Diamond- or diamond-like carbon coated hard materials

Abstract: A diamond-coated hard material having a diamond- or diamond-like carbon coated layer with a high bonding strength to a substrate is provided. The coated hard material comprising a diamond- and/or diamond-like carbon-coating layer formed on the surface of a hard material, i.e. substrate is characterized in that (I) (1) microscopic roughness is present on the surface of the substrate and (2) protrusive parts thereof are defined by the surface roughness Rmax within a range of 1.0 to 30 µ m in a standard length when the standard length is 50 µ m in the interface of the diamond- and/or diamond-like carbon coated layer and the substrate, and (II) (1) microscopic roughness is present on the surface of the substrate, (2) at least one protrusive part is present in a standard length when the standard length is 10 µ m in the interface of the diamond- and/or diamond-like carbon coated layer and the substrate, (3) the ratio of the sum A of the lenghts of dent parts to the sum B of the lenghts of the protrusions is in the rangeof 0.05 ≦ A/B ≦ 20 in the standard length in the interface and (4) the protrusive parts are intruded into the diamond-coated layer.

Description: This invention relates to a diamond-coated hard material having a diamond- or diamond-like carbon-coating layer with a high bonding strength to the substrate material. Diamond has many excellent properties, for example, very high hardness, chemical stability, high heat conductivity, high sound wave propagation speed, etc. and has widely been used as a hard material utilizing these properties or as diamond or diamond-like carbon coated hard materials, illustrative of which are as follows:- (i) 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, light metals or alloys thereof at a high temperature to produce well finished surfaces, because they hardly react with these metals or alloys. (ii) various wear resistance tools such as bonding tools capable of working for a long time with high dimensional precision, because of high wear resistance; (iii) various machine parts such as radiating plates; (iv) various vibration plates such as speakers, and (v) various electronic parts. In the production of artificial diamond, there are various methods of forming diamond cutting layers from the gaseous phase, for example, the 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 or combustion method. These methods are useful for the production of diamond-coated hard materials. Since many of the diamond-coated hard materials are lacking in the bond strength of the diamond-coating to the substrate, the diamond-coating becomes stripped off, to shorten the life in many cases. The main reason therefor is that diamond is not capable of forming intermediate layers with all materials and it has low wettability with other materials. In order to obtain a diamond-coated hard material having a high bonding strength, there have been proposed a method comprising selecting a substrate having the same heat expansion coefficient as diamond (Japanese Patent laid-Open Publication No. 291493/1986, proposing sintered compacts containing Si 3 N 4 , as a predominant component, and sintered compacts containing SiC as a predominant component), 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 Publication No.124573/1986, subjecting the surface of a substrate to a scratching treatment with diamond grains or a diamond wheel and thereby improving the nuclei forming density on the surface of the substrate), etc. EP-A-0445305 relates to a method for the vapour phase synthesis of diamond on an electrochemically treated substrate and is comprised in the state of the art by virtue of Article 54(3) and (4) EPC. As described above, diamond is chemically stable and does not form intermediate compounds with all materials. When a diamond-coated hard material having an excellent bonding strength is prepared, therefore, such a condition must be provided that the diamond coating layer and the substrate are strongly physically bonded. We have found that when protrusions having a high bonding strength to a substrate are formed on the surface of the substrate by chemical or mechanical means and a diamond coating layer is formed thereon, thereby forming such a state that the protrusions intrude into the diamond coating layer, the bonding strength between the diamond cutting layer and the substrate is very high. This can be considered to be due to the fact that the contact area of the diamond coating layer with the substrate is increased and the protrusions have an anchoring action in the diamond coating layer, whereby the diamond coating layer is hard to strip from the substrate. Accordingly, for the contracting states other than DE and SE, the present invention provides (I) a coated hard material comprising a diamond- and/or diamond-like carbon-coating layer formed on the surface of a hard material, i. e. substrate, characterized in that (1) microscopic roughness is present on the surface of the substrate and (2) protrusive parts thereof are defined by the surface roughness Rmax within a range of 1.0 to 30 µm in a standard length when the standard length is 50 µm in the interface of the diamond- and/or diamond-like carbon coated layer and the substrate, and wherein the protrusive parts are of a columnar or hexagonal pillar shape and/or needle shape and (II) a coated hard material comprising a diamond- and/or diamond-like carbon-coating layer formed on the surface of a hard material, i.e. substrate, characterized in that (1) microscopic roughness is present on the surface of the substrate, (2) at least one protrusive part is present in a standard length when the standard length is 10 µm in the interface of the diamond- and/or diamond-like carbon coated layer and the substrate, (3) the ratio of the sum A of the lengths of dent parts to the sum B of the lengths of the protrusions is in the range of 0.05 ≦ A/B ≦ 20 in the standard length in the interface and (4) the protrusions are intruded into the diamond-coated layer, and wherein the protrusive parts are of a columnar or hexagonal pillar shape and/or needle shape. For the contracting states of DE and SE, the present invention provides a process for coating a substrate of a hard material as defined in the claims headed "For the contracting states of DE and SE only". The present invention is further described hereinbelow with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a coating layer-substrate interface in one embodiment of the present invention; Figure 2 is a schematic view to illustrate the state shown in Figure 1 by linearly drawing it; and Figure 3 is a schematic view of a coating layer-substrate interface in another embodiment of the present invention. In the present invention, the roughness is not a macroscopic roughness formed by scratching with (1) a diamond wheel or (2) diamond grinding grains, but a microscopic roughness in a very small range, i.e. roughness in a standard length of 50 µm or 10µm in a diamond coating layer-substrate interface. We have made various roughened states and consequently, have found that when the surface roughness in the substrate interface is defined by Rmax of 1.0 to 30 µm in the standard length of 50 µm and the protrusive parts are intruded by at least 0.2 µm into the diamond coating layer-substrate interface, a strong bonding strength is obtained. This surface roughness is defined as a surface roughness (Rmax) of a substrate after coating by lapping a cross-section of the substrate coated with diamond, observing and photographing to review the boundary line of the diamond coating layer-substrate interface. This corresponds to the above described invention (I). We have made various roughened states and consequently, have found that when at least one protrusive part is present in the standard length of 10 µm and the ratio of the sum A of the lengths of dent parts to the sum B of the lengths of the protrusions is in the range of 0.05 ≦ A/B ≦ 20 in the standard length and the protrusions are intruded by 0.2 µm into the diamond-coated layer, a high density strength is obtained. This is calculated by lapping a cross-section of the substrate coated with diamond, observing and photographing to review and model a boundary line of the diamond coating layer-substrate interface. This corresponds to the above described invention (II). In the present invention, it is preferred to carry out the commonly used scratching treatment of a substrate with diamond grains in order to promote formation of diamond nuclei on the whole surface of the substrate during the initial coating period. At the same time, this scratching treatment is more preferably carried out by adding the substrate and diamond grains to a solvent such as water, ethyl alcohol, acetone, etc. and then applying ultrasonic wave thereto, since a scratching treatment by pressing hard diamond grains against the substrate in physical manner results in breakage of the resulting protrusions. Diamond nuclei are uniformly formed on the whole protrusive and non-protrusive parts of the substrate surface by this scratching treatment, whereby it is rendered possible to form such a state that the protrusions are intruded into the diamond coated layer. As a useful method for forming the specified roughness on a substrate, there are (1) a method comprising depositing columnar or hexagonal pillar crystal grains and/or needle crystal grains on the surface of a substrate. Method (1) consists in subjecting a substrate to some heat treatment, freely growing columnar or hexagonal pillar crystal grains or needle crystal grains and/or promoting secondary crystal generation on the surface thereof by the substrate component. The material for forming the protrusions may be silicon carbide, silicon carbide-containing materials, tungsten, tungsten carbides or carbonitrides, carbides or carbonitrides of tungsten with at least one metal, titanium nitrides, carbides, carbonitrides or solid solutions thereof or mixtures thereof and materials containing them. The material for forming the roughened part is preferably consolidated in one body with the substrate and is preferably the same material as that of the substrate. Of course, similar materials but differing in composition can be used. In Fig. 1, the state of the diamond-coated layer- or diamond-like carbon-coated layer-substrate interface according to the present invention (I) is schematically shown. That is, a macroscopic undulation appears in the inter-layer, but Rmax is calculated regarding this undulation as linear as shown in Fig. 2. In Fig. 3, the state of the diamond-coated layer- or diamond-like carboncoated layer-substrate interface according to the present invention (II) is schematically shown. Herein, the ratio of sum A of the protrusion lengths, i.e. Σ A to sum B of the dent lengths, i.e. Σ B must be in the range of 0.05 ≦ Σ A / Σ B ≦ 20 and the intruded lengths of the protrusions are preferably at least 0.2 µm. For example, when one protrusion of 0.5 µm is present in 10 µm, Σ A / Σ B = 19. In the present invention (I), the formed protrusive parts should satisfy the requirements that when a standard length is 50 µm in the interface of a diamond- and/or diamond-like carbon coated layer and a substrate, the surface roughness of the substrate interface is represented by an Rmax of 1.0 to 30 µm in the standard length and the protrusive parts are preferably intruded in the diamond coated layer with at least 0.2 µm. When the surface roughness at the substrate interface is represented by a Rmax of less than 1.0 µm, the bonding strength is not increased, while if more than 30 µm, on the contrary, the bonding strength is lowered. When the maximum intrusive depth of the protrusions is at most 0.2µm, the bonding strength is substantially similar to that in the case of providing no protrusion. In the present invention (II), it is required that when the standard length is 10 µm in the diamond- and/or diamond-like carbon coated layer-substrate interface, at least one protrusion is formed in this standard length, the ratio of sum B of the lengths of protrusions and sum A of the lengths of dent parts is in the range of 0.05 to 20 and the protrusions are intruded into the diamond-coated layer. In this case, the intruded length is preferably at least 0.2µm. When the ratio of sum B of the lengths of protrusions and sum A of the lengths of the protrusions is outside the range of 0.05 ≦ ΣA / ΣB ≦ 20, the bonding strength is not improved. As the substrate, any hard materials can be used, for example, cemented carbides, cermets, Al 2 O 3 , silicon carbide and other ceramics. Above all, when protrusions of titanium compounds such as titanium carbides, nitrides and carbonitrides and/or titanium compounds-containing materials, tungsten carbides and/or carbides of tungsten alloys and/ or materials containing these compounds or materials are present, a high bonding strength can be obtained. Furthermore, when the shape of the protrusion is a columnar or hexagonal pillar crystal or needle crystal with an aspect ratio of at least 1.5, a bonding strength is further increased. As to the thickness of the diamond coated layer, if less than 0.1 µm, no improvement of various properties by the coated layer, such as wear resistance, is found, while if more than 200 µm, further improvement of the properties cannot be given. Therefore, a thickness of 0.1 to 200 µm is preferable. The foregoing illustration is conducted as to a case where diamond is coated, but the present invention can be applied with similar benefits to cases where diamond-like carbon is present in a diamond-coated layer, one or more of these layers are coated and the coated layer contains foreign atoms such as boron, nitrogen, etc. Where diamond-like carbon is coated, the excellent advantages of the present Invention can also be obtained. The following examples are given in order to illustrate the present invention in detail without limiting the same. Example 1 A throwaway insert comprising silicon carbide whiskers ceramic (specifically, Al 2 O 3 -35 vol % SiC wiskers-5 wt % ZrO 2 ) as a substrate and having a shape of SPG 422 was made, brought into contact with fused NaOH and etched to expose needle crystals of silicon carbide whiskers having a minor axis of 1 µm and a major axis of 8 µm on the surface of the insert. This insert and 2 g of diamond grains each having a grain diameter of 8 to 16 µm were added to ethyl alcohol, to which supersonic wave vibration was added for 15 minutes. Using 2.45 GHz microwave plasma CVD apparatus, the thus resulting insert was heated at 1000°C and maintained In a mixed plasma of hydrogen-2 % methane at a total pressure of 10665.8 Pa (80 Torr) for 8 hours to prepare a cutting insert coated with diamond of 8 µm in layer thickness. For comparison, a comparative insert was prepared by using a substrate having the same shape and composition as described above without conducting the etching treatment and providing a diamond coated layer on the insert having no needle crystals of silicon carbide whiskers on the surface thereof (The ultrasonic wave treatment was not carried out for the comparative sample). In this test, it was confirmed by the Raman spectrometry that the coated layer deposited on the surface of the substrate was a diamond coated layer. Using these cutting inserts, intermittent cutting tests were carried out under the following conditions. Workpiece to be cut Al-24 wt % Si alloy (block material) Cutting Speed 400 m/min Feed 0.1 mm/rev Cutting Depth 0.5 mm When the flank wear width, the wear state of the edge and the deposition state of the workpiece, after 3 and 10 minutes, were observed, the cutting insert of the present invention showed normal wearing represented by a flank wear width of 0.05 mm after 10 minutes from start of cutting and deposition of the workpiece was hardly observed. On the other hand, in observation of the cutting edge after 3 minutes from start of cutting, a large peeling of the diamond coated layer was found, the flank wear width amounted to 0.16 mm and the workpiece was subject to marked metal deposition, so that the cutting had to be stopped. When the insert after the cutting test was cut, subjected to lapping and then the interface of the substrate and diamond coated layer was observed by an optical microscope, the insert of the present invention gave the results that silicon carbide whiskers were intruded into the diamond-coated layer by at most 3.5 µm and in the interface, the microscopic surface roughness was represented by an Rmax of 4 to 5 µm in the standard length of 50 µm. In the comparative insert, on the contrary, there were found no silicon carbide whiskers in the interface of the substrate and diamond-coated layer, nor intrusion of the substrate into the diamond-coated layer. Example 2 A throwaway insert comprising silicon carbide whiskers ceramic (specifically, AI 2 O 3 -35 vol % SiC whiskers-5 wt % ZrO 2 ) as a substrate and having a shape of SPG 422 was made, brought Into contact with fused NaOH and etched to expose needle crystals of silicon carbide whiskers having a minor axis of 1 µm and a major axis of 8 µm on the surface of the insert. This insert and 2 g of diamond grains each having a grain diameter of 8 to 16 µm were added to ethyl alcohol, to which supersonic wave vibration was added for 15 minutes. Using 2.45 GHz microwave plasma CVD apparatus, the thus resulting insert was heated at 1000°C and maintained in a mixed plasma of hydrogen-2 % methane at a total pressure of 10665.8 Pa (80 Torr) for 7 hours to prepare a cutting insert coated with diamond of 9 µm in layer thickness. For comparison, a comparative insert was prepared by using a substrate having the same shape and composition as described above without conducting the etching treatment and providing a diamond coated layer on the insert having no needle crystals of silicon carbide whiskers on the surface thereof (The ultrasonic wave treatment was not carried out for the comparative sample). In this test, it was confirmed by the Raman spectrometry that the coated layer deposited on the surface of the substrate was a diamond coated layer. Using these cutting inserts, Intermittent cutting tests were carried out under the following conditions. Workpiece to be cut Al-24 wt % Si alloy (block material) Cutting Speed 400 m/min Feed 0.1 mm/rev Cutting Depth 0.5 mm When the flank wear width, the wear state of the edge and the deposition state of the workpiece, after 3 and 10 minutes, were observed, the cutting insert of the present invention showed normal wearing represented by a flank wear width of 0.05 mm after 10 minutes from start of cutting and deposition of the workpiece was hardly observed. On the other hand, in observation of the cutting edge after 3 minutes from start of cutting, a large peeling of the diamond coated layer was found, the flank wear width amounted to 0.14 mm and the workpiece was subject to marked metal deposition, so that the cutting had to be stopped. When the insert after the cutting test was cut, subjected to lapping and then the interface of the substrate and diamond coated layer was observed by an optical microscope, the insert of the present invention gave the results that silicon carbide whiskers were intruded into the diamond-coated layer by at most 4 µm and in the interface, 3 to 6 protrusions were present and A/B was 1.0 to 1.6 in the standard length of 10 µm. In the comparative insert, on the contrary, there were found no silicon carbide whiskers in the interface of the substrate and diamond-coated layer, nor intrusion of the substrate into the diamond-coated layer. The diamond- and/or diamond-like carbon-coated hard material of the present invention has better peeling resistance than the diamond- and/or diamond-like carbon-coated hard materials of the prior art. The method of Example 1 and 2, relates to a surface treatment utilizing the properties of a substrate. The above described examples are given in the case of cutting tools, but of course, the hard materials of the present invention can be applied to not only wear resistance tools such as TAB tools, but also end mills, drills, drills for making hole on print substrates, reamers, etc.

Claims: Claims for the following Contracting States : FR, GB, IT A coated hard material comprising a diamond- and/or diamond-like carbon-coating layer formed on the surface of a hard material, i.e. substrate, characterized in that (1) microscopic roughness is present on the surface of the substrate and (2) protrusive parts thereof are defined by the surface roughness Rmax within a range of 1.0 to 30 µm in a standard length when the standard length is 50 µm in the interface of the diamond- and/or diamond-like carbon coated layer and the substrate, and wherein the protrusive parts are of a columnar or hexagonal pillar shape and/or needle shape. A coated hard material comprising a diamond- and/or diamond-like carbon coating layer formed on the surface of a hard material, i.e. substrate, characterized in that (1) microscopic roughness is present on the surface of the substrate, (2) at least one protrusive part is present in a standard length when the standard length is 10 µm in the interface of the diamond- and/or dimaond-like carbon coated layer and the substrate, (3) the ratio of the sum A of the lengths of dent parts to the sum B of the lengths of the protrusions is in the range of 0.05 ≦ A/B ≦ 20 in the standard length in the interface and (4) the protrusive parts intrude into the diamond-coated layer, and wherein the protrusive parts are of a columnar or hexagonal pillar shape and/or needle shape. A coated hard material as claimed in claim 1 or claim 2, wherein the protrusive part(s) intrude in the diamond- and/ or diamond-like carbon coated layer by at least 0.2 µm. A coated hard material as claimed in claim 2 or claim 3, wherein the protrusive part comprises silicon carbide or a silicon carbide-containing material. A coated hard material as claimed in claim 1 or claim 2, wherein the protrusive part comprises (1) tungsten, (2) tungsten carbide or carbonitride, (3) a carbide or carbonitride of tungsten and at least one other metal or (4) a material containing these materials. A coated hard material as claimed in anyone of claims 1 to 5, wherein the protrusive part is of a columnar or hexagonal pillar shape with an aspect ratio of at least 1.5. A coated hard material as claimed in anyone of claims 1 to 6, wherein the hard material (1) a cemented carbide, (2) a cermet, (3) a ceramic (4) a composite material thereof. A coated hard material as claimed in anyone of claims 1 to 7, wherein the material forming the roughness at the interface of the diamond- or diamond-like carbon-coated layer and the substrate is consolidated in one body with and of the same material as the substrate. A coated hard material as claimed in anyone of claims 1 to 7, wherein the material forming the roughness at the interface of the diamond- or diamond-like carbon-coated layer and the substrate is of the same material as the substrate but differs in composition therefrom. A coated hard material as claimed in claim 1 or 2, wherein the diamond- or diamond-like carbon-coated layer has a thickness of from 0.1 to 20 µm. Claims for the following Contracting States : DE, SE A process for coating a substrate of a hard material comprising the steps of forming microscopic roughness on the surface of the substrate by a method other than an electrochemical treatment, followed by coating the surface of the substrate with a diamond- and/or diamond-like carbon-coating layer, characterized in that protrusive parts of the microscopically roughened surface of the substrate are defined by the surface roughness Rmax within a range of 1.0 to 30 µm in a standard length when the standard length is 50 µm in the interface of the diamond- and/ or diamond-like carbon coated layer and the substrate, and wherein the protrusive parts are of a columnar or hexagonal pillar shape and/or needle shape. A process for coating a substrate of a hard material as claimed in claim 1, wherein the protrusive parts intrude in the diamond- and/or diamond-like carbon coated layer by at least 0.2 µm. A process for coating a substrate of a hard material as claimed in claim 1 or claim 2, wherein the protrusive parts comprise silicon carbide or a silicon carbide-containing material. A process for coating a substrate of a hard material as claimed in claim 1, wherein the protrusive parts comprise (1) tungsten, (2) tungsten carbide or carbonitride, (3) a carbide or carbonitride of tungsten and at least one other metal or (4) a material containing these materials. A process for coating a substrate of a hard material as claimed in any one of claims 1 to 4, wherein the protrusive parts are of a columnar or hexagonal pillar shape with an aspect ratio of at least 1.5. A process for coating a substrate of a hard material as claimed in any one of claims 1 to 5, wherein the hard material is (1) a cemented carbide, (2) a cermet, (3) a ceramic (4) a composite material thereof. A process for coating a substrate of a hard material as claimed in any one of claims 1 to 6, wherein the material forming the roughness at the interface of the diamond- or diamond-like carbon-coated layer and the substrate is consolidated in one body with and of the same material as the substrate. A process for coating a substrate of a hard material as claimed in any one of claims 1 to 6, wherein the material forming the roughness at the interface of the diamond- or diamond-like carbon-coated layer and the substrate is of the same material as the substrate but differs in composition therefrom. A process for coating a substrate of a hard material as claimed in claim 1 ,wherein the diamond- or diamond-like carbon-coated layer has a thickness of from 0.1 to 20 µm. A coated hard material comprising a diamond- and/or diamond-like carbon coating layer formed on the surface of a hard material, i.e. substrate, characterized in that (1) microscopic roughness is present on the surface of the substrate, (2) at least one protrusive part is present in a standard length when the standard length is 10 µm in the interface of the diamond- and/or diamond-like carbon coated layer and the substrate, (3) the ratio of the sum A of the lengths of dent parts to the sum B of the lengths of the protrusions is in the range of 0.05 ≤ A/B ≤ 20 in the standard length in the interface and (4) the protrusive parts intrude into the diamond-coated layer, and wherein the protrusive parts are of a columnar or hexagonal pillar shape and/or needle shape. A coated hard material as claimed in claim 10 wherein the protrusive part(s) intrude in the diamond- and/or diamond-like carbon coated layer by at least 0.2 µm. A coated hard material as claimed in claim 10 or claim 11 wherein the protrusive part comprises silicon carbide or a silicon carbide-containing material. A coated hard material as claimed in claim 10 wherein the protrusive part comprises (1) tungsten, (2) tungsten carbide or carbonitride, (3) a carbide or carbonitride of tungsten and at least one other metal or (4) a material containing these materials. A coated hard material as claimed in anyone of claims 10 to 13 wherein the protrusive part is of a columnar or hexagonal pillar shape with an aspect ratio of at least 1.5. A coated hard material as claimed in anyone of claims 10 to 14 wherein the hard material is (1) a cemented carbide, (2) a cermet, (3) a ceramic (4) a composite material thereof. A coated hard material as claimed in anyone of claims 10 to 15 wherein the material forming the roughness at the interface of the diamond- or diamond-like carbon-coated layer and the substrate is consolidated in one body with and of the same material as the substrate. A coated hard material as claimed in anyone of claims 10 to 16 wherein the material forming the roughness at the interface of the diamond- or diamond-like carbon-coated layer and the substrate is of the same material as the substrate but differs in composition therefrom. A coated hard material as claimed in claim 10 wherein the diamond- or diamond-like carbon-coated layer has a thickness of from 0.1 to 20 µm.

Inventors: NOMURA TOSHIO, OMORI NAOYA, NOMURA, TOSHIO, OMORI, NAOYA, NOMURA, TOSHIO, C/O ITAMI WORKS OF SUMITOMO, OMORI, NAOYA, C/O ITAMI WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1992
Main classification: C23C16
IPC codes: C04B41, C23C16, B23B27