JPS61291493A - Diamond coated hard material - Google Patents

Abstract

PURPOSE:In coating the surface of a hard material with diamond by precipitating the diamond from a gaseous phase, to raise bond strength the coefficient of linear thermal expansion of the hard material to become the substrate to <=a specific value. CONSTITUTION:Diamond is precipitated from a gaseous phase and the surface of a hard material is coated with the diamond to form a diamond coated hard material. In the operation, the coefficient of linear thermal expansion of the hard material to be a substrate is limited to <=4.0X10<-6>. Thus by limiting the coefficient of linear thermal expansion, since difference of the diamond is reduced, bond strength between them is enlarged. The above-mentioned diamond coated hard material is used as a diamond coated tool for cutting mainly Al, Cu and practically used alloys of these metals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a diamond-coated hard material that is capable of cutting light alloys such as M4i alloy at high speeds.

[Conventional technology]

Diamond has extremely high hardness and is chemically stable, so it hardly reacts with AJ, Cu, or alloys of these metals used in practical applications.When cutting such metals at high speed with diamond, the workpiece material Single crystal or sintered diamond is widely used as a cutting tool material because it produces an extremely well-finished surface.

[Problem that the invention seeks to solve]

In recent years, a technique has been developed for coating diamond on a substrate by decomposing and exciting a mixed gas of hydrogen and hydrocarbon in plasma, that is, by plasma CVD method.

When cutting soft alloys, the hardness difference between the work material and diamond is extremely large, the temperature of the tool tip is low, and there is almost no reaction with the work material, so expensive single crystals, It was thought that instead of a sintered diamond tool, a tool made of cemented carbide and whose surface was coated with diamond would be sufficient for practical use.

According to this idea, when a diamond-coated cemented carbide was actually produced and M-51 alloy was cut at high speed, the diamond coating peeled off at an early stage, and almost no effect was observed.

Therefore, various improvements have been made to increase the adhesive strength between the diamond coating and the cemented carbide substrate.

Various metals (T i + Mo
+ Wl Si, etc.) and various compounds (TiC, T
iN.

Attempts have been made to coat the surface with a base coat (wc, AftO, etc.). However, these attempts were largely ineffective.

[Means to solve the problem]

The inventors have continued research on coated cemented carbide for many years. The biggest factor that influences the adhesive strength between the coating film and the base material is the thermal expansion between the coating film and the base material.If there is a large difference in the coefficient of thermal expansion between the base material and the coating film, the bond The strength decreases, especially when the coating film has a smaller coefficient of thermal expansion.The knowledge that compressive residual thermal stress is applied to the coating film when it is cooled after coating treatment, which particularly reduces the adhesive strength with the base material. I got it.

The thermal expansion coefficient of cemented carbide is 5~6 x 10-”/d
eg, while diamond is 3 x 10-6
/deg, which is extremely small, and it is considered that the adhesive strength between the base material and the coating film is not sufficient.

It is thought that the thermal expansion coefficients of the materials considered for the intermediate layer were all those of a cemented carbide phase or higher, and therefore did not lead to an improvement in adhesive strength. After conducting various studies, the inventor came up with the idea that it would be better to use a hard base material that covers diamond, and the linear expansion coefficient of the base material is closer to that of diamond. is 4.0 x 10-'/deg
We have found that sufficient adhesive strength can be obtained by using the following hard base materials.

An object of the present invention is to provide a diamond-coated tool for cutting mainly AI, Cu, and alloys of these metals that are used in practical use. The cutting conditions are different from those used when cutting regular sea bream, etc., and the temperature at the tool edge is as low as 500 to 600°C, so so-called diffusion wear caused by chemical reactions between the tool and the workpiece material is almost never a problem. For this reason, chipping of the cutting edge due to thermal cracking, which is usually considered a drawback of ceramic tools, is less likely to occur. Therefore, it was thought that Si3N and SiC, which are not suitable for cutting steel due to defects due to diffusion wear or thermal cracking, could be used as hard base materials for diamond coating. The coefficient of linear expansion of these sintered bodies varies depending on the raw materials and manufacturing method, and has a certain range of values, but in the present invention, a sintered body with a coefficient of linear expansion of 4.0×10-”/deg or less is used as the base material. When we actually coated it with diamond, we found that the adhesive strength was significantly improved compared to the conventional one.

Furthermore, when M alloy was cut using the diamond-coated hard material, the effect of improving wear resistance due to the diamond coating was observed.

In the present invention, the linear expansion coefficient of the hard base material is set to 4.0×10−
'/deg or less is limited to a linear expansion coefficient of 4.0X
If it is larger than 10-h/deg, the compressive residual stress applied to the coating film during cooling after coating treatment will increase, the adhesive strength between the base material and the coating film will decrease, and the coating film will easily peel off.
This is because the life of the coated cutting tool, which is the object of the present invention, cannot be extended.

This will be explained in detail in Examples below.

〔Example〕

Si with a linear expansion coefficient of 2.6 x 10-/deg
3N<sintered body and linear expansion coefficient 4.0X10-'/de
We prepared StC sintered bodies with model number 5PG4.
Processed into 22 indexable tips. The surfaces of these chips were roughly polished with a No. 200 resin bond diamond grindstone, and then final polished to a thickness of 20 μm using a No. 800 resin bond diamond grindstone. 2.45G
The surfaces of these hard base materials were coated with diamond to a thickness of 1 μm in a mixed plasma of hydrogen and methane using a Hz microwave plasma CVD apparatus.

At this time, the hard base material was heated to about 950° C. by plasma. Also, Si3N4. The coating film deposited on the surface of the SiC hard base material was confirmed to be diamond by reflection electron beam diffraction.

Samples of 5j3Na+ sic coated with diamond are designated as A and B, respectively, and for comparison, 130 K-10
Cemented carbide (linear expansion coefficient 5.0 x 10-6/deg
), Model No. 5PG422, was subjected to similar polishing treatment and coated with diamond to a thickness of 1 μm using the same equipment, and this was designated as Sample C. In addition, the same base materials of 5iJa, SIC, and cemented carbide without diamond coating were prepared and designated as samples A', B', and C', respectively.

A cutting test was conducted using these samples under the conditions shown in Table 1.

Table 1 As a result, the flank wear width after 10 minutes of cutting is 0.0 for A.
9mmB is 0.1)mm, whereas A', B
'In each case, the flank wear width after 2 minutes of cutting is 0.22 m.
m, 0.281. On the other hand, for C and C', the flank wear width after 30 seconds of cutting is 0.22 mts and 0.2, respectively.
It was Qtsm. When diamond was coated on ffQ Chi, S+Ja, and SiC, a remarkable extension of life was observed, but when diamond was coated on cemented carbide, no effect of the coating layer was observed.

Claims (3)

[Claims] (1) In a diamond-coated hard material in which diamond is precipitated and coated on the surface of a harder material than in the gas phase, the linear expansion coefficient of the hard material serving as the base is 4.0 x 10^-^6d.
A diamond-coated hard material characterized by having a hardness of less than eg^-^1. (2) The diamond-coated hard material according to claim 1, wherein the hard material is Si_3N_4. (3) The diamond-coated hard material according to claim 1, wherein the hard material is SiC.