WerkzeugTechnik

Technologie - System - Logistik

Die deutsche Fachzeitschrift der Schneidwerkzeuge und Meßte

Reprint, Werkzeug Technik, No. 77, March/2003

Advanced Coating Systems

S W I S S Q U A L I T Y

LARC®: LAteral Rotating ARC-Cathodes

Nanostructured Coatingsfor High Performance Tools

Depending on which statistics youbelieve, the market shares of the (Ti, Al)-based PVD-coatings for coated high per-formance cutting tools amount to 25-55 % (Fig. 2). The reasons for that are the

outstanding features of the (Ti, Al)-based coatings:• High hardness (~25-38 GPa) at relati-

vely low residual stress ~ (-3 to -5GPa), • High hot hardness, resulting in low

hardness lost (~ 30-40%) up to tem-peratures of 800°C,

• High oxidation resistance (the sameoxidation rate (~ 15-20 µg/cm²) at800°C as for TiCN at 400°C and forTiN at 550°C),

• Low heat conductivity (up to 30% lo-wer relative heat indention coefficientthan for TiN).The coating industry is enormously

innovative. There are a huge numbers oftests and solutions even to improve theseoutstanding features of the (Ti, Al)-coatings [1]-[17]. E.g.:o Combination of ARC and sputtering,o Filtering of ARC-droplets,o Optimization of process parameters

like ARC-current, BIAS-voltage, N2-pressure etc.,

o Optimization of the crystalline struc-ture to avoid the columnar structureand to improve the corrosion resis-tance,

o Deposition of multilayers to increasecoating toughness and thickness,

o Addition of alloying components, suchas• chromium and yttrium to increase

oxidation resistance,

Nanostructured Coatingsfor High Performance Tools

No doubt (Ti, Al)-basedPVD coatings have

conquered the market ofhigh performance cutting

tools in the last years.The actual top

development trends,AlTiN-coatings andnanolayers will be

supplemented or evenreplaced by

nanocomposites.

Fig. 1 : Nanocomosites structure(nc-Ti1-x AlxN) / (a- Si3N4).

Fig. 3 : Superlattice Nanolayer (Source:Southwestern University, Chicago).

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Fig. 2 : Marketshares of Coatings on Carbide Tools.

• zirconium, vanadium, boron andhafnium to improve wear resistance, or

• silicon to increase hardness and resis-tance against chemical reactions.

The two most important developmenttrends for (Ti, Al)-based coatings are ac-tually the effortso to deposit nanolayers [6], [9], [11] ando to increase the aluminium content [1],

[2], [10], [11], [15].

Nanolayers effectThey emerge from the refinement of

the multilayer technique. At certain pe-riods, i.e. at certain thicknesses of na-nolayers significant hardness increasescan be achieved (Fig. 3 [6]).• The high hardness is realized through

the strongly different Young modulusof the sublayer materials. In the caseof the Fig. 3 it can be probably ex-plained by the cubic crystal structureof AlN, which will be hexagonal over~10 nm.

• The hardness decrease at smaller pe-riods below 6-7 nm is caused by the“rough” interface boundaries betweenthe sublayers [14]. If the interface bet-ween the components can be keptsharp (Fig. 4) no hardness decreasecan be observed. To produce nanolayers, it is essential

to synchronize cathode control and ro-tation of the substrates. This is relativelyeasy if you coat the same tools in largeseries. But it is much more difficult tocoat substrates with different sizes inthe same batch.

A constant nanolayer period for jobcoating is therefore practically impossi-

ble when you have small and big cuttingtools, inserts, mold and dies or even ma-chine parts in the chamber. Of coursechanging the nanolayer periods causedby the temperature variation during cut-ting process also reduces coating per-formance.

AlTiN-Coatingsimprovements

The leading equipment manufactu-rers are increasing the aluminium con-tent step by step in their latest indu-strial (Ti, Al)-based coatings to improvehardness, wear and heat resistance. Fordifferentiation beyond 50% aluminiumcontent these coating are referred as Al-TiN-coatings. Still, at some point, thereis a limit: beyond 67%, 75% or even at80% Al, further increases are neitheruseful nor meaningful (Fig. 5).

These limits are the period of nano-layers, which practically can’t be holdconstantly for job coating and the maximal meaningful aluminium contentof AlTiN-coatings can only be brokenby physically new solutions like the

nanocomposites [3], [7], [12], [13], [14],[17].

Nanocomposite coatingsIn nanocomposite coatings different

materials (e.g. Ti, Al, and Si) are de-posited. They cannot be mixed. For ex-ample two different phases are emergedin the plasma, the nanocrystalline TiAlNwill be embedded into the amorphousSi3N4-matrix (Fig. 1).

This structure enables extremely highhardness (40-50 GPa) maintained to hightemperatures (up to ~1100 °C, Fig. 6[13], [14]), even at a lower Al content(e.g. 50%). It can be extremely importantfor dry high performance cutting. Fur-ther improvement is possible if thenanocomposite coating is deposited witha nanolayer basic structure (Fig. 7). Thenanolayer period was calculated by FFTto 35Å.

To achieve this structure it is essentialto build the cathodes close to each other.This could be realized with the help ofthe LARC®–Technology (LAteral Rotat-ing ARC-Cathodes), Fig. 8.

LARC®-TechnologyTo deposit nanocomposites on an in-

dustrial and economic scale, new coatingequipment have to fulfil the followingbasic requirements:o The cathodes must be built in very

close to each other,o A highly ionized plasma,o Supported by a strong magnetic field

is necessary,o This requires a very fast motion of the

ARC track.Because the technologies, we know

today, fulfil only partly these require-

Fig 5 : Features of (Ti, Al)-based CoatingsDepending on Al-Contents.

(Source: NACODRY, EU-Project).

January/February/March 2003 - Werkzeug Technik - 3

Fig. 4 : Interface-Structure and Hardness of (nc-Ti1-xAlxN) / (a-Si3N4) Nanocomposite Coating.(Source: Platit AG, measured by EPF, Lausanne).

ments, we developed a new procedureand new coating equipment. Both to-gether implement the new LARC-Tech-nology. Both water-cooled cathodes arein permanent rotation. The magneticfield is generated by coils and perma-nent magnets controlled both, verticallyand radially. The most important ad-vantages of the LARC-technology comefrom the rotating cathodes and their la-teral position. Therefore they are calledπ-advantages (Fig. 9).

The π Advantages1. Optimal adhesion due to the VIR-

TUAL SHUTTER

Optimal adhesion is the most impor-tant criterion for good coating. Thelateral arrangement of the cylindri-cal cathodes makes VIRTUAL SHUT-TER possible, working without sen-sitive mechanical elements (Fig. 10).The magnetic field is turned by 180°and the ARC is ignited from the back.Due to this procedure it is possible toclean the targets before the coatingprocess begins - and to deposit theinitially large particles (droplets)

against the wall. Meanwhile the sub-strates can be cleaned in intensiveplasma. The ARC will be turned to-wards the tools without being distin-guished. In effect, it is possible toshorten the time of ion etching and todeposit the adhesive coating with me-tallic clean targets.

2. ”Wide” targets with Long WorkingLifeThe most trivial advantage of the ro-tating cylindrical cathodes is theirwidth. With the same space require-ment they are π-times wider than pla-

nar targets. A target can serve up to200 batches without a change.

3. Smooth layers by reduction of theARC-dropletsWith conventional ARC technology,most of the droplets are created atthe beginning of the process. It startsduring the ignition of the ARC, whenthe standing spot melts the largestbaths. These large droplets are depo-sited to the back by VIRTUAL SHUT-TER. The size and number of the dropletsdepend during the deposition amongothers on the speed of the ARC-spotmovement. It is created, respectivelyguided only by magnetic control forthe planar targets with steered ARC.The spot movement is considerablyfaster and more regular with rotatingcathodes. It is a result of the target ro-tation together with the vertical os-cillation of the wide magnetic field.With the help of the Virtual Shutter

and the rapid ARC spot movement,the LARC-technology can producelayers with signif icantly lower roughness (Fig. 11).

4. Deposition nanocompositesThe lateral cylindrical targets on theside require minimum space. It is thuspossible that several cathodes, requi-ring little space, deposit coatings withdifferent metallic components evenin small compact equipment.Due to the fast ARC-Spot low-costtarget materials can be used even withlow melting points (e. g. Al or AlSi).They can replace the expensive al-loyed targets (e. g. Al25%/Ti75%,Al50%/Ti50%, Al67%/Ti33%, etc.).

4 - Werkzeug Technik - January/February/March 2003

Fig. 6 : Hardness and heat Resistance of (nc-Ti 1-x AlxN) / (a-Si3N4). (Source: TU Munich).

Fig. 7 : Nanocomposite on Nanolayer-Structure.(Source: PLATIT AG, measured by EPL,

Lausanne).

Nanocomposite on Nanolayer-Structure (Source: Plattit AG, measured by EPL, Lausanne)

Fig. 8 : PVD-Coating Unit with Dynamic RotatingARC-Cathodes. (Source: PLATIT AG).

A target consisting of pure silicon isnot conceivable due to simple, me-chanical reasons. The silicon is depo-sited from alloyed targets (AlSi, CrSi,TiSi etc.) After the deposition fromthe target, Al and Si must be segre-gated. Silicon is not solved into me-tallic phase, the nanocrystalline grains(TiAlN) are embedded into an amor-phous Si3N4-matrix. For this highlyionized plasma, a highly intensivemagnetic field is necessary. A fastARC-spot movement will permit ahigh intensive magnetic field with-out “cutting through” the targets(which is a real danger with planartargets). The emergence of the nano-composite structure shows no “space”between the nanocrystalline grains,

chiometry (composition) is freely pro-grammable (continuously changeable= gradient) even during the processes.At the beginning of the gradientLARC-coating (Fig. 10), the alumi-nium will be deposited later to thetitanium, so that an optimum adhe-sion coating can emerge.Afterwards, during the deposition,the Al-content is continuously in-creased, so that the hardness, tempe-rature stability and oxidation resi-stance of the coating improve.At the end, the aluminium contentcan be taken back, whereas the Ti con-tent will be increased, and a beautiful,ilt surface will arise.

6. Deposition multi- respectively na-nolayersMultilayers (Fig. 13) are gradientswith periodical changes. Increasinghardness leads to higher internal (re-sidual) stress. With the help of themultilayer structure, the internal (re-sidual) stress can be kept at the ex-cellent values of ~ (-3 to -4 GPa) [7].

Size of the CoatingEquipment

As you can see on the pictures, thefirst LARC-coating units were designedto be compact – not of the size used bylarge tool manufacturers. Why?• Coating should not be a privilege of

the large coating centres and tool ma-nufacturers. Small and medium-sizeenterprises should be able to depositthe most modern layers in their ownworkshops.

• The new coatings cannot detach TiAlN& Co. immediately. At the moment,the market does not yet require vo-lume nanocomposite coating. The needof nanostructured coatings will in-crease continually within the nextyears, making utilization of larger coa-ting units possible.

January/February/March 2003 - Werkzeug Technik - 5

Fig. 9 : The π-Advantages of the LARC - Technology. (Source: PLATIT AG).

Fig. 10 : Working Principle of the VIRTUALSHUTTER (Source: PLATIT AG).

Fig. 11 : Comparison of Coating Surfaces:ARC < - > LARC. (Source: SHM).

keeps the crystal sizes small and theinterface boundaries sharp, thereforegiving a high hardness. An additionaladvantage is the stop of crack propa-gation at the grain boundaries.

5. Depos i t ion nanogradients wi th Programmable StochiometryDue to the fast ARC-spot and the useof different “pure” targets (e. g.“pure” Ti, Al or AlSi) the coating sto-

• After having mastered the technologyand production of cathodes in a mi-nimize space requirement, the up-sca-ling will be easier. It is important thatthe cathodes are installed by pairswith small intermediate distances (Fig. 8). This ensures the deposition ofnanocomposites with high produc-tivity and without expensive alloyedtargets (e.g. TiAl).

• In small units it is not absolutely necessary to coat totally different sub-strates together for economical rea-sons. One can separate the substratesinto groups according to the sizes orapplication and coat them in small de-dicated batches. Therefore and becauseof the small distance between the ca-thodes the optimum nanolayer periodcan be deposited much easier evenbelow 10 nm (Fig. 7).

• Several small coating units are not lessproductive than a large one. In factthey are much more flexible and pro-vide a reliability of service.

• On a side note, making small coatingunits results in a smaller profit for theequipment manufacturers than large

6 - Werkzeug Technik - January/February/March 2003

ones. Seen in a long term, it has al-ways been worthwhile.

Development Potential ofthe LARC-Technology

By introducing new equipment, tech-nologies or coatings, the commonly pre-sented results pretend that the new pro-duct, compared with the competition,shows the highest achievement, withhigher parameters and lower costs. Fromnow on, let’s put this established cu-

Fig. 12 : GDEOS-Analyses of (nc-Ti1-xAxN)/ (a-Si3N4) Coating with Gradient Structure, Deposited from Ti and AlSi Targets. (Source: Western Bohemia University, Brno).

Fig. 14 : Development Potential of LARC-Technology at Drilling. (Source: PLATIT AG,measured by iFT, Grenchen).

Fig. 13 : Mono- and Multilayer made by LARC-Technology (Source: PLATIT AG).

stom aside. Instead of these Fig. 14, 15and 16 clearly present the developmentpotential of this innovative technologyconcerning cutting tools made fromtungsten carbide. The presented impro-vements and cutting results can be achie-ved within the period of 2 months.

You also can see the importance ofthe dedicated coatings in these figures.For general milling operation the mul-tilayer nanocomposite coating is clearlythe best choice (Fig. 15). But for the spe-cial case of milling hardened steel theharder and thinner gradient coating ou-tperformed the universal multilayers(Fig.16).

ConclusionThe (Ti, Al)-based coatings are the

market leader in the sphere of high per-formance cutting tools. Further deve-lopment of the current top-coatings likenanolayers and AlTiN is limited, due tophysical features. Nanocomposite-coa-tings break through these limits.

This article presents a fundamentallynew development. The new LARC-technology works with rotating cylin-drical cathodes in lateral positions. Con-sidering this, the following so called π-advantages can be achieved:– Optimal coating adhesion with the

VIRTUAL SHUTTER

– “Wide” targets with a longer workinglife

– Smooth coatings by reducing ARC-droplets

– Deposition of nanocomposites– Deposition of nanogradients with pro-

grammable stochiometry– Deposition of multi- and nanolayers.

Nowadays, large and expensive coa-ting equipment are no longer necessaryto deposit competitive, simple or com-plicated coating structures dedicated forindustrial application. On the contrary,with the help of the LARC-technologymedium sized enterprises can producethe newest nanostructured coatings by themselves and even generate their highly productive own brands.

January/February/March - Werkzeug Technik - 7

References[1] Derflinger, V., Schütze, A. a.o.: Mechanical, Structural and Performance

Properties of Various Aluminium Containing Wear Protecting Films,PSE, Garmisch Partenkirchen, Sept/2002

[2] Erkens, G. a.o.: About the Performance of Crystalline PVD-Alumina Coatingsin Cutting Applications,ICMCTF, San Diego, May/2002,

[3] Holubar, P., Jilek, M., Sima, M.: Present and Possible Future Applications of Superhard Nanocomposite Coatings,ICMCTF, San Diego, April/2000

[4] Jehn, H.: Praxishandbuch: Moderne Beschichtungen,Carl Hanser Verlag, München, 2001

[5] Karimi, A. a.o.: Fracture Behaviour of Nanocomposite Thin Films by Nanoindentation, ICMCTF, San Diego, May/2001

[6] Madan, A., Barnett, S. a.o.: Stability of Nanometer-Thick Layers in Hard Coatings,MRS Bulletin, Warrendale, March/2003, p.169-172

[7] Morstein, M. a.o.: Nanocomposite and Nanogradient Coatings for CuttingTools,MRS Fall Meeting, Boston, Dec/2002

[8] Musil, J., Mitterer, C. a.o.: Structure-Hardness Relations in Sputtered Ti-Al-V-N Films,PSE, Garmisch Partenkirchen, Sept/2002

[9] Münz, W.: Large-Sc ale Manufacturing of Nanoscale Multilayered Hard CoatingsMRS Bulletin, Warrendale, March/2003, p.173-179

[10] Schulz, H.: Coating Industry – Quo Vadis?Gorham Conference, Atlanta, Nov/2002

[11] Paldey, S., Deevi, S.: Single and Multilayer Coatings of (Ti,Al)N: a Review, Materials Science and Engineering, Elsevier B.V., New York, A342 (2003), p.58-79

[12] Patscheider, J.: Nanocomposite Hard Coatings for Wear ProtectionMRS Bulletin, Warrendale, March/2003

[13] Veprek, S.: Ultra Hard Nanocomposite Coatings with Hardness of 80 to105 GPaVide, Nancy, March/2000, p.185-192

[14] Veprek, S., Jilek, M.: Super- and Ultra Hard Nanocomposite Coatings,Elsevier, Vacuum/67, New York, Sept/2002, p. 443-449

[15] Vetter, J. a.o.: AlTiCrN Coatings for Dry CuttingPSE, Garmisch Partenkirchen, Sept/2002

[16] Cselle, T.: Go into the New Economy, with High Performance Machining and Flexible Coating,Gorham Conference, Atlanta, May/2001,

[17] Cselle, T. a.o.: Nanostructured Coatings and Processes on an Industrial Scale,Gorham Conference, Atlanta, Nov/2002.

Authors of this paper:Dr. T. Cselle, Platit, CEO,Dr. M. Morstein, Platit, Head R&D,O. Coddet, Platit, R&D,L. Geisser, Head Production,Dr. P. Holubar, SHM, CEO,M. Jilek, SHM, Head R&D,M. Sima, SHM, R&D,M. Janak, SHM, Head Production.

PLATIT (Grenchen, Switzerland) andSHM (Novy Malin, Czech Republic)established a joint venture companyto develop and produce the LARC® -technology, coatings and equipment.

Fig. 15 : Development Potential of LARC-Technology at End Milling.(Source: PLATIT AG, measured by iFT, Grenchen).

PLATIT AGAdvanced Coating SystemsMoosstrasse 68CH-2540 GrenchenSwitzerlandPhone : +41 (32) 654 26 00Fax : +41 (32) 654 26 83E-mail : info@platit.comWeb : www.platit.com

Fig. 16 :Development Potential of LARC- Technology at Hard Milling.

CrN+CBC

TiAlCN+CBC

TiCN-MP+MOVIC

Specia

lB

reak-

thro

ugh

Basi

c

Monolayer Multilayer

Nanolayer Structure of AlTiN Coatings

20 nmcarbide substrate

coating

3nm

~1nm

Si N3 4

AlTiN

Nanocomposite StructureSurface Comparison

AlTiN®

µAlTiN

Hei

ght

ran

ge:

2µ

m

10 µm

R ~ 0.07 µma R ~ 0.02 µma

µ

Nanocrystalline grains are embedded

into an amorphous matrix.

Color Nanohardness Thickness Friction (fretting) Max. usage Symbol

[GPa] [µm] coefficient temperature [°C] color

TiN gold 24 1 - 7 0.55 600

TiAlN Monolayer violet black 35 1 - 4 0.5 800

TiAlN Multilayer violet black 28 1 - 4 0.6 700

TiCN-MP red-copper 32 1 - 4 0.2 400

TiCN blue-grey 37 1 - 4 0.2 400®

MOVIC green-grey - 0.5 - 1.5 0.15 400®

STARVIC green-grey 32 1.5 - 5.5 0.15 400

CrN metal-silver 18 1 - 4 0.3 700

Ti N silver 25 1 - 3 0.45 6002

TiAlCN burgundy-violet 28 1 - 4 0.25 500®

CROMVIC grey 20 1.5 - 6 0.15 400

CBC (DLC) grey 20 0.5 - 4 0.15 400®

GRADVIC grey 28 1.5 - 6 0.15 400

AlTiN black 38 1 - 4 0.7 800®

µAlTiN black 38 1 - 2 0.3 800

AlTiN/SiN violet blue 45 1 - 4 0.45 1100

Bre

akth

rough C

oati

ngsAlTiN/SiNAlTiN

®µAlTiN

Special high-performance PLATIT coating:

• very high aluminum content

• very high heat resistance

• for dry high speed machining

• especially at hard machining

Monolayer: for stable finishing and roughing

Multilayer: for interrupted cuts

Special high-performance PLATIT coating:

• very high aluminum content

• very high heat resistance

• finest coating surface

• highest edge stability

• especially for precision machining

and tapping

Nanocomposite PLATIT coating:

• extremely high nanohardness

• extremely high heat resistance

• for high performance and for

normal machining conditions

Coati

ng P

ropert

ies

First Nanocomposite Coatings on Industrial Scale ...

... Inspired by Nature's Excellence!