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Ceramic Coating
Thermal spray, CVD and PVD
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Outline:
� Materials, applications
� Processing
� Factors
� Thermal spray
� Physical vapor deposition (PVD)
� Chemical vapor deposition (CVD)
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Properties of ceramic films and coating
� High hardness
� Inertness
� Corrosion, oxidation and wear resistance
� Electronic and optical properties
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Application of ceramic coating
� Aircraft-engines
� Fan blades
� Metal cutting tools
� Racing cars, Automobile manufacturers
� Diesel engines (piston dome and exhaust)
� Land-based turbines and marine engines
� Carbon-carbon composites
� Heat exchangers
� Wear resistant products
� Aerospaces
� Medical implants
� Electronic and optical devices: wave guides, detectors
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Simple materials
� Metals:� Al, gold, tungsten, nickel, chromium, platinum
� Nitrides and Carbides:� SiC,SiN,TiN
� Insulating and protective coatings:� SiO2,ZrO2
� Optical coatings:� MgF2, ZnS, ZrO2
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Complex oxides
� Electronic insulators: SiO2, Al2O3, Y2O3, Ta2O5� Ionic insulators: ZrO2, CeO2� Electron conductors: RuO2, ReO2, IrO2� Transparent conductors: SnO2, Indium tin oxide
� Non-stoichiometric compounds: La1-xSrxVO3-x/2� Superconducting oxides:YBa2Cu3O7� Ferroelectrics:PbTiO3-PbZrO3,Ba1-xSrxTiO3
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Surface coating techniques
� Traditional enamels: glass-based coatings of inorganic composition applied in one or more layers to protect steel, casting iron or aluminium surfaces
� Chemical coatings: electroplating of metals such as copper and nickel
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� Sol-gel coatings: the pyrolysis of organometallic precursors such as metal alkoxides
� CVD: vapor phase transport to grow epitaxial and highly structured thin film including insulating oxide films on single crystal silicon substrate
� PVD: evaporation, sputtering, laser ablation and iron bombardment
Surface coating techniques
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Evaporation
� Materials � melted and vaporized by heated tungsten/molybdenum boat/electron beam� deposited on substrate
� For metal, alloys and stable compounds such as silica, yattria
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Sputtering
� ก��ก�ก��� ���������� ���� ��������ก��ก����ก target ������ก�����ก��� ������ �����!����� �"� �# gas plasma ��$� excited ion beam ��ก �% � ������������ ��ก� � ��& '� substrate
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Thermal spray
� '�(���ก��$�'���� )"ก������ !# '#� &��*�������*�+"��"� �����,���,��ก� ��-../� ���01 Gas plasma �� /��$� Combustion gas flame
� Flame spraying
� Plasma spraying
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Thermal spray processes
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Flame spraying
� Powder feed (wire) of coating material is fed through an oxy-fuel gas->ex. C2H2 or C3H8 flame
� ZrO2+Al2O3, Al2O3, ZrO2
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Wire spray coating
Specifications:
� Coating Material Form: Wire
� Heat Source: Oxy-Fuel Combustion
� Flame Temperature (in ºC): 3000
� Gas Velocity (m/sec): Up to 300
� Porosity: 10 to 15%
� Coating Adhesion (MPA): 14 to 20
Figure from Plasmatron
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Powder flame spraying
Specifications: � Coating Material Form: Powder � Heat Source: Oxy-Fuel Combustion� Flame Temperature (in ºC): 3000� Gas Velocity (m/sec): Up to 300� Porosity: 10 to 15 % � Coating Adhesion (MPA): 14 to 20
Figure from Plasmatron
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Wire Arc spray coating
Specifications:
� Coating Material Form: Wire
� Heat Source: Electric Arc
� Flame Temperature (in ºC): 3600
� Gas Velocity (m/sec): Upto 300
� Porosity: 10 to 15 %
� Coating Adhesion (MPA):28 to 40
Figure from Plasmatron
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Plasma spraying
� Thickness > 50µm
� Substrate: metal alloy, ceramics
� Applications:
� wear/erosion and corrosion resistance
� Thermal barriers
� Electrical and magnetic
� Aircraft
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What is Plasma?
� A gaseous collection of electrons, ions and neutral molecules
� Plasma gun:
� Cathode (-)
� Anode (+) with water cooling
� Inert gas (Ar, N2)
� Powder feeder
� Nozzle (+)
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Air plasma coating
Specifications:
� Coating Material Form:
Powder
� Heat Source: PlasmaFlame
� Flame Temperature (in ºC): 12000 to 20000
� Gas Velocity (m/sec):500
� Porosity: 2 to 10 %
� Coating Adhesion(MPA): 40 to 70
Figure from Plasmatron
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High velocity Oxy-fuel (HVOF)
Specifications:
� Coating Material Form: Powder
� Heat Source: Oxy-Fuel Combustion
� Flame Temperature (in ºC): 1500 +
� Gas Velocity (m/sec): 1500 +
� Porosity: 1 to 5 %
� Coating Adhesion (MPA): 70 +
Figure from Plasmatron
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Detonation gun (D-gun)
� D-gun spraying is a form of thermal spraying which consisted of heating and directionally propelling powder on to the work piece from a combustion chamber by a stream of gas detonation products
� Simple in design
� Low porosity and high bond strength
� Moderate substrate heating
� High rate of growth of coating thickness
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Detonation gun (D-gun)
Picture from www.gordonengland.co.uk/ds.htm
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Temperature & Velocity
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Thermal spray microstructure
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Microstructures of ceramic TBCs by various processes
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Coating materials
� TiC
� TiN
� Titanium carbo-nitride
� Alumina etc.
Thermal spray gun
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The most common control parameters
� Power input� Arc gas pressure� Gas pressure (He, H2, N2)� Powder gas pressure� Powder feed rate� Grain size/shape� Injection angle � Surface roughness� Substrate heating� Spray distance� Spray divergence� Spray atmosphere
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Vapor deposition techniques
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PVD and CVD
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Chemical Vapor Deposition(CVD)
� Chemical Vapor Deposition (CVD) – ก� &� ก��2�$�&��$�ก��ก�.3��4&����& '��% �� �����2����,� +��5 &����ก�6�ก7� �� ก�08ก������2�� �9�5�,ก�ก��2�&� # ����ก:���& '�����% �� �����ก��ก� nucleate �� film growth ����������%��, ���01 �ก:���$�������� ���#�� �# Halides, hydrides
� Applications of CVD:
� Resist� wear, corrosion and erosion of metal cutting tools, turbine and bearing
� Protect -> oxidation at high temperature� Integrated circuits;� Optoelectrical devices;� Micromachines;� Fine powders;� Protective coatings;� Solar cells;� Refractory coating for jet engine turbine blades.
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CVD control parameters
� Pressure
� Temperature
� Reactant/product-activity
� Mass transfer
� Gas/vapor-flow dynamics
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CVD reactor
� The reactant supply
� The deposition system
� Reactant/product retrieval
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CVD � chemical reaction
� Thermodynamic (chemical reaction)
� Basic chemical kinetics (reaction rate)
� Mass and heat transfer (reactor and substrate size, design)
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Basic steps in CVD (Jenson&Kern 1991)
� Reactants in gas flow –inlet-> deposition region� Gas phase reaction -> film precursors + by products� Film precursors � substante surface� Adsorbed on substrate� Adsorbed precursors -> growth site or desorbed� Surface reaction -> film + reaction products� Reaction products -> desorbed from surface� Desorbed products in the gas flow � outlet
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Principle of CVD
� 3SiH4 (g) + 4 NH3 (g) � Si3N4 (s) + 12 H2� SiH4 (g) + 2 H2O (g) � SiO2 (s) + 4 H2� 2AlCl3 (g) + 3 CO2 (g) + 3H2 (g) � Al2O3 (s) + 3CO (g) + 6HCl (g)
� 2Al(CH3)3 (g) + 8O2 (g) � Al2O3 (s) + 6CO (g) + 9H2O (g)
� Al(CH3)3 (g) + NH3 (g) � AlN (s) + 3 CH4 (g)
� BCl3 (g) + NH3 (g) � BN (s) + 3 HCl (g)
� SnCl4 (g) + O2 (g) � SnO2 (s) + 2 Cl2 (g)
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Principle of CVD
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SiO2
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CVD system
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CVD reactor
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Physical Vapor Deposition (PVD)
� Physical Vapor Deposition (PVD) 01 ก� &� ก��2�$�&���ก���ก-�������5 ��;;�ก�6 ���ก��ก�-�������ก������� ������4ก� � ก�&��������01 �2��� �� � ���������������,��ก��2�$�& �%� ������ก���� -0�ก� ก� ��5��#& '��% ��
� Evaporation
� Sputtering
� Arc Vaporization
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Applications of PVD:
� Metals, alloys, ceramics and some polymersmay be deposited onto metals, ceramicsand polymers by Physical Vapor Depositionmethod.� TiN, TiAlN, TiCN and CrN coating for cutting tools;
� AlSn coating on engine bearings, diamond likecoating for valve trains;
� Coating for forming tools;� Anti-stick wear resistant coating for injection molds;
� Decorative coatings of sanitary and doorhardware.
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PVD coating products
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Steps of PVD (Bunshah 1982)
� Step 1: Creation of deposition species
� Step 2: Transport from source to substrate (collision + ionized)
� Stop 3: Film growth on substrate (condensation, nucleation and growth)
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Sputtering
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DC Plasma sputtering
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Sputtering
E-beam
Laser ablation
Heat
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Evaporation process characteristics
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Reactive evaporation
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Reactive sputtering
www.alacritas-consulting.com
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Magnetron sputtering
www.engr.uky.edu
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Microstructure of coating
PVD
CVD
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PVD reactor
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Process parameters & limitation of evaporation and sputtering process
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VDO presentation
� Sputtering Process
� Plasma spray and thermal spray