Structure and properties of the multi-component TiAlSiN coatings obtained in the PVD process in the...

Journal of Materials Processing Technology 157–158 (2004) 331–340

Structure and properties of the multi-component TiAlSiN coatingsobtained in the PVD process in the nitride tool ceramics

L.A. Dobrzanski∗, D. Pakuła, E. Hajduczek

Division of Materials Processing Technology and Computer Techniques in Materials Science, Institute of Engineering Materials and Biomaterials,Silesian University of Technology, Konarskiego St. 18a, 44-100 Gliwice, Poland

Abstract

Comprehensive structure and properties investigation results of the multilayer, multi-component PVD coatings developed on the Si3N4

nitride tool ceramics substrate are presented in the paper. The detailed results are presented of examinations carried out on the transmission andscanning electron microscopes, as well as of the mechanical properties and tribological tests of the investigated coatings. Examinations of thechemical compositions of the deposited coatings were also carried out using the X-ray energy dispersive spectrograph EDS, glow-dischargeoptical emission spectroscope GDOS, and using the X-ray diffractometer. The inserts made from Si3N4 were multilayer coated in the PVDprocess with the TiN, TiN + multiTiAlSiN + TiN, TiN + TiAlSiN + TiN, and TiN + TiAlSiN + AlSiTiN coatings. Additional investigations werec the CVDc er PVDa und out int lso that allC itative phasea and GDOSc en in thei©

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arried out to compare coatings obtained in this way on inserts from various manufacturers offering the nitride tool ceramics withoatings based on the Al2O3 and TiN layers. Basing on the metallographic examinations results it was found out that the multilaynd CVD coatings were uniformly put down onto the substrate and the particular layers adhere closely to each other. It was fo

he microhardness tests of the coatings that the TiN + multiTiAlSiN + TiN one has the highest hardness. It was demonstrated aVD coatings are characterised by very good adhesion to the substrate compared to the PVD coatings. Results of the X-ray qualnalysis confirm occurrences of phases coming from coatings and the substrate. Analyses of the chemical composition – EDSonfirm presence of both titanium, aluminium, silicon, nitrogen, and oxygen in the investigated coatings and of silicon and nitrog

nvestigated substrate.2004 Elsevier B.V. All rights reserved.

eywords:Nitride ceramics; Si3N4; Multi-layer coating; Multi-component coatings; PVD; CVD; TEM; SEM; Micro-hardness; Scratch test; Pin-on-di

. Introduction

The tool material should have a set of properties that willnable it to work in various conditions. The requirementsosed to cutting tools include[1–4,9]:

high hardness and compression, tensile, torsion, and bend-ing strength;high wear resistance (abrasion, adhesion, diffusion, chem-ical);high mechanical and thermal fatigue resistance;significant resistance to change of the machining capabilityat elevated temperature and ductility;good thermal conductivity and high specific resistance.

∗ Corresponding author.E-mail address:[email protected] (L.A. Dobrzanski).

None of the tool materials available on the marketrently possesses all the desired properties simultanewhich is understandable, as some of them mutually excthemselves. This has been the reason for establishing thmains of applications for the particular material groupswhich minimizing of wear, and in consequence extensiothe tool edge life, features the main selection criterion foparticular material[1,6,8,12,26].

The nitride ceramics was developed with the aim of ming hardness and ductility of sintered carbides with thequired oxidation resistance at high temperature in one mrial. Employment of the nitride ceramics makes machinat high feed rates and speeds possible. This ceramics beto materials that may be used in the conventional toolmachine tools that do not require any special stiffeninmay be used for rough machining of nickel alloys andrough and finishing machining of grey cast iron. The nit

924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved.oi:10.1016/j.jmatprotec.2004.09.052

332 L.A. Dobrzanski et al. / Journal of Materials Processing Technology 157–158 (2004) 331–340

ceramics is used less often for alloys containing Fe becauseof its chemical wear at high temperature[1,3,7,9,22,23].

The contemporary technologies of materials forming em-ployed in the machining, plastic forming, casting, and alsoplastics forming domains call for using more and more effi-cient tool materials. These requirements pertain mostly ex-tension of life and reliability of tools used in machining pro-cesses, and also of limiting employment of cutting fluids stillcommonly used, however degrading the environment con-siderably. Improvement of the functional properties of toolsand reduction of the ecological threats may be accomplishedby employing the technology of putting down hard coatingson tools in the CVD processes, and sometimes also in thestate-of-the-art PVD processes, mostly by improvement ofthe tribological contact conditions in the cutting zone and byeliminating the cutting fluids[5,10–26].

The goal of this work is investigation of structure andproperties of the multi-component PVD coatings put downonto the Si3N4 tool nitride ceramics substrate and comparingthem with the commercially available CVD coatings.

2. Experimental procedure

The investigations were carried out on the multi-point in-s ndc ertsm o-c aredn ousm fc pre-s

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rationmethod. Just before the coating deposition process thespecimens were prepared applying the standard procedureof chemical cleaning using the multi-stage washing in ultra-sonic cleaner, then they were ion-etched in the chamber toclean the coated surfaces in the atomic scale and to activatethem.

Observations of the investigated coatings’ structures werecarried out on the transverse fractures on the scanning elec-tron microscope (SEM) Philips XL-3. To obtain the fractureimages the secondary electrons (SE) and the back scatteredelectrons (BSE) detection methods were used with the ac-celerating voltage in the range of 15–20 kV, maximum mag-nifications are 10 000×. The specimens with notches cut onthem were cooled in liquid nitrogen. Topography of the inves-tigated coatings’ surfaces was also examined on the scanningelectron microscope.

The X-ray qualitative and quantitative microanalysis andsurface distribution analysis of elements in the investigatedcoatings were made using the EDS X-ray energy dispersiveradiation spectrometer, featuring the standard equipment ofthe scanning microscope.

The diffraction examinations and examinations of thinfoils were made on the JEOL JEM 3010UHR transmissionelectron microscope at the accelerating voltage of 300 kVand maximum magnification 300 000×. The diffraction pat-terns from the transmission electron microscope were solvedu lon-g thickl ODd ur-f theD du

atingc ando andt ationsm mis-s eterG thee

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erts made from the Si3N4 nitride ceramics uncoated aoated in the PVD process with thin coatings. The insade from Si3N4 were multilayer coated in the PVD pr

ess – cathodic arc evaporation (CAE), and were compext with the commercially available inserts from varianufacturers offering the Al2O3 + TiN type combination o

oatings. Specifications of the investigated materials areented inTable 1.

The CAE method was employed in own research forositing the hard wear resistant coatings onto the subs

rom cemented carbides. The coatings deposition proas carried out in the arc-vacuum chamber based orc evaporation method, the so-calledcathodic arc evapo

able 1pecifications of the PVD and CVD coatings put down on the Si3N4 nitrideeramics

aterial type Coating Coatingthickness(�m)

Processtype

Si3N4

nitrideceramics

TiN 0.8 PVD

TiN + multiTiAlSiN + TiN 4.0 PVDTiN + TiAlSiN + TiN 2.0 PVDTiN + TiAlSiN + AlSiTiN 2.5 PVDTiN + Al 2O3 + TiN 3.8 CVD (1)a

Al2O3 + TiN 2.6 CVD (2)a

Al2O3 + TiN 1.7 CVD (3)a

TiN + Al 2O3 + TiN + Al 2O3

+ TiN4.5 CVD (4)a

a Commercially available inserts from various manufacturers.

sing the computer program. Thin foils were made in theitudinal and transverse sections from the 0.2–0.5 mm

aminae cut from the solid specimens, from which 3 mmisks were cut out, with the initially ground and levelled s

aces. The lamellae were next mechanically thinned onisc Grinder to thickness of about 80�m and ion polishesing the Gatan firm equipment.

Changes of the chemical concentrations of the coonstituents in the direction perpendicular to its surfacef concentrations in the interlayer between the coating

he substrate material were evaluated basing on examinade in the Leco Instruments glow-discharge optical e

ion spectroscope GDOS-850A. The following spectromrimm lamp working conditions were determined duringxaminations:

lamp internal diameter: 4 mm;lamp power supply voltage: 700 V;lamp current: 20 mA;working pressure: 100 Pa.

The continuous concurrent spectrometer inaschen–Runge configuration was used in the deith the focal length of 750 mm, with the holographic mf 2400 lines per millimeter. The maximum depth ofhemical composition analysis is a dozen or so microm

Phase compositions of the obtained coatings were dined using the Dron 2.0 X-ray diffractometer, using

ltered radiation from the cobalt lamp with the voltage0 kV and heater current of 20 mA. The measurementsade in the 2Θ angle ranging from 10 to 95◦.

L.A. Dobrzanski et al. / Journal of Materials Processing Technology 157–158 (2004) 331–340 333

The Seifert-FPM XRD 7 X-ray diffractometer, equippedwith the texture add-on, was used for evaluation of the coat-ings’ structures. The X-ray radiation was used of the CoK� cobalt lamp with the 35 kV supply voltage and currentof 40 mA. Analysis of the investigated coatings texture wasmade using the inverse pole figures method. Intensity of the(1 1 1), (0 0 2), (0 2 2) and (1 1 3) diffraction lines was anal-ysed – in case of the TiC, TiN and Ti(C,N) phases, and ofthe (0 1 2), (1 0 4), (1 1 0), (1 1 3), (1 1 6), (0 3 0), and (1 0 1 0)ones in case of the Al2O3 phase. The line intensity was mea-sured after the graphical separation of the overlaying linesand after isolating the clear profile of the analysed line. Themeasured line intensity was divided by the relative intensityof this line specified in the catalogues, and in case of the Ti(C,N) phase diffraction lines – by the value interpolated usingthe TiC and TiN catalogue values. Basing on these values andon location of traces normal to the (0 0 1), (0 1 1), (1 1 1) and(1 1 3) planes – the equal density isolines of spatial distribu-tion of the normal direction to the sputtered plane (KN) wereplotted in the base triangle. Further, the figures were normal-ized to make determining the isolines values possible in unitsbeing multiples of density for the uniform distribution in thespace that is for the specimen that does not reveal texture.This made it possible to assess how strongly the investigatedspecimens are textured.

The microhardness tests of coatings were made on theS on-d le tesr sure-m f thes

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singt f thec xam-i entsw ition,t tingsw n thef

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observations on the light microscope and on the scanningelectron microscope.

3. Discussion of investigation results

It was found out, as a result of the fractographic exam-inations of the analysed PVD and CVD coatings made onthe electron scanning microscope, that the particular coat-ings are uniformly put down and are characterised by tightadherence to the substrate material from the Si3N4 tool nitrideceramics.

The PVD coatings, both the TiN monolayer andthe TiN + multiTiAlSiN + TiN, TiN + TiAlSiN + TiN, TiN +TiAlSiN + AlSiTiN multilayer ones reveal dense structureswith not visible delaminations and defects. In case of theTiN + multiTiAlSiN + TiN coating, a structure of about 150nanolayers of the complex TiAlSiN nitride with the totalthickness in the 2 – 2.2�m range was observed between theTiN layers 0.8 – 1.2�m thick (Fig. 1a). The TiAlSiN mono-layer of the TiN + TiAlSiN + TiN coating, between the TiN(0.1 – 0.2�m) layers, is about 1.6 – 1.8�m thick. However, incase of the TiN + TiAlSiN + AlSiTiN coating no clear three-ply structure put down onto the nitride ceramics was foundout. Topography observations of the investigated PVD coat-ings reveal their inhomogeneity connected with occurrenceso ace,w tingd -p of am eveala veralm iclesd ggerd osi-t rom-e ium,k lid-i a-s testm s ont hemtTo

mi-n m-i thatt erTo rmlyo a com-p rencet se ofm sti-g erous

HIMADZU DUH 202 ultra microhardness tester. Test citions were selected so that the required and comparabesults would be obtained for all analysed coatings. Meaents were made at 0.07 N load, eliminating influence o

ubstrate on the measurement results.Adhesion evaluation of the coatings on the investig

nserts was made using the scratch test on the CEVETEST device, by moving the diamond penetrator a

he examined specimen’s surface with the graduallyreasing load. The tests were made with the followingameters: load range 0–100 N, load increase rate (dL/dt)00 N/min, penetrator’s travel speed (dx/dt) 10 mm/mincoustic emission detector’s sensitivity AE 1. The cal loadLc, at which coatings’ adhesion is lost, wasermined basing on the registered values of the acomission AE.

Examinations of coatings’ thicknesses were made uhe “kalotest” method, consisting in the measurement oharacteristic dimensions of craters developed on the ened specimen surface with a coating. The measuremere made on the device developed in house. In add

o verify the obtained results, measurements of the coaere made also on the scanning electron microscope o

ractures perpendicular to their free surfaces.Tribological tests were carried out on the CSEM “pin-

isk” tester in the following conditions: counter-specimeall made from the WC titanium carbide with the 6 mmmeter, counter-specimen load – 5 N, friction radius – 5

inear velocity – 0.1 m/s, ambient temperature – 20◦C. Theharacter of the developed failure was evaluated basin

tf multiple drop shaped micro-particles on coating surfhich is connected with the nature of the employed coaeposition PVD process (CAE) (Fig. 1b). Sizes of the microarticles are diversified and range from several tenthsicrometer to a dozen or so micrometers. One can also rgglomerates developed on the coating surface from seerged micro-particles and agglomerates of micro-parteveloped on the already developed particles with biiameter. Examinations of the particles’ chemical comp

ions carried out using the X-ray energy dispersive spectter EDS indicate they develop from pure metal – titannocked out from the titanium disk, which deposits and sofies on the substrate surface (Fig. 1c and d). Thickness meurements of the PVD coatings carried out with the kaloethod were confirmed with measurements on fracture

he electron scanning microscope. It turns out from that this thickness is within the range from 0.8�m for theiN coating to 4�m in case of the TiN + multiTiAlSiN + TiNne.

It was found out basing on the metallographic exaations of the commercially available tool nitride cera

cs carried out on the scanning electron microscopehe Al2O3 + TiN bilayer coatings, as well as the multilayiN + Al 2O3 + TiN and TiN + Al2O3 + TiN + Al 2O3 + TiNnes deposited in the CVD process were put down unifonto the substrate. These coatings are characterised byact structure with no pores and cracks and by tight adhe

o the substrate. A laminar structure was observed in caultilayers. Surface topography of this group of the inveated materials is characterised by occurrences of num


Fig. 1. (a) Fracture surface; (b) surface topography and the X-ray energy dispersive plots from the microzones of the TiN + multiTiAlSiN + TiN coating surface,put down onto the Si3N4 nitride ceramics – (c) region X1, (d) region X2.

spherical micro-particles and fine pores as well as of a denseminute network of micro-crevices which rarely occur on theTiN + Al 2O3 + TiN coating surface (Fig. 2).

Examinations of thin foils of the TiN + multiTiAlSiN+ TiN coating confirm that, according to the original assump-tions, coatings containing the TiN type phases were put downonto the Si3N4 based tool nitride ceramics substrate. It is

not feasible to differentiate these phases from the diffractionpoint of view, due to isomorphism of the TiN and TiAlSiNphases. Structure of the TiN + multiTiAlSiN + TiN coatings,presented inFig. 3, is fine grained (which is, among others,attested by clear reflex rings in the diffraction patterns) andsize of the TiN phase particles with the cubic lattice does notexceed 50 nm.

Fig. 2. (a) Fracture surface; (b) topography of the TiN + Al2O3 + TiN coating surface, put down onto the Si3N4 nitride ceramics substrate.


Fig. 3. Structure of TiN + multiTiAlSiN + TiN coating: thin foil structure parallel to the layer surface (TEM): (a) light field; (b) diffraction patternfrom the areaas in (a); (c) dark field from the (1 1 1) reflex TiN; (d) solution of the diffraction pattern from (b).

Examinations of thin foils carried out both in paral-lel and perpendicularly to the surface of the investigatedTiN + Al 2O3 + TiN + Al 2O3 + TiN coating confirm that thecoating containing phases of the TiN and Al2O3 types was putdown onto the substrate from the tool nitride ceramics. Thestructure of the Al2O3 layer with the trigonal lattice is char-acterised in the parallel section by fine grains with grain sizenot exceeding 500 nm. The fine-grained structure of the TiNphase with the cubic lattice is also visible between the Al2O3phase grains in the same thin foil section (Fig. 4). Analysisof thin foils made in the transverse section of the investigatedcoating makes it possible to examine the structure of the inter-face between the substrate from the�-Si3N4 phase with thehexagonal lattice and the TiN layer with the cubic lattice. TheTiN layer consists of the neatly arranged grains of the colum-nar shape, whose maximum width is about 500 nm (Fig. 5).The Al2O3 layer with the trigonal lattice, in the transverse sec-tion of the examined TiN + Al2O3 + TiN + Al 2O3 + TiN layer,reveals structure close to the columnar one.

Examinations in the glow-discharge optical emissionspectrometer GDOS make it possible only to evaluate thequalitative differences of the chemical compositions in the se-lected micro-area of each specimen (Fig. 6). Basing on these

examinations, certain regularity was found out of the distri-bution of elements included in both coatings and substrate.All elements included in the investigated coatings occur ex-clusively in the area of coatings; whereas elements includedin the ceramics occur in the area of the substrate. These exam-

Fig. 4. Structure of TiN + Al2O3 + TiN + Al 2O3 + TiN coating-layerAl2O3 + TiN; thin foil parallel to the layer surface (TEM).


Fig. 5. Structure of TiN + Al2O3 + TiN + Al 2O3 + TiN coating-deposited onSi3N4 substrate + layer TiN; thin foil from cross section of the layer surface(TEM).

inations confirm presence of the alloying elements includedin the coatings. The analysis made using the glow-dischargeoptical emission spectrometer GDOS indicates that in theanalysed cases, in the joint zone, concentration of elementsincluded in the substrate grows from the coating surface withthe simultaneous decreasing concentration of elements con-stituting the coatings.

This may attest to the existence of the interface betweenthe substrate material and the coating, resulting in improve-ment of adherence between the deposited coatings to the sub-strate, albeit these results cannot be interpreted unequivocallybecause of the inhomogeneous vaporizing of the materialfrom the specimens’ surfaces during the analysis. One mayjudge that the interface, both for the PVD and CVD coatings,has the diffusion character, albeit the PVD coatings deposi-tion temperature is much lower than for the CVD ones. Theexistence of the interface should be also connected with theincrease of desorption of the substrate surface and develop-ment of defects in the substrate as well as with displacementof elements in the joint zone due to interaction of the high-energy ions.

F iN +T di

Fig. 7. X-ray diffractions pattern of the Si3N4 nitride ceramics with theTiN + multiTiAlSiN + TiN coating.

It was found out using the X-ray qualitative phase analy-sis methods that, according to the assumptions, coatings weredeposited on surface of the investigated tool nitride ceramics,containing the TiN phases in case of the PVD coatings andthe TiC, Ti(C,N), Al2O3, and TiN phases in case of the CVDcoatings. Occurrences of the�-Si3N4 phase reflexes wererevealed in the X-ray diffraction patterns, coming from thesubstrate, especially in case of inserts with the PVD coatings.This results from the small thickness of coatings put downonto the ceramics substrate, smaller that the X-ray penetra-tion depth into the material. Reflexes from the titanium nitridewere revealed in the X-ray diffraction patterns in case of thePVD coatings, most probably of the complex TiAlSiN nitride.Distinction of the TiN and TiAlSiN phases with the diffrac-tion methods is not feasible because of the isomorphism ofthese phases, as – in fact – the TiAlSiN one is the secondarysolid solution based on the TiN titanium nitride, which wasconfirmed by research (Fig. 7).

In case of texture of the investigated coatings on the nitrideceramics, when the particular phase was put down in severallayers, the presented pole figures should be treated as the av-eraged figures for all layers of that phase; however, bearingin mind that it is not an arithmetic average: the outer layer hasthe biggest effect on the pole figure of the particular phase.This is not that important, assuming that texture of all lay-ers is similar. As regards the SiN substrate texture, it wase s int thatt theI rial isu

TiNl thesi 1.15o and

ig. 6. Changes of concentrations of constituents of the TiN + TiAlSiN coating and of the substrate materials of Si3N4 ceramic nitride analyse

n GDOES spectrometer.

3 4valuated basing on the diffraction lines intensity ratiohe diffraction pattern of this specimen. It was found outhese ratios only slightly differ from those published inCDD catalogues, which proves that the substrate matentextured in fact.

Most of the pole figures prove that the texture of theayers put down is very weak. It is especially weak inpecimens with the TiN + Al2O3 + TiN + Al 2O3 + TiN coat-ng, where the density of normals ranges from 0.85 tof the density corresponding to the uniform distribution,


Fig. 8. Exemplary inverse representing the distribution of normal to theTiN + TiAlSiN + AlSiTiN coating surface in the (0 0 1)–(0 1 1)–(1 1 1) basetriangle (KN – normal direction).

with the TiN + multiTiAlSiN + TiN coating (from 0.8 to 1.3).The distinguished TiN deposition plane, in most cases, isthe crystallographic plane from the{1 1 1} family, or the{1 1 1}+{0 0 1}double texture occurs. This is the situation incase of specimens with the TiN + multiTiAlSiN + TiN, Ti(C,N) + Al2O3 + TiN, TiN + Al 2O3 + TiN, and Al2O3 + TiN (2)coatings, where only the{1 1 1} orientation occurs. Itis also one of the two distinguished planes – apartfrom the {0 0 1} one – in specimens with the TiN,TiN + TiAlSiN + TiN, TiN + TiAlSiN + AlSiTiN, TiC + TiN,Al2O3 + TiN (3), and TiN+Al2O3 + TiN+Al 2O3+TiN coat-ings. In the TiN coating and – to some extent only – inthe TiN+Al2O3 + TiN + Al 2O3 + TiN one the{1 1 1} orien-tation prevails, and the{0 0 1} in other ones. The TiC + Ti(C,N) + Al2O3 + TiN coating reveals the{0 0 1} single textureof the TiN layer; whereas the TiN + Al2O3 coating – the{0 1 1} single texture, and the Ti(C, N) + TiN specimen –the{0 1 1}+{1 1 1} double one. The texture of the TiN lay-ers in the examined material with the TiN + TiAlSiN + TiNand TiN + TiAlSiN + AlSiTiN (Fig. 8) coatings is relativelystrong, and it is slightly weaker for the Al2O3 + TiN (3) one.The texture is rather weak or very weak in the remainingcoatings.

The microhardness tests revealed that the uncoated ni-tride ceramics has hardness equal to 18.5 GPa. Depositionof the PVD and CVD coatings onto the specimens causest .82 to3 strateh rved ic do vail-a theA s of2 chara cew nesst

Table 2Hardness, critical load and cycle number of the PVD and CVD coatings putdown on the Si3N4 nitride ceramics

Coatings Hardness(GPa)

Criticalload (Lc)

Cyclenumber

– 18.50 –TiN 22.12 20.14 2000TiN + multiTiAlSiN + TiN 35.24 22.40 500TiN + TiAlSiN + TiN 23.33 21.65 2000TiN + TiAlSiN + AlSiTiN 26.79 18.30 250TiN + Al 2O3 + TiN (1)a 24.40 47.78 11000Al2O3 + TiN (2)a 26.25 44.60 5000Al2O3 + TiN (3)a 27.23 26.53 5000TiN + Al 2O3 + TiN + Al 2O3

+ TiN (4)a25.22 40.52 5000

a Commercially available inserts from various manufacturers.

The critical load valuesLc (AE) were determined us-ing the scratch method with the linearly increasing load(“scratch test”), characterising adherence of the investigatedPVD and CVD coatings to the Si3N4 nitride ceramics. Thecritical load was determined as the one corresponding to theacoustic emission increase signalling beginning of spallingof the coating. To determine the character of the defect re-sponsible for the acoustic emission increase examinationsof scratches developed during the test were carried out onthe scanning electron microscope and on the light micro-scope coupled with the measurement device, determiningthe critical loadLc value basing on the metallographic ex-aminations. It was found out in case of the PVD coat-ings that the highest critical load ofLc = 22.4 N reveals theTiN + multiTiAlSiN + TiN coating; whereas the lowest one ofLc = 18.3 N the TiN + TiAlSiN + AlSiTiN coating (Table 2).

Defects of the PVD coatings, and especially of the threelayer TiAlSiN based ones, put down onto the nitride ceram-ics are characterised by a significant number of the coatingspalling defects on both scratch edges and by delaminationwithin the scratch ending up at its final part with the local coat-ing delamination at its contact with the scratch. Load increaseduring the test leads to intensifying the spalling defects and

F ur-f

he surface layer hardness increase reaching from 195.24 GPa, that is up to 100% more compared to the subardness. The highest hardness of 35.24 GPa was obsease of the TiN + multiTiAlSiN + TiN coating. It was founut, basing on microhardness tests of the commercially able CVD coated inserts, that the nitride ceramics withl2O3 + TiN (3) coating is the hardest one, with hardnes7.23 GPa; whereas the lowest hardness of 24.4 GPa iscteristic for the TiN + Al2O3 + TiN coating. No dependenas revealed between the substrate hardness and hard

he deposited surface layer (Table 2).

n

-

ofig. 9. Defects characteristic of the TiN + multiTiAlSiN + TiN coating sace deposited onto the Si3N4 nitride ceramics substrate.


Fig. 10. Defects characteristic of the Al2O3 + TiN (2) coating surface de-posited onto the Si3N4 nitride ceramics substrate.

joining the craters as “teeth” on scratch edges, which leads tothe band-like, partial coating delamination. One can observerepeatedly the conformal cracks and periodic peeling off thecoating. The smallest number of defects among this group of

coatings is characteristic for the TiN monolayer coating, forwhich the small single-side spallings were observed in thebeginning part of the scratch, and the two-sided ones at thescratch end (Fig. 9).

Defects of the CVD coatings on the commerciallyavailable inserts are characteristic for their periodic de-lamination at the first stage, that changes into single-sided spallings for the Al2O3 + TiN (2) – Fig. 10 coat-ing and into the two-sided spallings for the Al2O3 + TiN(3) and TiN + Al2O3 + TiNAl 2O3 + TiN ones. Two-sidedspallings on the entire scratch length were observed in theTiN + Al 2O3 + TiN coating after exceeding the critical load.Total delamination of any investigated PVD and CVD coat-ings does not occur in all examined cases even at the highestload.

The abrasive wear resistance test for the coatings withthe “pin-on-disk” method was carried out to obtain the com-plete functional and working characteristics of the investi-gated PVD and CVD coatings put down onto the Si3N4 basedceramics. It is one of the most popular tribological tests, de-termining the friction effect on the abrasive wear. Basing on

FX

ig. 11. (a) Trace of the tribological failure on the surface of TiN + TiAlSiN + T-ray energy dispersive plots from the surface of TiN + TiAlSiN + TiN coating

iN coating put down onto the Si3N4 nitride ceramics, number of cycles 500 and; (b) region 1; (c) region 2; (d) region 3.


Fig. 12. Friction coefficient plot vs. friction trace length during the “pin-on-disk” test for the TiN + TiAlSiN + AlSiTiN coating put down onto the Si3N4

nitride ceramics substrate.

the preliminary tests and basing on the previous thickness,adherence, and hardness tests results, the tribological exami-nation parameters and the number of cycles were selected foreach coating. The coating defect moment due to the counter-specimen interaction was determined basing on observationsmade on the light microscope.

The extensive adherence coating defects were revealed atthe contact zone with the counter-specimen in the tribolog-ical examinations of the PVD coatings put down onto thenitride ceramics substrate (Fig. 11), for the cycle numbersranging from 250 to 2000 (Table 2). The number of defectsin case of the TiN + multiTiAlSiN + TiN coating is lowerthan for the other PVD coatings. No total delamination ofthis coating from the substrate was observed. Fusion of thecounter-specimen material and of the removed coating ma-terial to the TiN + multiTiAlSiN + TiN coating was noticedwhile comparing the defects observed on the light micro-scope. The friction coefficient values are different for thisgroup of coatings depending on the number of cycles. In caseof the TiN + multiTiAlSiN + TiN coating the friction coeffi-cient assumes initially the value of 0.2, which increases nextup to the value of 0.7 at the test end. As regards the other threePVD coating systems, the friction coefficient assumes value

Fc .

Fig. 14. Friction coefficient plot vs. friction trace length during the “pin-on-disk” test for the TiN + Al2O3 + TiN + Al 2O3 + TiN coating put down ontothe Si3N4 nitride ceramics substrate.

of 0.9 at the beginning of test and then stabilizes reaching thevalue of 0.5 (Fig. 12).

In case of the tribological tests of the commercially avail-able inserts (Fig. 13), the same cycle number of 5000 wasemployed for all coatings of this series, apart from theTiN + Al 2O3 + TiN one (11 000 cycles) (Table 2). No coat-ing defect or its removal from the substrate material due tothe tribological load occurred for any of the examined coat-ings of this series, except the TiN + Al2O3 + TiN one. It wasfound out by analysing the friction coefficient for these coat-ings that only the TiN + Al2O3 + TiN + Al 2O3 + TiN multi-layer coating reaches the globally high value of the frictioncoefficient, which does not fall below 0.6. Other coatings ofthis material group are characterised by a varying value ofthe friction coefficient, depending on the number of cycles,which ranges from 0.2 to 0.6 (Fig. 14).

4. Summary

All PVD and CVD coatings put down onto the nitride toolceramics are characterised by a structure without pores anddiscontinuities and by tight adherence to themselves and ofthe entire multilayer coating to the substrate. The comprehen-sive examinations on the transmission electron microscope( iblet d int

ob-t at –i sicald nt oftt lys

ub-s to theP

ig. 13. Trace of the tribological failure on surface of the Al2O3 + TiN (2)oating put down onto the Si3N4 nitride ceramics, number of cycles 500

thin foil perpendicular to the layer surface) make it posso reveal the columnar structure for the TiN layer includehe TiN + Al2O3 + TiN + Al 2O3 + TiN coating.

Evaluating differences of textures of the TiN layersained with the PVD and CVD methods one can state thn the most general understanding – the method of phyeposition from the gaseous phase favours developme

he relatively strong texture. It is the{1 1 1}+{0 0 1} doubleexture most often; however the{0 0 1} component is usualtronger.

The CVD coatings put down onto the investigated strate are characterised by good adherence comparedVD ones. Undoubtedly, the fact that the Si3N4 based nitride


tool ceramics does not conduct electric current, which sig-nificantly renders difficult development of the PVD coatingson such substrate, has the effect on so significant adherencedifferences of the investigated coatings. The characteristicfeatures of defects responsible for initiation of spallings ob-served on the scanning microscope developed at the scratch-coating contact and inside of scratches are also different.

The abrasive wear resistance tests made with the “pin-on-disk” method revealed that the PVD coatings have worsetribological properties compared to those put down with theCVD method. In nearly all cases damage of coatings occursup to the Si3N4 nitride ceramics substrate zone. Hardnessof the investigated coating systems determines their abra-sion wear resistance, which was revealed most clearly forthe Al2O3 + TiN coating – the hardest among the CVD ones,contributing at the same time to decreasing the cutting tooledge wear intensity during machining.

Regrettably, poor adherence of the PVD coatings resultsin the unsatisfactory tribological properties of these coatingsystems. Recapitulating results of these investigations onehas to stress that there are still chances to substitute the PVDcoatings put down onto the Si3N4 nitride ceramics in futurefor the CVD ones. Undoubtedly these chances will grow withchange of parameters and with modernizing of the PVD pro-cesses.

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[4] S. Hogmark, S. Jacobson, M. Larsson, Wear 246 (2000) 20–33.

[5] W. Grzesik, Z. Zalisz, P. Nieslony, Surf. Coat. Technol. 155 (2002)37–45.

[6] P. Holubar, M. Jilek, M. Sima, Surf. Coat. Technol. 133/134 (2000)145–151.

[7] L.A. Dobrzanski, D. Pakuła, J. Kopac, M. Sokovic, Inzynieria Ma-teriałowa 6 (2003) 461–464 (in Polish).

[8] S. Dolinsek, J. Kopac, Wear 225–229 (1999) 295–303.[9] L.A. Dobrzanski, D. Pakuła, Inzynieria Materiałowa 3 (2004)

568–571.[10] Y.Z. Lee, K.H. Jeong, Wear 217 (1998) 175–181.[11] K.D. Bouzakis, N. Michailidis, S. Hadjiyiannis, K. Efstathiou, E.

Pavlidou, G. Erkens, S. Rambadt, I. Wirth, Surf. Coat. Technol.146/147 (2001) 443.

[12] L.A. Dobrzanski, K. Gołombek, Proceedings of the Scientific Con-ference on the Occasion of the 55th Anniversary of the FacultyMechanical Engineering of the Silesian University of Technology inGliwice, 2000, pp. 117–122.

[13] L. Lin, G.S. Blackman, R.R. Matheson, Progr. Org. Coat. 40 (2000)85–91.

[14] J. Kopac, J. Mater. Process. Technol. 78 (1998) 95–103.[15] P. Richard, J. Thomas, D. Landolt, G. Gremaud, Surf. Coat. Technol.

91 (1997) 83–90.[16] L.A. Dobrzanski, K. Gołombek, M. Sokovic, Proceedings of the

Seventh International Scientific Conference on Achievements in Me-chanical and Materials Engineering (AMME’98), Gliwice-Zakopane,1998, pp. 111–114.

[17] L.A. Dobrzanski, W. Kwasny, R. Shishkov, Proceedings of the EighthInternational Scientific Conference on Achievements in Mechanicaland Materials Engineering (AMME’99), Gliwice-Rydzyna, 1999, pp.

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cknowledgements

Investigations were financed within the framework ofolish State Committee for Scientific Research No. 3 T4726 grant headed by Dr. K. Lukaszkowicz. The reseas carried out partially in cooperation with Dr. J. Holund Dr. M. Sima from SHM-Sumperk (Czech Republic). Tuthors would like to express their thanks also to Dr. Z. W

rom LECO firm for the help in the realisation of examinions on the glow-discharge optical emission spectromDOS.

eferences

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