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

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. Coating-substrate system

4. Structures’ types of the coatings

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

6. Comparison of the coating processes

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

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

9. Sprayed coatings’ materials

10. 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.

11. 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.

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

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

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

15. Detonation gun spraying
flame temperature: 4000 ºC.

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

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

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

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

21. 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
290 – 590
MCrAlY
Plasma spraying
400
Self-fluxing alloy (NiCrSiB)
Flame spraying/HVOF
250 – 780
360 – 820
WC-Co
Plasma spraying (powder)/HVOF
1100 – 1300
Al2O3
1800 – 2000

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

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

24. Coatings’ properties (5) Hardness vs. fracture toughness

25. Applications of sprayed materials

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

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

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

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

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

31. Thank you for the attention! Questions?