JPH06287076A - Production of functionally gradient material - Google Patents

Abstract

PURPOSE:To retain excellent characteristics of a material, minimize the residual stress and improve the efficiency, quality and reliability by using a forming outer frame as an electrically conductive passage and regulating the wall thickness thereof. CONSTITUTION:A lower pressing rod (2B) is set in a forming outer frame 2 made of a cermet material such as a metal or graphite and a raw material powder green compact 3 is filled therein. An upper pressing rod (2B) is then pushed into the forming outer frame 2 to press the raw material powder green compact under loads (2A1) and (2B1). When the melting points are (a1)<(a2) [(a1) is the melting of metal; (a2) is the melting point of ceramic], a part where the wall thickness is continuously and/or stepwise reduced from the side of the metal to the side of the ceramic is at least partially provided in the forming outer frame 2. When the melting points are (a1)>(a2), a part where the wall thickness is continuously and/or stepwise reduced from the side of the ceramic to the side of the metal is at least partially provided in the forming outer frame 2, which is used as at least one electrically conductive passage so as to form a temperature gradient in the direction of the pressurizing axis during the electrical conduction. Thereby, a pulsed DC electric current is applied across an upper electrode (2A2) and a lower electrode (2B2) to superpose discharge plasma effects on intergranular discharge effects. As a result, the green compact is sintered at a low temperature in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a functionally graded material composed of a combination of a metal material and a ceramic material. In particular, this type of functionally graded material is manufactured by powder metallurgy to obtain high quality and low cost. To provide a manufacturing method.

[0002]

2. Description of the Related Art A functionally graded material is a new type of function which has, as at least a part of its material, at least a portion in which a portion made of 100% ceramic and a portion made of 100% metal are joined or joined by their mixed graded layers. It is a material.
In addition to structural materials, it is also expected as various functional materials including biomaterials. The ceramic-to-metal graded composition portion of this type of material is 100% metal.
The mixed powder with the ceramic content increased in sequence from step 1 is laminated stepwise or continuously to 100% ceramic, and this is molded into a green compact, which is then sintered under normal pressure.
Sintered and integrated by hot pressing. Also,
The raw powder compact 3 as shown in FIG. 1 is also manufactured by an electric sintering method in which a simple cylindrical molding outer frame and a push rod are used to sinter and integrate electricity while applying pressure.

[0003]

In the conventional sintering method,
A metal 100% portion and a ceramic 100% portion having different melting points and other thermal properties are heated and sintered at the same temperature. Further, the cooling is performed at almost the same speed although there may be a slight difference due to the difference in heat capacity. Therefore, in the case of a combination of a metal and a ceramic material having a large difference in coefficient of thermal expansion, a large heat shrinkage strain is generated in both materials during cooling. In many cases, the brittle ceramic side is likely to be affected, and there has been a problem that cracking occurs, or even if cracking does not occur, strength decreases due to residual stress.

Further, in the conventional sintering method, different materials having different temperatures required for sintering and solidification are simultaneously sintered at one temperature, and even if they are sintered under optimum conditions of ceramics, they are not on the metal side. There was a problem that the sintered body was over-sintered and voids were generated, or the target shape could not be maintained near the melting point. On the contrary, if sintering is performed at the optimum temperature on the metal side with a low melting point,
On the ceramic side, there was a problem that the temperature was too low and sintering failed. The present invention has been made in view of the above circumstances, while maintaining the excellent characteristics of the functionally gradient material made of a combination of metal and ceramic material, while improving the problems in the conventional manufacturing method as described above, It is intended to manufacture a reliable and high-quality functionally graded material at low cost.

[0005]

Means for Solving the Problems The inventors of the present invention have mainly continued research from the following two points in order to solve the above problems. 1. Search for a means and method for reasonably sintering a material with a gradient in composition according to the gradient. 2. Search for a sintering method that enables low temperature and short time sintering to minimize residual stress. As a result, in the electric current sintering method under pressure, the molding outer frame is designed to have a mold configuration having one of its current-carrying paths, and the thickness of the molding outer frame is appropriately adjusted. By controlling the amount of heat generated in the sample, it is possible to obtain a temperature gradient in the direction of the pressing axis of the sample part as required, and to obtain a functionally graded material that does not have excess or deficiency in the sintered state and has very little residual stress. The present invention has been accomplished and the present invention has been completed.

That is, the present invention provides a method for producing a functionally gradient material having a gradient mixed layer composed of both components between a metal and a ceramic by current-flow sintering using a molding outer frame and a push rod. When the melting point is al and the melting point of the ceramic is a2, in a combination of a1 <a2, at least a portion where the thickness of the molding outer frame continuously and / or stepwise decreases from the metal side to the ceramic side is In a combination having a part of the molding outer frame and having a1> a2, at least a portion where the wall thickness of the molding outer frame continuously and / or stepwise decreases from the ceramic side to the metal side is outside the molding side. Provided is a method for manufacturing a functionally graded material, which is provided in a part of a frame and has the molding outer frame as at least one energization path, and forms a temperature gradient in a pressure axis direction of the functionally graded material during energization. Is shall.

[0007] In the usual energization sintering method, referring to FIG. 3, a molded outer frame 2 made of graphite and vertical push rods 2A and 2B are used. Therefore, first, the lower push rod 2B is attached to the molding outer frame 2.
Raw material powder compact 3 to be sintered in the state of setting
Then, the upper push rod 2A is pushed in and pressurized. In this state, a direct current, an alternating current, or a current in which they are superimposed is passed through the vertical push rod, and the electrical resistance of the sample is used to sinter by Joule heat. In the figure, 2A1 is an upper electrode,
2B1 is a lower electrode, 2A2 and 2B2 are hydraulic loads,
2C indicates a power source, respectively.

Although this method can efficiently sinter with respect to the input energy, it cannot be expected to have a great effect on lowering the sintering temperature of the material itself. However, if the direct current applied here is pulsed instead of continuous, even if the total input electric energy is the same, it is possible to instantaneously input a large amount of electric energy by applying it in a pulsed manner. The discharge effect between grains and the effect of discharge plasma accompanying it are superposed. Due to these effects, the surface of the powder particles is remarkably activated, so that sintering at a lower temperature for a short time becomes possible.

If the forming die is designed so that the molding outer frame serves as one energizing path and the wall thickness of the molding outer frame is changed in the pressing axis direction, the thickness of the molding outer frame is changed in accordance with the change in thickness. It has been found that the amount of heat generated there can be controlled and a temperature gradient including irregularities can be provided in the direction of the pressing axis of the sample portion. In the part where the wall thickness of the molding outer frame is thinner than the other parts, the electrical resistance is high, and the amount of heat generated under a constant current is large and the temperature is high. On the other hand, in the thick portion, on the contrary, the resistance is low, the heat generation is small and the low temperature region is formed. By this method, on the side of the material that requires high temperature for sintering, the temperature can be raised by making the thickness of the surrounding molding frame thinner than others, and at the same time, on the other side, the temperature does not become higher than necessary. Can be suppressed to.

Regarding the degree of change in the wall thickness of the molding outer frame for imparting a temperature gradient during sintering, the difference in the melting points of the materials forming the functionally gradient material can be used as one guide, but the molding outer frame Although it has a low pressure, it also has a role as a pressure vessel, and it is necessary that the strength be within the range allowed. By this method, the over-sintering phenomenon and the sintering failure, which are problems in the sintering of the functionally gradient material by the conventional method, can be solved, and the generation of residual stress can be considerably improved. In order to carry out the manufacturing method more effectively, it is preferable that the sintering temperature is as low as possible, and it is desirable to use a low-temperature, short-time sintering method combined with the pulse current method.

[0011]

EXAMPLES The present invention will be specifically described below with reference to examples. 1 and 2 show examples of cross sections of raw material powder compacts 3 and 4 used in the method for producing a functionally graded material of the present invention. The raw powder green compacts 3 and 4 have a structure in which either the metal layer 3A or the ceramic layer 3C is provided at both ends as shown in FIG. 1, and the gradient mixed layer 3B of both components is inserted between them, or As shown in FIG. 2, the first component of the metal layer 4A or the ceramic layer 4C is arranged in the central portion in the thickness direction, and the second component of the other component is disposed on both ends of the first component through the mixed gradient layer 4B of both components.
It is also possible to adopt a configuration in which the components are arranged. The thickness of these both end components and the thickness of the mixed gradient layer can be appropriately selected according to the purpose.

FIG. 4 shows an outline of the pulse current sintering method for explaining one embodiment of the present invention. The raw material powder compact 3 of the functionally gradient material is set in the molding outer frame 1 so that the metal component having a melting point lower than that of the ceramic component and the temperature required for sintering thereof is lower than that of the ceramic component is on the side of the lower push rod 1B. It shows an example of sintering. The lower push rod 1B is set on the molding outer frame 1 which has been subjected to the wall thickness processing according to the structure of the raw material powder compact 3, and then the raw material powder compact 3 is filled. Set the upper push rod 1A on this and set the upper electrode 1A
Load 1A2, 1B by hydraulic pressure through 1 and lower electrode 1B1
The raw material powder compact 3 is pressed by 2.

In this state, a pulse voltage is applied to the raw material powder compact 3 through the upper electrode 1A1 and the lower electrode 1B1 by the pulse power source 1C, and the self-heating of the raw material powder compact and the heat generation of the molding outer frame 1 at the same time are performed. The raw material powder compact 3 is sintered at a low temperature in a short time by the controlled temperature gradient field. The shape of the molding outer frame 1 is an important component of the present invention, but the material is not particularly limited as long as it is a heat resistant and conductive material, and a cermet material such as metal, graphite, or cemented carbide should be used. You can The same applies to the vertical push rod, which can be made of metal, graphite, or cermet material.

5 to 8 show examples of the cross-sectional shapes of the molding outer frame 1 and the raw material powder compact 3 of the functionally gradient material which can be used in the manufacturing method according to the present invention. 5 to 8
Then, the thickness of the molding outer frame 1 is configured so as to increase stepwise as it goes downward. These optimum shapes are appropriately selected according to the final shape as the functionally gradient material.

9 to 12 show examples of the cross-sectional shape of the molding outer frame which can be used in the method of manufacturing a functionally graded material of the present invention. The molding outer frames 11 and 12 shown in FIGS. 9 and 10 are configured such that the wall thickness increases continuously as it goes downward. In the molding outer frame 13 shown in FIG. 11, the wall thickness is thin so that the central portion in the pressing axis direction of the molding outer frame exhibits a trapezoidal depression in cross section. In the molding outer frame 14 shown in FIG. 12, the wall thickness is configured such that the central portion in the pressing axis direction of the molding outer frame exhibits a trapezoidal ridge in cross section.

Therefore, in the sintering of the raw material powder compact 3 of the functionally gradient material having the mixed gradient composition of metal and ceramic having different melting points and different required sintering temperatures as the both end layers, It is advisable to arrange the material having the lower melting point on the thicker side of the molding outer frame and sinter it, and use the molding outer frames 11 and 12 having the cross-sectional shapes as shown in FIGS. 9 and 10.

Further, a metal layer or a ceramic layer having a high melting point and requiring a high temperature for sintering is arranged in the central portion in the thickness direction,
Raw material powder compact of functionally graded material having a mixed gradient layer on both sides, and having a metal layer or a ceramic layer with a low melting point at both ends, which does not require a high temperature as much as the central component for sintering, through the layer In the sintering of the body 4, the component of the central portion is set and sintered so as to come to the central portion of the thinned portion in the molding outer frame 13 shown in FIG. On the contrary, in the sintering of the raw material powder compact 4 of the functionally-graded material in which the central component has a lower melting point and does not require a high temperature for sintering, the cross-sectional shape shown in FIG. 12 is formed. The outer frame 14 can be used, the green compact of the raw material powder is set in the central portion in the height direction, and is sintered by utilizing the temperature gradient.

In the method of manufacturing a functionally graded material according to the present invention, the fitting condition between the molding outer frame 1 and the vertical push rods 1A and 1B is a very important factor in achieving the desired temperature gradient during energization. Is. The clearance between the molding outer frame and the vertical push rod is 2/100 mm or less, preferably 1/100 m, when the gap between the two is not filled with a conductive material.
m or less.

Example 1 Stainless steel powder having an average particle size of 5 μm, Y ₂ O ₃ 3% partially stabilized zirconia having a particle size of 1 μm or less, and those materials were used in a stainless steel / zirconia volume ratio of 3/1, 1/1. , 1/3 was used as the raw material powder of the gradient functional material. The melting point of the stainless powder was about 1440 ° C, and the melting point of the partially stabilized zirconia was 2680 ° C. As the molding outer frame, a molding outer frame 11 made of graphite having a sectional shape of FIG. 9 and a height of 40 mm and a medium hole diameter of φ20 mm was used. The thickness of this molding outer frame was 7 mm from one end to 17 mm and 20 mm from the bottom to 17 mm, and the thickness was continuously reduced from 20 mm to 7 mm between them.

Also, when the thin side of this molding outer frame is up, the position is 17 mm from the top and 23 mm from the top.
A hole having a diameter of 3 mm was opened at a position of 4 mm so that the distance from the inner hole was 4 mm, and the temperature during sintering was measured at two points with a radiation thermometer. The vertical push rod is made of graphite with a length of 20 mm, and the clearance with the inner hole of the molding outer frame is 1/100 mm.
Below. Using these sintered parts, first, the lower push rod was set on the molding outer frame with the larger wall thickness facing down, and then the lower push rod was brought into contact with this to push the stainless powder to a thickness of 3 mm,
On top of that, mix powder with a stainless steel / zirconia ratio of 3/1,
1 mm each in the order of 1/1, 1/3 mm, and zirconia powder on the pressure of 100 mm so that the thickness becomes 3 mm.
It was filled with kg / cm ² .

After setting the upper push rod on this and adjusting the length of the vertical push rod protruding outward so that the sample portion comes to the center in the height direction of the molding outer frame, this sintered sample constitution is It was set in an electric sintering machine and pressurized to a pressure of 500 kg / cm ² .
While pressurizing to this pressure, pulse energization was started to start sintering. Here, the on / off ratio of the DC pulse is 12 /
It was set to 2. Sintering is 1 at the temperature measured on the zirconia powder side.
After the temperature reached 200 ° C., the shrinkage of the sample portion stopped and the test was carried out under the condition of holding for 1 minute.

The total sintering holding time at 1200 ° C. under these conditions was 2.5 minutes. The temperature on the stainless steel powder side during the sintering holding time was 840 ° C to 880 ° C. After cooling, the height of the sintered body taken out from the sintered sample structure was about 5.4 mm. When the cut surface was polished and observed, no cracks or pores were observed, and it could be sintered as a good functionally gradient material. Zirconia 100% of this sample
The microhardness on the side was 1350 kg / mm ² .

(Comparative Example) The molding outer frame has an outer diameter of 50 mm, a hole diameter of 20 mm, and a height of 40 mm having the cross-sectional shape shown in FIG.
The graphite simple cylinder of No. 1 was made of graphite of the same material as the graphite used in Example 1, and the same temperature measurement hole processing as in Example 1 was performed, and the same as in Example 1. A vertical push rod was used. Using these sintered parts, the same raw material powder as in Example 1 was incorporated into a sintered sample structure by the same method and procedure and set in an electric sintering apparatus.

Next, the same as in Example 1 500 kg / cm ²
It was pressurized up to, and pulse energization was started. DC pulse o
The n / off ratio was set to 12/2 as in Example 1. Sintering was carried out under the condition of holding for 1 minute after the temperature reached 1200 ° C. on the zirconia side and the shrinkage stopped. At this time, the total holding time at 1200 ° C. was 2 minutes.

After cooling, when the sintered structure was taken out, a metal ball of several mm was observed at the push rod on the stainless steel side, and it was found that part of the stainless steel melted and exudation occurred. When recovered, the sintered body is zirconia 100
Destroyed at the% layer. Further, generation of many pores was observed in the cross section of the 100% stainless steel layer.

Example 2 A silicon nitride (Si ₃ N ₄ ) sintered body pellet having an outer diameter of 20 mm, a height of 5 mm and a density of 3.15 g / cm ³ , Si ₃ N ₄ powder having an average particle size of 0.3 μm, Iron powder having a particle size of 10 μm or less, and Si ₃ N _{4 of} those powders
/ Iron ratio, 4/1, 2/1, 1/1, 1/2, 1/4 5
The seed mixed powder was used as the raw material powder and the sintered body of the functionally gradient material. The melting point of silicon nitride is 1900 ° C, and the melting point of iron is 153.
It was 0 ° C. The outer frame has a height of 50 mm and a medium hole diameter of 20 m.
m, the thickness from one end to 15 mm is 6.0 mm,
A thickness of 15 mm to 20 mm is 10.0 mm, and a thickness of 20 mm to 50 mm is 20 mm, which consists of three discontinuous steps, and the thickness of 15 mm is 17.5 mm from the top. Position and 3 from the top
A temperature measuring hole having a diameter of 3 mm was machined at a position of 0 mm so that the distance from the center hole of the molding outer frame was 4 mm.

The vertical push rod had a length of 25 mm, and the clearance from the central hole of the molding outer frame was 1/100 mm or less.
When filling the raw material powder, first, the thickness of the molding outer frame is 6.0 mm.
Set with the side up and the bottom push rod on it.
A 100% iron layer was filled to a thickness of 20 mm in contact with this lower push rod, and then a Si ₃ N ₄ / iron ratio of 1/4, 1/2, 1/1,
2/1, 4/4 mixed powder in order of 1mm each, pressure 1
Fill with 00 kg / cm ² .

Further, in contact with this, Si ₃ having a thickness of 5 mm
The N ₄ sintered body was arranged and the upper push rod was set. This sample composition for sintering was set in an electric sintering machine and the pressure was 600 kg /
After pressurizing to cm ² , pulse energization was started in a pressurized state. The pulse on / off ratio here was 20/1.
Sintering was performed at 1350 ° C. at the temperature of the Si ₃ N ₄ side, and after the shrinkage of the sample portion stopped at that temperature, it was held for 1 minute. The total sintering holding time at 1350 ° C. was 1.5 minutes. At this time, the temperature measured on the 100% iron layer side is 810.
The temperature was from ℃ to 830 ℃. No cracks or pores were found in the cross section of the recovered sintered body, and a good functionally graded material was obtained.

Example 3 Alumina powder having an average particle size of 1 μm, NiTi alloy powder having a particle size of 5 μm or less, and three kinds of mixed powders having an alumina / NiTi volume ratio of 1/3, 1/1, 3/1. Was used as the raw material powder of the functionally gradient material.
The melting point of alumina is 2050 ° C, and the melting point of NiTi alloy is 1
It was 380 ° C. For sintering, a molded outer frame 13 made of graphite having a cross-sectional shape shown in FIG.
The thickness is 30 mm from both ends to 15.5 mm,
The center portion 8 mm width in the height direction of the molding outer frame had a thickness of 10 mm, and the space between them was continuously reduced from 30 mm to 10 mm.

For temperature measurement, a hole having a diameter of 3 mm and a depth of 6 mm was opened in the center of the molding outer frame in the height direction. The vertical push rod has a length of 25 mm, and the clearance with the inner hole of the molding outer frame is 1 /
It was set to 100 mm or less. Set a lower push rod on one end of the molding outer frame, and contact it with NiTi alloy powder to a thickness of 4
mm, then 1/3 of the alumina / NiTi alloy mixed powder
The thickness was 1 mm in the order of 1/1 and 3/1, and further 100% of alumina powder was applied to this to obtain a pressure of 1 mm so that the thickness was 5 mm.
It was filled with 50 kg / cm ² .

Further, the alumina / NiTi alloy mixed powder was brought into contact with the alumina layer in the order of 1/3, 1/1 and 3/1 to have a thickness of 1 mm, and the NiTi alloy 100% was brought into contact therewith.
This pressure is also 150 kg / c so that the layer has a thickness of 4 mm.
filled with m ² . Set the upper push rod on this, adjust the length of the part protruding outside the vertical push rod to adjust the position of the raw material powder so that it comes to the center of the molding outer frame in the height direction, and then turn on the power. It was set in a sintering machine and pressurized to a pressure of 500 kg / cm ² . Pulse energization was started in this pressurized state. The on / off ratio of the pulse was 32/2.

Sintering was carried out at 1200 ° C. at the temperature measured on the alumina side of the central portion, and after the shrinkage of the sample stopped, it was held for 1 minute to stop the energization. At this time, the total sintering holding time at 1200 ° C. was about 2.2 minutes. The sintered body recovered after cooling had a thickness of about 10.8 mm, and cracks and pores were not observed on its cross section, and it could be sintered as a good functionally gradient material. At this time, the microhardness of the 100% alumina portion was 1950 kg / mm ² .

The operation and effects will be described.

[0034]

As described above, according to the present invention, in the production of a functionally gradient material made of a combination of a metal and a ceramic material by an electric current sintering method, the wall thickness of the molding outer frame in the pressure axis direction is sintered. By appropriately adjusting the thermal properties of the constituent material of the functionally gradient material to be obtained, the functionally gradient material can be reasonably sintered under a temperature gradient matched to the gradient composition. By this method, a highly functional and highly functional gradient material can be manufactured with high efficiency in a short time.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a raw material powder compact used in the method of manufacturing a functionally gradient material of the present invention.

FIG. 2 is a cross-sectional view of a raw material powder compact used in the method for producing a functionally graded material of the present invention.

FIG. 3 is a schematic vertical cross-sectional view illustrating an electric sintering method using a conventional simple cylindrical molding outer frame.

FIG. 4 is a schematic view illustrating an electric current sintering method of the present invention.

FIG. 5 is a sectional view taken along line AA.

FIG. 6 is a sectional view of another embodiment taken along line AA.

FIG. 7 is a sectional view of another embodiment taken along line AA.

FIG. 8 is a sectional view of another embodiment taken along line AA.

FIG. 9 is a vertical sectional view of another embodiment of the molding outer frame portion.

FIG. 10 is a vertical cross-sectional view of another embodiment of the molding outer frame portion.

FIG. 11 is a vertical cross-sectional view of another embodiment of the molding outer frame portion.

FIG. 12 is a vertical cross-sectional view of another embodiment of the molding outer frame portion.

[Explanation of symbols]

 1 Molding outer frame 1A Upper push rod 1A1 Upper electrode 1A2 Load 1B Lower push rod 1B1 Lower electrode 1B2 Load 1C Pulse power supply 3 Raw powder compact 3A Metal layer 3B Gradient mixing layer 3C Ceramic layer 4 Raw powder compact 4A Metal layer 4B Mixed gradient layer 4C Ceramic layer 11, 12, 13, 14 Molded outer frame

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Matsui 1-4-5 Marunouchi, Chiyoda-ku, Tokyo Sumitomo Coal Mining Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a functionally gradient material having a gradient mixed layer composed of both components between a metal and a ceramic by electric current sintering using a molding outer frame and a push rod, wherein the melting point of the metal is al, When the melting point of the ceramic is a2, in a combination of a1 <a2, at least a portion where the wall thickness of the molding outer frame continuously and / or stepwise decreases from the metal side to the ceramic side is formed in the molding outer frame. In a combination having a part and a1> a2, at least a part of the molding outer frame where the wall thickness of the molding outer frame continuously and / or stepwise decreases from the ceramic side to the metal side And a temperature gradient is formed in the pressure axis direction of the functionally gradient material during energization by using the molding outer frame as at least one current-carrying path.