M. STASZUK et al.: INVESTIGATION STUDIES INVOLVING WEAR-RESISTANT ALD/PVD ...
755–759
INVESTIGATION STUDIES INVOLVING WEAR-RESISTANT
ALD/PVD HYBRID COATINGS ON SINTERED TOOL
SUBSTRATES
PREISKAVE OBRABNE ODPORNOSTI HIBRIDNEGA NANOSA
ALD/PVD NA SINTRANEM ORODJU
Marcin Staszuk, Daniel Paku³a, Tomasz Tañski
Silesian University of Technology, Institute of Engineering Materials and Biomaterials, Konarskiego Street 18A, 44-100 Gliwice, Poland
marcin.staszuk@polsl.pl
Prejem rokopisa – received: 2015-07-22; sprejem za objavo – accepted for publication: 2015-10-13
doi:10.17222/mit.2015.236
This paper is an important research contribution to the development of PVD coatings, in particular, on ceramic substrates,
which, due to their dielectric properties, are difficult materials to coat using this technique. In order to satisfy the desired
expectations relating to the PVD coatings, one of the basic properties must be provided for, the adherence to the substrate. The
main aim of this research is to investigate the structure and mechanical properties of the coatings deposited in a hybrid process,
comprising the atomic-layer deposition (ALD) and cathodic-arc evaporation (CAE-PVD) on sintered carbides and multipoint
ceramic cutting tools. The concept of this research study involves an execution and investigation of ALD + PVD hybrid coatings
on sintered carbides and a sialon-ceramic substrate, and defining the influence of the ALD interlayer on the adherence of the
investigated coatings. The critical load Lc, which is the adhesion measure of coats, was determined with the scratch-test method
and a tribological test made with a pin-on-disk tester. Observations of the surface topography and wear mechanism were
performed using a scanning electron microscope and atomic-force microscopy. The investigation studies showed that an ALD
layer considerably improves the adherence of the PVD layer to the tool-ceramic substrate. The research of the coatings on
sintered-carbide substrates showed that the adherence of the PVD coating to the substrate deteriorates in the case of applying an
ALD interlayer.
Keywords: PVD, ALD, hybrid coatings, tool ceramics, sintered carbides
^lanek je pomemben raziskovalni prispevek k razvoju PVD nanosov, {e posebno na kerami~ni podlagi, ki je zaradi dielektri~nih
lastnosti zahteven material za nana{anje s to tehniko. Da bi zadovoljili pri~akovanja na delu s PVD nanosom, je oprijemljivost
na podlago osnovna lastnost, na katero je potrebno biti pozoren. Glavni namen raziskave je preiskati strukturo in mehanske
lastnosti nanosa, nane{enega s hibridnim postopkom, ki obsega nanos atomskih plasti (ALD) in katodno izparevanje v obloku
(CAE-PVD) na sintrane karbide in ve~to~kovno kerami~no rezilno orodje. Koncept te raziskave vklju~uje izvedbo in preiskavo
hibridnega nanosa ALD + PVD na podlago iz sintranih karbidov in sialon keramike ter dolo~itev vpliva vmesne plasti ALD na
oprijemljivost preiskovanih nanosov. Kriti~na obremenitev Lc, ki je merilo oprijemljivosti nanosov, je bilo dolo~eno s
preizkusom razenja in s tribolo{kim preizkusom trn na plo{~i. S pomo~jo vrsti~nega elektronskega mikroskopa in mikroskopa
na atomsko silo je bilo izvedeno opazovanje topografije povr{ine in mehanizma obrabe. Izvedene preiskave ka`ejo, da ALD
nanos mo~no izbolj{a oprijemljivost PVD nanosa na orodno keramiko. Pri nanosu na podlago iz sintranega karbida je raziskava
pokazala, da je pri uporabi ALD vmesne plasti, oprijemljivost PVD nanosa slab{a.
Klju~ne besede: PVD, ALD, hibridni nanosi, keramika za orodja, sintrani karbidi
1 INTRODUCTION
Sialon-tool ceramics are a group of tool materials
combining the mechanical properties of silicon nitride
Si3N4 and the chemical properties of Al2O3. Ceramic
sinters are fabricated with powder-metallurgy methods,
but in contrast to sintered carbides, they do not contain a
metallic binder. The use of tool ceramics as compared to
sintered carbides is still considerably small but it is
growing, also due to the application of thin wear-resis-
tant layers PVD and CVD.1,2
Surface engineering technologies play a significant
role in material engineering and are viewed as the fun-
damental scope of knowledge in this field of engi-
neering. The research entities working in this field try to
investigate and identify the phenomena taking place on
the surfaces of the machined materials. In order to
improve the operating properties of products, various
surface-machining technologies are applied.2–6 The
advantages arising from the application of PVD coatings
on cutting tools such as a high microhardness and resis-
tance to abrasion, a low friction coefficient of the tool
covered with the coat, the resistance to oxidation or to
the formation of build-up edges on the tool, combined
with the possibility to machine materials without liquid
cooling lubricants are important contributions advocating
the development of this technological field. However, in
order to improve the desired properties of PVD coatings,
one of the basic properties must be taken care of, which
is the adherence to the substrate. The coating of ceramic
materials in PVD processes, including also tool cera-
mics, is difficult due to dielectric properties, since the
inability of the substrate polarization during the coating
Materiali in tehnologije / Materials and technology 50 (2016) 5, 755–759 755
UDK 620.19:620.178.16:621.793.8 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(5)755(2016)
process makes it difficult to obtain coatings with a good
adherence to ceramic substrates.2,7–11
The fabrication technology of stratified coatings of
the type "adhesive layer/PVD layer" using the multi-
stage surface machining is one of the most modern
methods to modify the properties of the surface layer and
it consists, in a successive application, of two (or more)
technologies of surface engineering. In terms of material
effects, we obtain multilayer systems whereof one part is
made up of an appropriately selected adhesive layer
fabricated on the surface of the substrate, which protects
the "proper" PVD layer against a loss of internal cohe-
sion and an insufficient adhesion to the substrate. And on
the other end of the system, we obtain a PVD coating
which efficiently insulates the substrate, limiting the
impact of the external harmful factors encountered in the
operating process.2,12
The coatings of the (Ti,Al)N type are isomorphic,
with titanium nitride which is still widely applied. The
presence of aluminum in the coatings of this type brings
about the situation where the service-life temperature of
these coatings exceeds 970 K, and in such operating con-
ditions of raised temperature, a layer of Al2O3 is formed
on the surface, which forms a diffusive barrier for the
atmospheric oxygen.13,14
Zinc oxide is a semiconductor characterized by a
high energy gap (3.4 eV), high exciton binding energy
(60 meV) and easy n-type doping.15,16 Zinc oxide, ZnO,
obtained with the use of the ALD technique on a sialon-
ceramic substrate enables the polarization of this sub-
strate during the technological process of PVD and,
hence, the objective of this paper is to investigate the im-
pact of the ZnO layer obtained with the use of the ALD
technique on the adhesion of the hybrid coating
ALD/PVD of the ZnO/(Ti,Al)N type to the sialon sub-
strate. For the sake of comparison, we also investigated
the coatings on sintered carbide substrates.
2 MATERIALS AND METHOD
The research studies were carried out on multipoint
cutting tools made of sintered carbides WC-Co and
sialon-tool ceramics covered in the PVD and ALD/PVD
processes. The tools were covered during the cathodic-
arc evaporation process CAE-PVD with the (Ti,Al)N
coating type and in the ALD/PVD hybrid process using
the ZnO/(Ti,Al)N coating type.
The topography of the surfaces and wear mechanisms
of the coatings was viewed with a Supra 35 scanning
electron microscope from Zeiss. The secondary-electron
(SE) detection was used to obtain the images of the
tested samples, with an acceleration voltage of 5–20 kV.
The topography of the coatings was tested using a
Park Systems XE-100 atomic-force microscope. The
tests were carried out in the non-contact mode.
The adherence of the coatings to the substrate was
assessed with a scratch test on a Revetest device from
CSEM. The method consists of moving a Rockwell C
diamond indenter through the surface of a tested sample
at a constant speed, with the applied force growing
linearly. The ranges of the applied load were 0–100 N
and 0–200 N. The Lc critical load, at which the coating
adhesion is lost, was determined according to the acou-
stic-emission value registered during the measurement
and by observing the scratches formed during the scratch
test.
The abrasive-wear-resistance tests and the wear-fac-
tor tests for the tested coatings were performed with the
pin-on-plate method using a CSEM Tribometer (THT).
A 6 mm Al2O3 ball was used as the counter specimen.
The tests were made at room temperature. The following
test conditions were applied: a normal force of FN = 10 N
and a movement speed of v = 0.1 m/s. The total distance
of 1 km was set for all the tested specimens.
3 DISCUSSION AND TEST RESULTS
The value of critical load Lc, being the adherence
measure for the investigated coatings on sintered-carbide
substrates or sialon-tool ceramic substrates, was deter-
mined using a scratch test (Figure 1). The research
studies show that the ALD/PVD hybrid coat has a much
M. STASZUK et al.: INVESTIGATION STUDIES INVOLVING WEAR-RESISTANT ALD/PVD ...
756 Materiali in tehnologije / Materials and technology 50 (2016) 5, 755–759
Figure 1: a) Acoustic emission (AE) and friction force Ft depending
on load Fn for the ZnO/(Ti,Al)N coating on sialon ceramics, b) scratch
failure at Lc (opt) = 65 N, magnified 200×
Slika 1: a) Akusti~na emisija (AE) in sila trenja Ft v odvisnosti od
obremenitve Fn pri ZnO/(Ti,Al)N nanosu na sialon keramiko, b) po-
{kodba z razo pri Lc (opt) = 65 N, pove~ano 200×
higher adherence to the sialon-ceramic substrate than the
PVD coating without the adhesive layer (Table 1). A re-
verse situation takes place in the case of coatings on
sintered-carbide substrates. Due to high adhesion of the
PVD coating to the sintered-carbide substrate, the ALD
layer causes a drop in the critical load from 109 N to
55 N.
Table 1: Critical loads Lc of the investigated coatings
Tabela 1: Kriti~ne obremenitve Lc preiskovanih nanosov
Type of coating
Critical load Lc, N
Sialon substrate Cemented-carbidesubstrate
(Ti,Al)N 21 109
ZrO/(Ti,Al)N 64 55
The damage done to the coats during the performed
adhesion/scratch tests was identified on the basis of
observations with the scanning electron microscope. The
studies carried out show that it is the delamination,
which is the principle mechanism of the coat damage on
the sialon-ceramic substrate after the critical load Lc has
been exceeded. In the case of the PVD coat, which is
characterised by a low adherence to the ceramic substra-
te, a total delamination with vast chipping was identified.
Furthermore, a low adherence of the PVD coat to the
ceramic substrate indicates a considerable morphological
non-homogeneity and, in particular, the presence of
chippings found on the whole surface of the coat (except
for the scratch area) (Figure 2). A low adherence of the
coat to the substrate results in its unprompted chipping
due to the internal strain of the coat. In the case of the
ZnO/(Ti,Al)N hybrid coat on the sialon substrate, dela-
mination was identified on both sides of the sample
(Figure 3). The chipping on both sides of the scratched
sample is definitely less vast than that observed in the
case of the (Ti,Al)N coat on the same substrate. The only
morphological defects of the hybrid coat are the drop-
shaped microparticles, inseparably connected with the
cathodic-arc evaporation process (Figure 4). In the case
M. STASZUK et al.: INVESTIGATION STUDIES INVOLVING WEAR-RESISTANT ALD/PVD ...
Materiali in tehnologije / Materials and technology 50 (2016) 5, 755–759 757
Figure 4: Surface topography of the ZnO/(Ti,Al)N coating deposited
onto the sialon-ceramic substrate: a) SEM, b) AFM
Slika 4: Topografija povr{ine ZnO/(Ti,Al)N nanosa, nane{enega na
podlago iz sialonske keramike: a) SEM, b) AFM
Figure 2: Characteristic failure obtained with the scratch test of the
(TiAl)N coating deposited on the sialon-ceramic substrate
Slika 2: Zna~ilna po{kodba pri preizkusu z razenjem nanosa (Ti,Al)N,
nane{enega na podlagi iz sialonske keramike
Figure 3: Characteristic failure obtained with the scratch test of the
ZnO/(TiAl)N coating deposited on the sialon-ceramic substrate
Slika 3: Zna~ilna po{kodba pri preizkusu razenja ZnO/(Ti,Al)N
nanosa, nane{enega na podlago iz sialonske keramike
of the coats on sintered-carbide substrates, friction is the
dominant mechanism. In the case of the PVD coat on the
sintered-carbide substrate, which is characterised by the
highest adherence among the investigated samples, no
abrasion deep down in the substrate was identified until
the maximum load was reached during the scratch test.
However, numerous cohesive cracks were identified after
surpassing the critical load Lc. In the ZnO/(Ti,Al)N coat
on the same substrate, we identified a uniform abrasion
spreading down into the substrate after the critical load
was exceeded.
With the tests on the abrasive-wear resistance of the
coats deposited on sialon ceramics and on sintered car-
bides using the pin-on-plate method, we found that in
almost all the cases where the coats were applied the
coats were damaged down to the substrate zone (Figures
5 and 6). The dominant wear mechanism of the investi-
gated coats was attrition. We also found that in some
cases the damaged coat sticks onto the material of the
counter specimen, which has a direct impact on the
changing values of the friction coefficient. The research
studies also confirm a positive impact of the ZrO layer
on the attrition resistance as compared to the specimen
without such a layer. At one end of the scratch, we ob-
served a lot of damage to the coat deposited on the sialon
substrate without the ZrO layer. The damage is of
adhesive character – we can observe stratifications and
cracks of the layer (Figure 5). And in the case of the
coat deposited with the ZrO layer, the end of the scratch
is uniformly grated without any adhesive damage (Fig-
ure 6).
4 CONCLUSION
Nowadays, the improvement of the wear resistance of
cutting tools mainly involves surface machining, while
the selection of the technology or coating material aims
at ensuring the proper resistance of a tool to dominant
wear mechanisms. The operating properties of the coats
resistant to the wear are the results of many components,
primarily the microhardness, the grain size and the
adherence to the substrate. Especially the last property is
of key importance, and in view of the performed research
studies2, the grain size, the thickness and the micro-
hardness of the obtained coats have smaller impacts than
the adhesion on the durability of cutting tools since the
changes in these properties have smaller impacts on
service life.
The paper presents the results of research studies in-
volving the application of an ALD layer to obtain a
better adhesion of the PVD coat to the tool sialon-cera-
mic substrate or sintered-carbide substrate. We inve-
stigated the (Ti,Al)N coat deposited on both substrates,
with the ZnO layer and without it. On the basis of the
investigation studies, we can state that zinc oxide con-
siderably improves the adherence of the PVD coat to the
ceramic substrate, which was confirmed with scratch
tests and observations of the damage made during the
tests, using a scanning electron microscope. The critical
load, being the adherence measure of the PVD coat on
the ceramic substrate, increased due to the application of
the adhesive layer by over 200 %. With respect to the
investigated coats on sintered carbides, the adherence of
the PVD coat to the ALD layer decreased as compared to
the coat without ALD.
The improvement in the adherence of the PVD coat
to the ceramic substrate is undaubtly connected with the
possibility to polarize the substrate during the coating
process involving the application of the ZnO layer. The
results of the research studies are important since the
deposition of ceramics in PVD processes is hindered due
to the dielectric properties of ceramics.
M. STASZUK et al.: INVESTIGATION STUDIES INVOLVING WEAR-RESISTANT ALD/PVD ...
758 Materiali in tehnologije / Materials and technology 50 (2016) 5, 755–759
Figure 6: Trace of tribological damage on the surface of the
ZnO/(Ti,Al)N coat deposited on the sialon-ceramic substrate
Slika 6: Sled tribolo{ke po{kodbe na povr{ini ZnO/(Ti,Al)N nanosa,
nane{enega na podlago iz sialonske keramike
Figure 5: Trace of tribological damage on the surface of the (Ti,Al)N
coat deposited on the sialon-ceramic substrate
Slika 5: Sled tribolo{ke po{kodbe na povr{ini (Ti,Al)N nanosa,
nane{enega na podlago iz sialonske keramike
Acknowledgements
The publication was co-financed by the statutory
grant of the Faculty of Mechanical Engineering of the
Silesian University of Technology in 2015.
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