JPH0763878B2 - High temperature triaxial compression method for materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for densifying mainly the inner surface quality of various materials by performing high temperature isotropic pressure treatment.

[Conventional technology]

There are many known methods for forming a powder material into a fixed product. The most common method is to form the material by cold pressing and then sinter at a high temperature, but the sintered mechanical parts obtained by such a method usually have a density of 100% or a value close to it. The drawback is that it is often not.

In order to improve the density to 100% or a value close to 100%, it is necessary to give a high compressibility at high temperature by forging, rolling, extruding, etc., or to apply high isotropic pressure at high temperature by HIP (hot isotropic compression). is necessary. For parts with complicated shapes, HIP using argon or nitrogen gas as a pressure medium is suitable, but it has the disadvantage of high cost due to complicated mechanism, use of expensive gas and long cycle time. However, it is currently applied only to high-grade parts.

Liquid pressure HIP (Japanese Patent Laid-Open No. 58-22307), which uses a liquid as a pressure medium, is known as a method that can greatly reduce the cycle time. There is a problem with the sealing property against the high temperature liquid between the cylinder parts, and it seems that much improvement efforts are required for practical use.

In order to eliminate these drawbacks of HIP, a series of technologies collectively called pseudo-HIP was developed (The International Jour.
nal of Powder Metallurgy and Powder Technology JUL
It is explained in detail in Y1985).

Typical examples thereof include a Ceracon method using ceramic particles as a pressure medium, an ROC method using a pressure medium such as a metal having fluidity at high temperature and ceramic particles.

The Ceracon method is one in which ceramic particles and materials heated to a required temperature are charged into a pressing container and then pressed, and has the advantage that the operation is simple and the cycle time is extremely short compared to HIP. However, the pressure distribution is made uniform and HI
It is difficult to achieve an isotropic pressure equivalent to P.

Further, in the ROC method, the material is cooled as it is together with the pressure medium, so that the work of removing the medium later is complicated and the cost becomes high.

[Problems to be solved by the invention]

The present invention is intended to develop a new process that has a short cycle time, does not require a troublesome sealing mechanism, and can exert a pressure extremely close to isotropic pressure on a material.

[Means and actions for solving problems]

The present invention, when the material is subjected to high temperature isotropic pressure treatment, the material to be compressed is covered with a granular substance that is solid at the processing temperature, and these are encapsulated to produce a structure, and the structure is formed into a desired structure. After being heated to a temperature, a compressive force is mechanically applied from the periphery of the structure to exert an isotropic pressure on the material to be compressed inside the structure.

Pressure media capable of exerting isotropic pressure on a material having a complicated shape include gas, liquid and solid. There are several methods of using a solid as a pressure medium, but the simplest method may be a seracon method in which a solid granular material is placed in a press container and uniaxially compressed by the press. However, it is quite difficult to achieve isotropic pressure by this method.

This is because the compression pressure in directions other than the pressing direction is smaller than the compression pressure in the pressing direction. In order to make the difference between the compressive pressure in the pressing direction and the compressive pressure in the direction perpendicular thereto zero, it is necessary to reduce the friction between the particles so that they behave like a liquid.

For this reason, it is effective to mix a heat-resistant lubricating substance such as graphite or mica with the granular substance, but there is a limit to this as well, and it is quite difficult to reduce the compression pressure difference to zero.

Therefore, as a result of various studies on a method of exerting isotropic pressure on a material using a granular material, the following conclusion was reached.

First, the material to be compressed, which is to be subjected to high temperature isotropic pressure treatment, is a solid granular substance or a mixture of the same granular substance and a solid lubricating substance at a high processing temperature, and it is housed in a capsule so that it can be enclosed. The capsule structure is produced by evacuating or without evacuating and sealing this capsule by means such as welding.

FIG. 1 shows the basic concept of the present invention. FIG. 1 shows a capsule structure, and in this case, the appearance has a cubic shape. After heating the capsule structure to a required temperature, compressive forces of Px, Py, and Pz are applied to the structure 1 from three directions orthogonal to each other as shown in FIG. At this time
When Px = Py = Pz is set, an isotropic pressure region is formed inside the structure 1.

FIG. 2 shows an XY cross section perpendicular to the Z axis of FIG. 1, and the portion surrounded by a dotted line a inside the structure shows an isotropic pressure region.

Reference numeral 2 is a material to be compressed, 3 is a granular substance, 4 is a capsule, and 5 is a punch, but its cross section is smaller than one surface of the capsule structure.

Because there are generally voids between the granular materials within the capsule structure, the volume of the capsule structure decreases when subjected to a compressive force. Therefore, it is necessary to prevent the punches from contacting each other.

Therefore, at the initial stage of compression, there is a portion where the punch and the surface of the capsule structure do not come into contact with each other, as shown by the portion 6 in FIG. The area of the isotropic pressure shown by the dotted line a inside the capsule structure becomes wide because this portion 6 has a small area.

As described above, 3 is applied to the heated capsule structure.
By applying the same amount of compressive force with six punches from the direction, high temperature isotropic pressure processing of the material becomes possible.

In order to improve the density to 100% or a value close to 100% by sintering the ceramic metal material by the above-mentioned method, it is usually performed at a temperature of about 7700 ° C to 2500 ° C.
0kg / cm ² ~1000kg / cm ² about to add a higher Ho圧desirable, this can be easily accomplished according to the method of the present invention.

That is, the press pressure is within the range of ordinary high-pressure technology, and the temperature is such that if the amount of the particulate matter in the capsule structure is sufficiently large, heat removal from the punch surface, which is not normally high, will occur. Before it even reaches the materials inside
The high temperature and high pressure processing is completed.

It should be noted that if the values of temperature and pressure are set sufficiently large, the above-mentioned high temperature isotropic pressure treatment is completed on the order of minutes.

As the pressure medium, ceramic particles such as Al ₂ O ₃ and BN, refractory metal particles, and intermetallic compounds such as Ni ₃ Al and AlTi may be used.

As the encapsulation material, a thin plate of an iron-based material is usually processed and used, but other metals such as Al, Cu, and superalloys may be used.

Although the basic concept of the present invention is as described above, since a press machine using six punches is uneconomical, a method for reducing the number of punches will be described below.

FIG. 3 shows that the three faces of the capsule structure 1 are brought into close contact with the three faces of the block structure 7, and the compression forces Px, Py, and Pz are applied to the three faces that are not in close contact with each other by a punch. It shows the method to reach. With this method, the number of punches can be reduced to three.

FIG. 4 shows an example of a press device that can generate a triaxial indentation stress in the capsule structure with only one punch that moves in one direction by devising a compression tool.

That is, when the upper punch 8 is lowered, the central portion 8-1 of the punch head is displaced by Uy. Four punch head portions 8-2 having an inclined surface with an angle θ are attached to the punch head so as to surround the portion 8-1.

This punch head 8-2 portion is provided with four blocks 10 provided with slant surfaces 10-2 which are placed so as to slide on the portion of the kerf 13 formed on the press machine bottom plate portion 11, One part is in sliding contact with the slope of the block.

The angle of this slope is φ as shown in FIG. Although there is a slope in the kerf in the figure, this slope is an adjustment slope for making the relative displacement between the capsule structure 1 and the block 10 zero.

That is, when the upper punch 8 is displaced downward by Uy, the lower punch 9 is fixed to the bottom plate portion 11, so that the center of the capsule structure is lowered by 1/2 Uy. So block 10 is also 1
It is necessary to make a rigid displacement downwards by / 2Uy.

When the displacement of the block 10 in the X direction is Ux and the displacement in the Y direction is Uy ', the following relational expression is derived.

Ux / (Ux−Uy ′) ＝ tanθ …… (1) Uy ′ / Ux ＝ tanφ …… (2) In order to equalize the triaxial pressure of the capsule structure 1, the triaxial strains should be equal. Must. To do so, the displacement of the lower punch 9 is zero, so Ux / Uy = 1/2 (3). .

Further, as described above, Uy ′ / Uy = 1/2 (4) from the condition that there is no difference in rigidity displacement between the structure 1 and the block 10, and therefore tan θ = from equations (1) to (4). 1.0 tan φ = 1.0, that is, θ = 45 ° φ = 45 °.

If the above geometrical conditions are satisfied, a uniaxial press machine capable of exerting isotropic pressure and the capsule structure can be manufactured.

Also in this case, there is a portion of the capsule structure to which the compressive force is not exerted, such as the portion 14 shown in FIG. 5 which is a sectional view taken along the line AA of FIG.

In order to reduce this portion, it is desirable to eliminate voids in the granular material portion of the capsule structure so that the volume compression amount of the capsule structure is eliminated.

Although the upper punch 8 is lowered in the above description, the upper punch 8 and the cylinder portion 12 are fixed and left stationary,
The same effect can be obtained by raising the lower punch 9, the bottom plate portion 11 and the block 10 integrally. However, in this case, relative displacement of the kerf sliding portion of the block 10 and the bottom plate portion 11 is allowed.

Further, in order to reduce the compressive force of the punch, it is possible to fix the two adjacent blocks 10 of FIG. 5 to the bottom plate 11. In this case, the two upper punch head portions 8-2 contacting the two fixed blocks are unnecessary.

In this case, (3) of (1) to (4) changes and Ux / Uy = 1 (3) '.

Therefore, from (1), (2), (3) ', and (4), tan θ = 2 tan φ = 0.5, that is, θ = 63.4 ° φ = 26.6 °.

However, in this case, the rigid displacement difference in the X and Z directions between the punch head 8-1 and the capsule structure 1 cannot be completely reduced to zero, but the compression is performed under a condition close to isotropic pressure. Is possible.

If there is a surface on the surface of the capsule structure that does not come into contact with the compression tool surface, such as the portion 6 in Fig. 2 or the portion 14 in Fig. 5, this portion of the capsule will be broken and the particulate matter will be ejected. There is.

However, even if some particulate matter is jetted out, if compression progresses soon, the portion 6 in FIG. 2 and the portion 14 in FIG. 5 become smaller, and the particulate matter will not jet out.

That is, the tool should be designed so that the pressure becomes highest in the latter half of the compression and that these portions become exactly zero. Also, by rounding the corners corresponding to these parts of the capsule structure, the volume expected in the latter stage of compression of the capsule structure is made equal to the cubic space volume enclosed by the compression tool surface in the latter stage of compression. The method of keeping is also effective.

When the material to be compressed to be subjected to high-temperature isotropic pressure treatment is a molded part having an axisymmetric shape, the capsule has a cylindrical shape,
Compression molding may be carried out by arranging a large number of blocks 10 shown in FIGS. 4 and 5 around the pressing shaft of the punch and by making the number of punch portions 8-2 the same as that of the block 10. . In this case, the axis of symmetry of the molded part is made to coincide with the axis of pushing by the punch.

Next, a method of compressing the capsule structure by compressing the volume of the sealed space in the sealed state will be described.

FIG. 6 shows an example thereof.

This is known as a triaxial compression test method for powder materials, etc.
This device is designed to reduce the volume of the enclosed space.
(For example, "Plasticity and processing" 1986-10, vol27, No.309, P11
26 etc.).

FIG. 7 is a sectional view taken along the line AA shown in FIG.

No capsules are of course used when testing powders with this tester.

Hereinafter, a method of triaxially compressing the capsule structure 1 using this device will be described.

The numbers in the figure indicate blocks. The arrow shown with a number is the direction in which the block corresponding to that number moves. The blocks corresponding to the numbers without arrows do not move.

The capsule structure 1 includes six blocks 15, 15 ',
It is surrounded by 16, 16 ', 17, 17'. The block 15 is lowered by a punch (not shown), but at this time, the block 15 pushes down the capsule structure 1 and the blocks 16 and 17.

The back surfaces of the blocks 16 and 17 are inclined, and the capsule structure 1 is compressed in the X direction and the Y direction by sliding on the inclined surfaces of the blocks 18 and 19 having inclined surfaces of the same angle.

At this time, the block 16 is pushed by the block 17 and moves also in the Y direction. The block 17 'is pushed by the block 16 and moves in the X direction. The block 15 'is pushed by the blocks 16 and 17 and moves in the X and Y directions.

If φ = 45 ° here, the capsule structure 1 is compressed by the same amount in the three axial directions, so that the intended purpose is achieved.

However, at this time, since the surface area of the capsule structure is reduced, wrinkles are formed on the surface of the capsule. However, if the amount of the solid particulate matter in the capsule structure is sufficiently large, it becomes possible to prevent the influence of the uneven deformation of the surface from reaching the material to be treated inside.

Also in this case, by rounding the corners including the sides of the capsule structure 1, the amount of wrinkles generated due to the decrease of the capsule surface when the volume compression rate of the capsule structure 1 at the initial stage of compression is large. , Can be kept small.

In addition, it is desirable to apply a liquid or solid lubricant to the part where the block contacts the capsule structure and the part where the blocks slide.

However, in this method, a large number of blocks move relative to each other, so it may be difficult for the compressive force from the punch to be sufficiently transmitted to all blocks due to running out of lubricant, etc., and extra energy for compression is consumed. The need arises.

In order to prevent this, an auxiliary cylinder for smoothing the movement of the blocks is provided, and the blocks such as 15 ′ and 17 ′ are moved in the directions of the dotted arrows shown in FIGS. 6 and 7. Is also a preferred method.

Further, a method of arranging a spring or the like between the blocks which are related to each other so as to mutually assist the relative motions of the blocks is also effective.

For example, in the spring shown by the dotted concentric circles b in FIG. 7, the downward movement of the block 16 assists the lateral movement of the block 15 '.

〔Example〕

SUS304 stainless steel powder with a particle size of -100 mesh was compressed to a density of 90% with a cold press. The size of this compression molded product is 10
It is mmφ x 10 mm high.

This is made of mild steel plate with a wall thickness of 1 mm, and enclosed in a cubic capsule of 40 mm on a side with a mixture of alumina powder with an average particle size of 100M and mica powder with an average particle size of 10% at 2% by volume. did.

This was soaked in a heating furnace at 1100 ° C. for 10 minutes and then pressed by a compressor of the same type as that shown in FIG.

The pressure for lowering the block 15 was 100 tons, and the holding time was 5 minutes. The density of the obtained stainless steel cylindrical block is about 10
It was 0%. This is usually of the same quality as HIP processed for several hours.

〔The invention's effect〕

As described above, it was proved that a molded product having the same quality as that obtained by the conventional HIP can be obtained on the order of 10 minutes per cycle.

By the method of the present invention, a high-density molded product using a powder material or the like can be easily manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory view of the basic concept of the present invention, FIG. 2 is an XY sectional view perpendicular to the Z axis of FIG. 1, and FIG. 3 is an explanatory view of a method of compressing a capsule structure using three punches. , FIG. 4 is an explanatory view of an apparatus that enables three-direction compression with one punch, and FIG.
FIG. 6 is a cross-sectional view taken along the line AA of FIG. 4, and FIG. 6 is an explanatory view of a method of compressing a capsule structure with a closed cubic space.
FIG. 7 is a sectional view taken along line AA of FIG. 1: Structure, 2: Compressed material 3: Granular substance, 4: Capsule 5: Punch

Claims (1)

[Claims] 1. When a material is subjected to a high temperature isotropic pressure treatment, a material to be compressed is covered with a granular substance which is a solid at a processing temperature and encapsulated to prepare a structure, and the structure is heated to a desired temperature. A high-temperature triaxial compression method for a material, characterized in that an isotropic pressure is exerted on the material to be compressed inside the structure by mechanically applying a compressive force from the periphery of the structure after being heated to the inside.