WO2009058082A1

WO2009058082A1 - Coated cutting insert for machining of aluminium based alloys

Info

Publication number: WO2009058082A1
Application number: PCT/SE2008/051230
Authority: WO
Inventors: Tommy Larsson; Anna Sandberg; Andreas Larsson
Original assignee: Seco Tools Ab
Priority date: 2007-11-01
Filing date: 2008-10-29
Publication date: 2009-05-07
Also published as: EP2217743A1; SE0702411L

Abstract

The present invention relates to a cutting tool insert, particularly useful for machining of aluminiumalloys, comprising a cemented carbide substrate and a coating. The cemented carbide has a composition of 4-14 wt% Co, up to 5 wt% of the elements Ti, Ta, and/or Nb and/or Cr or other element from groups IVb, Vbor VIband rest WC. The coating is composed of one or more layers of refractory compounds of which at least one layer comprise ZrN.

Description

Coated cutting insert for machining of aluminium based alloys

The present invention relates to machining of aluminium alloys. More particularly, the present invention relates to using inserts consisting of a substrate based on WC-Co and a hard and wear resistant refractory layer of ZrN resulting in an unexpected increase in tool life and in productivity.

Aluminium is a material which, in general, is easy to machine with cemented carbide tools. Often, very high metal removal rates in combination with long tool life can be obtained. However, in some abrasive aluminium alloys e.g. high silicon content alloys, the machinability with cemented carbide tools is limited and the use of for instance diamond tools or diamond coated tools is most effective . Uncoated cemented carbide is normally used for the machining of aluminium alloys because uncoated cemented carbides provide wear resistance, toughness and good high temperature properties. So far no improvement has been found when using coated inserts except for diamond and diamond-like carbon coatings. US 5651295 discloses the use of a sharp edge physical vapor deposition coated cemented carbide cutting tool for machining of internal and external grooves in aluminium based alloys. The tool is coated with a TiN layer.

US 4859124 discloses methods of making and of using a high density high strength titanium diboride comprising material. The method of use is as a cutting tool at relatively high speeds against aluminium based materials.

US 5069092 provides an iron-based cutting tool, useful for machining aluminium based workpieces. The cutting tool is coated with a layer of silicon carbide having a thickness in the range of about 1-4 μm.

EP 1563933 relates to coated cemented carbide cutting tool inserts for bimetal machining under wet conditions at moderate cutting speeds, particularly useful for face milling of engine blocks comprising alloys of aluminium and/or magnesium and cast iron. The inserts are characterized by a submicron WC-Co cemented carbide and a coating including an inner layer of TiCN with columnar grains followed by a layer of K-AI2O3 and a top layer of TiN.

US 6617271 discloses a high-performance binder-less high purity tungsten carbide material, its manufacturing and applications as a cutting tool material such as for the use to machine aluminium alloys.

US 6896452 relates to method of milling a material comprising aluminium and cast iron. By using a silicon nitride based cutting tool insert at a cutting speed of more than 1000 m/min an unexpected increase in tool life has been obtained.

It is an object of the present invention to provide a cutting tool insert for machining of aluminium alloys by chip removal with improved properties.

It has been found that inserts provided with a ZrN layer display enhanced performance in aluminium alloy cutting preferably turning or milling.

Brief description of the drawings

Fig 1. Fracture cross-section of the ZrN-layer according to the invention in as-deposited condition. "A" denotes the ZrN layer, and "B" denotes the WC-Co substrate.

Fig 2. X-ray diffraction patterns using CuKCC radiation and

(a) Θ-2Θ geometry and (b) a constant gracing incident angle of 1° between primary beam and sample surface and by scanning only the detector from a ZrN-layer obtained from a ZrN layer on a WC-Co substrate, according to the invention, in the as-deposited condition .

According to the present invention a coated cutting tool insert is provided with a cemented carbide substrate having a composition of 4-14 wt% Co, preferably 5-11 wt% Co, elements Ti,

Ta, and/or Nb and/or Cr or other element from groups IVb, Vb or

VIb corresponding to a total content of less than 5 wt%, preferably less than 2.5 wt% and rest WC.

Furthermore, the mean intercept length of the tungsten carbide phase measured on a ground and polished representative cross section is in the range 0.25-0.75 μm, preferably 0.3-0.7 μm.

The intercept length is measured by means of image analysis on micrographs with a magnification of 1000Ox and calculated as the average value of about 1000 intercept lengths.

In a first embodiment the cemented carbide contains only WC and Co . In a second embodiment the cemented carbide contains 0.1-5.0 wt%, preferably 0.1-2.5 wt% of the cubic carbide forming elements Ti, Ta and/or Nb, which may be replaced by other carbides of elements from groups IVb, Vb or VIb of the periodic table.

In a third embodiment the cemented carbide contains 0.1-0.7 wt% Cr and/or V in addition to WC and Co.

In a fourth embodiment particularly for turning applications, the Co content is 4-9 wt%, preferably 5-8 wt%.

In a fifth embodiment particularly for milling applications, the Co content is 5-11 wt%. The cemented carbide substrate is provided with a coating of at least one layer of ZrN, preferably only one ZrN-layer, of a crystalline phase (PDF 35-0753) , as detected by X-ray diffraction (XRD) using CuKCC radiation in Θ-2Θ and/or gracing incidence geometry. The ZrN phase may contain elements from the groups IVb-VIb, for example Ti, Nb, Hf, Cr, V up to 20 at-%, preferably up to 10 at-%, of the metal content.

Nitrogen can partly be replaced by carbon, oxygen and/or boron corresponding to a concentration of up to 25% of the N concentration.

The total layer thickness, measured on the clearance face, of the ZrN-layer (s) according to the present invention is between 0.1 and 10 μm, preferably between 0.5 and 5 μm with the total thickness of the non ZrN containing layer (s) being less than 10 μm. The present invention also relates to a method of making a cutting insert by powder metallurgical technique, wet milling of powders forming hard constituents and binder phase, compacting the milled mixture to bodies of desired shape and size and sintering, comprising a cemented carbide substrate and a coating. According to the method a substrate is provided consisting of 4-14 wt% Co, preferably 5-11 wt% Co, elements Ti, Ta, and/or Nb and/or Cr or other element from groups IVb, Vb or VIb corresponding to a total content of less than 5 wt%, preferably less than 2.5 wt%, and rest WC, and a mean intercept length of the tungsten carbide of 0.3-0.8 μm, preferably 0.4-0.8 μm, and depositing a coating by arc evaporation composed of one or more layers of refractory compounds of which at least one layer comprises a ZrN crystalline phase (PDF 35-0753) as detected by X-ray diffraction (XRD) in Θ-2Θ and/or gracing incidence geometry. The ZrN phase may contain elements from the groups IVb-VIb, for example Ti, Nb, Hf, Cr, V up to 20 at-%, preferably up to 10 at-%, of the metal content. Nitrogen can partly be replaced by carbon, oxygen and/or boron corresponding to a concentration of up to 25% of the N concentration.

The method used to grow the layer, comprising ZrN phase of the present invention, is based on arc evaporation of a cathode, under the following conditions:

The evaporation current is between 70 A and 150 A depending on cathode size and cathode material. When using cathodes of 63 mm in diameter the evaporation current is preferably between 80 A and 140 A.

The substrate bias is between -10 V and -80 V, preferably between -20 V and -60 V. The deposition temperature is between 400°C and 700°C, preferably between 500°C and 700°C.

The atmosphere consists preferably of N₂ at a total pressure of 0.5 Pa to 10 Pa, preferably 2 Pa to 8 Pa.

The present invention has been described with reference to layer (s) containing a ZrN phase deposited using arc evaporation. It is obvious that ZrN phase containing layer (s) also could be produced using other PVD-technologies such as magnetron sputtering, electron beam evaporation, ion plating or laser ablation . The present invention also relates to the use of inserts according to above for machining of aluminium alloys, at cutting speeds of 500-1600 m/min, cutting depths of 0.5-10 mm and feeds of 0.05-2.0 mm/rev in turning applications or 0.05-2.0 mm/tooth in milling applications.

Example 1

Grade A: A cemented carbide substrate according to the invention, with the average composition 6.0 wt% Co, 0.28 wt% Cr and balance WC, and a mean intercept length of WC in the sintered substrate of about 0.45 μm was produced by conventional milling of powders, pressing of green compacts and subsequent sintering at 1400 °C. The substrate was coated, as described below, with a 3.5 μm thick layer of ZrN, see Fig. 1.

Grade B: A cemented carbide cutting tool, with a cemented carbide substrate according to Grade A was coated with a 3.4 μm thick layer of Tio.33Alo.67N.

Grade C: A uncoated cemented carbide cutting tool with a cemented carbide according to grade A.

Grade D: A cemented carbide substrate according to the invention, with the average composition 10.0 wt% Co, 0.45 wt% Cr and balance WC, and a mean intercept length of WC in the sintered substrate of about 0.4 μm was produced by conventional milling of powders, pressing of green compacts and subsequent sintering at 1400 °C. The substrate was coated, as described below, with a 2.1 μm thick layer of ZrN.

Grade E: A cemented carbide cutting tool, with a cemented carbide substrate according to Grade D was coated with a 2.2 μm thick layer of Tio.33Alo.67N.

Before deposition, the substrates were cleaned in ultrasonic baths using alkali solution and alcohol and subsequently placed in the PVD-system using a fixture of three-fold rotation. The shortest cathode-to-substrate distance was 130 mm. The system was evacuated to a pressure of less than 2.0xl0^~3 Pa, after which the substrates were sputter cleaned with Ar ions. The layers were grown using arc evaporation of Zr cathodes (63 mm in diameter) . The deposition was carried out in a 99.995% pure N₂ atmosphere at a total pressure of 7.0 Pa, using a substrate bias of -52 V. The deposition temperature was about 530°C. The thickness of the coating layer was measured in the middle of the clearance face of the cutting tool insert.

The X-ray diffraction pattern (CuKCC radiation, Θ-2Θ geometry) of the as-deposited ZrN (PDF 35-0753) layer is shown in Figure 2 a.

Phase identification of the ZrN in as-deposited condition was made by X-ray diffraction using a constant gracing incident angle of 1° between primary beam and sample surface and scanning the detector in order to magnify peaks originating from the layer, see Figure 2 b.

Tio.₃₃Alo.₆₇N layers were deposited using conventional arc technology.

Example 2

Grades A, B and C were tested in a turning operation of aluminium.

The test was stopped when the flank wear reached a maximum value of 0.15 mm.

Example 3 Grades A, B, and C were tested in machining of an aluminium gear casing.

The test was stopped when the surface integrity of the machined component was unsatisfactory.

Example 4

Grades D and E were tested in square shoulder milling of an aluminium alloy component.

The test was stopped when the flank wear reached a maximum value of 0.2 mm.

Claims

1. Cutting tool insert, particularly useful for machining of aluminium alloys, comprising a cemented carbide substrate and a coating, c h a r a c t e r i s e d in - the cemented carbide having a composition of 4-14 wt% Co, preferably 5-11 wt% Co, elements Ti, Ta, and/or Nb and/or Cr or other element from groups IVb, Vb or VIb corresponding to a total content of less than 5 wt%, and rest WC, with a mean intercept length of the tungsten carbide in the range 0.25-0.75 μm, and - the coating being composed of one or more layers of refractory compounds of which at least one 0.1 to 10 μm thick layer comprises ZrN of a crystalline phase (PDF 35-0753) , as detected by X-ray diffraction (XRD) using CuKCC radiation in Θ-2Θ and/or gracing incidence geometry and that the ZrN phase may contain elements from groups IVb-VIb, preferably Ti, Nb, Hf, Cr, V up to 20 at-%, preferably up to 10 at-%, of the metal content, nitrogen being partly replaced by carbon, oxygen and/or boron corresponding to a concentration of up to 25% of the N concentration.

2. Cutting tool insert according to claim 1 c h a r a c t e r i s e d in that the layer consists of pure ZrN.

3. Cutting tool insert according to claim 1 c h a r a c t e r i s e d in that the cemented carbide contains only WC and Co.

4. Cutting tool insert according to claim 1 c h a r a c t e r i s e d in that the cemented carbide contains 0.1-5.0 wt-% of the elements Ti, Ta and/or Nb.

5. Cutting tool insert according to claim 1 c h a r a c t e r i s e d in that the cemented carbide contains 0.1-0.7 wt% Cr and/or V in addition to WC and Co.

6. Cutting tool insert according to any of the preceding claims c h a r a c t e r i s e d in that the coating consists of an only layer of ZrN.

7. Method of making a cutting tool insert comprising a cemented carbide substrate and a coating, c h a r a c t e r i s e d in

- preparing by conventional powder metallurgical technique a substrate with a composition of 4-14 wt% Co, preferably 5-11 wt% Co, elements Ti, Ta, and/or Nb and/or Cr or other element from groups IVb, Vb or VIb corresponding to a total content of less than 5 wt%, and rest WC, with a mean intercept length of the tungsten carbide of 0.25-0.75 μm, and - depositing a coating composed of one or more layers of refractory compounds of which at least one layer comprises a ZrN crystalline phase (PDF 35-0753) as detected by X-ray diffraction (XRD) in Θ-2Θ and/or gracing incidence geometry and that the ZrN phase may contain elements from the groups IVb-VIb, for example Ti, Nb, Hf, Cr, V up to 20 at-%, preferably up to 10 at-%, of the metal content and that nitrogen can partly be replaced by carbon, oxygen and/or boron corresponding to a concentration of up to 25% of the N concentration, whereby the ZrN-layer is deposited from a Zr containing cathode at an evaporation current between 70 A and 150 A, a substrate bias of between -10 V and -80 V, a deposition temperature of between 400°C and 700°C, in an atmosphere of N₂ at a total pressure of 0.5 Pa to 10 Pa.

8. Use of inserts according to above for machining of aluminium alloys, at cutting speeds of 500-1600 m/min, cutting depths of 0.5-10 mm and feeds of 0.05-2.0 mm/rev, or 0.05-2.0 mm/tooth in milling applications.