JPS6114107B2 - - Google Patents

Description

[Detailed description of the invention]

Currently, for cutting nonferrous alloys, plastics, and ceramics, there are tool materials in which a sintered body with a diamond content of 70% by volume and a metal whose main component is Co as a bonding material is bonded to a cemented carbide base material. It is commercially available. Although this tool material is expensive,
It has gained popularity as a cutting tool for materials such as Al alloys and copper alloys that contain a large amount of Si. The present inventors conducted various investigations into the characteristics of this tool material. When we made a cutting tool using this tool material and actually cut the materials mentioned above, it was found that it was indeed compared to the conventionally used cemented carbide tool in terms of wear resistance. It also has the characteristic of being much stronger against impact than a tool made 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. Observing the structure of a commercially available diamond sintered body, the grain size of the diamond crystals is 3 to 10μ, and the diamond crystals are bonded to each other to form a skeleton structure, and there is metal as a binding material between the particles.
Co exists. If you look at the cutting edge of a cutting tool made from this sintered body, you will see irregularities that are almost the same size as crystal grains, and the cutting edge is not as sharp as a natural diamond tool. This is considered to be one reason why it is difficult to obtain a beautiful finished surface. In addition, the metallic Co binding phase that exists between diamond particles can cause adhesion with the metal workpiece, which also poses 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 approximately 30 to 60 microns. Diamond dies made from a single natural diamond have traditionally been used as wire drawing dies, but compared to commercially available sintered dies, they have longer lifespans and are less likely to break. As in the case of cutting tools, there are problems such as the formation of 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 these drawbacks of conventional diamond sintered tool materials, and found that
We have arrived at the present invention. That is, by making the crystal grain size of the diamond sintered body extremely fine, 1 micron or less, preferably 0.5 micron or less, the above-mentioned drawbacks of the commercially available diamond sintered material 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 for diamond sintered bodies currently on the market is as described in Japanese Patent Publication No. 52-12126, in which diamond powder is placed in contact with WC-Co cemented carbide, and the Co in the cemented carbide is heated under ultra-high pressure.
The method used is to infiltrate this Co into the diamond powder layer by heating it above the temperature at which it melts. 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, about 0.3μ as raw diamond powder
When the fine particles were mixed with metal Co powder and packed in a container and sintered at a pressure of 55 Kb and a temperature of 1450°C in an ultra-high pressure device used for diamond synthesis, a dense sintered body was obtained, but The diamond particles in the compact had grown to a size of approximately 300μ, and the desired sintered compact 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. When the amount of diamond becomes significantly less than 70% by volume, the diamond particles are no longer adjacent to each other.
The inventors' previous application (patent application) showed that diamond sintered bodies with a small amount of diamond exhibit good characteristics for applications such as cutting Cu and Al alloys.
52-51381), its properties are inferior to those of a sintered body with a high diamond content in the case of rock cutting or wire drawing dies.
The present invention relates to a sintered body of fine diamond particles having a particle size of 1 μm or less, preferably 0.5 μm or less and having a composition in which the amount of diamond exceeds 70% by volume and the diamond particles are adjacent to each other. Creating such a sintered body is not easy. The inventors investigated various methods for producing the desired microcrystalline sintered body of 1μ or less, and found that WC or (Mo, W) was added to the raw material diamond powder of 1μ or less.
It was discovered that when fine powder of C is mixed in, the growth of diamond grains is suppressed even when it coexists with an iron group metal melt, and a patent application has been filed (Japanese Patent Application 1983-
22333). Subsequently, as a result of various experiments, we found that even when carbides, nitrides, and borides of Ti, Zr, Hf, V, Nb, Ta, and Cr were added, they were sufficiently effective against coexisting iron group metals. The present invention was achieved by confirming that a large addition amount has the effect of suppressing diamond grain growth. 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, inhibiting the growth, or It is thought that grain growth is suppressed by partially dissolving into the iron group metal melt at high temperatures and precipitating as carbides on the diamond crystal surface. In order to have such an effect, it is necessary that the compound is 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 uniformly mixed with the diamond crystal powder. According to the experimental results, among the compounds, carbides of Ti, Zr, Hf, V, Nb, and Ta had the most remarkable grain growth suppressing effect. In addition, in terms of the performance of the sintered body as a tool, these compounds remain in the sintered body as binding materials for diamond crystals 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 ball mill or other means. 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 pots and balls used in ball milling are made of a sintered body of a compound such as carbide and an iron group metal, and the diamond powder is ground at the same time as the ball milling. There is also a method of mixing a compound such as a carbide with fine powder of a sintered body of an iron group metal through a pot and a ball. The mixed powder is placed in an ultra-high pressure device and sintered under conditions where the diamond shown in FIG. 1 is stable. At this time, it is necessary to sinter at a temperature higher than the temperature at which a eutectic liquid phase appears between the iron group metal and the compound such as carbide used. For example, when TiC is used as the compound and Co is used as the iron group metal, 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. In this case, it is sintered 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 70% by volume. 95%
With the above diamond content, the amount of intervening compound powder is insufficient, and the effect of suppressing diamond grain growth during sintering is diminished. Furthermore, if the diamond content is less than 70%, the diamond particles will no longer be adjacent to each other and grain growth will not occur, leaving the technical scope of the present invention. In addition, it has poor wear resistance as a tool, and cannot achieve the desired performance comparable to natural diamond. 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 TiC is used as a compound and Co is used as a binding metal, the quantitative ratio of TiC and Co must be 7% or more by weight of the former. The sintered body of the present invention is particularly suitable for wire drawing dies, Al alloys, Cu, etc., which require a beautiful finishing surface.
There are cutting tools for which single-crystal diamond tools are currently used, which require a rainbow surface of the alloy. This will be explained in detail below using examples. Example 1 Synthetic diamond powder with a particle size of 0.5 μ and TiC and
Co powder was pulverized and mixed using a pot and ball made of TiC-Co cemented carbide. The composition of the prepared mixed powder is as follows.

[Table] This mixed powder was packed in a container made of Ta and first a pressure of 55kb was applied using an ultra-high pressure device, and then the temperature was increased to 1450°C.
and held for 20 minutes to sinter. When the sintered body was taken out and the structure was observed, No.A and B were found.
In this case, coarse diamond crystals of about 300μ were formed, and a sintered body with a uniform structure could not be obtained. Nos. C to F were all microcrystalline sintered bodies containing diamond of 0.5μ or less and TiC of 1μ or less. The diamonds formed a skeleton structure. The Vickers hardness of the sintered body is shown in Table 1. A chip for cutting was made by cutting the sintered body of No. C. This was used to conduct cutting tests on Al alloys. The work material is an Al alloy round bar with a diameter of 60 mm.
Cutting speed 250m/min, feed 0.02mm/rotation, depth of cut
Cut at 0.07mm. 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 A mixed powder having the composition No. C of Example 1 was used to fill a Ta container with an inner diameter of 5 mm, a depth of 5 mm, and a wall thickness of 50 μm. This was charged into a pre-sintered WC-10% Co alloy ring with an outer diameter of 15 mm, an inner diameter of 5.2 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 is WC
It was a composite body with a diamond sintered body inscribed in a -10% Co cemented carbide ring. The interface is 50μ
A thick Ta container remained, and some of this had reacted with diamond or cemented carbide to form TaC. Due to the existence of this interface, there was no infiltration of the Co liquid phase from the cemented carbide ring during sintering, and the diamond sintered body had an extremely fine structure with a grain size of 0.5μ or less. 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 processed wire remained in the same condition as before. . Example 3 Using diamond powder with a particle size of 1μ or less, Table 2
A mixed powder with the composition was created.

[Table] A sintered body was obtained under all the same sintering conditions as in Example 1. All of the diamonds were sintered bodies in which fine crystals of 0.5μ or less formed a skeleton structure, but the sintered bodies No. J and K in particular had layered cracks in the sintered bodies; Its strength was inferior compared to that of

[Brief explanation of the drawing]

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

Claims (1)

[Claims] 1 Diamond with a diameter of 1μ or less occupies 95 to 70% of the capacity, and the remainder is Ti, Zr, Hf, V, Nb,
A microcrystalline sintered body for tools consisting of a binder of Ta, Cr carbides, nitrides, borides, solid solutions or mixture crystals of these, and iron group metals. 2. In the sintered body described in claim 1, the binder is made of carbides of Ti, Zr, Hf, V, Nb, Ta, and Cr and iron group metals, and the ratio of these carbides to iron group metals is the same. A microcrystalline sintered body for tools, characterized by having a higher carbide content than that corresponding to a eutectic composition. 3 Diamond powder of less than 1μ and diamond powder of less than 1μ
One or two of carbides, nitrides, borides of Ti, Zr, Hf, V, Nb, Ta, Cr, and solid solution powders of these
1μ or less, which is characterized by creating a mixed powder of a diamond or more and an iron group metal powder, molding it into a powder form or molding it by molding, and hot-pressing it under high temperature and high pressure using an ultra-high pressure and high temperature device to make the diamond stable. Carbides, nitrides, borides, solid solutions or mixtures of Ti, Zr, Hf, V, Nb, Ta, Cr, solid solutions or mixture crystals of these, and iron group metals, with diamond accounting for 95 to 70% of the volume, and the remainder being less than 1μ. A method for manufacturing a microcrystalline sintered body for tools made of a binding material. 4 Ti, Zr, Hf, V, Nb, Ta, Cr as the binder forming powder in the method described in claim 3
Using carbide powder and iron group metal, a mixed powder of diamond powder and this binder powder is heated at a high temperature and pressure at which diamond is stable, and at a temperature higher than the eutectic formation temperature of the carbide in the binder and iron group metal. A method for producing a microcrystalline sintered body for tools, characterized by sintering while suppressing grain growth.