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

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).

Coating-substrate system

Structures’ types of the coatings

Coatigns’ processes CHEMICAL ELECTROCHEMICAL THERMOCHEMICAL THERMOCOATING VAPOR DEPOSITION MECHANICAL

Comparison of the coating processes

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

Sprayed coating’s structure Typical structure of a coating

Sprayed coatings’ materials

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.

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.

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

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

Laser cladding virtually all metal alloys, cermets and ceramics.

Detonation gun spraying flame temperature: 4000 ºC.

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.

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

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

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

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

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

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

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

Coatings’ properties (5) Hardness vs. fracture toughness

Applications of sprayed materials

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

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

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

Applications (4) Sprayed coatings in an aircraft engine

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

Thank you for the attention! Questions?