WO2012079769A1

WO2012079769A1 - Coated cubic boron nitride tool for machining applications

Info

Publication number: WO2012079769A1
Application number: PCT/EP2011/006379
Authority: WO
Inventors: Rachid Msaoubi; Tommy Larsson; Sakari Ruppi
Original assignee: Seco Tools Ab
Priority date: 2010-12-17
Filing date: 2011-12-16
Publication date: 2012-06-21

Abstract

The present invention relates to a cutting tool insert for machining by chip removal comprising a body, either as a solid insert or attached to a backing body, onto which is deposited a hard and wear resistant coating. The said body is a polycrystalline cubic boron nitride compact (PCBN) containing at least 30 vol% of cubic phase boron nitride (c-BN) in a binder comprising at least one compound selected from nitrides, borides, oxides, carbides and carbonitrides of one or more of the elements belonging to the groups 4, 5 and 6 of the periodic table and Al. The said coating comprises a textured CVD α-Αl₂O₃ layer, with a thickness of 0.5-10 μm, having an ODF texture index >1, and at least one dominant texture component with 2 < ODF density < 100 within the layer.

Description

Coated cubic boron nitride tool for machining applications

BACKGROUND OF THE INVENTION

The present invention relates to a cutting tool for machining by chip removal consisting of a substrate of polycrystalline cubic boron nitride (PCBN) based material and a hard and wear resistant refractory coating consisting of layers of Ti(C,N) and α-Α1₂0₃ formed by a vapour deposition process. The tool according to the invention is useful in a variety of metal cutting applications such as machining of hardened steels, heat resistant alloys and cast iron where remarkable increase in productivity can be obtained when compared to coated cemented carbides and cermets.

It is well known that cubic boron nitride (c-BN) has a high hardness, excellent thermal stability and low reactivity with ferrous metals.

PCBN sintered bodies for cutting tools comprise c-BN particles and a binder. The sintered bodies can be applied either as a solid inserts or attached to a backing body. They are generally classified into the following main groups:

- Sintered bodies, well-balanced in wear resistance as well as strength mainly used for machining hardened steel and/or heat resistant alloys, comprising 30 to 70 volume % of c-BN particles bonded through a binder predominantly consisting of Ti type ceramics such as TiN, TiC, Ti(C,N).

- Sintered bodies, displaying high thermal conductivity as well as strength mainly used for machining cast iron and/or powder metallurgy steels, comprising 80 to 90 volume % of c- BN particles and the balance of a binder generally consisting of an Al or Co compound.

However, c-BN particles have the disadvantages that their affinity for ferrous metals is larger than TiN, TiC, Ti(C,N) binders. Accordingly, cutting tools employing c-BN often have a shortened service life due to chemical wear, which eventually causes the tool edge to break. In order to further improve the wear resistance and fracture strength of a PCBN tool, it has been proposed to coat a PCBN tool with a layer of TiN, Ti(C,N), (Ti,Al)N, etc , e.g. US 5853873 and US 6737178.

EP 1736565 discloses a cutting tool for machining by chip removal consisting of a substrate of PCBN and a hard and wear resistant refractory coating of which at least one layer comprises an Me-Si-X phase formed by PVD deposition.

US-A-5,583,873 discloses a TiN layer as an intermediate layer between a c-BN substrate and (Ti,Al)N-coated film to bond the (Ti,Al)N-coated film thereto with a high adhesive strength.

US 6,737,178 discloses layers of TiN, Ti(C,N) and (Ti,Al)N on PCBN.

US 6,620,491 discloses a PVD coated boron nitride tool, with a hard coated layer and an intermediate layer consisting of at least one element selected from the Groups 4a, 5a and 6a of Periodic Table and having a thickness of at most 1 μπι. The hard coating contains at least one layer containing at least one element selected from the group consisting of Group 4a, 5a, 6a elements, Al, B, Si and Y and at least one element selected from the Group consisting of C, N and O with a thickness of 0.5-10 μπι. The intermediate layer contains at least one of the elements Cr, Zr and V.

US5503913 discloses a tool with improvement of the wear properties of tools with cutting edge of cubic boron nitride (c-BN) or polycrystalline cubic boron nitride (PCBN) by coating the c-BN or PCBN body with a 0.5 to 6 μπι thick layer of one or more oxides of the metals zirconium and/or yttrium and/or magnesium and/or titanium and/or aluminium, preferably aluminium oxide.

US6090476 discloses a multilayer coated cutting tool comprising a cemented carbide body with at least one sintered-on inlay containing polycrystalline cubic boron nitride. Crater wear is reduced on the rake face by applying a multilayer CVD coating consisting of layers of Ti(C,N) (1-8 μπι) and A1₂0₃ (2-10 μηι).

US6599062 comprises a cutting tool and method for machining hardened steel including a substrate of polycrystalline cubic boron nitride having one or more layers of a hard refractory coating containing aluminum. The coating may contain a titanium aluminum nitride layer applied by a physical vapor deposition (PVD). Alternatively, the coating may include a layer of aluminum oxide applied by chemical vapor deposition.

US2008193724 comprises a surface-covered c-BN sintered body tool including a base material formed with a cubic boron nitride (c-BN) sintered body and a coating. The coating includes a nitride or a carbonitride of a compound including at least one element selected from the group consisting of Ti, Cr, Zr, and V and at least one element selected from the group consisting of Al, Si and B, or a nitride or a carbonitride of Ti.

US2004256442 discloses a coated cutting tool that comprises a body containing a pocket. The tool further includes a polycrystalline cubic boron nitride blank that is brazed into the pocket using a braze alloy. The braze alloy has a liquidus temperature of at least about 900 degrees Centigrade. There is a coating applied to the cutting tool.

US681 1580, US6382951 and US6383624 disclose cubic boron nitride inserts coated with A1₂0₃.

Recent advances in CVD include the control of the α-Α1₂0₃ with preferred coating textures, described in US5766782, US 5,654,035, US 5,980,988, US 6,333,103, US 7,01 1,867, US 2006199026 and US 2006141271.

US 2007104945 relates to a coated cutting tool insert comprising a substrate and a coating to be used in metal machining. The coating is composed of one or more refractory layers of which at least one layer is α-Α1₂0₃. The layer is characterised by a strong (006) diffraction peak, measured using X-ray diffraction (XRD), and by low intensity of (012), (104), (1 13) (024) and (1 16) diffraction peaks.

US RE41 1 1 1 discloses a {001 } textured oc-Al₂0₃ layer as obtained using an initial heat treated alumina core layer (conversion layer) with a thickness of 20-200 nm. The texture is determined by electron back scattering diffraction (EBSD).

An explanation of EBSD and the analysis for texture evaluation by using pole figures, pole plots, orientation distribution functions (ODFs) and texture indexes can for instance be found in Introduction to Texture Analysis: Macro texture, Microtexture, and Orientation Mapping, Valerie Randle and Olaf Engler, (ISBN 90-5699-224-4) pp. 13 - 40.

Typically, the evaluation of texture may comprise

i) construction of the ODF,

ii) identifying the components Euler angles φΐ, Φ and φ2 (cf. Fig 1) and their

corresponding ODF densities and texture indexes,

iii) construction of pole figure(s) of relevant texture components and

iv) construction of pole plot(s) of the relevant texture components.

Most of the aforementioned patents are concerned with CVD coated cemented carbide tools finding applications in general machining.

In the context of more demanding operations, e.g. machining of case hardened steels for automotive applications (gears, shafts) and through hardened steels (ball bearing steels, tools steels) hard turning with PCBN tools is generally preferred. However, the high hardness of the work material to be machined (often ranging 45-65 HRC) and the high demands on precision and surface finish of the component requires the use of adequate cutting tools with sufficient high wear resistance and toughness.

In other automotive applications where machining of cast iron is required, e.g. finish turning of break discs, PCBN offers substantial productivity improvement compared to cemented carbide or ceramics since higher cutting speeds can be employed.

Similarly, recent applications of PCBN in high speed machining of heat resistant alloys, e.g. Inconel 718 (turbine component, shaft), have also shown remarkable productivity improvement and surface quality compared to traditional cutting tool materials.

It is an object of the present invention to provide an improved cutting tool for difficult- to-machine materials such as those mentioned above.

Surprisingly, it has been found that by coating a PCBN tool with a texture controlled CVD cc-Al₂0₃ layer, a significant improvement in cutting performance can be gained.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1. Definition of the Euler angles φΐ, Φ, and φ2 used in the ODF representation with respect to the crystallographic orientations.

Figure 2. Back scattered SEM micrographs of ion polished cross sections of a textured a- A1₂0₃ layer (4) and Ti(C,N) layers (3 + 2) on a PCBN substrate (1) according to the invention.

Figure 3. ODF contour charts (ODF Euler angles and densities) of textured a- A1₂0₃ layers where density lines in multiples of unit distribution are indicated.

Figure 4. EBSD pole figures (equal area projections) corresponding to ODFs shown in Figure 3. Figure 5. EBSD pole plots corresponding to pole figures shown in Figure 4. χ is the angle from the centre (χ=0) to the rim (χ=90) of the pole figures. MUD is the multiples of unit distribution. DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a cutting tool for machining by chip removal comprising a body of a PCBN based material, onto which a wear resistant coating is deposited. Tools according to the present invention are particularly useful in metal cutting applications of difficult-to-machine materials where a good surface quality as well as a long tool life are two important requirements.

Said PCBN body contains at least 30 vol-% of c-BN in a ceramic binder. The binder contains at least one compound selected from a group consisting of nitrides, borides, oxides, carbides and carbonitrides of one or more of the elements belonging to the groups 4, 5 and 6 of the periodic table as defined according to IUPAC (The International Union of Pure and Applied Chemistry), and Al, e.g., Ti(C,N) and A1N.

In a preferred embodiment, said PCBN body contains 30 vol% < c-BN < 70 vol%, preferably 40 vol% < c-BN < 65 vol%, with an average c-BN grain size between 0.5 μπι and 4 μπι. The binder contains 80 wt% < Ti(C,N) < 95 wt% and rest containing mainly other compounds comprising two or more of the elements Ti, N, B, Ni, Cr, Mo, Nb, Fe, Al and/or O, e.g., TiB₂ and A1₂0₃.

In another preferred embodiment, said PCBN body contains 45 vol% < c-BN < 70 vol%, preferably 55 vol% < c-BN < 65 vol% with an average c-BN grain size between 0.5 μπι and 4 μιη, preferably between Ι μπι and 3μπι. The binder contains 80 wt% < Ti(C,N) < 90 wt%, 1 wt.% < alloy containing one or more of the elements Ni, Co, Cr and/or Mo < 10 wt%, and the rest mainly TiB₂ and A1₂0₃.

In another preferred embodiment, said PCBN body contains 45 vol% < c-BN < 70 vol%, preferably 55 vol% < c-BN < 65 vol% with an average c-BN grain size between 0.5 μιη and 4 μηι, preferably between Ι πι and 3μπι. The binder contains 80 wt% < Ti(C,N) < 90 wt%, 1 wt.% < SiC based ceramic material preferably in the form of SiC whiskers < 10 wt%, and the rest mainly TiB₂ and A1₂0₃.

In another preferred embodiment, said PCBN body contains 70 vol% < c-BN, preferably 80 vol% < c-BN < 95 vol% with an average c-BN grain size either between 0.5 μηι and 10 μπι, preferably between 1 μπι and 6 μπι or between 10 μπι and 25 μηι, preferably between 15 μπι and 25 μ^ηι. The binder contains compounds of two or more of the elements Al, B, N, W, Co, Ni, Fe, Al and/or O.

The coating comprises:

-a first (innermost) layer of TiC_xN_yO_z with 0.7<x+y+z<l, preferably z<0.5, more preferably y>x and z<0.2, most preferably y>0.7, with equiaxed grains and a total thickness <1 μπι preferably >0.1 μπι. -a layer of TiC_xN_yO_z with 0.7<x+y+z<l, preferably with z<0.2, x>0.3 and y>0.2, most preferably x>0.4, with a thickness of 0.1-10 μπι, with columnar grains.

-a layer of oc-Al₂0₃. The A1₂0₃ layer has a thickness of 0.5-10 μπι,

In a preferred embodiment, said TiC_xN_yO_z layer thickness is 0.1-2.0 μιη, preferably 0.5-1.5 μη .

In a preferred embodiment, said TiC_xN_yO_z layer thickness is 1.5-10 μηι, preferably 4-8 μιτι.

In a preferred embodiment, said α-Α1₂0₃ layer thickness is 0.5-4 μπι, preferably 1.5- 3.5 μm.

In a preferred embodiment, said 0c-Al₂O₃ layer thickness is 3-10 μηι, preferably 4-8 μιτι.

In a preferred embodiment the total coating thickness is between 1 and 10 μπι, preferably between 2 and 8 μπι.

In a preferred embodiment the total coating thickness is between 5 and 20 μπι, preferably between 8 and 15 μπι.

In a preferred embodiment, there is a thin, less than 2 μπι thick, TiN top layer on the α-Α1₂0₃ layer.

According to one embodiment of the invention the coating comprises at least one a- A1₂0₃ layer, designed with a texture (crystallographic orientation), preferably with a rotational symmetry (fibre texture), with reference to the surface normal of the coated body.

Said texture exhibits an ODF texture index >1, preferably 1 < texture index < 50, most preferably 2 < texture index < 20, and texture components in the ODF representation (Euler space) with texture components according to

i) 0° < φΐ < 90°, 0° < Φ < 50°, preferably 5° < Φ < 45°, and 0° < φ2 < 120°, with 1 < ODF density < 50, preferably 2 < ODF density < 20 or

ii) 0° < φΐ < 90°, 15° < Φ < 60°, preferably 20° < Φ < 50°, and 0° < φ2 < 60°, preferably 5° < φ2 < 60°, with 1 < ODF density < 50, preferably 2 < ODF density < 20, and/or 60° < φ2 < 120°, preferably 60° < φ2 < 1 15°, with 1 < ODF density < 50, preferably 2 < ODF density < 20, and 0° < φΐ < 90°, 60° < Φ < 90°, preferably 65° < Φ < 85°, and 0° < φ2 < 60°, preferably 10° < φ2 < 50°, with 1 < ODF density < 50, preferably 2 < ODF density < 20, and/or 60° < φ2 < 120°, preferably 70° < φ2 < 110°, with 1 < ODF density < 50, preferably 2 < ODF density < 20.

Said textures are evaluated by ODFs by using EBSD data obtained on the ion polished α-Α1₂0₃ layer. The ODF is constructed using series expansion with a resolution of 32x32x32 points using a Gaussian half width of 5° and Lmax=34 from data with a clustering of 5° over a representative area.

Said coating may comprise an inner single- and/or multilayers of, e.g. TiN, TiC or Ti(C,0,N), (Ti,Si)N or other A1₂0₃ polymorphs, preferably Ti(C,0,N) or (Ti,Si)N, and/or an outer single- and/or multilayers of, e.g. TiN, TiC, Ti(C,0,N) or other A1₂0₃ polymorphs, preferably TiN and/or Ti(C,0,N), to a total thickness <40 μπι.

The deposition method for the α-Α1₂0₃ layer of the present invention is based on chemical vapour deposition at a temperature between 950 °C and 1050 °C in mixed H₂, C0₂, CO, H₂S, HC1 and A1C1₃ at a gas pressure between 50 and 150 mbar as known in the art.

In one embodiment the gas composition during the growth process is as follows (all values in vol-%): 2.5<C0₂<3.5, 1.5<CO<2.5, 0.2<H₂S<0.4, KHCK3 and 1<A1C1₃<2, and balance H₂.

In another embodiment the gas composition during the growth process is as follows (all values in vol-%): 3.5<C0₂<4.5, 1.5<CO<2.5, 0.2<H₂S<0.4, 1<HC1<3 and 1<A1C1₃<2, and the remaining part H₂.

It is within the purview of the skilled artisan to determine the gas flows and gas mixture in accordance with the present invention.

Optionally, said coated body is post treated with, e.g., wet blasting, brushing operation, etc. such that the desired surface quality is obtained.

The present invention also relates to the use of a cutting tool insert according to the above in continuous and interrupted machining of difficult-to-machine materials.

In one embodiment, the present invention relates to the use of CVD-coated PCBN inserts according to above for finish machining hardened steel and/or heat resistant alloys. The PCBN substrate comprises 30 to 70 volume % of c-BN particles bonded through a binder predominantly consisting of Ti type ceramics such as TiN, TiC, Ti(C,N). The CVD coating comprises of TiC_xN_yO_z layer thickness is 0.1-2.0 μπι, preferably 0.5-1.5 μπι and α-Α1₂0₃ layer thickness is 0.5-4 μπι, preferably 1.5-3.5 μηι. Typical cutting conditions for finish turning of hardened steels are vc=l 70-220 m/min, feed rate f=0.05-0.25 mm/rev. and depth of cut ap=0.1-0.5 mm. Typical cutting conditions for finish turning of heat resistant superalloys would be vc=200-400 m/min, feed rate f=0.05-0.25 mm/rev. and depth of cut ap=0.1-0.5 mm.

In another embodiment, the present invention relates to the use of CVD-coated PCBN inserts according to above for finish machining of cast iron. The PCBN substrate comprises 80 to 90 volume % of c-BN particles and the balance of a binder generally consisting of an Al or Co compound. The CVD coating comprises of TiC_xN_yO_z layer thickness is 0.1-2.0 μπι, preferably 0.5-1.5 μπι and oc-Al₂0₃ layer thickness is 0.5-4 μπι, preferably 1.5-3.5 μπι. Typical cutting conditions for finish turning of cast iron are vc=500-800 m/min, feed rate f=0.1-0.3 mm/rev. and depth of cut ap=0.1-0.5 mm.

In another embodiment, the present invention relates to the use of CVD-coated PCBN inserts according to above for rough machining of hardened steel and/or cast iron. The PCBN substrate comprises 80 to 90 volume % of c-BN particles and the balance of a binder generally consisting of an Al or Co compound. The CVD coating comprises of TiC_xN_yO_z layer thickness is 1.5-10 μηι, preferably 4-8 μηι and oc-Al₂0₃ layer thickness is 3-10 μπι, preferably 4-8 μπι. Typical cutting conditions for roughing of cast iron are vc=800-1200 m/min, feed rate f=0.2-0.6 mm/rev. and depth of cut ap= 1-3 mm. Typical cutting conditions for roughing of hardened steel are vc=120-160 m/min, feed rate f=0.1-0.3mm/rev. and depth of cut ap=0.5-1.5 mm.

Example 1

Variant Al (prior art). A solid PCBN insert consisting of a c-BN content of 50 vol-% with a grain size of about 2 μπι in a TiC binder phase (Seco commercial grade CBN 100).

Variant Bl, according to one embodiment of the invention: A PCBN from Variant Al was CVD coated with a 0.2 μπι layer of TiN, having equiaxed grains, a 0.5 μπι layer of columnar TiC_xN_yO_z deposited at 850°C with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=l with z<0.1, and a 2.0 μιη layer of <x- A1₂0₃ deposited at 1000°C using the following gas composition (all values in vol-%): C0₂ = 3.1 %, CO = 2.1 %, H₂S = 0.3, HC1 = 2 and A1C1₃ = 1.8, and the remaining part H₂. The insert was treated after coating with a wet blasting operation.

Variant CI according to one embodiment of the invention. A PCBN from Variant Al was CVD coated with a 0.2 μηι layer of TiN, having equiaxed grains, a 0.5 μπι layer of columnar TiC_xN_yO_z deposited at 850°C with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=l with z<0.1, and a 2.0 μπι layer of a- A1₂0₃ deposited at 1000°C using the following gas composition (all values in vol-%): C0₂ = 3.9 %, CO = 2.1 %, H₂S = 0.3, HC1 = 2 and A1C1₃ = 1.8, and the remaining part H₂. The insert was treated after coating with a wet blasting operation.

Variant Dl according to one embodiment of the invention. A PCBN from Variant Al was coated with a 1.0 μπι layer of Ti_{0 8}Sio.₂N , having equiaxed grains, using conventional arc PVD technique using alloyed Ti-Si cathodes, a 0.5 μπι layer of columnar TiC_xN_y0₂ deposited at 850°C using CVD with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=l with z<0.1, and a 2.0 μιη layer of α-Α1₂0₃ deposited at 1000°C using CVD using the following gas composition (all values in vol-%): C0₂ = 3.9 %, CO = 2.1 %, H₂S = 0.3, HC1 = 2 and A1C1₃ = 1.8, and the remaining part H₂. The insert was treated after coating with a wet blasting operation.

The α-Α1₂0₃ layers from variant Bl and CI were characterized by SEM and EBSD using a LEO Ultra 55 scanning electron microscope operated at 15 kV and equipped with a HKL Nordlys II EBSD detector. The commercial Channel 5 software version 5.0.9.0 was used for data collection. The same software was used for data analyses: calculations of ODFs, i.e. the Euler angles and densities as well as texture indexes, pole figures, and pole plots. Samples for EBSD were obtained by ion polishing the top surface of the α-Α1₂0₃ layers using a JEOL SM-09010 Cross Section Polisher system. The ODFs was constructed using series expansion with a resolution of 32x32x32 points using a Gaussian half width of 5° and Lmax=34 from data with a clustering of 5° over a representative area.

Figure 2 shows a scanning electron microscopy image of an ion polished cross section of the coated PCBN of variant Bl .

Figure 3a shows ODF contour charts (ODF Euler angles and densities) as deduced from the EBSD data of variant Bl with a textured α-Α1₂0₃ layer with a texture index of 2.2. The Euler angles φι, Φ and φ₂ for the texture components are centred (highest ODF density) at 0° < φι < 90°, 5° < Φ < 45°, and 0° < φ2 < 120°. The highest density value is 7.8.

Figure 3b shows ODF contour charts as deduced from the EBSD data of variant CI with a textured α-Α1₂0₃ layer with a texture index of 2.6. The Euler angles φι, Φ and φ₂ for the texture components are centred at 0° < φι < 90°, 20° < Φ < 60°, 5° < φ2 < 60° and at 0° < φ, < 90°, 65° < Φ < 85°, 10° < φ2 < 50°. The highest density value was 6.4.

In addition, pole figures and pole plots of the textures were plotted.

Figure 4a and 4b shows pole figures of variant B 1 and C 1 respectively.

Figure 5a and 5b shows pole plots from the pole figures of Figure 4a and 4b of variant Bl and CI respectively, χ is the angle from the centre (χ=0) to the rim (χ=90) of the pole figures in Figure 4a and 4b. MUD is the multiples of unit distribution.

Example 2

Variant A2 (prior art). A solid PCBN insert consisting of a c-BN content of 90 vol-% with a grain size of about 16 μπι in a Al Ceramic binder phase (Seco commercial grade CBN350).

Variant B2 according to one embodiment of the invention. Same coating as variant B 1 deposited on substrate A2.

Variant C2 according to one embodiment of the invention. Same coating as variant CI deposited on substrate A2.

Example 3

Variant A3 (prior art). Same as variant A2.

Variant B3 according to one embodiment of the invention. A PCBN from Variant A3 was CVD coated with a 0.2 μπι layer of TiN, having equiaxed grains, a 6 μιη layer of columnar TiC_xN_yO_z deposited at 850°C with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=l with z<0.1, and a 5 μπι layer of a- A1₂0₃ deposited at 1000°C using same gas composition as variant Bl. The insert was treated after coating with a wet blasting operation.

Variant C3 according to one embodiment of the invention. A PCBN from Variant A3 was CVD coated with a 0.2 μπι layer of TiN, having equiaxed grains, a 6 μπι layer of columnar TiC_xN_yO_z deposited at 850°C with acetonitrile as carbon and nitrogen source, yielding an approximated carbon to nitrogen ratio x/y=l with z<0.1, and a 5 μπι layer of a- A1₂0₃ deposited at 1000°C using same gas composition as variant CI . The insert was treated after coating with a wet blasting operation. Example 4

The coated cutting tool inserts from Example 1 consisting of solid PCBN inserts of round type ISO RCGN0803M0S were tested in finish turning of a gear wheel component made of a case hardened steel. The cutting data used was as follows:

- Material: SAE 5120 (DIN 20MnCr5), 59-61 HRC

- Cutting speed, Vc = 190 rn/min

- Feed, f = 0.25 mm/rev.

- Depth of cut, ap = 0.15 mm

- Cooling conditions: Dry machining

- Criterion: Surface finish

Surface roughness was measured using stylus type profilometer after machining 25 gear wheel components corresponding to an overall cutting time of 5 minutes.

The surface roughness values (Ra) are indicated in Table 1.

Table 1.

This test shows that the quality of the machined surface is improved (lower Ra value) when the gear wheel component is machined with variants Bl, CI, and Dl (embodiments according to the present invention) when compared to variant Al (prior art).

Example 5

Cutting tool inserts similarly as in Example 1 consisting of solid PCBN inserts of triangular type ISO TNGNl 10308S-01525 were used in a finish turning operation of a case hardened steel bar. The cutting data used was as follows:

- Workpiece Material: SAE 5115 (DIN 16MnCr5), 58-62 HRC

- Cutting speed, Vc = 200 m/min

- Feed, f = 0.1 mm/rev.

- Depth of cut, ap = 0.15 mm

- Cooling conditions: Dry machining

- Criterion: Surface finish

The surface roughness values Ra were measured after a cutting time of 8 minutes. The results are indicated in Table 2 Table 2.

The results show that the quality of the machined surface is improved (lower Ra value) when the case hardened steel is machined with variants Bl, CI, and Dl (embodiments according to the present invention) when compared to variant Al (prior art).

Example 6

The cutting tool inserts from Example 1 consisting of solid PCBN inserts of type ISO TNGN110312S-01525 were tested in a finish turning of a ring component made of through hardened ball bearing steel. The cutting data used was as follows:

Workpiece Material: SAE 52100 (DIN 100Cr6), 58-62 HRC

- Cutting speed, Vc = 180 m/min

- Feed, f = 0.2 mm/rev.

- Depth of cut, ap = 0.25 mm

- Cooling conditions: Dry machining

- Criterion: number of parts machined within acceptable tolerances.

The number of parts machined within the tolerance requirements are indicated in table

Table 3.

This Results show that number of parts machined within acceptable tolerance are improved with variant Bl, CI, and Dl (embodiments according to the present invention) when compared to variant Al (prior art).

Example 7

The cutting tool inserts from Example 2 consisting of solid PCBN inserts of type ISO RNMN120400S-04015 were tested in rough turning of a ring component made of through hardened ball bearing steel. The cutting data used was as follows: Workpiece Material: SAE 52100 (DIN 100Cr6), 58-62 HRC

- Cutting speed, Vc = 120 m/min

- Feed, f = 0.6 mm/rev.

- Depth of cut, ap = 1 mm

- Cooling conditions: Dry machining

- Criterion: number of parts machined with acceptable tool

Table 4.

The Results show that number of parts machined with variant B2 and C2 (embodiments according to the present invention) are increased noticeably when compared to variant A2 (prior art).

Example 8

The cutting tool inserts from Example 1 consisting of solid PCBN inserts of type ISO TNGNl 10308E25 were tested in semi-finish turning of a shaft component made of super alloy Inconel 718. steel. The cutting data used was as follows:

Workpiece Material: Inconel 718, 35 HRC

- Cutting speed, Vc = 300 m/min

- Feed, f = 0.1 mm/rev.

- Depth of cut, ap = 0.25 mm

- Cooling conditions: Flood cooling

- Criterion: Tool life (minutes) corresponding to a maximal flank wear VB=0.3 mm Table 5.

The Results demonstrate that an appreciable increase in tool life (50%) can be obtained when the Inconel 718 shaft component is machined with variant Bl and CI (embodiments according to the present invention) when compared to variant Al (prior art). 1

Example 9

The cutting tool inserts from Example 2 consisting of solid PCBN inserts of type ISO SNMN090308E-WZ-85 were tested in finish turning of a brake disc component made of grey cast iron grade GG25, 230 HBN

- Cutting speed, Vc = 600 m/min

- Feed, f = 0.3 mm/rev.

- Depth of cut, ap = 0.3 mm

- Cooling conditions: Flood cooling

- Criterion: Surface finish

Surface roughness was measured using stylus type profilometer after machining 5000 brake disc components.

The surface roughness values (Rz) are indicated in Table 6.

Table 6.

The results show that the quality of the machined surface is improved noticeably (lower Rz value) when the cast iron brake disc is machined with variants B2 and C2 (embodiments according to the present invention) when compared to variant A2 (prior art).

Example 10

The cutting tool inserts from Example 3 consisting of solid PCBN inserts of type ISO CNMN120412S were tested in rough machining a brake disc component made of grey cast iron grade GG25, 230 HBN

- Cutting speed, Vc = 1 100 m/min

- Feed, f = 0.6 mm/rev.

- Depth of cut, ap = 2 mm

- Cooling conditions: No

-Criterion: Number of parts machined with acceptable tool wear. Table 7.

The results show that number of parts machined with variant B3 and C3 are increased noticeably when compared to variant A3 (prior art).

Claims

Cutting tool insert for machining by chip removal comprising a body, either as a solid insert or attached to a backing body, onto which is deposited a hard and wear resistant coating, c h a r a c t e r i s e d in that said body is a polycrystalline cubic boron nitride compact (PCBN) containing at least 30 vol% of cubic phase boron nitride (c-BN) in a binder comprising at least one compound selected from nitrides, borides, oxides, carbides and carbonitrides of one or more of the elements belonging to the groups 4, 5 and 6 of the periodic table and Al, and in that said coating comprises a textured CVD a- A1₂0₃ layer, with a thickness of 0.5-10 μπι, having an ODF texture index >1, and at least one dominant texture component with 2 < ODF density < 100 within the layer.

Cutting tool insert according to claim 1 , wherein the 1 < ODF texture index < 50.

Cutting tool insert according to claim 1 , wherein the 1 < ODF texture index < 10.

Cutting tool insert according to any of the preceding claims, wherein the 2 < ODF density < 50.

Cutting tool insert according to any of the claims 1 to 3, wherein the 3 < ODF density < 25.

Cutting tool insert according to any of the preceding claims, wherein the said layer is fibre textured.

Cutting tool insert according to any of claims 1 to 6, wherein said α-Α1₂0₃ layer exhibits texture components in the ODF representation, satisfying solutions with Euler angles

- 0° < φ, < 90°, 5° < Φ < 45°, 0° < φ2 < 120° or

- 0° < φ, < 90°, 15° < Φ < 60°, 5° < φ2 < 60° and 0° < φι < 90°, 65° < Φ < 85°, 10° < φ2 < 50°.

Cutting tool insert according to any of claims 1 to 7, wherein a first

(innermost) layer of TiC_xN_yO_z with 0.7<x+y+z<l with equiaxed grains and a thickness <1 μιη and a layer of TiC_xN_yO_z with 0.7<x+y+z<l with a thickness of <10 μηι, with columnar grains.

Cutting tool insert according to claim 8, wherein said TiC_xN_yO_z layer with columnar grains has a thickness that is 0.1-2.0 μπι.

Cutting tool insert according to claim 8, wherein said TiC_xN_yO_z layer with columnar grains has a thickness that is 1.5-10 μηι. Cutting tool insert according to any of the preceding claims, wherein said a- A1₂0₃ layer thickness is 0.5-4 μπι.

Cutting tool insert according to any of claimsl-10, wherein said α-Α1₂0₃ layer thickness is 3-10 μπι.

Cutting tool insert according to any of the preceding claims, wherein the total thickness of the coating is between 1 and 10 μπι.

Cutting tool insert according to any of claims 1-12, wherein the total thickness of the coating is between 5 and 20 μηι.

Cutting tool insert according to any of the preceding claims, wherein said coating has a thin, less than 2 μιη thick, TiN top layer.

Cutting tool insert according to any of the preceding claims, wherein said coating comprises an inner single- and/or multilayer coating of, e.g. TiN, TiC, Ti(C,0,N), (Ti,Si)N, or other A1₂0₃ polymorphs and/or an outer single- and/or multilayer coating of, e.g. TiN, TiC, Ti(C,0,N) or other A1₂0₃ polymorphs, with a total coating thickness <40 μπι.

Cutting tool insert according to any of the preceding claims, wherein said PCBN body contains 30 vol% < c-BN < 70 vol% with an average c-BN grain size between 0.5 μπι and 4 μιη and that the binder phase contains 80 wt% < Ti(C,N) < 95 wt% and rest mainly other compounds comprising two or more of the elements Ti, N, B, Ni, Cr, Mo, Nb, Fe, Al and/or O, e.g., TiB₂ and A1₂0₃.

Cutting tool insert according to any of claims 1-16, wherein said PCBN body contains 45 vol% < c-BN < 70 vol% with an average c-BN grain size between 0.5 μηι and 4 μιη and that the binder phase contains 80 wt% < Ti(C,N) < 90 wt%, 1 wt.% < alloy containing one or more of the elements Ni, Co, Cr and/or Mo < 10 wt%, and the rest mainly TiB₂ and A1₂0₃.

Cutting tool insert according to any of claims 1-16, wherein said PCBN body contains 45 vol% < c-BN < 70 vol% with an average c-BN grain size between 0.5 μπι and 4 μπι and that the binder phase contains 80 wt% < Ti(C,N) < 90 wt%, 1 wt.% < SiC based ceramic material preferably in the form of SiC whiskers < 10 wt%, and the rest mainly TiB₂ and A1₂0₃.

Cutting tool insert according to any of claims 1-16, wherein said PCBN body contains 70 vol% < c-BN with an average c-BN grain size either between 0.5 μηι and 10 μπι and that the binder phase contains compounds of two or more of the elements Al, B, N, W, Co, Ni, Fe, Al and/or O.

Method of making a cutting tool insert according to any of claims 1-20, comprising

-coating the cutting tool insert by chemical vapour deposition at a temperature between 950 °C and 1050 °C at a gas pressure between 50 and 150 mbar in a gas composition comprising mixed H₂, C0₂, CO, H₂S, HC1 and A1C1₃, c h a r a c t e r i s e d in the gas composition, vol-%, C0₂ = 3.1 %, CO = 2.1 %, H₂S = 0.3, HCl = 2, A1C1₃ = 1.8, with the remaining part H₂.

Method of making a cutting tool insert according to any of claims 1 -20, wherein comprising

- coating the cutting tool insert by chemical vapour deposition at a temperature between 950 °C and 1050 °C at a gas pressure between 50 and 150 mbar in in a gas composition comprising mixed H₂, C0₂, CO, H₂S, HCl and A1C1₃, c h a r a c t e r i s e d in the gas composition, vol-%, C0₂ = 3.9 %, CO = 2.1 %, H₂S = 0.3, HCl = 2, A1C1₃ = 1.8, with the remaining part H₂.

Use of a cutting tool insert according to any of claims 1-8, 9, 11, and 17 for machining of hardened steels by chip removal at cutting speeds between 170 and 220 m/min, with an average feed, per tooth in the case of milling, between 0.05 and 0.25 mm depending on cutting speed and insert geometry.

Use of a cutting tool insert according to any of claims 1-8, 9, 11, and 17 for machining of heat resistant superalloys by chip removal at cutting speeds between 200 and 400 m/min, with an average feed, per tooth in the case of milling, between 0.05 and 0.25 mm depending on cutting speed and insert geometry.

Use of a cutting tool insert according to any of claims 1-8, 9, 1 1, and 20 for machining of cast iron by chip removal at cutting speeds between 500 and 800 m/min, with an average feed, per tooth in the case of milling, between 0.1 and 0.3 mm depending on cutting speed and insert geometry.

Use of a cutting tool insert according to any of claims 1-8, 10, 12, and 20 for machining of cast iron by chip removal at cutting speeds between 800 and 120 m/min, with an average feed, per tooth in the case of milling, between 0.2 and 0.6 mm depending on cutting speed and insert geometry

Use of a cutting tool insert according to any of claims 1-8, 10, 12, and 20 for machining of hardened steel by chip removal at cutting speeds between 120 and 160 m min, with an average feed, per tooth in the case of milling, between 0.1 and 0.3 mm depending on cutting speed and insert geometry.

Use of a cutting tool insert according to any of claims 1 to 9 for machining by chip removal at cutting speeds between 75 and 600 m/min, preferably between 150 and 600 m/min, with an average feed, per tooth in the case of milling, between 0.08 and 0.8 mm, preferably between 0.1 and 0.6 mm, depending on cutting speed and insert geometry.