Diamond-coated hard material, throwaway insert and a process for

Details Diamond-coated hard material, throwaway insert and a process for Diamond-coated hard material, throwaway insert and a process for

1992-07-14

1994-07-12

Turner, A. A.

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

428141, 428156, 428408, 428698, 51307, B23B 2714

Patent

active

053287614

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a diamond-coated hard material having a high bonding strength to a substrate and a diamond-coated throwaway insert capable of cutting various light metals such as Al-Si alloys at a high rate for a long time.


BACKGROUND TECHNIQUE

Diamond having many excellent properties for example very high hardness, chemical stability, high heat conductivity, high sound wave propagation speed, etc. has widely been used as hard materials utilizing these properties or diamond or diamond-like carbon coated hard materials, illustrative of which are as follows:
1 single crystal diamond, sintered diamonds or diamond-coated cutting tools such as throwaway inserts, drills, microdrills, endmills, etc., which are capable of cutting Al, Cu, various practically used light metals or alloys thereof at a high rate and obtaining well finished surfaces, because of hardly reacting with these metals or alloys.
2 various wear resistance tools such as bonding tools capable of working for a long time with a high dimensional precision, because of high wear resistance.
3 various machine parts such as radiating plates.
4 various vibration plates such as speakers.
5 various electronic parts.
In the production of artificial diamond, there are methods of forming diamond coating layers from gaseous phase, for example, microwave plasma CVD method, RF-plasma CVD method, EA-CVD method, induction field microwave plasma CVD method, RF hot plasma CVD method, DC plasma CVD method, DC plasma jet method, filament hot CVD method, combustion method and like. These methods are useful for the production of diamond-coated hard materials.
As a surface-coated tool, there have widely been used surface-coated throwaway inserts in which a monolayer or multilayer consisting of carbides, nitrides and carbonitrides of Ti, Hf or Zr or oxide of Al is formed on the surface of a cemented carbide substrate by PVD or CVD method.
Diamond has a very high hardness and chemical stability and hardly reacts with Al, Cu, practically used light metals, etc. as described above. Thus, when diamond is applied to a cutting tool and subjected to cutting of such light metals or alloys thereof at a high rate, the surface of a workpiece is well finished. Accordingly, single crystal diamond, sintered diamond cutting tools or diamond-coated cutting tools have widely been put to practical use.
Since many of the diamond-coated tools are lacking in bonding strength of the diamond-coated layer to a substrate, the diamond-coated layer is stripped to shorten the life in many eases. The reason therefor is given below:
1) Since diamond is a very stable material and does not form compounds with all materials, it is considered that a diamond-coated layer and substrate are bonded by an intermolecular force. The intermolecular force provides a lower bonding strength to a substrate as compared with a coated layer bonded through formation of a chemical compound.
2) The thermal expansion coefficients of diamond and a substrate are so different that a residual stress is caused in a diamond-coated layer and the bonding strength between them is decreased.
At the boundary between a substrate and a diamond-coated layer, the intermolecular force is increased with the increase of the contacted area thereof and the bonding strength of the diamond-coated layer to the substrate is thus increased. The higher is the nuclei-generating density of diamond on the surface of the substrate, the larger is the contacted area of the substrate and the diamond-coated layer.
Thus, there has been proposed a method comprising subjecting the surface of a substrate to etching to remove metals having bad influences upon formation of the diamond coating layer on the substrate surface and thereby increasing the formation density of diamond nuclei on the substrate surface (Japanese Patent Laid-Open Publication No. 201475/1989, etching the surface of a cemented carbide with an acid solution to remove Co metal component and to suppress graphitization of the diamond nuclei; Japanese Patent Laid-Open

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