JPH04236779A - High-toughness polycrystalline diamond and production thereof - Google Patents

Abstract

PURPOSE:To obtain the polycrystalline diamond which has high toughness and is suitable as a tool blank material required to have high strength. CONSTITUTION:This high-toughness polycrystalline diamond is the polycrystalline diamond having a multilayer-laminated structure alternately laminated with 1st layers and 2nd layers. The 1st layers are the polycrystalline diamond layers having the crystal shape of hexahedron or octahedron and the 2nd layers are the twin diamond layers or amorphous diamond layers having the grain sizes smaller than the grain sizes of the 1st layers. The surface of the polycrystalline body having the multilayer-laminated structure is coated with the 1st polycrystalline diamond layers having the crystal structure of the hexahedron or octahedron.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dense polycrystalline diamond structure with high toughness suitable for use in fields requiring high strength, such as tools, and a method for producing the same by vapor phase synthesis.

0002

2. Description of the Related Art Diamond sintered bodies produced by sintering fine diamond powder under ultra-high pressure have already been widely used in cutting tools for nonferrous metals, drill bits, wire drawing dies, and the like.

For example, Japanese Patent Publication No. 52-12126 discloses this type of diamond sintered body, in which diamond powder is arranged so as to be in contact with a compact or sintered body of WC-Co cemented carbide. However, a method is used in which sintering is performed at a temperature higher than the temperature at which the liquid phase of cemented carbide occurs and under ultra-high pressure. The diamond sintered body produced by this method contains about 10 to 15% by volume of Co, and has sufficient practical performance as a cutting tool for nonferrous metals.

However, this diamond sintered body has poor heat resistance; for example, when heated to a temperature of 700°C or higher, wear resistance and strength decrease, and furthermore, at a temperature of 900°C or higher, the sintered body is destroyed. I end up. This is thought to be due to the graphitization of diamond occurring at the interface between the diamond particles and Co, which is a binder, and thermal stress due to the difference in thermal expansion coefficients during heating of the two.

[0005] Furthermore, it is known that when a diamond sintered body using Co as a binder is acid-treated to remove most of the bonding metal layer, the heat resistance of the sintered body is improved. For example, JP-A-53-114589 discloses a diamond sintered body with improved heat resistance in this manner. However, since the portion of the bonding metal layer removed by this method becomes a void, there is a problem in that although the heat resistance is improved, the strength is reduced.

On the other hand, tools are known in which a diamond thin film is coated on a substrate using a vapor phase synthesis method. However, diamond films formed by conventional vapor phase synthesis methods are thin and have insufficient adhesion strength to the substrate, so they have not been able to provide sufficient performance as tools for cutting and the like.

[0007]

[Problems to be Solved by the Invention] The present inventors have investigated the above-mentioned problems of conventional diamond tools, and have improved the strength and wear resistance according to Japanese Patent Application No. 63-34033 and Japanese Patent Application No. 63-34034. We also proposed a polycrystalline tool consisting essentially of diamond with improved heat resistance.

However, even this diamond polycrystalline tool has the problem of being prone to breakage when a high pushing force or impact force is applied to the cutting edge, such as in interrupted cutting or cutting of hard ceramics.

[0009] Therefore, in view of the conventional circumstances, it is an object of the present invention to provide a high-strength, high-toughness polycrystalline diamond that can withstand use as a tool, and a method for producing the same.

0010

[Means for Solving the Problem] A high toughness polycrystalline diamond according to claim 1 has a first layer and a second layer stacked on each other.
and a layer of. The first layer is a polycrystalline diamond layer whose crystal grains have either a hexahedral or octahedral shape, and the second layer is a twinned diamond layer whose grain size is smaller than the crystal grains of the polycrystalline diamond. , or an amorphous diamond layer.

[0011] In the highly tough polycrystalline diamond according to the second aspect, the thickness of the first layer is approximately 1 to 2 times the grain size of the crystal grains of the polycrystalline diamond.

[0012] In the high toughness polycrystalline diamond according to claim 3, the grain size of the crystal grains of the first polycrystalline diamond layer is 0.1 μm to 10 μm.

[0013] In the high toughness polycrystalline diamond according to claim 4, the thickness of the second layer is 1/10 to 1/10 of the thickness of the first layer.
/2.

[0014] In the high toughness polycrystalline diamond according to claim 5, the first layer and the second layer are laminated in plural layers, and the layer laminated on the bottom layer and the top layer is the first layer and the second layer. This is a polycrystalline diamond layer constituting one layer.

[0015] In the high toughness polycrystalline diamond according to claim 6, the second layer is composed of a twinned diamond layer having a grain size smaller than the crystal grains of the polycrystalline diamond layer.

[0016] In the high toughness polycrystalline diamond according to claim 7, the grain size of the crystal grains of the twinned diamond layer is 0.05.
It is μm to 8 μm.

[0017] In the high toughness polycrystalline diamond according to claim 8, the thickness of the laminated second layer is 50 μm to 300 μm.
It is.

[0018] In the highly tough polycrystalline diamond according to claim 9, the second layer is composed of an amorphous diamond layer.

In the high toughness polycrystalline diamond according to claim 10, the amorphous diamond layer has a Vickers hardness of 3.
000 to 10000 kg/mm2.

[0020] In the method for producing high-toughness polycrystalline diamond according to claim 11, first, crystal grains thereof are either hexahedral or octahedral on the surface of a base material using a low-pressure gas phase method under first synthesis conditions. A first layer of polycrystalline diamond having the above shape is formed. Next, a second layer of either a twinned polycrystalline diamond layer or an amorphous diamond layer is formed on the surface of the first layer of polycrystalline diamond under a second synthesis condition using a low-pressure vapor phase method. Form.

In the manufacturing method according to the twelfth aspect, the step of forming the first layer and the step of forming the second layer are repeatedly performed.

In the manufacturing method according to the thirteenth aspect, the first synthesis condition and the second synthesis condition are converted within 10 seconds.

In the manufacturing method according to the fourteenth aspect, the temperature of the base material is different between the first synthesis condition and the second synthesis condition.

In the production method according to the fifteenth aspect, the first synthesis condition and the second synthesis condition differ in the concentration of the organic carbon compound in the raw material gas used in the low-pressure gas phase method.

In the manufacturing method according to the sixteenth aspect, the first layer is synthesized so that its thickness is one to two times the crystal grain size.

In the manufacturing method according to claim 17, the first synthesis conditions are selected so that the crystal grain size of the first layer is 0.1 to 10 μm.

[0027] In the manufacturing method according to claim 18, the second layer is formed so that the thickness of the second layer is 1/10 to 1/2 of the thickness of the first layer.

In the manufacturing method according to the nineteenth aspect, the second synthesis conditions are selected such that the grain size of the twinned diamond layer is 0.05 μm to 8 μm.

In the manufacturing method according to claim 20, the amorphous diamond layer has a Vickers hardness of 3000 to 1000.
The second synthesis conditions are selected so that the weight is 0 kg/cm2.

[0030]

Effects of the Invention The present inventors first discovered the
The cross-sectional structures of the polycrystalline bodies disclosed in JP-A No. 2766 and JP-A-1-212767 were observed. As a result, they found that these polycrystalline bodies, which are prone to breakage due to interrupted cutting, have the following common features: ■ They are columnar crystals; ■ As the thickness of the polycrystalline increases, the precipitated particles become coarser. . These characteristics were considered to suggest that the strength of the polycrystalline body decreases in the thickness direction, and that falling off of one particle leads to a large defect. Therefore, it was considered that in order to improve the fracture resistance of a polycrystalline body, it is necessary to make the constituent particles granular and to control the particle size to be small.

Based on these considerations, the present invention first uses a low-pressure gas phase method as a method for synthesizing polycrystalline diamond. All known methods can be used to synthesize this polycrystalline diamond, including a method that uses thermionic radiation or plasma discharge to separate and excite the raw material gas, and a method that uses combustion flame to form a film. It is valid. Further, as the raw material gas, it is common to use a mixed gas containing an organic carbon compound and hydrogen as main components. In addition to these, inert gases such as argon, oxygen, carbon monoxide, water, etc. may also be contained in the raw materials as long as they do not interfere with the synthesis reaction or properties of polycrystalline diamond. .

[0032] Polycrystalline diamond is also synthesized on the surface of the base material. The base material used is preferably one that has as small a difference in thermal expansion coefficient as possible from diamond in order to avoid peeling of the synthetic film due to thermal stress. For example, silicon (Si), molybdenum (Mo), tungsten (
W) etc. are preferred. When using these base materials,
After film formation, the base material can be dissolved and removed by chemical treatment such as immersion in acid, and only the synthetic film can be recovered.

Furthermore, in the method for producing polycrystalline diamond according to the present invention, the synthesis conditions are intermittently varied during synthesis to suppress crystal granulation and grain growth. Specific methods include gas composition,
When the pressure is kept constant, the shape of the precipitated particles can be changed by adjusting the substrate temperature. Furthermore, when the gas composition, pressure, and substrate temperature are kept constant, the morphology can be similarly changed by adjusting the concentration of the organic carbon compound in the raw material gas. Figure 1 shows the three forms deposited by these methods.
Figure 1(a) shows a polycrystalline diamond whose grain shape is euhedral with hexahedrons and/or octahedrons, Figure 1(b) shows a twinned diamond which is finer than that in Figure 1(c). shows a finer amorphous diamond crystal structure.

In the manufacturing process, first, a film is formed for a certain period of time under the first synthesis condition to synthesize the polycrystalline diamond layer shown in FIG. A twinned diamond layer or an amorphous diamond layer (c) is formed. After that, return to the first synthesis conditions again,
A film of polycrystalline diamond (a) is formed. By repeating this process until the required thickness is reached, a multilayered polycrystalline material can be obtained. The time period for which the first synthesis condition is maintained is such that the polycrystalline diamond layer to be synthesized is
It is important that the time required to form a film thickness that is 1 to 2 times the crystal grain size is set, and that the crystal grain size is in the range of 0.1 to 10 μm. Here, the reason why the time for maintaining the first synthesis condition is specified within this range is that if the time is shorter than this range, the film may not be completely formed over the entire surface and may not become granular. . Further, if the heating time is longer than the above range, the diamond layer becomes columnar and tends to have low strength. Furthermore, the reason why the grain size of the crystals is specified is that if the grain size is smaller than 0.1 μm, the wear resistance decreases;
This is because if the size is larger than μm, the strength will be low even if it is granulated.

Next, in the step of forming a twinned diamond layer or an amorphous diamond layer under the second condition, the thickness of the polycrystalline layer is The thickness of the underlying polycrystalline diamond layer is 0.
It is important to set the time required to increase the amount by 1 to 0.5 times. The thickness of this twinned diamond or amorphous diamond layer is 0.1 to 0 of the thickness of the polycrystalline diamond layer.
．． The reason for specifying the range of 5 times is as follows. first,
The lower limit is determined by the minimum time required for twin diamond or amorphous diamond to form over the entire surface of the polycrystalline diamond layer. Additionally, if the film continues to be formed for a longer time than this, the proportion of twinned diamond and amorphous diamond layers, which have lower strength than the underlying polycrystalline diamond layer, in the entire polycrystalline layer will increase. This is because the amount increases and the overall strength decreases.

When the layer formed on the surface of the polycrystalline diamond layer is twinned diamond, the grain size is 0.0.
It is preferable that it is 5-8 micrometers. This has a particle size of 0.
If it is smaller than 0.05 μm, the strength of the polycrystalline body is high, but the wear resistance is reduced. Furthermore, if the particle size is larger than 8 μm, the strength will be low even if it is granulated. In addition,
It is important that the grain size of this twinned diamond is smaller than the grain size of the polycrystalline diamond layers stacked above and below this twinned diamond layer.

[0037] When amorphous diamond is formed as the second layer, the Vickers hardness of the surface is 3.
It is preferable that it is 000-10000 kg/mm2. This is because if the hardness is less than 3000 kg/mm2, both the strength and wear resistance of the amorphous diamond layer decrease, and the performance as a tool material is impaired. Further, in the case of 10000 g/mm2, it shows a general value of the highest hardness identified as amorphous diamond by X-ray diffraction or Raman spectroscopy.

Furthermore, in addition to the above-mentioned conditions, the second layer has a total thickness of 50 to 300 μm, preferably 1 μm.
The film is formed to have a thickness of 00 to 200 μm. Here, the lower limit of this film thickness is determined from the fact that tools are normally used until wear of about 50 μm occurs, and the upper limit is 3
This is determined by the high cost of producing a film thicker than 00 μm.

The time required to change the first synthesis conditions for a polycrystalline diamond layer having an euhedral crystal shape as described above and the second synthesis conditions for forming a twinned or amorphous diamond layer is It is preferable that this is carried out in 10 seconds or less. This is because if the time for changing these conditions is prolonged, the resulting crystal structure changes slowly, making it impossible to obtain desirable granular crystals. The polycrystalline body synthesized under the above conditions has a multilayer laminated structure with fine grains, so it has high strength and is suitable for tool materials and the like.

[0040]

[Examples] Specific examples will be described below. Example 1 Polycrystalline diamond was synthesized and deposited on a Mo substrate under the following fixed conditions for 10 hours by microwave plasma CVD.

Mixed gas (flow rate): H2 200cc/min
CH4 4cc/min Ar 50cc/min Mixed gas pressure: 100 torr
r Microwave oscillation output: 800 W When the cross section of the polycrystalline diamond (A) obtained in the above example was observed using an electron microscope, it was found that the diameter was at most 25 μm.
It exhibited a structure consisting of columnar crystals with a length of about 150 μm. Also, from observation of the top surface of the growth, the grain size was approximately 25
It turned out to be an aggregate of μm octahedral crystals.

Next, using the same base material as above, the gas flow rate,
The two conditions of 800 W and 1200 W were intermittently varied by maintaining the gas pressure at the above conditions and adjusting the microwave oscillation output. The holding time of each output is 800W
for 30 minutes, 1200W for 15 minutes, and the time required for variation was 5 seconds. The polycrystalline diamond (B) obtained by forming a film under these conditions for 10 hours has a thickness of 180 μm.
Met. Observation of its cross section reveals that this polycrystal has a layer of aggregates of octahedral granular crystals with a diameter of about 5 μm and a length of about 8 μm, and an aggregate of twinned diamonds with a diameter of about 4 μm and a length of 4 μm. It was found that the structure consists of alternating layers.

Next, these polycrystalline diamonds (A)
, (B), the substrate was dissolved and removed by acid treatment, brazed to a cemented carbide base metal, and then ground to produce a cutting tip. As a comparative material, a cutting tip was also prepared using ultra-high pressure sintered diamond containing 10% by volume of a conventional binder Co and having an average grain size of 10 μm in the same manner as described above.

In the evaluation test, A390 alloy (Al-1
Using a round bar (7Si), cutting was performed in the longitudinal direction of the outer periphery under the following conditions, and the evaluation results are shown in Table 1.

Cutting speed: 300m/min Depth of cut:
0.2mm Feed: 0.1mm/rev.

[0046]

[Table 1]

[0047] From these results, the polycrystalline diamond (B) according to the present invention has improved strength and is less prone to chipping compared to ordinary columnar polycrystalline diamond (A), and is more durable than conventional ultra-high pressure sintered diamond. It was found to be highly abrasive. Example 2 By thermal CVD method using a linear tungsten filament with a diameter of 0.5 mm and a length of 20 mm as the thermionic emitting material,
Polycrystalline diamond was synthesized and deposited on the substrate for 10 hours under each of the conditions shown in Table 2 below.

[0048]

[Table 2]

In Table 2, for materials C, E, G, and H, attempts were made to alternately stack octahedral crystals and twin crystals by varying each condition. For material F, attempts were made to alternately stack hexahedral crystals and amorphous diamond by varying the concentration of organic carbon compounds. Note that material D was formed under certain conditions for comparison.

The obtained polycrystalline diamonds were all black and translucent, and were found to be diamond carbon from the results of Raman spectroscopic analysis. When these cross-sectional structures were observed using an electron microscope, the change in grain size in the thickness direction was as shown in FIG. 2. Referring to FIG. 2, except for material H, for which it took a long time to change the conditions, materials C, E, F, and G obtained by the method of the present invention all had the effect of suppressing grain growth, especially when they were formed under certain conditions. It has become clear that this is more noticeable than in Material D.

[0051] Cutting chips were prepared from each of these polycrystalline diamonds in the same manner as in Example 1, and the outer circumference of the chips was turned using the same work material to evaluate the cutting performance. The results are shown in Table 3. Ta.

Cutting speed: 400m/min Depth of cut:
0.2mm Feed: 0.1mm/rev. Cutting time: 60min

[0053]

[Table 3]

Example 3 In a reaction tube containing a Si substrate, C2 H6 and H2
The mixed gas was supplied at a flow rate of 200 cc/min, and the pressure was adjusted to 180 torr. Next, from the high frequency oscillator, 9
A high frequency (13.56 MHz) was applied with an output of 00 W to excite the mixed gas and generate plasma.

Thereafter, film formation was carried out for a total of 20 hours while changing the gas composition ratio between two conditions (X) and (Y) every 30 minutes as shown in Table 4. Note that the time required to change the conditions was 5 seconds in each case. Further, at the end of film formation, conditions (X) were set in all cases.

[0056]

[Table 4]

As a result, the obtained polycrystalline diamond had a film thickness of about 0.2 mm, and observation with an electron microscope revealed that it was a fine crystal with an average grain size of about 5 μm on the top surface of the growth. It was also revealed that the cross-sectional structure was layered.

For comparison, C2 H6 in the mixed gas
The concentration was set at 1.2% by volume (constant), and the other conditions were set as above, and film formation was performed for 20 hours. The obtained polycrystalline diamond (O) has an average grain size of 50
It was a columnar crystal with a length of 250 μm.

These materials were brazed to a cemented carbide holder, and the cutting edge was treated to produce a dressing tool. When dressing alumina grinding wheels using these tools, tools for materials I, J, K, L, and N were 3
Although the tools of materials M and O could be used continuously without any damage for 0 minutes, damage occurred 25 minutes and 10 minutes after the start of dressing, respectively.

[0060] Material M has too high a concentration of C2 H6,
The hardness of the precipitated amorphous diamond is 2000 kg/c
It was presumed that the overall strength had decreased because it was as low as m2.

[0061] As described above, the polycrystalline diamond according to the present invention is a polycrystalline body with a dense granular structure consisting of fine grains with suppressed grain growth, and is particularly suitable as a tool material that requires high strength.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the crystal structure of diamond synthesized by a low-pressure gas phase method, in which (a) is a polycrystalline diamond with a hexahedral or octahedral crystal shape, and (b) is a
) is a twinned diamond with a finer crystal structure than (c), and (c) shows an even finer amorphous diamond layer.

FIG. 2 is a correlation diagram between crystal grain size and film thickness of polycrystalline diamond synthesized according to a second embodiment of the present invention.

Claims (20)

[Claims] 1. A polycrystalline diamond layer comprising a first layer and a second layer stacked on each other, the first layer being a polycrystalline diamond layer whose crystal grains have a hexahedral or octahedral shape. and the second layer is composed of either a twinned diamond layer or an amorphous diamond layer having a grain size smaller than the crystal grains of the polycrystalline diamond layer.
High toughness polycrystalline diamond. 2. The high toughness polycrystalline diamond according to claim 1, wherein the thickness of the first layer is approximately 1 to 2 times the grain size of the crystal grains of the polycrystalline diamond layer. 3. The highly tough polycrystalline diamond according to claim 1, wherein the crystal grains of the polycrystalline diamond in the first layer have a particle size of 0.1 μm or more and 10 μm or less. 4. The high toughness polycrystal according to claim 1, wherein the thickness of the second layer is 1/10 or more and 1/2 or less of the thickness of the first layer. diamond. 5. The first layer and the second layer are laminated in plural layers, and the layers laminated on the bottom layer and the top layer are made of polycrystalline diamond constituting the first layer. The high toughness polycrystalline diamond according to any one of claims 1 to 4, which is a layer. 6. The high toughness polycrystalline diamond according to claim 1, wherein the second layer comprises a twinned diamond layer having a grain size smaller than the crystal grains of the polycrystalline diamond layer. . 7. Claim 6, wherein the crystal grains of the twinned diamond layer have a particle size of 0.05 μm or more and 8 μm or less.
High toughness polycrystalline diamond as described. 8. The thickness of the laminated layers is 50 μm or more3
The highly tough polycrystalline diamond according to claim 5, which has a diameter of 00 μm or less. 9. The high toughness polycrystalline diamond according to claim 1, wherein the second layer comprises the amorphous diamond layer. 10. The amorphous diamond layer has a Vickers hardness of 3000 kg/mm2 or more and 10000k.
The highly tough polycrystalline diamond according to claim 9, which has a toughness of less than g/mm2. 11. Forming a first layer of polycrystalline diamond, the crystal grains of which have a hexahedral or octahedral shape, on the surface of a substrate using a low-pressure gas phase method under first synthesis conditions. and forming a second layer of either a twinned diamond layer or an amorphous diamond layer on the surface of the first layer of polycrystalline diamond under second synthesis conditions using a low-pressure vapor phase method. A method for producing high toughness polycrystalline diamond, comprising a process. 12. The method for producing high-toughness polycrystalline diamond according to claim 11, wherein the step of forming the first layer and the step of forming the second layer are performed repeatedly. 13. The method for producing high toughness polycrystalline diamond according to claim 11, wherein the first synthesis condition and the second synthesis condition are converted within 10 seconds. 14. The method for producing high toughness polycrystalline diamond according to claim 11, wherein the first synthesis condition and the second synthesis condition are different in temperature of the base material. 15. The first synthesis condition and the second synthesis condition differ in the concentration of the organic carbon compound in the raw material gas used in the low-pressure gas phase method.
4. The method for producing high toughness polycrystalline diamond according to 4. 16. The high-toughness polycrystalline diamond according to any one of claims 11 to 15, wherein the first layer is synthesized so that its film thickness is 1 to 2 times the crystal grain size. Production method. 17. The high toughness according to claim 11, wherein the first synthesis conditions are selected such that the crystal grain size of the first layer is 0.1 μm or more and 10 μm or less. Method of manufacturing polycrystalline diamond. 18. The second layer is formed to have a thickness that is 1/10 to 1/2 times the thickness of the first layer. A method for producing high-toughness polycrystalline diamond. 19. The grain size of the twinned diamond layer is 0.
．． 19. The method for producing high-toughness polycrystalline diamond according to any one of claims 11 to 18, wherein the second synthesis conditions are selected so that the toughness is 0.05 μm or more and 8 μm or less. 20. The amorphous diamond layer has a Vickers hardness of 3000 kg/cm2 or more and 10000 k.
19. The method for producing high-toughness polycrystalline diamond according to any one of claims 11 to 18, wherein the second synthesis condition is selected to be less than or equal to g/cm2.