Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
  • C23C30/005—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process on hard metal substrates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material

Definitions

• the present invention relates to a composition for use as a coating on a cutting tool and, in particular, to a low friction, wear-resistant coating formed from a hard phase of, for example, TiN and a soft, lubricating phase of, for example, MoS 2 .
• TiB 2 has been investigated as a hard matrix material with a lubricating phase of MoS 2 . Whilst hardness and low friction properties can generally be obtained, such coatings can sometimes fail owing to the brittleness of the TiB 2 phase.
• the present invention aims to address the problems associated with the prior art and to provide dense, relatively hard and wear-resistant coatings with a sufficiently high enough concentration of MoS 2 or WS 2 to obtain self lubrication. This is preferably achieved by co-depositing a lubricating material with a hard coating material.
• composition for use as a coating on a cutting tool, which composition comprises:
• a first material selected from TiN x , TiAlN x , TiAlYCrN x and CrN x , and
• x is from 0.5 to 1.5
• z is from 0.8 to 2.2
• the atomic ratio (y) of Mo or W to Ti or Cr is from 0.1 to 0.8.
• x is from 0.5 to 1.5
• z is from 1 to 2.2
• the atomic ratio (y) of Mo or W to Ti or Cr is from 0.2 to 0.8.
• x is from 0.7 to 1.3, more preferably 0.8 to 1.2, still more preferably equal to or approximately equal to 1 for even higher hardnesses and lower coefficients - 3 -
• z is preferably from 1.2 to 2, more preferably from 1.4 to 1.8, still more preferably equal to or approximately equal to 1.6.
• y is preferably from 0.2 to 0.5, more preferably from 0.2 to 0.4, still more preferably equal to or approximately equal to 0.3.
• the composition according to this embodiment has a hardness typically of at least 14 GPa, more typically from 15 to 23 GPa, still more typically from 16 to 22 GPa.
• x is from 0.5 to 1.5
• z is from 0.8 to 2.2 and the atomic ratio (y) of Mo or W to Ti or Cr is between 0.1 to 0.2 when z is from 0.8 to 2.2, and is from 0.1 to 0.8 when z is between 0.8 and 1.
• x is advantageously from 0.7 to 1.3, more preferably 0.8 to 1.2, still more preferably equal to or approximately equal to 1 for even higher hardnesses and lower coefficients of friction.
• z is preferably from 0.8 to 1.4.
• y is preferably from 0.12 to 0.18, more preferably from 0.14 to 0.16, still more preferably equal to or approximately equal to 0.15.
• the composition according to this embodiment has a hardness typically of at least 14 GPa, more preferably from 22 to 32 GPa, still more preferably from 25 to 30 GPa.
• the first material may comprise more than one of TiN x , TiAlN x , TiAlYCrN x and CrN x and the second material may comprise one or both of MoS 2 and WS Z .
• composition according to all of the embodiments of the present invention will generally have a friction coefficient of from 0.08 to 0.3, more - 4 -
• the composition comprises:
• a first material selected from TiN x , TiAlN x , TiAlYCrN x and CrN x , and
• x is equal to or approximately equal to 1
• z is equal to or approximately equal to 1.6
• the atomic ratio (y) of Mo or W to Ti or Cr is from 0.2 to 0.4
• the composition has a friction coefficient of from 0.08 to 0.2, preferably from 0.08 to 0.12, and a hardness of from 16 to 22 GPa, preferably from 18 to 22 GPa, more preferably from 20 to 22 GPa.
• the composition comprises:
• a first material selected from TiN x , TiAlN x , TiAlYCrN x and CrN x , and
• x is equal to or approximately equal to 1
• z is equal to or approximately equal to 1.1
• the atomic ratio (y) of Mo or W to Ti or Cr is between 0.1 and 0.2
• the composition has a friction coefficient of from 0.08 to 0.2, preferably from 0.08 to 0.12, and a hardness of from 22 to 32 GPa, preferably from 25 to 30 GPa, more preferably approximately equal to 27 GPa.
• the microstructure of a coating according to the present invention typically comprises a soft, lubricating phase of MoS z or WS Z in a hard matrix phase of TiN x , TiAlN x , TiAlYCrN x or CrN x , with nanometre grain size, typically of from 1 to 10 nm.
• a ⁇ lubricant reservoir' substantially throughout the coating thickness allows lubrication to be maintained even as the coating wears away.
• An additional advantage arises because the MoS. or WS Z , phase is incorporated within a hard matrix and this provides a degree of oxidation protection.
• TiN, TiAIN, TiAlYCrN or CrN are used as a hard phase because, in addition to their outstanding mechanical properties (superhardness and high toughness) , these nitrides display relatively good tribological properties compared with other hard coatings.
• TiN has a friction coefficient typically quoted between 0.4 and 0.8 against steel, or even less than 0.2 when rubbing against itself or certain hard counter-faces, such as A1 2 0 3 .
• the present invention also provides a wear- resistant, self-lubricating coating comprising a composition as herein described and, additionally, an article having such a coating.
• the present invention also provides a cutting tool comprising a substrate having one or more coatings thereon, wherein at least one of the said coatings comprises a composition as herein described.
• the substrate may have more than one such coating, for example a first coating of TiN x and MoS z and a second coating of, for example, TiAlN x and WS 2 .
• compositional variations may exist within each coating. For example, a gradient coating may be - 6 -
• MoS z content is zero (or at least approaching zero) at the substrate surface and is continuously increased with distance into the coating (and away from the substrate) until the required level is reached.
• the substrate material may be formed from any of the conventional cutting tool materials, such as, for example, a hard metal, a high speed steel or a cermet.
• a layer consisting essentially of Ti, TiAl, TiAlYCr, Cr, TiN, TiAIN, TiAlyCrN or CrN is advantageously disposed between a surface of the substrate and the one or more coatings, since this has been found to improve adhesion between the coating (s) and the substrate.
• the choice of the material for this intermediate layer is advantageously based on the nitride constituent of the coating. For example, if the coating comprises TiN x , then the intermediate layer would preferably be formed from Ti or TiN.
• a first layer consisting essentially of Ti, TiAl, TiAlYCr or Cr and this layer is disposed adjacent a surface of the substrate, and a second layer consisting essentially of a nitride of the material of the first layer, i.e. TiN, TiAIN,
• TiAlYCrN or CrN is disposed between the first layer and the one or more coatings as herein described.
• the choice of the material for the first layer is advantageously based on the nitride constituent of the coating.
• the coating comprises TiAlN x
• the first layer would preferably be formed from an alloy of Ti and Al .
• a three-component adhesion-promoting underlayer may advantageously be used.
• a first layer of Ti may be deposited on to the surface of the substrate.
• a layer of TiN may be deposited on to the first layer.
• MoS z may be deposited, starting off with 0% MoS z (or at least approaching zero) and then continuously increasing the MoS z content to that of the functional TiN x (MoS 2 ) y self-lubricating layer as herein described.
• the cutting tool according to the present invention may be used with a lubricant and/or a cooling fluid, it is particularly suited to dry- machining applications, i.e. no lubricant or cooling fluid, or micro-lubrication applications, where very little lubricant and/or cooling fluid is/are required.
• the present invention also provides for the use of a composition as herein described as a low- friction, wear-resistant coating. Whilst the coating composition will generally be used in the manufacture of cutting tools, it will be appreciated that it can be used in any area requiring low-friction and good wear-resistance .
• a process for forming a wear resistant, low friction coating on a substrate which process comprises the steps of:
• the deposition chamber may comprise a sputtering system, for example an unbalanced dc magnetron sputtering system, in which the means to deposit the first and second deposition materials simultaneously preferably includes a target comprising the first deposition material and a target comprising the second deposition material.
• a composite target may be used. In this way. Tin and MoS 2 , for example, can be co-sputtered on to the surface of the substrate.
• the composite target may take the form of a mosaic target having, for example, one or more TiN portions adjacent one or more MoS 2 portions.
• Magnetron sputter ion plating is described in detail in GB-2 258 343.
• the substrate is typically maintained at a temperature of from 80 to 500°C, preferably from 100 to 300°C, more preferably from 150 to 250°C and still more preferably approximately 200°C during deposition.
• Deposition is preferably carried out in a vacuum or an inert gas atmosphere.
• Deposition is generally carried out using a power density typically in the range of from 5 to 20 Wcirf 2 , preferably from 5 to 15 Wcirf 2 .
• a target current typically in the range of from 5 to 20 Wcirf 2 , preferably from 5 to 15 Wcirf 2 .
• a target current typically in the range of from 5 to 20 Wcirf 2 , preferably from 5 to 15 Wcirf 2 .
• a target current typically in the range of from 5 to 20 Wcirf 2 , preferably from 5 to 15 Wcirf 2 .
• a target current of from 0.5 to 1.5 A (equivalent to a target voltage of from 250 to 800 V) and preferably approximately 1 A (equivalent to a target voltage of approximately 520 V) .
• a bias voltage of approximately -100 V has been found to provide the best results.
• the hard matrix TiN for example, reactively by introducing a sufficient quantity of nitrogen into the process gas whilst sputtering from a Ti target.
• the MoS 2 reactively deposit the MoS 2 , for example, by reactive deposition using a Mo target and the addition of a sulphur containing process gas such as H 2 S.
• an arc/sputter hybrid device may be used to deposit, for example TiN and MoS 2 simultaneously on the surface of the substrate.
• the hard phase of, for example, TiN is deposited from a titanium cathodic arc and MoS 2 , for example, is simultaneously deposited by magnetron sputtering.
• the nitrogen allows the reactive deposition of TiN in conjunction with the Ti arc source whilst the argon provides an efficient sputtering gas for the MoS 2 . In effect, nitrogen is not particularly effective for the sputtering of MoS 2 .
• any other deposition process which would allow the deposition of the first deposition material in conjunction with magnetron sputtering of the second deposition material such as plasma- assisted CVD or photon-induced deposition, may be used.
• plasma- assisted CVD or photon-induced deposition
• the arc current should be adjusted so as to obtain a suitable TiN deposition rate with respect to the MoS 2 deposition rate in order to produce a coating within the given composition.
• the arc current is at least 50 A.
• the pressure inside the deposition chamber is provided by the nitrogen and argon process gases.
• a pressure of from 0.1 to 1 Pa is preferred with the volumic flow ratio of nitrogen to argon preferably being approximately 10:1, so as to provide a suitable compromise between the reactive deposition of TiN with nitrogen and the sputtering of MoS 2 using argon.
• the volumic flow ratio of nitrogen to argon preferably being approximately 10:1, so as to provide a suitable compromise between the reactive deposition of TiN with nitrogen and the sputtering of MoS 2 using argon.
• the present invention also provides a process for machining, for example milling, a cast iron component, which process comprises the step of machining a component using a cutting tool as herein described.
• the step of machining may be carried out in the absence of a lubricant or a cooling fluid (dry machining) or, alternatively, using a minimum amount of a lubricant and/or a cooling fluid (micro- lubrication) .
• machining may be applied to a variety of materials as well as cast iron - 11 -
• components for example carbon steels, stainless steels, aluminium, copper, and including alloys thereof.
• Figure 1 is a schematic representation of a co- deposition process according to the present invention
• Figure 2 shows the variation of atomic ratios for the overall composition TiN x (MoS 2 ) y with substrate position and substrate bias as measured by GDOES (x and y) , EDX (y and z) and XPS (x and z) .
• Figures 3(a) and (b) shows SEM cross-sections for coatings deposited on Mo substrates in positions -30 at 0 (a) and -100 V (b) .
• Figures (a) and (b) shows the variation in X-ray diffraction spectra with substrate position for 0 V bias (a) and -100 V bias (b) . Each spectrum is labelled with substrate position in mm.
• Figure 5 shows the variation in hardness and friction coefficient as a function of substrate position for 0 V and -100 V bias. Friction values are taken over the whole sliding distance, except for biased coatings produced in positions -40 to -65, for which the first 50 m of unstable friction are excluded from the average calculation. - 12 -
• Figure 6 are friction curves showing a typical behaviour for biased coatings in positions -40 to -65, characterised by an initial maximum in friction (curves a, b and c) , and friction behaviour typical of all other coatings, characterised by practically featureless low friction (curve d) .
• Figure 7 is a schematic top view of a deposition chamber according to the present invention.
• Figure 8 shows room temperature pin-on-disk test results for TiN-MoS z coatings as compared to TiN standard coatings using either 6 mm diameter 100Cr6 steel or A1 2 0 3 balls as counterfaces .
• Figure 9 shows comparative lifetime test results for uncoated HSS drills, TiN-coated drills and TiN- MoS, coated drills.
• Film deposition may be performed using an unbalanced dc magnetron sputtering system 1, schematically represented in Figure 1 and described in detail by P. Losbichler and C. Mitterer in Surf. Coa t . Technol . , 97 (1997), 568-574.
• a composite TiN-MoS 2 target 5 was used, made up of two halves cut from 150 mm diameter TiN and MoS 2 targets, 6 and 7 respectively, which were bonded to a water-cooled backing plate 8.
• Substrates 10 were mechanically polished and degreased stainless steel rectangles (10 x 20 mm) .
• the substrates 10 were fixed to a holder 11, located 6 cm above the target 5 and placed at various positions between -75 and + 75 mm (this number refers to the horizontal distance between the centre of the substrate 10 and the target's 5 central dividing line, negative on the TiN side and positive on the MoS 2 side) .
• the chamber 2 was pumped down to a base pressure of 10 "3 Pa with a turbo-molecular pump 3. - 13 -
• the target 5 Prior to film deposition, the target 5 was sputter cleaned for 5 minutes behind a shutter 13 and substrates 10 were sputter etched for 20 minutes with an Ar pressure of 3.5 Pa and a dc voltage of -1500 V. Deposition was then carried out, with the substrate 10 temperature maintained at 200°C by a resistance heater 12, using 0.7 Pa Ar pressure, 1 A target 5 current (around 520 V) and either 0 or -100 V substrate 10 bias. Deposition time was 45 minutes and resulted in a coating thickness in the 0.5 to 3 ⁇ m range, depending on substrate 10 position.
• the overall coating chemistry and the phase composition was investigated by XPS on a Cameca- Nanoscan 50, incorporating a MAC2 semi-imaging analyser, set at an energy resolution of 0.5 eV.
• the unmonochromated MgK ⁇ source was operated at 12 kV and 30 mA.
• a rastered 3 keV, 0.2 ⁇ A Ar + ion beam was employed to remove the surface oxide, the 0 Is peak being monitored until it no longer decreased.
• the energy scale was calibrated using the Cu 2p 3/2 and Au 4f 72 peaks at 932.67 and 83.98 eV respectively.
• Quantification of the spectra was performed using relative sensitivity factors determined from Ti Mo, TiN and MoS 2 standards. Due to the preferential sputtering of S, the S content was estimated from the Mo 3d 52 (sulphide) peak position in the spectra from the native surface.
• GDOES Glow Discharge Optical Emission Spectroscopy
• GDOES Glow Discharge Optical Emission Spectroscopy
• EDX analysis X-ray microstructural analysis of the samples was performed by Glancing Angle X-ray Diffraction (GAXRD) using an unmonochromated copper source at an incident angle of 1.0°, a high precision beam collimation and sample positioning system, and a - 14 -
• Hardness and Young' s modulus were determined by an ultra-low load depth-sensing nanoindenter (Nanoindenter II, from Nano Instruments Inc.) described in detail by R. Gilmore, M.A. Baker, P.N. Ginbson and W. Gissler in Surf. Coa t , Technol . (in press) .
• a pin-on-disk tribometer (CSEM) was used to determine the friction coefficient.
• Counterface material was 6 mm diameter steel ball and track radius was 3.5 mm.
• a normal load of 1 N and a sliding speed of 0.05 m/s were used over a sliding distance of 250 m in laboratory air and at an ambient temperature (24°C ⁇ 1) •
• Coating composition as a function of substrate position and bias voltage is shown in Figure 2. Because coatings from position +20 to +75 tended to rapidly spall off once removed from the vacuum chamber, characterisation results are available for substrate positions -75 to +15 only.
• the MoS 2 content decreases progressively from a maximum value of approximately 66% at position +15 to a lower limit of around 18% at position -75.
• the MoS 2 content is calculated as 100 x 1/(1 + y) for the overall composition TiN x (MoS z ) y .
• the TiN is generally stoichiometric with only very slight variation with substrate position and no measurable effect due to - 15 -
• the MoS z phase is slightly sub- stoichiometric at about MoSj.g, showing relatively little variation with substrate position or bias.
• Figure 4 shows GAXRD spectra for the various coatings with superimposed MoS z and TiN x phases to separate.
• the TiN phase is obviously nanocrystalline, and it shows a more ordered structure under the TiN half of the target (from positions -15 to -75) with an average crystallite size of the order of several run.
• TiS As a reference for the S 2p 32 peak position, TiS has a quoted binding energy of 163.5 eV, but has an h.c.p. structure. Possibly a better reference is f.c.c. MnS (Mn having an electronegativity very similar to Ti) for which the binding energy is quoted as 162.0 eV, which would lead to a peak overlapping that of MoS 2 . Even for the lowest MoS 2 contents (18%), it seems reasonable to conclude that an MoS 2 phase exists since only a small part could substitute into the TiN lattice. At first sight, this observation appears to be in contradiction - 17 -
• Figure 5 shows the hardness and friction results.
• Hardness passes through a maximum around position -40, for both the biased and non-biased coatings with maximum average values of about 20 and 17 GPa respectively.
• the increase in hardness between position +15 and -40 can be attributed to the improving crystal structure of the TiN phase as the MoS 2 content diminishes.
• the systematically higher hardness values in the case of -100 V bias for positions left of 20 may be attributable to the optimum deposition conditions for the TiN phase. It is, however, not clear why the hardness then diminishes for positions to the left of -40. It would rather be expected that hardness continues to increase or stabilise as MoS 2 content decreases.
• film deposition was performed using the system schematically represented in Figure 7.
• the deposition facility 20 was composed of two opposing arc evaporation Ti sources 25 and two opposing MoS 2 magnetron targets 30, which could be operated independently.
• the samples (drills and flat substances) were positioned in a carousel-type sample holder 35 with three rotational axes.
• the drills were of the type HSS DIN 338 of 6 mm diameter and 100 mm length and the flat samples were hard metal discs of diameter 23 mm.
• the flat samples were later used for mechanical and structural characterisation (such as glancing angle X-ray diffractometry, EDX, nanoindentation, pin-on-disk testing, scratch testing) whilst the drills were used for field tests.
• Samples were cleaned in an ultrasonic bath in a benzene/alcohol solution. Before deposition, the chamber was evacuated to a residual pressure of 5xl0 "5 mbar and then heated to 250°C for 30 minutes using infra red heaters 40, 41 and 42. Coating was then performed as follows.
• the chemical composition of the co-deposited coatings was determined using EDX analysis and found to be (TiN) 0 . 87 (MoS z ) o . 13 wherein z is in the range of 0.8 ⁇ z ⁇ 1.4.
• the coating was found to display a f.c.c. structure typical for TiN with a slightly enlarged lattice parameter as determined by Glancing T ⁇ ngle X- Ray Diffraction.
• the hardness of the coatings was determined to be about 27 GPa with a nanoindenter, approximately the - 21 -
• the nanoindenter was calibrated with a Si 111 wafer, assuming for this material a hardness of 11 GPa.
• the adhesion was determined with a scratch tester. A critical load value of 105 N was found.
• the friction coefficient was measured with a pin- on-disk tester using a steel (100Cr6) or A1 2 0 3 sphere of diameter 6 mm as a counterface at a sliding speed of 0.1 m/s (track radius 8 mm) and a load of 5 N at room temperature and with a relative humidity of about 40%.
• Figure 8 displays the friction coefficient of a TiN and a TiN-MoS 2 coating as function of the distance. After a short running-in phase the friction coefficient of the TiN-MoS 2 coating assumes a constant value of less than 0.2 for both types of counterface in comparison to 0.8 for the TiN coating.
• the lifetime was determined by the number of holes drilled before the drill broke. In order to facilitate the running-in phase the first five holes were drilled with a depth of 20 mm. The results are shown in Figure 9, where the lifetimes of several TiN- MoS 2 coated drills are compared with uncoated drills and TiN-coated drills. The expected increase in lifetime is observed for the TiN coated drills with - 22 -
• the present invention provides a process for producing dense, well adhering coatings which can combine a hardness exceeding about 20 GPa with a friction coefficient of less than about 0.2.
• the TiN-MoS 2 system has potential for producing well-adhering films comparable with standard TiN tool coatings by the use of a TiN underlayer then graded interlayer.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cutting Tools, Boring Holders, And Turrets (AREA)
• Physical Vapour Deposition (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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• 1999
  • 1999-04-27 CA CA002328152A patent/CA2328152A1/en not_active Abandoned
  • 1999-04-27 EP EP99919392A patent/EP1076728A1/en not_active Withdrawn
  • 1999-04-27 JP JP2000546069A patent/JP2002513088A/ja not_active Withdrawn
  • 1999-04-27 WO PCT/GB1999/001311 patent/WO1999055930A1/en not_active Application Discontinuation
• 2000
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