the gradient layer. Since a simple method is used, stable production of metal-ceramic gradient composite materials is possible.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the process of manufacturing a metal-ceramic gradient composite material according to the present invention, Fig. 2 is a schematic diagram showing the implementation state of a thermal stress durability test, and Fig. 3 is a test in the thermal stress durability test. Graphs showing temporal changes in the temperature of the piece, FIGS. 4 to 6, are graphs for explaining the influence of the thickness of the gradient layer on the generated thermal stress.

Claims (1)

[Claims] 1. In a method for producing a metal-ceramic gradient composite material in which the volume fraction of ceramics contained changes stepwise in one direction, the porosity increases from the bottom layer to the top layer. a step of stacking and placing a plurality of porous ceramic plates with different porosities in a pre-mold while filling the powder; heating the inside of the pre-mold to 80% or more of the melting point of the metal powder; A step of creating a preliminary composite of a porous ceramic plate and a metal, and placing the preliminary composite upside down in the main mold having an injection hole at the bottom, with the preliminary composite placed upside down. A method for manufacturing a metal-ceramic gradient composite material, comprising the steps of: installing a metal-ceramic gradient composite material in the injection hole; and injecting molten metal from the injection hole to integrate the molten metal and the preliminary composite.