This document discusses thermal spray coating processes. It describes several thermal spray methods like flame spraying, arc spraying, plasma spraying, and cold spraying. These methods create coatings through different combinations of melted or partially melted spray materials deposited with kinetic energy. The document compares the properties of coatings produced with different methods, like hardness, porosity, adhesion and wear resistance. Finally, it outlines several applications of thermal spray coatings in areas like wear and corrosion resistance, high temperatures, and size restoration.

1. 1
SURFACE ENGINEERING (2)
THERMAL SPRAY
Prof. Priit Kulu, Andrei Surzhenkov

2. 2
Surface properties of material/part
 Wear
− mechanical;
− corrosive-mechanical.
Criteria: wear resistance (by mass/volume, relative)
 Methods of surface reinforcement
− peening;
− surface alloying and hardening;
− coatings (sprayed coatings, vapor deposited coatings, cladded
coatings, galvanic coatings, diffusion coatings);
− metal cladding (bimetal materials).

3. 3
Coating-substrate system

4. 4
Structures’ types of the coatings

5. 5
Coatigns’ processes
 CHEMICAL
 ELECTROCHEMICAL
 THERMOCHEMICAL
 THERMOCOATING
 VAPOR DEPOSITION
 MECHANICAL

6. 6
Comparison of the coating processes

7. 7
Thermal spray methods
 CHEMICAL
 ELECTROCHEMICAL
 THERMOCOATING
 VAPOR DEPOSITION
 MECHANICAL
cold gas spraying
(CGS)
laser spraying
(LS)
molten-metal
flame spraying
Thermal spraying

8. 8
Typical structure of a coating
Sprayed coating’s structure

9. 9
Sprayed coatings’ materials

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Flame spraying
- flame temperature:
• acetylene/oxygen 3160 ºC;
• propane/oxygen 2850 ºC;
• hydrogen/oxygen 2660 ºC.
- sprayed materials:
• wire: metals and metal alloys;
• powder: pure metals, alloys, oxides, cermets,
composite powders.

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Arc spraying
• temperature inside the arc: 6500 ºC;
• voltage 18 – 40 V, current 50 – 150 A;
• sprayed materials: electroconductive alloys,
ceramics can be deposited, when using core wires.

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Plasma spraying
• plasma temperature: up to 30000 ºC.
• virtually all existing materials.

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Plasma transfered arc spraying (PTA)
• Fe, Ni, Co, Cr based alloys,
stainless steels, cermets

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Laser cladding
• virtually all metal alloys, cermets and
ceramics.

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Detonation gun spraying
• flame temperature: 4000 ºC.

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High-velocity oxy fuel spraying (HVOF)
• gas temperature: 3000 ºC;
• sprayed materials: virtually all existing
materials, in practice mostly carbide/metal
and carbide / self-fluxing alloy mixtures.

17. 17
Cold spraying
• gas temperature: under the
phase transition temperature;
• sprayed materials: pure Al, Zn, Cu, Ni
and babbites.

18. 18
Thermal energy vs. kinetic energy
in thermal spray
ThermalEnergy
Kinetic Energy
WARCS
PS
FS
HVOF
CS
Wirearc Spray
Plasma Spray
Flame Spray
High velocity oxy fuel
Cold Spray
Melt or partially melt
Solid

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Coatings’ properties (1).
Influence of velocity and temperature

20. 20
Coatings’ properties (2).
Adhesion and porosity
Spray technology Velocity, m/s Porosity, % Adhesion, MPa
Flame spraying
• powder
• wire
30
180
6 – 15 17 – 70
15 – 20
Arc spraying 240 2 – 8 40
Plasma spraying (different
modifications)
240 – 1200 < (0,5 – 2) 20 – 70
Detonation gun spraying 910 < 1 ≥ 100
HVOF, HVAF 610 – 1500 < 0,5 62 – 83
Cold spraying 500 – 1200 1 – 3 30 – 100

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Coatings’ properties (3).
Obtainable harndess.
Sprayed material Spraying technology Hardness, HV
Chrome steel Flame spraying (wire) 500 – 600
PTA 800 – 850
NiAl alloy Flame spraying 200 – 250
Copper Flame spraying (powder) 150
Stellite Flame spraying (powder)/HVOF 460 – 770
PTA 290 – 590
MCrAlY Plasma spraying 400
Self-fluxing alloy (NiCrSiB) Flame spraying/HVOF 250 – 780
PTA 360 – 820
WC-Co Plasma spraying
(powder)/HVOF
1100 – 1300
Al2O3 Plasma spraying 1800 – 2000

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Coatings’ properties (4).
Microhardness of WC-17Co coating, sprayed using
different technologies.HV0.3

23. 23
Coatings’ properties (4).
Wear vs. spray method
0
100
200
300
400
500
600
700
800
1 2 3 4 5 6
WeightLoss(mg)
7PSZ
Al2O3
Cr2O3
22x
32x 21x
APS HVOF APS HVOF APS HVOF

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Coatings’ properties (5)
Hardness vs. fracture toughness

25. 25
Applications of sprayed materials

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Applications (1)
 wear resistant coatings
(pumps, compressors,
camshafts, etc.) – except
for cold spraying;
 corrosion resistant
coatings (pipelines,
building constructions,
etc.);

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Applications (2)
 temperature resistant
and dielectrical coatings
(gas turbines, flue tubes);
 antifriction coatings
(sliding bearings);
 size restoration (shafts,
bearings, etc.)

28. 28
Applications (3).
HVOF sprayed pot rolls for continuous galvanizing line
for steel strips.

29. 29
Applications (4)
Sprayed coatings in an aircraft engine

30. 30
Applications (5)
Process automation. Flame spraying by Kuka robot.

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Thank you for the attention!
Questions?