Aurustussadestatud pinded / Vapour Deposited Coatings /

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Aurustussadestatud pinded / Vapour Deposited
Coatings / ????????, ?????????? ???????
??????????? ? ??????? Loengukonspekt
Koostas Andrei Surženkov
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Process definition.

• vapour deposition (either physical or chemical)
  is a coating
• process, where coating material is condensed
  in vacuum
• at the substrate from vapour phase, forming a
  thin
• ( 10 µm in the case of physical deposition and
  1000 µm
• in the case of chemical deposition) film.
  Sometimes
• the deposited material further reacts with
• the gaseous substances to form a final compound
  coating.
• Generally as metals, as non-metals can be
  deposited,
• certain case depends on the applied metod.

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Comparison of the coating processes.
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Development of vapour deposition technology.
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Process features.
Process type Material is introduced in
Thermochemical Solid / liquid / gaseous form
Chemical Solution form
Electrodeposition Solution form
Hot-dip Liquid melt
Cladding Solid form
Sol-gel Solution form
Thermal spraying Liquid form (except for cold spraying)
Vapor deposition Vapor (gaseous) form only

• process is carried out in vacuum only
• low productivity (several hours)
• high price
• but properties of the coatings (hardness, CoF,
  etc.),
• which can't be obtained by other methods.

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Process application fields.

• electrical devices (LCDs, touch panels,
  microelectronic
• devices, solar cells, etc.)
• magnetic devices (magnetic storage media)
• optics (laser mirrors, antireflection coatings,
  etc.)
• tool industry (plastic molds, cutting tools,
  blanking tools,
• etc.)
• aerospace devices (turbine blades, etc.)
• decorative purposes (watches bands, etc.).

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Process limitations.

• as the coatings are very thin, they can't
  improve bulk
• properties (tensile strength, fracture
  toughness, etc.),
• that is why good mechanical properties of the
  substrate
• are needed
• as vapour deposition is mostly a
  high-temperature process,
• the ability of the substrate to withstand high
  temperatures
• is required
• vapour deposition is a low production process
• vapour deposition equipment is relatively
  expensive
• (tens of thousands euros).

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Part I. Physical Vapour Deposited (PVD) Coatings
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General features.

• absence of chemical reaction during the
  deposition process
• relatively low temperatures (250 600 ºC) in
  comparison
• with chemical vapour deposition (CVD) processes
• electric and magnetic field is applied
• the variety of PVD technologies can be
  classified into three
• types evaporation, sputtering and arc
  evaporation.

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1. Evaporation technology. 1.1 Thermal
evaporation.

• in the simpliest variant the material of the
  future coating
• is resistance heated up to the evaporation
  temperature,
• and atoms of the material move towards the
  substrate by a
• straight trajectory and deposit on it, producing
  a film.
• in this case, only metals and metal alloys with
  a low
• melting points can be applied (for example, Zn,
  Al, etc.)
• such technology is used, for instance, for
  metallisation
• of fabrics.

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1. Evaporation technology. 1.2 Electron / laser
beam evaporation.

• coating material is ablated by a focused
  electron or laser beam at a
• small spot at the target, made of the coating
  material
• the ablated atoms / atom layers travel through
  the vacuum chamber
• and deposit at the substrate, forming the
  coating
• in contrast with thermal evaporation, all metals
  and metal alloys,
• as well as ceramics and polymers, can be applied
  as coating materials,
• whereas the temperature of the process can be as
  low as room temperature
• the main disadvantage of this method is the high
  price of the
• equipment (electron beam gun or laser)
• this method is applied, for example, for
  magnetic data storage media
• production, but for ultra-high rate
  aluminization of fabrics and
• transparent barrier coatings, as well.

Ablation removal of material by vaporization,
bypassing the liquid phase.
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Fig. 1. Pulsed laser deposition
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2. Sputtering. 2.1 General principles.

• the process finds place in a low vacuum (0.0005
  0.12 torr ?
• 0.07 16 Pa) with a presence of inert gas atoms
  (usually Ar)
• a high voltage (1 5 kV) is applied between the
  target, made of
• the sputtered material and the substrate to be
  coated
• due to high voltage, the inert gas atoms ionize,
  forming
• a plasma cloud near the surface of the sputtered
  material
• the ions become accelerated in the electric
  field between the substrate
• to be coated and the target of the sputtered
  material
• sputtered material is bombarded by accelerated
  inert gas ions from
• a plasma cloud, which is situated close to its
  surface
• as a result, atoms and atomic layers are
  extracted from the sputtered
• material, which are then directed to the
  substrate to be coated
• sputtered atoms form a coating.

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2. Sputtering. 2.2 Sputtering technologies.

• direct current (DC) diode sputtering (direct
  voltage is applied between
• the target (cathode) and substrate (anode))
• 2. triode sputtering (heated filament is used as
  a source
• of secondary electrons to help ignite and
  sustain the plasma)
• radio frequency (rf) sputtering (an alternative
  voltage at a high
• frequency (13.6 MHz) is applied between the
  target and the substrate)
• magnetron sputtering (an electron trap is formed
  by magnetic fields,
• what make electrons, extracted during the
  ionization and bombardment
• process, to arrive back at the target).

Conductive materials only
All materials
If the sputtered and deposited material further
reacts with gases, intentially introduced to the
vacuum chamber after the deposition process, the
process is called reactive sputtering.
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2. Sputtering. 2.2 Sputtering technologies. 2.2.1
Magnetron sputtering.

• distinct advantages of magnetron sputtering in
  comparison with other
• sputtering technologies are higher available
  deposition rates (10 times
• DC diode sputtering) and lower substrate
  heating
• both DC and AC current sources can be applied
  for magnetron
• sputtering (in other words, it can be eiter
  direct current magnetron
• sputtering or radio frequency magnetron
  sputtering)
• balanced and unbalanced magnetrons are used for
  sputtering
• magnetron sputtering is used in, for example,
  semiconductive industry,
• tool industry, etc..

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Fig. 2. Magnetron sputtering process.
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3. Arc evaporation. 3.1 General principle.

• a high-current low-voltage strikes at the
  surface of the target, made of
• the material of the future coating
• due to arc striking, a highly energetic emitting
  area (so-called cathode
• spot) appears at the surface of the target
• the temperature inside the cathode spot is
  extremely high (around
• 15000 ºC), causing the evaporation of the target
  material with
• the formation of a highly ionized quasi-plasma
  cloud
• this quasi-plasma cloud is directed towards the
  substrate and
• is deposited onto it, forming a film
• if necessary, a reactive gas is introduced after
  this, so that gas molecules
• react with the deposited film, creating a
  coating.

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Fig. 3. Schematic representation of the arc
evaporation process.
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3. Arc evaporation. 3.2 Technological features.

• in comparison with other PVD technologies, arc
  evaporation is
• the most productive one in addition to that, it
  casually allows to deposit
• denser coatings with highest mechanical
  properties
• also arc evaporation provides the highest target
  utilization among
• the PVD technologies
• the main disadvantage of arc evaporation is the
  formation of
• macrodroplets during the evaporation process,
  what leads to higher
• surface roughness of the coatings (highest among
  all PVD technologies)
• and lowers their adhesion to the substrate
• one possible solution to the problem of
  macrodroplets is seen in magnetic
• filtering systems, however, their application
  lowers the deposition range.

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4. Comparison of PVD technologies.
Process Deposition rate, µm/s Pressure, Pa Particle energy, eV Adhesion
Evaporation 0.05 25 10-3 lt 2
Sputtering 0.0001 0.7 10-1 ... 10 10 100
Arc evaporation 0.0003 1.85 0.5 10-2 1.510-2 10 100
Unbalanced magnetron sputtering
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Part II. Chemical Vapour Deposited (CVD) Coatings
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General features.

• chemical reaction is applied to deposit a
  coating
• precursor is decomposed, and the decomposition
  products
• form a coating at the substrate
• relatively high process temperature in
  comparison with
• the PVD processes (600 1100 ºC)
• the three main CVD technologies are thermal CVD,
  
• plasma-enhanced CVD (PECVD), and laser CVD
  (LCVD).

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Fig. 4. Example scheme of a CVD process (TiC
deposition).
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Comparison of CVD processes.
Process name Precursor decomposition Decomposition process Process temperature
Thermal CVD In contact with hot substrate Dissociation
PECVD In contact with plasma Dissociation
LCVD In contact with laser heated substrate Photochemical process / pyrolysis
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III Applications.
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Cutting tools.

• TiN, TiAlN, AlTiN, CROMVIc (Platit AG), ALCRONA
  
• (Balzers), etc.

Fig. 5. Comparison of uncoated and coated drills.
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Punching and forging tools.

• CrN, TiAlCN, ALCRINVIc (Platit AG), etc.

Fig. 6. Comparison of uncoated and coated forging
tools.
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Injection molding.

• TiCN, CrN, nACRo (Platit AG, etc.)

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Fig. 8. Comparison of nitrided and coated molds.
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Diamond-like carbon (DLC) CVD coating.

• Low-friction hard chemically inert coating, used
  for coating
• tools, machine parts and for decorative purposes.

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References.

• Coatings Technology Handbook. Ed. By A. A.
  Traction.
• Taylor Francis Group, Boca Raton, 2006.
• Modern Surface Technology. Ed. By F.-W. Bach, A.
  Laarmann,
• T. Wenz. Wiley-VCH Verlag GmbH Co. KgaA,
  Weinheim,
• 2006.
• Platit Compendium 2012, 49th edition. Platit AG,
  2011.
• C. Donnet, A. Erdemir. Historical Developments
  and New Trends
• in Tribological and Solid Lubrication Coatings.
  Surf. Coat. Tech.,
• 180 181, 2004, 76 84.
• Loengukonspekt Surface Engineering (1). Vapor
  Deposition.
• Koostajad Priit Kulu, Eron Adoberg.

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Smooth deposition!
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