JPH07156002A - Diamond coated tool and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a diamond coated tool provided with a long life and high performance by forming a carbon diffusion layer with a specific thickness in the vicinity of the surface of a silicon nitride sintered body in which multiple pin holes are formed and forming diamond coating layers inside the pin holes and the sintered body surface. CONSTITUTION:A silicon nitride sintered base body surface is activated, and pin holes are formed by means of acid treatment. Scratching process by means of diamond particles is carried out on the surface of the base body, on which erosion treatment by means of strong acid is carried out on nucleation points formed by scratching process, and multiple nucleation points for diamond are formed inside the pin holes and on the base material surface. Diamond anchor and fine grain coating layer with film thickness of 2mum or less are formed by means of the first step CVD. Then, diamond thick film with the film thickness of 20-200mum and a carbon diffusion layer with thickness of 5mum or more are formed by means of the second step CVD.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond coating tool having high adhesion and long life, which is used for various precision cutting of non-ferrous materials, and a novel manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, a diamond sintered body tool manufactured by an ultra-high pressure method has been used as a long-life tool for precision cutting of non-ferrous materials. However, this sintered diamond tool has drawbacks in that it is difficult to obtain a complicated cutting edge shape and it is difficult to machine the cutting edge, and the manufacturing and processing costs of the tool are high.

On the other hand, diamond coated tools are
Since it has a degree of freedom in the shape of the cutting edge and is relatively easy to finish the cutting edge, it has recently attracted attention as a precision cutting tool for non-ferrous materials replacing the sintered diamond tool.

At present, various types of vapor phase growth (CV) are applied to a substrate having a tool shape mainly made of cemented carbide or silicon nitride.
A tool in which a diamond film is coated by the method D) or a plate-shaped diamond produced by a vapor phase growth method is brazed to a support base has been developed. However, the latter has a problem that brazing and processing of the cutting edge are complicated, and the manufacturing cost becomes high.

Further, in the former case, when the diamond film is thickened, the diamond film peels off from the cutting edge of the tool at the initial stage of cutting because the adhesion between the diamond film and the substrate is poor.
It has fallen off, and it has not been possible to significantly extend the life of the tool by taking advantage of the excellent hardness of the original diamond.

For example, in milling an A1-Si alloy having a silicon content of more than 20%, peeling occurs before wear of the diamond film due to a strong mechanical impact during intermittent cutting. There is a problem that the coating tool cannot be used for a long time.

[0007]

Since the conventional diamond coating tool has poor adhesion between the substrate and the diamond film, many studies have been conducted for the purpose of improving it.
Many patents related to this have been filed.

An example of this is as follows. First, when a cemented carbide is used for the substrate, a Co deficient phase is formed on the surface of the substrate (for example, JP-A-3-177381).
No. 3, JP-A-3-219079), surface treatment of a substrate (for example, JP-A-3-183774) and introduction of a dispersion coating layer (for example, JP-A-3-219078, JP-A-3-219078).
No. 215393), etc., but even if these treatments are performed, the diamond film thickness that can maintain the adhesion is 10 μm.
Since it is less than m and there is a large residual stress generated between the substrate and the diamond film during cutting, sufficient adhesive strength is not obtained.

When silicon nitride is used as the substrate, controlling the coefficient of thermal expansion of the substrate is a method for improving the adhesion of the diamond coating (for example, Japanese Patent Application Laid-Open No. 4-56768), and silicon nitride porosity. Using the body as a substrate (for example, JP-A-1-162770) and inserting an intermediate layer (for example, JP-A-2-267268,
JP-A-3-197677, JP-A-3-291378
No. 5, JP-A-5-148068), two-stage CVD treatment (for example, JP-A-3-69595),
Performing a pretreatment with an acid (for example, Japanese Patent Laid-Open No.
No. 276077) has been proposed.

However, although the adhesion and the tool life are improved to some extent, it is not specified that the diamond-coated tool can be practically used without being peeled off when it is cut under the above hard conditions.

Therefore, an object of the present invention is to improve the adhesion between the substrate and the diamond film to such a level that the adhesion does not become the first factor that determines the tool life.

[0012]

In order to solve the above problems, the present invention has the following constitution. First, the diamond coating tool according to the present invention has a thickness of 5 mm near the surface of a silicon nitride sintered body on which a large number of pinholes are formed.
A carbon diffusion layer having a thickness of at least μm is formed, and a diamond coating layer having a thickness of 20 to 200 μm is formed in the pinhole and on the surface of the sintered body by the CVD method.

Further, in the method for manufacturing a diamond coating tool according to the present invention, the substrate surface of the sintered body having silicon nitride as a mother phase is immersed in a mixed solution containing hydrofluoric acid and another strong acid with a concentration of 20% or more. To form an active uneven surface and to create a large number of pinholes by etching the grain boundaries, and by performing a scratching treatment with a diamond powder having a diameter smaller than the pinholes, the substrate surface and the inside of the pinholes are A large number of diamond nucleation points are generated, and then fine-grained diamond coating with a grain size of 2 μm or less is performed in the first step CVD to form an underlayer consisting of a diamond anchor inside the pinhole and a thin film coating of 2 μm or less on the substrate surface. Then, a diamond film having a film thickness of 20 to 200 μm is further formed thereon by the second stage CVD. It is characterized by simultaneously forming a gradient structure having a thickness of 5μm or more carbon diffusion layer inside the substrate.

The present invention will be described in detail below with reference to specific examples. In the present invention, a diamond-coated tool is manufactured by using a silicon nitride sintered body having a heat shrinkage rate close to that of diamond as a base material, by a treatment method including four steps as shown in the process chart of FIG. Here, a commercially available cutting tool tip can be used in which the sintered body has silicon nitride particles with a particle size of several μm as a mother phase, and other ceramic particles are compounded as necessary and sintered by adding an auxiliary agent. Is.

(1) Activation of the silicon nitride sintered substrate surface and formation of pinholes by acid treatment Hydrofluoric acid (concentration: preferably 20 to 48%, more preferably 40 to 47%) and other strong acid That is, nitric acid (concentration: 20 to 65%, preferably 50 to 60%), sulfuric acid (concentration: 50 to 96%, preferably 80 to 96%),
Hydrochloric acid (concentration: 20-38%, preferably 35-38%)
In a strong acid consisting of a mixed solution containing one or more of the above, active surface irregularities are formed by etching the surface layer of the silicon nitride substrate at a treatment temperature of preferably 20 to 100 ° C. and a treatment time of 15 minutes or more. Form the surface. Further, due to the fact that the grain boundary portion containing the sintering aid is more easily eroded than the silicon nitride itself during the strong acid treatment, selective chemical etching of the grain boundary is preferably performed in the vicinity of the surface of the substrate, preferably with a pore diameter of 2 μm or less and a depth. A large number of pinholes of 0.5 μm or more are newly formed, and in the open pores of the sintered body, the pinholes are formed deep inside the pinhole. The mixing ratio of the strong acid may be one that effectively corrodes silicon nitride. For example, 48% without using other strong acid
The same treatment can be performed by using HF alone at 70 ° C. or higher for 3 hours or longer, but it is not suitable for industrial production, so an appropriate amount of another strong acid (mixing ratio is 90 vol.%) Is used.
It is preferable to add the following).

(2) Formation of Nucleation Points by Scratching Treatment The surface of the substrate that has been subjected to the erosion treatment with the strong acid is subjected to a scratching treatment with diamond particles to give diamond nucleation points inside the pinhole and on the substrate surface. To occur frequently. As this treatment, it is preferable to employ an ultrasonic scratching treatment in which an acid-treated substrate is immersed in a solution in which fine diamond powder is suspended and an ultrasonic wave is applied. In this case, the particle size of the diamond powder needs to be smaller than the inner diameter of the pinhole, and the particle size is preferably 1 μm or less. Further, it is preferable that the scratching treatment time is 15 minutes or more and the ultrasonic wave output is 200 W or more. It is considered that some diamond powder remains on the surface of the substrate and inside the pinholes during the scratching process, but this causes seeding or filling (filling) of the diamond on the surface of the substrate and inside the pinholes. It is rather suitable for nucleation. Instead of using the ultrasonic waves, a method using a jet flow or the like may be used.

(3) Formation of Diamond Anchor and Fine Grain Coating Layer by First Step CVD The diamond anchor is formed inside the pinhole and the diamond coating layer is formed on the surface of the active substrate under the fine grain coating conditions of diamond. The grain size of the diamond nuclei formed is preferably 2 μm or less at the end of the first stage CVD. The diamond deposition method is, for example, microwave plasma CVD or RF plasma CVD.
Method, hot filament method, ECR plasma CVD method, arc plasma method or any other known vapor phase growth diamond film synthesis method may be used. As the source gas, a reaction gas containing hydrogen and a known carbon-containing compound capable of synthesizing diamond can be used. In the microwave plasma CVD method using a CO-H ₂ -based reaction gas, high output (6
50-1100W, preferably 750W), low output (5
˜20 Torr, preferably 15 Torr), low CO concentration (5-15 vol%, preferably 10 vol%), substrate temperature (700-900 ° C., preferably 850 ° C.) C
VD conditions are preferred. At this time, diamond nucleates on the active surface as well, but at the same time, it also nucleates inside the pinhole, and after filling the inside of the pinhole with a diamond anchor, a fine diamond coating layer is formed on the entire surface of the substrate. The thickness of the fine particle coating layer is preferably 1 to 2 μm.

(4) Formation of Thick Film of Diamond and Formation of Carbon Diffusion Layer by Second Step CVD Following the above first step CVD, preferably a deposition rate of 1
A diamond film having a thickness of 20 μm or more is formed continuously or intermittently under a coating condition of μm / h or more. For forming the diamond thick film, for example, microwave plasma CVD, RF plasma CVD method, hot filament method, E
Any known vapor phase growth diamond film synthesis method such as a CR plasma CVD method or an arc plasma method may be used. As the raw material gas, a reaction gas containing hydrogen and a known carbon-containing compound that can synthesize diamond can be used. CO
Microwave plasma CVD using a reaction gas -H ₂ system
In the method, low output (450 to 600 W, preferably 550 W), high output (20 to 40 Torr, preferably 30 Torr), high CO concentration (20 to 45 vol%, preferably 25 vol%), substrate temperature (800 to 900
C., preferably 850.degree. C.) CVD conditions are suitable.
However, in this second-stage CVD, diffusion of carbon into the substrate proceeds, so that the substrate temperature is preferably 800 ° C. or higher and the treatment time is preferably 20 h or longer. The thickness of the coating layer is preferably 20 to 200 μm.

According to the present invention, as shown in the schematic view of FIG. 2, firstly, the base material and the diamond are formed by forming diamond anchors on the active irregular surface and pinholes formed near the surface of the silicon nitride base during the strong acid treatment. The contact area with and increases, and high adhesion is secured by nucleation of fine diamond. Moreover, the second stage CVD promotes the diffusion of carbon into the substrate through the active surface during processing,
A surface layer containing a strong i-C bond is formed, and the adhesion between the diamond and the silicon nitride substrate is further increased.

Therefore, during these treatments, the graded composition and the graded structure are spontaneously formed near the boundary layer between the substrate and the diamond film. Due to the thickening of the diamond layer, the diamond film absorbs impact energy during cutting, no peeling phenomenon is observed even under interrupted cutting conditions, and the tool life depends only on normal wear of diamond, and therefore on the thickness of diamond.

The treatment with the strong acid of the present invention is not only effective for forming a diamond anchor, but also facilitates the formation of a carbon diffusion layer in the second stage CVD by surface activation of the silicon nitride substrate itself. Indispensable, as shown in JP-A-4-276077, when the grain boundary phase is etched in a dilute hydrofluoric acid aqueous solution containing a few percent of hydrogen halide, pinholes are not formed as shown in FIG. It is fine and cannot expect a sufficient anchor effect.

In the etching with the concentrated solution containing hydrofluoric acid and other strong acid according to the present invention, not only the etching of a large amount of the grain boundary phase but also the etching of the silicon nitride itself as shown in FIG. Can be activated.

By this activation, some of the silicon nitride particles on the substrate are dropped off, and irregularities are generated on the surface of the substrate. The first-stage CVD is indispensable for the deposition of fine diamond on the active surface formed by the acid treatment and inside the pinhole, and the second-stage CVD as disclosed in JP-A-3-197677.
This is far superior to the effect of improving the adhesion by the step treatment.

Therefore, by sequentially performing the above-mentioned four steps of the present invention, diamond coating having a film thickness of 20 μm or more and high adhesion can be achieved for the first time, and a long-life diamond coating tool without peeling can be achieved.

[0025]

EXAMPLES Examples of the present invention are shown in Table 1 to more specifically show the effects of the four-step treatment.

[0026]

[Table 1]

A chip for a cutting tool having a commercially available silicon nitride as a mother phase (Toshiba Tungaloy FX-920, tool shape: T
PGN160304) 47% after pre-surface lap treatment
The etching treatment was performed in a strong acid aqueous solution of HF-60% HNO ₃ (mixing ratio is 1: 1 by volume) under the conditions of treatment temperature 40 ° C. and treatment time 60 min.

FIG. 3b shows the surface condition of the substrate after the strong acid treatment of Example 2. The presence of active irregular surfaces and pinholes can be confirmed.

Then, the acid-treated substrate was immersed in 50 ml of ethanol in which 1 g of diamond powder having a particle size of 0 to 1/4 μm was suspended, and the ultrasonic output was 200 W and the treatment time was 30 mi.
The scratching process was performed under the condition of n.

Next, a two-stage CVD process was performed by a microwave plasma CVD apparatus using a CO-H ₂ reaction gas and having a frequency of 2.45 GHz. First, the first stage C
In VD, diamond was deposited under the processing conditions shown in Table 2. In the second stage CVD, diamond was deposited under the processing conditions shown in Table 3.

[0031]

[Table 2]

[0032]

[Table 3]

A milling cutting test was conducted on the produced diamond-coated tool under the conditions shown in Table 4.

[0034]

[Table 4]

FIG. 4 shows the relationship between the flank wear amount V _B and the cutting amount in the milling cutting test of Example 2. No peeling of the diamond film was observed, and normal wear and abrasion of the diamond film were observed at a cutting amount of 216 cm ³ . The amount of V _B wear at this time is 0.15 mm.

FIG. 5 shows a photograph of the worn state of the tip of the blade of the embodiment. In the figure, “a” shows the state after the cutting test of 23 pass in Example 1, and “b” shows the state after the cutting test of 90 pass in Example 2.

FIG. 6 is a microscopic Raman spectrum of the tip portion of the tool of Example 1, in which the formation of diamond can be confirmed.

FIG. 7 is an E of the tool cross section at the tip of the cutting edge of the first embodiment.
The PMA surface analysis result shows that carbon is diffused in the silicon nitride substrate. In addition, some diffusion of silicon into the diamond coating was also observed.

[0039]

[Comparative Example] In order to compare with the above example, Table 1 also shows the method for producing a diamond-coated tool produced by different steps and treatment conditions and the cutting test result as a comparative example.

Comparative Example 1 is the second stage C without acid treatment.
This is the case only for VD, and in the cutting test, peeling of the diamond film occurs immediately after the start of cutting.

Comparative Example 2 is the first stage CVD without acid treatment.
And the second stage CVD is performed, the first stage C
Fine particle coating condition with VD, thick film CV with 2nd stage
It can be seen that the tool life is longer when the D condition is adopted.

Comparative sample 3 was treated with acid at 25 ° C. and 30 mi.
This is the case where the first-stage and second-stage CVD are continued after n, and the tool life is improved by the strong acid treatment.

Comparative sample 4 had an acid treatment temperature of 40 ° C.
The effect is shown when the processing time of the second stage CVD is increased and the film thickness is increased. It is clear that hard strong acid treatment and thick film improve the adhesion and the tool life.

[0044]

As described above, according to the manufacturing method of the present invention which is roughly divided into four steps, the graded structure composed of the diamond anchor by the first step CVD on the oxytreated silicon nitride substrate and the second step CVD are used. As a result of forming a graded composition layer having a strong Si-C bond by a carbon diffusion layer from an active uneven surface, high adhesion can be obtained even if the film thickness is increased, and a diamond coating tool with long life and high performance Can be manufactured. Further, since the diamond coating tool according to the present invention has high adhesion of the diamond coating film to the substrate as described above, it becomes possible to sufficiently withstand high-speed intermittent cutting of, for example, an A1-Si alloy containing a high amount of silicon. For precision machining of hard-to-cut alloys or ceramics such as members, it has become possible to apply to tools with lower cost and durability than sintered diamond tools.

[Brief description of drawings]

FIG. 1 is a schematic process diagram of the present invention.

FIG. 2 is a schematic view showing a method for manufacturing a diamond coating tool.

FIG. 3 is a photograph showing a metallographic structure of a substrate surface after acid treatment, where a is 5
% Aqueous solution at room temperature for 10 min, and b represents 47% HF-60% HNO ₃ aqueous solution (volume ratio 1: 1) at 40 ° C. for 60 min.

FIG. 4 is a graph showing the relationship between the wear amount and the cutting amount.

FIG. 5 is a photograph of a metal structure showing a worn state of a tip of a tool blade.

FIG. 6 is a microscopic Raman spectrum at the tip of a tool blade.

FIG. 7 is a metallographic photograph showing the results of carbon analysis by EPMA of the tool cross section at the tip of the cutting edge.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C30B 29/04 X 8216-4G Q 8216-4G

Claims (3)

[Claims] 1. A carbon diffusion layer having a thickness of 5 μm or more is formed in the vicinity of the surface of a silicon nitride sintered body on which a large number of pinholes are formed, and the thickness of the carbon diffusion layer within the pinhole and the surface of the sintered body is 20 to 20 μm by a CVD method. A diamond coating tool having a diamond coating layer of 200 μm formed. 2. An active uneven surface is formed by immersing a substrate surface of a sintered body containing silicon nitride as a mother phase in a mixed solution containing hydrofluoric acid having a concentration of 20% or more and another strong acid, and
The grain boundaries are etched to form a large number of pinholes, and a scratching treatment with a diamond powder having a diameter smaller than that of the pinholes is performed to generate a large number of diamond nucleation points on the surface of the substrate and inside the pinholes. 1
A fine diamond coating with a grain size of 2 μm or less is applied by stepwise CVD to form a base layer consisting of a diamond anchor inside the pinhole and a thin film coating of 2 μm or less on the surface of the substrate. A method for producing a diamond coating tool, which comprises forming a diamond film having a thickness of 20 to 200 μm and simultaneously forming a graded composition and a graded structure consisting of a carbon diffusion layer having a thickness of 5 μm or more inside a substrate. 3. The strong acid is one or more of nitric acid having a concentration of 20% or more, 50% or more sulfuric acid, and 20% or more hydrochloric acid, and the mixing ratio of the strong acid in the mixed liquid is 90 vol% or less. The method for manufacturing a diamond-coated tool according to claim 2, wherein