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SURFACE ENGINEERING (2)

THERMAL SPRAY

Prof. Priit Kulu, Andrei Surzhenkov

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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).

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Coating-substrate system

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Structures’ types of the coatings

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Coatigns’ processes

CHEMICAL ELECTROCHEMICAL THERMOCHEMICAL THERMOCOATING VAPOR DEPOSITION MECHANICAL

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Comparison of the coating processes

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Thermal spray methods

CHEMICAL ELECTROCHEMICAL THERMOCOATING VAPOR DEPOSITION MECHANICAL

cold gas spraying

(CGS)

laser spraying

(LS)

molten-metal

flame spraying

Thermal spraying

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Typical structure of a coating

Sprayed coating’s structure

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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.

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Cold spraying

• gas temperature: under the

phase transition temperature;• sprayed materials: pure Al, Zn, Cu, Ni

and babbites.

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Thermal energy vs. kinetic energy in thermal spray

The

rmal

Ene

rgy

WARCS

PS

FS

HVOF

Wirearc Spray

Plasma Spray

Flame Spray

High velocity oxy fuel

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

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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

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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

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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

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Coatings’ properties (5) Hardness vs. fracture toughness

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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.)

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

for steel strips.

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Applications (4)Sprayed coatings in an aircraft engine

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

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Thank you for the attention!

Questions?