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 VAPOR DEPOSITION MECHANICAL

cold gas spraying

(CGS)

laser spraying

(LS)

molten-metal

flame spraying

Thermal spraying

8

Typical structure of a coating

Sprayed coating’s structure

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

Thermal Energy

Kinetic Energy

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

30180

6 – 15 17 – 7015 – 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

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

22

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

different technologies.HV0.3

23

Coatings’ properties (4).Wear vs. spray method

0

100

200

300

400

500

600

700

800

1 2 3 4 5 6

Wei

ght L

oss

(mg)

7PSZ

Al2O3Cr2O3

22x 32x 21x

APS HVOF APS HVOF 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?