JPS5832224B2 - Microcrystalline sintered body for tools and its manufacturing method - Google Patents

Description

Detailed Description of the Invention Currently, when cutting non-ferrous alloys, plastics, and ceramics, a sintered body part in which diamond exceeds a capacity of 70 φ and a metal mainly composed of Co is used as a bonding material is used to cut non-ferrous alloys, plastics, and ceramics. Tool materials joined to are commercially available.

Although this tool material is expensive, it has gained some popularity as a cutting tool for materials such as A1 alloy and copper alloy, which contain a large amount of Si.

The present inventors conducted various investigations into the characteristics of this tool material.

When we created a cutting tool using this tool material and actually cut the materials mentioned above, we found that it was indeed superior to the conventionally used cemented carbide tool in terms of wear resistance. It is far superior in comparison, and it also has the characteristic of being stronger against impact than a tool bit machined from a single natural diamond stone.

However, although it has these characteristics, when observing the workpiece surface when cutting nonferrous alloys, for example, the surface roughness is rougher than that of natural diamond single stone tools, and a beautiful finished surface called a mirror surface cannot be obtained. It turned out that.

Furthermore, when cutting small or thin workpieces such as watch parts, there are problems in that the cutting resistance is large and the workpiece may be deformed and dimensional accuracy cannot be maintained.

As a result of examining the reason for this, the following was found.

Observation of the structure of a commercially available diamond sintered body reveals that the grain size of diamond crystals is 3 to 10 microns, and metal Co is present as a binder between the grains.

If you look at the cutting edge of a cutting tool made of this sintered body, you will see unevenness that is almost the same size as the crystal grains, and the cutting edge is not as sharp as a natural diamond tool.This is one of the reasons why it is difficult to obtain a beautiful finished surface. This is considered to be the reason.

Also, metal C exists between diamond particles. The bonding phase may cause adhesion with the workpiece metal, which is also a problem when a mirror-like finished surface is required.

Commercially available diamond sintered tools for wire drawing dies are sintered diamond crystals with coarse grains of about 30 to 60 microns.

Diamond dies that use a single layer of natural diamond have traditionally been used as wire drawing dies, but compared to dies that use commercially available sintered bodies, they have longer lifespans and are less likely to break, but they are still difficult to cut. As in the case of tools, there are problems such as streaks on the surface of the drawn wire, which are comparable to crystal grains, and it is not suitable for applications that require a beautiful finished surface.

The present inventors conducted research to overcome such drawbacks of conventional diamond sintered tool materials, and as a result, they arrived at the present invention.

That is, by making the crystal grain size of the diamond sintered body extremely fine, 1 μm or less, the above-mentioned drawbacks of the commercially available diamond sintered body can be overcome.

A method of creating a sintered body using diamond powder is, for example, as shown in Japanese Patent Publication No. 39-20483, by mixing diamond powder with iron group metal powder, which is melted under high pressure and high temperature. There is a method of melting this metal under pressure and temperature conditions where the diamond is stable and using it as a bonding material for the diamond.

The manufacturing method of diamond sintered bodies currently on the market is WC-Co as described in Japanese Patent Publication No. 12126/1983.
Diamond powder is placed in contact with the cemented carbide and heated under ultra-high pressure to a temperature above which the Co in the cemented carbide melts.
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A method of infiltration into a layer of diamond powder has been adopted.

In order to eliminate the drawbacks of the conventional commercially available diamond sintered bodies mentioned above, the inventors have prototyped various sintered bodies using these methods in order to obtain dense sintered bodies with extremely fine diamond crystals. I tried that, but I couldn't get a satisfactory result.

For example, using fine particles of about 0.3μ as raw material diamond powder, mixing it with metal Co powder and putting it in a container, die Y
When sintering was carried out at a pressure of 55 Kb and a temperature of 1450'C using an ultra-high pressure device used for Mondo synthesis, a dense sintered body was obtained, but the diamond particles in the sintered body grew to a size of approximately 300 μ. Therefore, the desired sintered body with fine crystals could not be obtained.

In this way, diamond crystals grow by the dissolution precipitation phenomenon when there is a liquid phase of iron group metal that dissolves diamond under high temperature and high pressure conditions at which diamond is stable.

Similar experiments were conducted using various grain sizes of raw diamond crystals, and it was found that no significant grain growth occurred when the grain size was 3 μm or more.

This corresponds to the finest grain size of diamond sintered bodies currently on the market.

The inventors investigated various methods for producing the desired microcrystalline sintered body of 1μ or less, and found that the raw material diamond powder contains Group 4a (Ti, Zr, Hf) and Group 5a (V, Nb) of the periodic table. , Ta), Group 6a (Cr, Mo.

It has been found that when fine powders of carbides, nitrides, and borides (W) are mixed in, diamond grain growth is suppressed even when they coexist with an iron group metal melt.

The reason for this is that the presence of these compound particles between the fine diamond crystal particles acts as an impurity on crystal growth and inhibits the growth, or that these compounds are present at high temperatures. It is thought that grain growth is suppressed by partially dissolving into the iron group metal melt and precipitating as carbides on the diamond crystal surface.

For something to have this effect, it must be present between fine diamond crystal particles, and these compound powders are also ground in advance to a particle size equal to or smaller than that of diamond crystals. It is necessary that it is evenly mixed.

According to the results of the experiment, compounds in the periodic table 4a and 5
The carbides of group a and group 6a metals had the most remarkable effect of suppressing grain growth.

In addition, in terms of the performance of the sintered body as a tool, these compounds remain in the sintered body as diamond crystal materials together with iron group metals, and these compounds themselves have excellent strength and wear resistance. It is necessary to be present.

From this point of view, a sintered body with higher strength and better wear resistance can be obtained by using carbide.

The diamond raw material powder used in the sintered body of the present invention is a micron powder of 1 μm or less, preferably 0.5 μm or less.

Either synthetic diamond or natural diamond may be used.

This diamond powder, one or more of the above compound powders, and iron group metal powders of Fe, Co, and Ni are uniformly mixed using a means such as a ball mill.

This iron group metal may be infiltrated during sintering without being mixed in advance.

In addition, as disclosed in the inventor's earlier patent application No. 52-51381, the pot and balls used in a ball mill are made of a sintered body of a compound such as a carbide and an iron group metal, and the diamond powder is ground at the same time as the ball mill. There is also a method in which a compound such as a carbide and fine powder of a sintered body of an iron group metal are mixed in from a pot and a ball.

The mixed powder was placed in an ultra-high pressure device under the conditions shown in Figure 1 where the diamond was stable; the pressure was 45Kb to 80Kb1.
Sintering is carried out within a temperature range of 1200'C to 2000C.

It is necessary to sinter at a temperature higher than the temperature at which a eutectic liquid phase appears between the iron group metal used at this time and compounds such as carbides.

For example, TiC is used as the compound and Co as the iron group metal.
When using this method, a liquid phase occurs at about 1260° C. under normal pressure.

It is believed that this eutectic temperature increases by several tens of degrees Celsius under high pressure.

Therefore, in this case, sintering is performed at a temperature of 1300'C or higher.

The composition of the diamond sintered body of the present invention has a diamond content in the range of 95 to 30% by volume.

When the diamond content is 95 or more, the amount of intervening compounds is insufficient, and the effect of suppressing diamond grain growth during sintering is diminished.

Furthermore, if the diamond content is less than 30 yen, the wear resistance as a tool is poor, and the intended performance comparable to natural diamond cannot be obtained.

Although the ratio of compounds such as carbides and iron group metals that serve as binding materials for diamond in the sintered body cannot be unambiguously determined, it is necessary that the amount is at least sufficient for the compound to exist as a solid during sintering. For example, when WC is used as a compound and Co is used as a binding metal, the quantitative ratio of WC and Co is 5 by weight.
Must include 0 or more rice cakes.

In general, the effect of suppressing diamond grain growth during sintering is observed when the carbide content in the binder is 20% by weight or more, and when the carbide content in the binder exceeds 95% by weight, sintering Body strength decreases.

Applications of the sintered body of the present invention include wire drawing dies that require particularly beautiful finishing surfaces, cutting tools for cutting A1 alloys and Cu alloys, and the like.

This will be explained in detail below using examples.

Example 1 Synthetic diamond powder with a particle size of 0.5μ, WC and Co powder were ground and mixed using a pot and ball made of WC-Co cemented carbide.

The composition of the prepared mixed powder is as follows.

This mixed powder was packed in eight containers made of Ta and first applied a pressure of 55 Kb using an ultra-high pressure device, then heated to 1450° C. and held for 20 minutes to sinter.

When the sintered body was taken out and the structure was observed/i6. In samples A and B, coarse diamond crystals of about 300 μm were formed, and a sintered body with a uniform structure could not be obtained.

All AC-G items contain diamonds of 1 μ or less and 1
It was a fine crystal sintered body containing WC of μ or less.

The Vickers hardness of the sintered body is as shown in Table 1.

The AC sintered body was cut to create a chip for cutting.

Using this, a cutting test of A1 alloy was conducted.

The work material is an A1 alloy round bar with a diameter of 60 gg+, and the cutting speed is 2.
50m/min, feed 0.02rnm/rotation, depth of cut 0.0
It was cut to 7mm.

When compared under the same cutting conditions as a natural diamond tool, there was almost no difference in the surface condition of the workpiece, and a beautiful mirror-like finished surface was obtained.

Example 2 Using a mixed powder having the composition of AC in Example 1, an inner diameter of 5 mm,
A Ta container with a depth of 5 mm and a wall thickness of 50 μm was filled.

The outer diameter of the WC-10%Co*alloy that has been sintered in advance is 1
It was charged into a ring with a diameter of 5.21 mm, an inner diameter of 5.21 mm, and a height of 5 mm.

This combination was placed in an ultra-high pressure device and sintered under the same conditions as in Example 1.

The obtained sintered body was a composite body in which a diamond sintered body was inscribed in a ring made of WC-10φCo cemented carbide.

A Ta container with a thickness of 50 μm remained at the interface, and a portion of this reacted with diamond or cemented carbide to become TaC.

Due to the existence of this interface, there is no intrusion of the Co liquid phase from the cemented carbide ring during sintering, and the diamond sintered body has a particle size of lμ
It had the following extremely fine structure.

This sintered body was further mounted on a stainless steel ring in the same manner as a normal natural diamond die manufacturing method, and a hole was formed in the diamond sintered body to create a wire drawing die.

When this was used to draw stainless steel wire with a diameter of 1 mm, which conventionally used natural diamond dies, the lifespan was three times longer than that of natural diamond dies, and the surface of the wire to be processed remained in the same condition as before. Ta.

Example 3 A mixed powder having the composition shown in Table 2 was prepared using diamond powder having a particle size of 1 μm or less.

A sintered body was obtained under all the same sintering conditions as in Example 1.

Although diamond was a sintered body with a fine structure of less than 1 μm, the sintered body of AJ and Ni in particular had layered cracks in the sintered body, and compared to other diamonds. The strength was inferior.

[Brief explanation of the drawing]

Figure 1 is for explaining the manufacturing conditions of the sintered body of the present invention, and shows the pressure and stability range of diamond. on the temperature phase diagram

Claims (1)

[Claims] Diamonds with a size of 11μ or less occupy the 95th to 30th rows in terms of capacity, and the remainder is 1μ or less, which are numbers 4a and 5a of the periodic table. 20 to 95% of one or more of carbides, nitrides, borides, and solid solutions or mixture crystals of group 6a metals.
A microcrystalline sintered body for tools, characterized by being made of a binding material of a weight bearing material and an iron group metal. 2. In the sintered body according to claim 1, the binder is composed of carbides of metals of groups 4a, 5a, and 6a of the periodic table and iron group metals, and these carbides have a weight coefficient of 20 in the binder. A microcrystalline sintered body for a tool, characterized in that it has a weight of at least 95 φ or less. A mixed powder of diamond powder of 31μ or less, one or more of carbides, nitrides, borides of group 4a, 5a, and 6a metals of the periodic table, solid solution powders of these, and iron group metal powder of 1μ or less. The diamond is made into a powder form or molded using an ultra-high pressure and high temperature equipment to make it stable.
Pressure 45Kb~80Kb1 Temperature 1200°C~2000
Diamonds with a diameter of 1μ or less account for 95-30% of the volume, with the remainder being 1.
A binder of 20 to 95% by weight of one or more carbides, nitrides, borides, and solid solutions or mixture crystals of metals of groups 4a, 5a, and 6a of the periodic table with a mass of 20 to 95 μm and iron group metals. A method for manufacturing a microcrystalline sintered body for tools comprising: 4. In the method according to claim 3, a carbide powder of metals in groups 4a, 5a, and 6a of the periodic table and an iron group metal are used as the binder-forming powder, and a mixed powder of diamond powder and this binder powder is used. The diamond is stable at high temperatures and pressures of 45Kb to 80Kb. It is characterized by sintering in a temperature range of 1200 to 2000°C while suppressing diamond grain growth, and characterized in that the carbide in the binder is 20 weight φ or more and 95 weight φ in the binder. A method for manufacturing a microcrystalline sintered body for tools.