JPH01259171A - Cutting tool member coated with hard film - Google Patents

Abstract

PURPOSE:To improve melt bonding and exfoliation resistances by coating a diamond film as an inner layer with an amorphous hard carbon film having no idiomorphic face as an outer layer. CONSTITUTION:The surface of the substrate of a cutting tool is coated with a high hardness polycrystalline diamond or diamondlike carbon film having the idiomorphic face as the inner layer and this inner layer is coated with the amorphous hard carbon film having no idiomorphic face as the outer layer. The surface of the resulting coating film can be made smooth, so the frictional resistance to a material to be cut is reduced, the film exfoliates hardly and the material to be cut melt-bonds hardly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a hard coating-coated cutting tool member that exhibits high wear resistance and adhesion resistance in cutting nonferrous metals, ceramics, and composite materials.

(Prior art) Conventionally, high-speed tool steel, tungsten carbide-based cemented carbide, cermets, or ceramics have been generally used for cutting tool bases, and in recent years, they have been made to have higher wear resistance. For this reason, the example is the
24914 or Japanese Patent Publication No. 62-56231, cutting tool members whose surfaces are coated with a hard layer consisting of a single layer or multiple layers of titanium nitride, carbide, carbonitride, and aluminum oxide are also used. There is.

However, these tool members are made of, for example, Al-5i alloy,
When a material containing a hard substance such as FRI' is cut at high speed, the tool life is short due to lack of wear resistance, and cutting tools with higher wear resistance have been required.

On the other hand, cutting tools made of single crystal diamond or sintered diamond have the highest hardness and hardness among existing materials, so they have extremely high wear resistance even when cutting the above-mentioned work materials. It is known for its □ characteristics, and there is little welding of the work material. However, these diamond cutting tools are expensive and difficult to machine into complex shapes.

In recent years, diamond vapor phase synthesis technology has progressed, and diamond or diamond-like hard carbon films (hereinafter collectively referred to as diamond films) are synthesized using thermal filament methods, DC discharge CVD methods, microwave discharge methods, or high-frequency discharge methods. As a result, attempts are being made to apply it to cutting tools. However, diamond film has poor adhesion to the base material compared to conventional hard ceramic coatings, so if strong stress is applied to the film during cutting, the film may peel off from the base material. was there.

(Problems to be Solved by the Present Invention) It is said that diamond films have lower adhesion to tool base materials and are more likely to peel off than conventional ceramic films.

This is because it is difficult for diamond to form an interdiffusion layer with the base material for tools, and because the coefficient of thermal expansion is significantly different from that of the base material, the temperature of the base material during diamond synthesis is 700°C to 1200°C.
This is thought to be due to the fact that large compressive stress remains in the diamond film when it is cooled from to room temperature.

The present inventors conducted cutting tests on Al-5i alloy under various conditions using diamond-coated cutting tools and investigated the peeling of the diamond film. It was found that the diamond film tends to peel off under conditions where cutting materials tend to adhere to the cutting tool edge. Next, when the diamond film on the cutting tool used in this test was observed using an optical microscope, it was found that the diamond film was composed of polycrystals with euhedral surfaces and had a highly undulating surface structure.

When observing the growth process of a diamond film, diamond grains grow over time after nucleation, and eventually come into contact with nearby diamond grains to form a film. After forming a film, selective growth of diamond grains occurs, and the average grain size of the diamond grains observed from the film surface increases and the surface roughness increases, but during this process, new diamond grains grow. nucleation occurs, and a rapid increase in surface roughness is suppressed. However, when synthesizing a film made of highly hard diamond with euhedral surfaces, it is unavoidable that the surface of the film becomes rough to some extent.

The present inventors found that because the diamond □ film has severe undulations on its surface, the frictional resistance against the flow of the work material becomes large, making it easy for the film to peel off and also promoting welding of the work material. It was determined that Therefore, in order to reduce the unevenness of the film surface, a cutting tool substrate was coated with diamond, and then the substrate surface was polished to a mirror surface by lapping with fine diamond powder, and a cutting test was conducted. As a result, it was found that the welding of the work material to the cutting tool edge was comparable to that of sintered diamond, and the life of the cutting tool was significantly extended. However, the method of further mirror-polishing the surface of the cutting tool coated with a diamond film has the disadvantages that there is a high risk of the diamond film peeling off during polishing, and this method cannot be applied to tools with complex shapes, so it is not practical. There are many problems in doing so.

(Means for Solving the Problems) By reducing the undulations on the surface of the diamond film, the adhesion of the work material to the cutting tool cutting edge is reduced and the peeling resistance is improved. The surface is first coated with a highly hard polycrystalline diamond film with an euhedral surface,
Next, they came up with the idea of smoothing the surface by coating the outer layer with an amorphous hard carbon film that does not have an idiomorphic surface.

The Vickers hardness of diamond is 7000~too.

kg/mm2, whereas the hardness of an amorphous hard carbon film varies greatly depending on its synthesis conditions, and its Vickers hardness ranges from less than 1000 kg/mm2 to approximately 7.
If the synthesis atmosphere contains hydrogen, the lower the synthesis temperature, the more hydrogen will be contained in the film. Furthermore, when a Raman spectrum is measured using a Raman spectrometer, diamond or a diamond-like hard carbon film is present in the spectrum at least +33
Whereas the amorphous hard carbon film has a sharp peak around 0cl'
It has a wide peak at half maximum with a maximum value at . The amorphous hard carbon film that is the aim of the present invention has a Hiracus hardness of 2000 kg/mm or more, is called 1-carbon or amorphous diamond, and exhibits sufficiently high wear resistance even when used in cutting tools. It is.

Since the amorphous carbon film is synthesized without an euhedral surface, it has the effect of smoothing the undulations of the diamond film on the euhedral surface coated on the inner layer of the cutting tool, reducing the adhesion of the workpiece material and reducing the adhesion of the diamond film. Expect a reduction in the frictional resistance between the cutting material and the hard coating.

The effect of coating a diamond film on a cutting tool made of a cemented carbide substrate to extend the life of the cutting tool is observed when the film thickness is 0.5 μm or more, but if the diamond film is coated with a diamond film over 100 μm, the effect of extending the life of the cutting tool is observed. If an attempt is made to coat the diamond, the diamond film will peel off from the base while the diamond film is being cooled down to room temperature, since the coefficients of thermal expansion of the cemented carbide and diamond are different.

Therefore, the present inventors synthesized and observed a diamond film having an euhedral surface on a cutting tool made of a cemented carbide base material with a thickness within this range by the DC discharge C-IO method and the microwave discharge method. As a result, the size of the diamond grains and the roughness of the film surface change depending on the synthesis conditions, the position on the substrate, and the synthesis time, that is, the film thickness. The width of the undulations is o, i ~ 1 μm when the film thickness is around 2 μm, and 0 when the film thickness is around 10 μm.
．． It was 5 to 2 μm, and 2 to 5 μm when the film thickness was around 50 μm.

Next, high-frequency CV [
Using method 1, an amorphous hard carbon film is coated with a diamond film.
Even though the target thickness was 172, the surface roughness was reduced to about 173 or less than before coating with the amorphous hard carbon film.

The thickness of the amorphous hard carbon film covering the outer layer of the diamond film should be changed depending on the surface roughness of the diamond film, and the surface roughness of the diamond film should be 0.5.
If it is μm, the thickness of the amorphous hard carbon film is 0.5 μm.
m, the surface of the substrate becomes sufficiently smooth, but when the thickness of the diamond film is around 100 μm, the surface roughness is about 5 μm.
Therefore, in order to make this smooth, it is necessary to cover it with an amorphous hard carbon film of 251 zm.

Specific examples of the present invention are shown below.

(Example) A mixed gas of methane and hydrogen was introduced into a vacuum chamber, a DC discharge plasma was generated between a filament provided in the vacuum chamber and an anode, and a WC-Co-based supercarbide placed on the anode was A cutting tip of type 5NGAI20408 made of alloy was coated with a diamond film. The diamond synthesis conditions at this time were a methane flow rate of 1105 CCM, a hydrogen flow rate of 5005 CCM, and a distance between the filament and the base material of 3 cm.
The synthesis was carried out for 3 hours at a filament temperature of about 2100° C. and a current of 3 A between the filament and the anode. When this sample was examined using an optical microscope, the diamond was found to be composed of polycrystals with euhedral surfaces, and its surface roughness was approximately 1 μm.

Next, an amorphous hard carbon film was coated on this substrate using methane as a raw material using a capacitively coupled high-frequency plasma CVD device at an output of 1501 wJ for 3 hours, and a smooth surface with a difference in undulation of 0.5 μm or less was observed. was gotten.

A cutting test was conducted under the following conditions using this cutting tip coated with the present invention and a cutting tip coated only with a diamond film under the conditions described above.

Work material Al-Si alloy (contains 13χ Si) Cutting speed 800 m/m i m Depth of cut 0.2 mm Feed rate 0.15 mm/rev Cutting method Dry continuous cutting As a result, a carbide tip coated only with a diamond film After cutting for 1 hour, the diamond film on the cutting edge peeled off and flank wear progressed, whereas with the cutting tip of the present invention, the hard coating on the cutting edge remained even after 3 hours of cutting, and the workpiece material on the cutting edge There was also less welding compared to cutting tips coated with only a diamond film.

After the cutting test, these cutting tips were cut and the thicknesses of the diamond film and the amorphous hard carbon film were examined.
μm, the thickness of the amorphous hard carbon film is 3 μm,
The film thickness of the comparative chip coated with only the diamond film was about 8 μm.

In this example, the diamond film was coated by a DC discharge plasma method, which is a CV method using a hot filament.
D method, CVD method using microwaves or high frequency waves, and other known methods can be used to coat the amorphous hard carbon film. This can be done by

(Effects) The hard film-coated cutting tool of the present invention has excellent adhesion and peeling resistance due to the inner layer being coated with a highly wear-resistant diamond film and the outer layer being coated with an amorphous hard carbon film to make the surface smooth. It is possible to maintain excellent cutting performance for a long time when cutting composite materials such as nonferrous metals, sintered ceramics, and FRP.

Claims (3)

[Claims] (1) In a cutting tool member coated with a hard coating, the innermost coating in contact with the base material is composed of polycrystalline diamond or diamond-like carbon film with euhedral surfaces, and the outer layer of the coating is amorphous without euhedral surfaces. A hard film-coated cutting tool member characterized by being coated with a hard carbon film. (2) The diamond or diamond-like carbon film having an euhedral surface has a thickness of 0.5 to 100 μm, and the amorphous hard carbon film has a thickness of 0.5 μm to 25 μm. The hard film-coated cutting tool member described above. (3) The hard film-coated cutting tool according to claim 1, wherein the base of the cutting tool member is made of a cemented carbide whose main component is tungsten carbide.