5th International DAAAM Baltic Conference
“INDUSTRIAL ENGINEERING – ADDING INNOVATION CAPACITY OF LABOUR
FORCE AND ENTREPRENEURS”
20–22 April 2006, Tallinn, Estonia
HARD COATINGS MANUFACTURING TECHNOLOGY
USED IN TOOLING
Gregor, A., Podgursky, V., Adoberg, E. & Kulu, P.
of their higher hardness compared to high
speed steel and cemented carbide and for
decorative purposes because of their
attractive appearance. These PVD coatings
are still available and in many applications
they are the best option. However their
temperature resistance is insufficient for
applications to as high speed machining.
TiN for example decomposes at 450 °C.
Therefore the next step in the development
of hard PVD coatings was the improvement of the oxidation resistance to make
the coatings more suitable for applications
such as high speed machining and general
high temperature wear protection.
Improvement
in
temperature
resistance was achieved by introducing
other alloyed elements such as Cr, Al or Y,
into the TiN lattice. Further improvement
in the properties of hard PVD coatings was
achieved in the third generation of hard
PVD coating through the deposition of
multilayers and superlattices. These
coatings are achieved by alternatively
depositing two different components to
form layered structures. Multilayers
become superlattices if the thickness of the
different layers is less than 10 nm.
Multilayered coatings of materials
with similar crystal structures tend to form
columnar structure which extends through
the whole coating. Such coatings are
referred as superlattice coatings. First
superlattice coatings were obtained by
combining TiN/VN and TiN/NbN. This
type of multi-layered coating structure
have shown improvement in hardness as
well as in toughness, compared to single
layers of the same materials.
Abstract:
Present paper gives an overview of the
hard coating technology in the world and
in the Estonia. Variety of coatings used in
tooling, their structure, hardness and
some examples of application discussed in
the work. Analysis of the influence of
different deposition parameters to the
coating properties is given.
Key words: hard coatings, PVD, arc
evaporation, tool coating
1. INTRODUCTION
The term physical vapour deposition
(PVD) seems to have been originally
termed by the authors Powell, C.F.; Oxley,
J.H. and Blocher, J.M. Jr. in 1968. [1].
PVD is used in manufacturing to
improve mechanical, tribological and
decorative properties of components
beyond those available by traditional
methods and in an environmentally safe
manner. In the mid 1970s the magnetron
sputtering, controlled reactive sputter
deposition and the use of controlled
concurrent ion bombardment as a process
parameter were commercially introduced.
Since 1980, tool coatings formed by PVD
technologies have become reality, and an
industry has envolved around PVD tool
coatings based on the work of the early
pioneers in this field.
The first generation of hard PVD
coatings were single metal nitrides such as
TiN, CrN and ZrN. They have been
exploited commercially since the middle of
the 1980s in cutting applications because
255
Superlattice strengthening is well
known from classical metallurgy. By
selecting a suitable combination of
materials for the multilayered structure it is
possible to improve the resistance against
wear, corrosion, oxidation, etc.
study published in 1996 (Fig. 1) estimated
the market value for wear protective coatings as 83 billion EUR. It was predicted
that the world market value for the coatings
produced under vacuum is to be well over
200 billion EUR in 2004. Market forecasters expected a growth of the machine
tooling market at least 8% by 2005.
In 2004 Balzers announced that company
employed 2252 people and generated 235.7
million EUR in turnover with an operating
result (EBIT – Earnings Before Interest
and Taxes) of 36.6 million EUR.
Another company Bodycoat, from
England as an establishment of a joint
venture with IonBond.
2. MARKETS
2.1 PVD world market
There are several companies in the market
which provide state of the art of hard
coatings. During the last 25 years PVD
hard coatings have played a key role in tool
manufacturing industries as well as in
vehicles and machinery.
In 1978 Balzers launched its
revolutionary tool coating technology.
Very hard, adherent coatings were applied
at temperatures below 500 °C degrees.
Market trends – at first a few all
purpose coatings (mostly titanium nitride)
let to performance breakthroughs
in a wide variety of fields. Todays market
requires custom coatings systems created
and optimised for fairly narrow
applications. Best results achieved in
practice can only be attained if tool and
coating are perfectly matched.
Know-how and innovation are
crucial but cannot lead to success unless
both parties have access to the needed
personnel, plant and financial resources.
Balzers possess a network of more than 70
certified coating centres located in 26
countries including Europe, Asia and
United States. Tool coatings continue to
represent a significant proportion of the
applications for PVD technology. In the
area of PVD coated components, nowadays
typical applications are fuel injection
systems, roller and plain bearings for harsh
environments, gears, pumps and compressors. A world-wide market value for
the PVD components was estimated to be
worth of approximately 1.5 billion EUR in
1990. A BMBF (Federal Ministry of
Education and Research, Germany)
Table 1 Bodycote interim results in GBP in
2005 [5]
INTERIM
RESULTS
BODYCOTE
Total Revenue
Revenue 1
EBITDA
Headline
Operating Profit
Headline Profit
before Tax
Profit before
Tax 1
Tax
Profit after Tax
Free casflow
Headline EPS
Dividend/Share
1 continuing
H1
2005
(£m)
230.7
229.3
53.5
H1
2004
(£m)
231.4
211.5
48.6
Change
%
+8
+10
33.1
27.1
+22
29.2
22.3
+31
27.3
7.3
20
14.2
6.7p
2.35p
24.7
5.6
19.1
24.4
6.0p
2.25p
+11
+5
+12
+4
operations
Market value for thin hard coatings (BMBF Studie 1996 SehOHTA)
surface protection
decorative
optics
electronics
memory technology
barrier technology
optoelectronics
medical technology
0
20
40
60
80
100
billion EUR
Fig. 1 Market value for thin hard coatings
in 1996 [4]
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IonBond PVD services are now available
from 25 locations in 12 countries with an
experienced and qualified staff of more
than 600. Bodycote generated 353.8
million EUR turnover with an operating
result (EBIT) of 82 million EUR compared
to 2004 as following: 354 million EUR
turnover with an operating result (EBIT) of
74.5 million EUR.
Another company Platit AG, founded in
1992 as a part of a Blösch group, has
announced that turnover in their coating
centers locating at U.S.A, Asia and Europe
in 2005 has increased compared to 2003 in
order to: 340%, 130% and 190% in Europe
[3] as shown in Fig. 2.
University of Technology. This coating
system is mainly used experimentally, but
industrial services are provided as well.
Due to the basic design of Bulat-6 only
single metal coatings can be deposited.
Robot paws have been coated regularly for
JOT Estonia OÜ and Pioneer AS.
Fig. 3 Robot paw coated with TiN
Production plan for coated parts of
companies mentioned above is around 500
parts per annual. Tööriistavabrik AS is
probably a biggest toolmaking plant in
Estonia. Production capacity for coated
moulds, dies and punches is around 300…
400 kg a year. Platit AG and Balzers AG
are used as subcontractors so far. Viro
Tools AS plans to coat from 10 to 15 parts
a year and Vasar Instruments AS few times
over the year. Along with the increasing
competition,
market
demands
and
expectations, coatings soon will be
everyday phenomenon here as well.
Fig. 2 Announced turnover in Platit coating
centers locating on U.S.A, Asia and Europe
[3].
So the market shows promising numbers
for coating future.
2.2 Estonian PVD market
Estonian PVD market SWOT analysis has
been done in June 2005. Eight Estonian
tool manufacturing companies (JOT
Estonia OÜ, Pioneer AS, Roomet &
Melrosten OÜ, Sumar AS, Tööriistavabrik
AS, Vasar Instrument AS, Viro Tools AS
and Zircon Tools OÜ) were included into
the study. For our knowledge in Estonia is
only one working example of PVD
equipment (Cathodic Arc Evaporation
plant Bulat-6) in Estonia in Tallinn
Fig. 4 Multilayer
TiN
coating
experimental metal sheet forming tool
257
on
triode high voltage electron beam
evaporation and magnetron sputtering. The
direct current (DC) cathodic arc
evaporation (CAE) is introduced shortly. It
is said to be one of the most important
PVD technique, witch is mainly used to
create hard, wear resistant coatings for
tooling and for machine building industry.
The cathode is evaporated by the means of
arc in a cathode spot, arcs are sustained by
voltages in the range of 15 to 50 V. Arc
creates a conductive medium necessary for
sustaining the discharge by intensive
evaporation of the cathode material. Due to
the very high power density concentration
of arc (up to 1000 Wcm-2), small molten
pools will arise in the surface of cathode.
Typical arc currents are in the range of
30… 400 A. The evaporated material is
ionized in collisions with electrons and
accelerated away from cathode due to a
nonuniform potential distribution and
plasma expansion. The dense plasma flux
contains electrons, ions, atoms, and
microparticles – often called as droplets.
The droplets size varies in the range of
0.1…100 µm. The content of the plasma
flux depends enormously on a cathode
material and its purity, the temperature of
the cathode surface, working gas pressure
and composition as well as arc current.
Emitted ions have a kinetic energy in the
range of 40… 100 eV. The substrate can be
heated by radiation, heat conductor from
the substrate holder or by the means of
accelerated particles (electrons, gas phase,
and metallic ions). Usually ion energy is
given by a negative substrate bias of about
25 V to 2 KV.
The cathodic arc technique has
proven to be extremely successful in
cutting tool applications. The sucsess has
been achieved by having a droplet free
hard surface. The phenomena of droplets or
macroparticles is closely related to arc
movement on the surface of cathode. It has
been noticed that the arc movement of a
conventional arc source is about 8 m/s. By
applying a suitable external magnetic fields
to the cathode, the speed of the arc spot
3.
DEPOSITION
METHODS,
PROCESSES AND COATINGS
3.1
Deposition methods and
processes
The meaning of this article is to shortly
introduce cathode arc evaporation (CAE)
methods, the process and different coatings
achievable with this technology. Process
and equipment. Mainly all PVD hard
coating techniques are reactive processes,
i.e., the metal pieces are vaporized and a
gas is fed into the coating chamber which
reacts with the metal spieces to form the
desired compound
[3]. The first
commercial use of the arc evaporation –
deposition method was for TiN coatings
deposited at low temperatures, particularly
for high-speed steel (HSS) cutting tools by
arc evaporation of titanium in nitrogen
plasma [1].
Fig. 5 Direct Current
Evaporation schematic
Cathodic
Arc
There are four basic types of PVD
equipment in use. The differences between
the four types are the way that the source
material is vaporized, either by evaporation
or sputtering; the way that the plasma is
created; and the number and type of ions,
electrons, and gas atoms that constitute the
plasma [4]. These four different techniques
are: low voltage electron beam evaporation
(EBE), cathodic arc evaporation (CAE),
258
was found to be in the range of 17 m/s. The
higher arc spot velocity results in a low
residence time of the arc spot on a given
area, thus this fast movement reduces
localized overheating and hence the density
and size of the droplets are minimized.
Generally microdroplet emission is greater
for metals with low boiling points [3,8], eg.
Al, Cu etc. Reduced current density and
effective cathode cooling helps to reduce
macroparticle generation as well.
Because of the fact that first commercial
coatings found their application mainly in
tooling (cutting applications), there soon
appared demand for coatings with
enhanced thermal stability and oxidation
resistance. Hence alloyed elements (Cr, Al,
Y) were introduced into the TiN lattice of
the second generation coatings. Coatings as
TiAlN, AlTiN (high Al content >50%),
3.2 Coatings properties
PVD coatings generally have good
homogeneity of coatings on substrates of
different
complex
shape,
friction
coefficient in the range of 0.15…0.55,
nanohardness in the range of 18…52 GPa,
thickness of about 1…5 µm, thermal
conductivity in the broad range of
1.7…0.055 K·cm²/s, oxidation resistance
in air appears to be 400…1200 °C.
The first coating to be used
sucsessfully in tooling and still most
recognized by its attractive appearance –
TiN. The deposition temperature is lower
than the critical 500 °C for the HSS steel.
The first TiN coated cemented carbide
cutting tool inserts were introduced in
1985. TiN together with TiCN, CrN, ZrN,
will lead us into the area of the first stage
of the coatings, where single metal atoms
were reacted with nitrogen or other
reactive gases in a vacuum chamber (single
metal nitrides and carbonitrides). TiN is a
wear resistant ceramic coating having a
nanohardness of 24 GPa. It is widely used
in machining of non alloy-, alloy and
stainless steels, cast irons and aluminium
alloys. The thickness of TiN is usually in
the range of 2…5 µm, deposition
temperature of 300…450 °C, substrate bias
voltage of -180…-240 V. Partial nitrogen
pressure is in the range of 2…5·10-5 torr.
The effect of N2/Ar pressure on the
morphology of TiN coatings can be
qualitatively predicted using Tornton´s
structure zone model for magnetron
sputtered coatings [4] as shown in Fig. 6.
Fig. 6 Thornton stuctural zone model [6].
AlCrN, CrTiN.
These second generation coatings have
increased performance due to alloyed
elements, higher thermal stability and
better heat resistance, higher hardness and
toughness. TiAlN has high hardness from
28 … 35 GPa, coating thichness varies
usually from 1…4 µm, it has enhanged
thermal stability up to 700…900 °C
depending on coating structure (mono- or
multylayer).
Along with increasing demand for better
coatings, multilayered coatings were
introduced. Multilayered coatings of
evaporated materials with similar crystal
structures tend to form columnar crystals.
The coatings are called as superlattices
when the thickness of the individual
lamellae is around 5…25 nm. Generally
multilayered coatings become superlattices
(nanolayered coatings) when the period of
the different layer is less that 10 nm. List
of nanolayered coatings are TiAlN/TiN,
TiN/VN, CrN/NbN, W/NbN, NbN/VN and
TiN/NbN [7]. Nanolayered coatings have
improved hardness and toughness compared to single layers of the same
materials. The latest achievement in
259
coatings technology is nanocomposite
structures. These coatings are generated by
deposition of different kind of materials
(e.g. Ti, Al, Cr) in the first group and
followed by deposition of Si in the other.
The groups are not completely mixed,
instead two phases are formed. Finally
nanocrystalline TiAlN- or AlCrN-grains
become embedded into the amorpheus
Si3N4- matrix and become nanocomposite
coating.
CORRESPONDING ADDRESS
M.Sc. Andre Gregor
TUT, Department of Machinery
Institute of Materials Engineering
Ehitajate tee 5, 19086 Tallinn, Estonia
Phone: 372+6203371
Fax: 372+6202020
E-mail: andre.gregor@ttu.ee
REFERENCES
1. Bunshah R. F. Handbook of Hard
Coatings, William Andrew Publishing,
LLC, Norwich, New York, U.S.A, 2001.
2. Tracton A.A. Coatings Technology
Handbook, CRC Press, Taylor&Francis
Group, Boca Raton, Florida, U.S.A., 2006.
3. http://www.platit.com/download/platit_
press_release_ev_preview.pdf, 13.03.2006
4. http://www.pvd-coatings.co.uk/historyof-pvd-coatings.htm#Physical_
Vapour_Deposition, 13.03.2006
5. http://www.bodycote.com/resources/
2005_Results_Presentation.pdf, 13.03.2006
6. http://www.esm.psu.edu/htmls/
stf/thinfilms/, 13.03.2006
7. http://www.pvd.ch/SanDiego.pdf,
13.03,2006
8. Podgursky V., Torp B., Traksmaa R.,
Veinthal R., Viljus M., Coddet O.,
Morstein M., Gregor A. and Kulu P.,
Investigation of (Ti, Al)N Based Coatings
Grown by Physical Vapour Deposition,
MATERIALS SCIENCE
(MEDŽIAGOTYRA), 2005, Vol. 11, No. 4.,
352…355.
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