JPH0154302B2 - - Google Patents

Description

[Detailed description of the invention]

Diamond is the hardest substance. It is currently used as an abrasive grain for grinding, and sintered bodies made of diamond bonded with metal such as Co are also used in some cutting applications. When this sintered body of diamond bonded with metal is used as a cutting tool, the wear resistance decreases due to the softening of the bonded metal phase at high temperatures, and the tool is damaged because the workpiece metal is easily welded. There are drawbacks. The present invention is not a sintered body bonded with such metals, but a new diamond sintered body suitable for tool applications such as cutting tools that uses a hard metal compound as a binder phase that has high strength, excellent welding resistance, and heat resistance. It is about the body. When viewed as a tool material, diamond has the characteristics of high hardness and extremely high thermal conductivity. Taking a cutting tool as an example, if other conditions are the same, the higher the thermal conductivity of the tool material, the lower the temperature at the cutting edge during cutting, which is advantageous for tool wear. Furthermore, when performing intermittent cutting such as milling, thermal shocks due to heating and rapid cooling are applied to the tool, which causes thermal cracks. Even in this case, if the thermal conductivity of the tool is high, the temperature difference between the tool surface and the inside will be small, making it difficult for cracks to occur. Taking advantage of these excellent characteristics of diamond, the inventors have developed composite sintering of diamond and various heat-resistant compounds with the aim of obtaining a high-strength sintered body required for tools such as cutting tools. Created a body. The properties required of a heat-resistant compound to obtain the desired composite sintered body are first of all high strength;
In addition, in order to maintain the high thermal conductivity characteristic of diamond when it is made into a composite sintered body, the heat-resistant compound itself to be combined is required to have high thermal conductivity. Such heat-resistant compounds include carbides of transition metals from groups 4a, 5a, and 6a of the periodic table;
Possible materials include nitrides, borides, silicides, or mutual solid solution compounds thereof. What these compounds have in common is high hardness and high melting point.
Furthermore, these compounds have metallic physical properties compared to oxides. In particular, the thermal conductivity of these compounds is close to that of metals. Al ₂ O ₃ has excellent properties among oxides in terms of heat resistance and strength, and has relatively high thermal conductivity near room temperature, but as shown in Figure 1, it has excellent thermal conductivity at high temperatures. Thermal conductivity decreases significantly under This is a major drawback in applications such as cutting tools where properties at high temperatures are a problem. On the other hand, many of the compounds described above have rather high thermal conductivity at high temperatures, as shown in FIG. The method for producing a composite sintered body of the heat-resistant compound and diamond selected in this way is to first mix diamond powder and one or more of the heat-resistant compound powders using a means such as a ball mill. The powder is then molded into a predetermined shape in powder form or at room temperature, and sintered at high pressure and high temperature using an ultra-high pressure device. The ultra-high pressure equipment used is a girdle type, belt type, etc. equipment used for diamond synthesis. A graphite cylinder is used as the heating element, and an insulating material such as talc or NaCl is filled inside the cylinder, and a diamond mixture end molded body is included. A pressure medium such as pyroferrite is placed around the graphite heating element. It is desirable that the pressure and temperature conditions for sintering be within the stability region of diamond shown in FIG. 2, but this equilibrium line is not always accurately determined and is only a guideline. Moreover, the conditions can be changed depending on the type of heat-resistant compound with which the diamond is combined. A very noteworthy feature of the sintered body according to the invention, which makes the invention useful, is that the heat-resistant compound forms a continuous phase on the structure of the sintered body. That is, in the sintered body of the present invention, the tough heat-resistant compound penetrates into the gaps between the high-hardness diamond particles and forms a continuous bond, just like the metal Co phase that is the binding phase in WC-Co cemented carbide. It exhibits a phase state, which gives the sintered body toughness. Experiments have revealed that in order to obtain a sintered body with such a structure, the diamond content must be 80% or less by volume. The lower limit of the amount of diamond phase in the sintered body according to the present invention is up to 20% by volume. If it is less than this, the performance as a tool that takes advantage of the characteristics of diamond will not be exhibited. The reason why the bonding phase exhibits a continuous phase is thought to be that TiN, which is relatively easily deformed compared to diamond at high temperatures, penetrates between diamond particles during sintering. Considering the use as a tool, the heat-resistant compounds in the diamond binder phase of the sintered body of the present invention include transition metals belonging to Group 4a of the periodic table, namely, Ti, Zr, and Hf.
carbides, nitrides and their mutual solid solution compounds, or carbides of W in group 6a of the periodic table, WC
is particularly suitable. These are currently used as hard wear-resistant ingredients in WC-based cemented carbides and cermets used in cutting tools, etc., and have excellent wear resistance.
It is a high strength compound. Another reason why carbides, nitrides, and their mutual solid solutions of Ti, Zr, and Hf are excellent as the heat-resistant binder phase compound of the present invention is that, taking nitrides as an example, nitrides of these metals are Denoted in the form MN _1±X ,
(M represents a metal such as Ti, Zr, or Hf, and X means the presence of an atomic vacancy or a relative excess of atoms.)M
- Has a wide range of existence on the N phase diagram. As a result of trial production of sintered bodies using MN _1±X with various X values as raw materials for the sintered bodies, it was found that the sintering properties were particularly excellent within a certain range of X values. The reason for this will be discussed below. When considered as a tool material, especially for cutting tools, it is desirable that the crystal grain size of the sintered body be several microns or less, and in order to obtain such a crystal grain size,
The diamond particle size of the raw material must be finer than this. Micron or sub-micron fine powder contains a fairly large amount of oxygen. In general, most of this oxygen exists on the powder surface in the form of a compound close to the hydroxide form. This hydroxide-like compound decomposes when heated and comes out as a gas. When the material to be sintered is not sealed, it is not difficult to get this gas out of the system. However, when sintering is performed under ultra-high pressure as in the present invention, it is almost impossible for the generated gas to escape outside the heating system. Generally, in such cases, it is common knowledge in the powder metallurgy industry to perform a degassing treatment in advance, but this poses a problem if the degassing temperature cannot be raised sufficiently. This case corresponds to exactly that. That is, when considering the transformation of diamond into a low-pressure phase, there is an upper limit to the heating temperature. The degassing process of fine powder involves the following stages depending on the temperature. First, at low temperatures, physically adsorbed substances and hygroscopic water are removed. Decomposition of chemisorbed substances and hydroxides then occurs. At the end, oxide remains. In the case of diamond, it is stable up to about 1000 degrees Celsius in a vacuum, so it can be heated to at least this temperature in advance. Therefore, it can be considered that almost no residual gas components remain if the gas is degassed and heated in advance. Conversely, since it is desired that gas components remain in the sintered body as little as possible, it is preferable to remove all water and hydrogen as a preliminary treatment. In the present invention, all degassing treatments at temperatures of 1000° C. or higher are performed in vacuum based on this idea. The reason why a good sintered body can be obtained when MN _1±X is added is considered to be as follows. That is, although adsorbed oxygen remains on the surface of the diamond powder, when sufficient degassing treatment is performed, a very small amount of graphite produced by transformation exists on the surface of the powder. When this oxygen reacts with graphite and M corresponding to the (-x) part of MN _1±X , O+M→MO C+M→MC and no gas is generated. And MO and MC
It has the same crystal structure as MN and forms a mutual solid solution. This is thought to be the reason why Ti, Zr, and Hf nitrides represented by MN _1±X exhibit particularly excellent sinterability. This is not limited to nitrides, but also carbides represented by MC _1±X , carbonitrides represented by M(C,N) _1±X , or the above-mentioned compounds containing two or more metals as M. The same can be said about The inventors are in the form of MN _1±X , MC _1±X , M(C,N) _1±X
When showing compounds of Ti, Zr, and Hf, the value of 1±x is
It was confirmed that sinterability is excellent when these compounds with a particle size of 0.97 or less are used as raw materials. Furthermore, when nitrides, carbonitrides, carbides, and especially nitrides of Ti, Zr, and Hf are used as binders, there are advantages in terms of properties as tools. A major feature of diamond is that it rarely adheres to the workpiece. Therefore, if the bonding material also has this feature, it becomes a feature of the entire tool. In this respect, it can be said that diamond sintered bodies using metal as a binder do not possess the great features of diamond. Ti, Zr, Hf
Nitride, carbonitride, and carbide have the advantage of not destroying the characteristics of diamond because they have a low welding reactivity with the workpiece material. especially
TiN is excellent in this respect. In addition, the sintered body according to the present invention contains an element that is used in the synthesis of diamond and is believed to be soluble in graphite and diamond under high temperature and high pressure.
For example, it may contain iron group metals such as Ni, Co, and Fe, Cr, Mn, etc. as additives. It is thought that in many cases, it is synthesized under ultra-high pressure using diamond, which is used as a raw material for the sintered body of the present invention. Therefore, there is a possibility that graphite remains as an impurity in the diamond powder. Furthermore, even when sintering under ultra-high pressure, the diamond particles are not subjected to external pressure hydrostatically until the binder penetrates between the individual diamond particles, and the heating during this time causes the graphite to reversely form. There is also the possibility of metamorphosis. In such a case, it is thought that if an element that has a catalytic effect on graphite is added to the mixed powder, there is an effect of preventing this reverse transformation. A comparison of sintered bodies containing iron group metals and sintered bodies containing no iron group metals by polishing and microstructural observation revealed that the sintered bodies containing iron group metals had more diamond particles on the polished surface. It is thought that the bonding strength between the diamond particles and the binder phase is strong because it is less likely to peel off than the sintered body. Furthermore, when comparing the performance as a cutting tool, it was found that the one containing an iron group metal was superior in both wear resistance and toughness. Note that this effect appeared when the sintered body contained 0.1% or more by weight of iron group metals, Cr, or Mn. The sintered body according to the present invention has high hardness and toughness,
It has excellent heat resistance and wear resistance, and is suitable not only for cutting tools but also for tools such as wire drawing dies, peeling dies, and drill bits. Depending on the application, the product of the present invention is inferior in performance to a diamond sintered body containing 80% or more by volume of diamond with Co as a binder, but it is clearly superior in the following respects. i.e.
(1) When Co is used under high temperatures that soften it, and (2) When welding resistance with workpiece materials becomes a problem, it has much better welding resistance than Co.
This is the case when using TiN etc. (3) When the re-polishing cost is a problem, the product of the present invention is useful because the diamond content is small, so re-polishing is easy, and when the re-polishing cost is a problem in use. Examples will be described below. Example 1 Diamond powder with an average particle size of 7μ and an average particle size of 1μ
and TiN0.92 powder at a volume ratio of 60% and 40%, respectively, and thoroughly mixed in a mortar. 2% camphor was added to this mixed powder, and it was molded into a mold with an outer diameter of 10 mm and a height of 1.5 mm. This was inserted into a stainless steel container. The container was degassed by heating it to 1100° C. for 20 minutes at a vacuum of 10 ⁻⁴ mmHg in a vacuum oven. This was charged into a cardle type ultra-high pressure device. Pyroferrite was used as the pressure medium, and a graphite cylinder was used as the heater. Note that there is a gap between the graphite heater and the sample.
Filled with NaCl. First, the pressure was raised to 55 Kb, then the temperature was raised to 1400°C, held for 30 minutes, and then the temperature was lowered and the pressure was gradually lowered. The obtained sintered body had an outer diameter of about 10 mm and a thickness of about 1 mm. This was ground to a flat surface using a diamond grindstone, and further polished using diamond paste. When the polished surface was observed using an optical microscope, diamond crystals were found.
It exhibited a structure existing in a continuous matrix of TiN. The hardness of the sintered body was measured using a micro-Vickers hardness meter. The average value of hardness was 5300. The sintered body was cut using a diamond cutting blade to create a cutting chip, which was brazed to a steel support. For comparison, cutting tools of the same shape were made using a commercially available diamond sintered body made of diamonds with an average particle size of 3 μ bonded with metal Co, and a JIS classification KO1 cemented carbide. 2% for the work material after heat treatment
Beryllium copper containing beryllium was used.
The hardness of the work material is H _RB 400. Cutting conditions are cutting speed 200m/min, depth of cut 0.2mm, feed 0.12mm/rev.
And so. When a cutting test was conducted under these conditions, the alloy according to the present invention could be cut for 35 minutes before the wear width on the flank surface of the tool edge reached 0.2 mm, but the diamond sintered tool bonded with metal Co was able to cut the same amount in 5 minutes. It reached the width. That is, the tool life of the present invention is seven times longer. In addition, the wear width of the carbide metal tool reached 0.42 mm in 1 minute. Example 2 Diamond powder with an average particle size of 4μ and an average particle size of 1μ
Ti(C _0.5 , N _0.4 ) _0.90 powder 70% and 30% by volume respectively
It was blended in the proportion of A sintered body was then produced in the same manner as in Example 1. The obtained sintered body was ground with a diamond grindstone and brazed to the tip of a cemented carbide cutting tip for milling. 60 using a face milling machine
A casting of high Si-containing Al alloy with a width of 300 mm and a length of 300 mm was machined in the longitudinal direction. Cutting speed is 500m/min, depth of cut
Water-soluble cutting oil was used under the conditions of 0.5 mm and table feed of 2800 mm/min. The sintered body of the present invention could be cut over 1000 passes. In contrast, a commercially available cemented carbide tool equivalent to KO5 used for comparison became unable to cut after 200 passes. Example 3 Diamond powder and heat-resistant compound powder were mixed in the composition shown in Table 1. The diamond powder used had an average particle size of 4μ. An embossed body of mixed powder was created in the same manner as in Example 1, and placed in a container made of Mo.
After performing pretreatment in the same manner as in Example 1, sintering was performed under the conditions shown in Table 1 using an ultra-high pressure device. The heating holding time was 20 minutes in both cases. In both cases, dense sintered bodies were obtained.

[Table] Example 4 Using diamond powder with an average particle size of 7 μm, a mixed powder was prepared in which the balance was 60% by volume and the remainder was as shown in Table 2.

[Table] A mixed powder stamped body placed in a Mo container in the same manner as in Example 1 was sintered under the conditions shown in Table 2. When the sintered bodies were polished with diamond paste and their structures were observed, the structures were found to be dense and diamond crystals were uniformly dispersed. This sintered body was finished into a die with a hole diameter of 1.0 mm using the same processing method as in the case of making a diamond wire drawing die. For comparison, cemented carbide and commercially available metals
A die with the same shape was created using a diamond sintered body bonded with diamond powder using Co. Using this die, a W wire drawing test was conducted. As a result of testing under the condition that the W wire rod supplied to the die was preheated to approximately 800℃, it was found that the die of the present invention
It was possible to draw 2.1 tons of wire, but the cemented carbide die was used at 200 kg, and the sintered diamond die was used at 1 ton, but the dies wore out and reached the end of their service life.

[Brief explanation of drawings]

FIG. 1 explains the characteristics of the sintered body of the present invention, and shows changes in thermal conductivity of various compounds with respect to temperature. FIG. 2 relates to the manufacturing conditions of the sintered body of the present invention and shows the stable existence region on the pressure and temperature phase diagram of diamond.

Claims (1)

[Claims] 1. Containing 80 to 20% diamond by volume, the remainder being carbides of transition metals from groups 4a, 5a, and 6a of the periodic table;
50% by volume of nitrides, borides, silicides or mixtures thereof or mutual solid solution compounds in the binder phase.
% or more and less than 99.9% and Fe, Ni, Co, and Mn, and this compound forms a continuous binder phase in the structure of the sintered body. 2 Compounds forming a continuous bonded phase are listed in the periodic table.
The sintered body for a high-hardness tool according to claim 1, which is mainly composed of carbides, nitrides, and carbonitrides of Ti, Zr, and Hf of group 4a. 3 Compounds forming a continuous bonded phase are listed in the periodic table.
Mainly composed of carbides, nitrides, and carbonitrides of group 4a Ti, Zr, and Hf, with 0.1% by weight of iron group metals, Mn, or their alloys in the sintered body.
A sintered body for a high-hardness tool according to claim 1, characterized in that the sintered body contains the following.