WO1998015670A1

WO1998015670A1 - Post treated diamond coated body

Info

Publication number: WO1998015670A1
Application number: PCT/SE1997/001689
Authority: WO
Inventors: Ingrid Reineck; Bengt Edholm; Christian Strondl
Original assignee: Sandvik Ab (Publ)
Priority date: 1996-10-10
Filing date: 1997-10-09
Publication date: 1998-04-16
Also published as: DE69713356D1; EP0931177A1; SE9603721D0; US6221493B1; ATE219163T1; DE69713356T2; JP2001501873A; EP0931177B1; SE9603721L

Abstract

According to the present invention there is now provided a body of cemented carbide or cermets coated with at least one diamond layer. The diamond layer is smooth on all sides of the body with an Ra ∫1 νm. According to the present invention there is also provided a method for reactive ion etching of a diamond layer on a complex shape body where the etching is efficient at all sides of the body exposed to the plasma. The etching is made using a C1- or oxygen-containing plasma with the possibility of etching of a diamond layer covered by an outer layer of preferably a Si containing material.

Description

POST TREATED DIAMOND COATED BODY

The present invention relates to a diamond coated body for which the diamond layer is smoothened which increases its wear and flaking resistance, in particular to be used as a cutting tool aimed for cutting Al-alloys containing e.g. Si and Cu as alloying elements and the like.

After many years of research efforts, the production of thin layers of diamond directly from the gas phase by CVD plasma technique for coating of cutting tools has been realised. Gas phase deposition of diamond on cemented carbide tools has been assessed by a variety of methods where the tailoring of the cemented carbide has proven to be of great importance.

The predominant growth manner for CVD plasma diamond layers is that the grain size grows markedly with deposition time. Typically, for a 6-10 μm thick diamond layer, the diamond grain size is 2-5 μm giving a surface roughness in this regime. One way to avoid the increase in grain size by growth time is to apply a bias voltage onto the tools which gives a smooth diamond surface but with the risk of achieving a deteriorated diamond quality. Besides, large scale production involving biasing puts demands on careful and hence more elaborate fixturing .

Smoothening of the diamond layers is generally regarded as being beneficial in cutting applications since the cutting forces are reduced upon lowering the coefficient of friction. Measurements of the coefficient of friction have shown that a much lower value is obtained for a polished CVD diamond layer compared to an as-deposited layer. A method for achieving a smooth diamond layer on cutting tools is mechanical polishing but due to the three-dimensional and often complicated shape, the polishing has only been possible to apply on flat rake surfaces or on a small part of the flank just below the cutting edge.

Polishing of diamond layers for electronic purposes, i.e. diamond layers on flat Si wafers and the like is known from the literature (see e.g. US pat. 5,500,077). The methods applied have been, for example, reactive ion etching using RF plasma generation with different gases such as O2 , CF4 etc. A highly efficient etching process is described in Llewellyn et. al . , SPIE Vol.2286, (1994) 198-204, still only for a two-dimensional set-up. Reactive ion etching (RIE) constitutes a combination of a chemical reaction and physical ion bombardment of a surface. Typical for RIE as compared with plasma etching in general is that the ion energies are high, this due to a low pressure during the process (<100 Torr) .

It is surprising to find that reactive ion etching of diamond can be achieved for diamond layers on cemented carbide or cermet bodies of complex, three- dimensional shapes, such as cutting tools including chip-breakers on the top surface so as to provide chips formed during machining in a desired and controllable configuration. This is in particular so since the etching per se is most efficient at protruding parts where a higher electric field strength is present. Cutting tool inserts prepared in this way have been found to generate a higher workpiece surface finish and to have a longer life-time in Al-alloy machining operations compared to as-coated diamond cutting tools. Fig 1 shows in 1500X magnification the topography of the surface of a diamond layer etched according to the invention (a) and before etching (b) .

According to the present invention there is now provided a cemented carbide or cermet body coated with a CVD diamond layer of high diamond quality for which the diamond grains have been etched so as to achieve a less rough surface compared to the untreated layer . The diamond layer may have deposits of non-diamond material in the space between the diamond grains creating a very smooth surface. A CVD diamond coated cutting tool insert prepared in this way proves to give a prolonged tool life in machining operations of Al-alloys.

A three dimensional body according to the invention shows diamond coated surface with a topography as in Fig la. The surface roughness is R_a <1.0 μm, preferably R_a <0.5 μm on the rake phase as well as on the clearance faces. At least 80% of the surfaces fulfil the R_a criterion for all cases. In a preferred embodiment, R_a is <1.0 μm at all places on both the rake face and the clearance face, and preferably <0.5 μm.

Spotwise, in the space between the diamond grains there may exist a non-diamond material deposited during or prior to the RIE process. The material is preferably a non-diamond carbon material or a Si containing material. The size of the non-diamond containing spots are 0-5 μm, preferably 0-1 μm.

According to the present invention there is also provided a method for manufacturing of said body. The method involves reactive ion etching of diamond coated inserts in a gas plasma atmosphere using gases with oxygen or halogen content such as Cl or F containing gases, preferably HC1, CI2, SFg or O2 and most preferably CCI4. The etching of the diamond layer is effective at all sides of the body that are exposed to the plasma. Another method involves the deposition of an outer layer onto the diamond layer, which layer subsequently is etched away to a large extent. The layer material may be deposited by any CVD or PVD method, including deposition during a RIE process, or the deposition may be made by sol-gel technique. The preferred method of manufacturing involves dipping in a sol-gel medium, preferably containing SiO_x. The preferred method of drying the sol-gel coating involves spinning of the sol gel by using a rotating device onto which the body is fixed. The spinning device is then rotated with rotation speed 0-5000 rpm, preferably 1000

- 3000 rpm. The sol-gel application /spinning treatment may be repeated several times resulting in a multiple layer structure which fully covers the peaks of the underlying diamond coating. Subsequently, the body is heat treated at 300-500°C. The etching of a diamond coated insert provided with such an outer layer is preferably made using O2 and/or SF as the etching medium . The etching method according to the invention involves typically a bias voltage at the sample of -200

- -1000 V, preferably -400 - -700 V. The gas pressure is 0.5 - 50 mtorr, preferably 1 - 30 mtorr and most preferably 2 - 15 mtorr. The invention can be applied to diamond coated cutting tools, tools for rock drilling and wear parts as well as to other layers such as cBN layers deposited by CVD or PVD methods .

Example 1

A C-6%Co cemented carbide insert provided with a chip breaker and with a cobalt depleted surface zone was diamond coated according to a standard coating procedure in a high current DC-arc diamond coating reactor to a diamond layer thickness of 10 μm. The insert was then etched during lh in an RIE etching device using CCI4 as the reactant medium. The process parameters were: p = 9 mtorr V_bias= -500 V DC Fig la shows the diamond coated surface topography at the point in the chip breaker labelled 'A' .

As a reference insert served a cemented carbide insert prepared as described above but without the RIE treatment. Fig lb shows the diamond coated surface topography.

The two inserts were subjected to a turning test in an Al-9%Si alloy using the following cutting data: v = 300 m/min f = 0.3 mm a = 3 mm wet cutting intermittent cut The RIE treated diamond coated insert generated a perfectly clean cut without any defects. For the non- etched insert small droplets of work-piece material remained on the machined surface. The size of the droplets was 50-100 μm and they occurred with a density of 50 pcs/mm^ giving rise to a less shiny machined surface.

Example 2

A C-4%Co insert with a cobalt depleted surface zone was diamond coated to a layer thickness of 20 μm using a micro-wave plasma depositing method. The insert was then etched in an RIE-plasma in CI2 during 1.5h at parameters : p = 2 mtorr

V_bias= -430V DC

As a reference, a second insert was diamond coated as described above, but no RIE etching was applied.

The two inserts were subjected to a turning test in an Al-9%Si alloy using the following cutting data: v = 700 m/min f = 0.3 mm a = 1 mm wet cutting intermittent cut

The RIE treated diamond coated insert generated a perfect, defect-free cut while for the non-etched insert an inferior surface finish was obtained.

Example 3

A WC-4%Co insert with a cobalt depleted surface zone was diamond coated to a layer thickness of 10 μm using a high current DC arc discharge depositing method. The insert was dipped in a SiO_x gel, dried and then etched in an RIE-plasma in O2/SF during 2h at parameters: p = 20 mtorr mass flow ratio O2/SF5 = 400

The two inserts were subjected to a turning test in an Al-18%Si alloy using the following cutting data: v = 700 m/min f = 0.1 mm a = 1 mm wet cutting continuous cut The RIE treated diamond coated insert generated a perfect, defect-free cut while for the non-etched insert an inferior surface finish was obtained. Example 4

A WC-4%Co insert with a cobalt depleted surface zone was diamond coated to a layer thickness of 20 μm using a high current DC arc discharge depositing method. SiO_x sol-gel was applied to the diamond surfaces and the sol- gel was spun at 2500 rpm for 20s so as to generate a thin, homogeneous gel film. The sol-gel application/spinning treatment was repeated three times. The insert was heat treated at 425°C for 60 min and then etched in an RIE-plasma in O2/SF5 during 30 min at parameters : p = 20 mtorr mass flow ratio O2/SF5 = 400

After etching the diamond coating surface roughness was Ra = 30 nm measured with Atomic Force Microscopic technique (AFM) . The measure area was 100x100 μm.

As a reference, a second insert was diamond coated as described above, but no RIE etching was applied. The diamond surface roughness for this insert was R_a = 200 nm measured by AFM.

Claims

1. Body of cemented carbide or cermet coated with at least one diamond layer characterised in that the surface roughness of the diamond layer at all of the sides the intersections of which generate cutting edges, is less than 1.0 μm, preferably less than 0.5 μm, on all diamond coated surfaces but preferably on 80% of all surfaces .

2. Body according claim 1 characterised in that said body includes a chipformer on the top surface so as to provide chips formed during machining in a desired and controllable configuration.

3. Body according to any of the preceding claims characterised in that the diamond surface of said body contains spots of non-diamond material with a size of 0-5 μm, preferably 0-1 μm, the non-diamond material preferably being carbon in non-diamond configuration or a Si containing material .

4. Method for producing a smooth diamond layer on a complex shaped body characterised in that the body is first diamond coated and then etched in a reactive ion etching device whereby the etching takes place at all sides of the body that are exposed to the plasma.

5. Method according to claim 4 characterised in that the etching is made using gases with oxygen or halogen content such as Cl or F containing gases, preferably HCl, Cl₂ or O₂ and most preferably CCI₄.

6. Method according to claim 4 characterised in that the etching is made after coating of the diamond coated body by one or several layers where the layer/layers preferably is/are Si and 0 containing layer/layers and the etching preferably is made using O2 and/or SF₆ as etching medium.

7. Method according to claim 4 and 6 characterised in that the layer applied on top of the diamond layer is applied by spinning a sol-gel at 0 - 5000 rpm, preferably at 1000 - 3000 rpm and then preferably heat treated at 300 - 500°C.

8. Method according to claims 4, 5, 6 or 7 characterised in that the etching is made at pressure 0.5-50 mtorr, preferably 1-30 mtorr and most preferably at 2-15 mtorr.