Thermal Spray Coatings Asst.Prof.Dr. Ali Sabea Hammood Materials Engineering Department Materials Engineering Department Faculty of Engineering Faculty of Engineering University of Kufa University of Kufa

Introduction: Surface engineering techniques generally consist of surface treatments, where the composition or physical, chemical, and mechanical properties of existing surface are altered. They are achieved by adding different material deposited as a thin or thick layers (coatings) to creat anew surface.

Laser coated by-pass valve spindle.

It should be noted that surface engineering may be used effectively to improve the surface properties, without changing the chemical composition of the bulk materials. Is frequently used to satisfy engineering requirements.

It provides an important means of increasing the life of engineering component by increasing oxidation, corrosion, wear and erosion resistance.

Surface Treatments: Mechanical Processes: Shot preening. Shot preening. Rolling. Rolling. Thermal Treatments; Laser beam treatment. Laser beam treatment. Electron beam treatment. Electron beam treatment. Flame treatment. Flame treatment. Induction treatment. Induction treatment.

Thermochemical diffusion treatments: *Carburizing*Carbonitriding*nitriding*Nitrocarburizing*Chromizing Physical vapor deposition. Ion implantation

Functionally Effective Coatings Using Thermal Spray Coatings The development of new technologies and processes requires suitable materials for their realization. The development of new technologies and processes requires suitable materials for their realization. Since many forms of attack, such as: -Corrosion-Wear-Heat-Impact - Radiation ;

Figure: Principle of laser coating.

Power = 2430 watts, Velocity = 4.23 mm/s,Beam Diameter = 0.5 mm Nickel Powder Thickness = 1.0 mm

occur on the surface of a component, or are transferred via the surface into the component, surface protection has a considerable significance as regards modern materials technology.

The purpose of surface technology is to produce functionally effective surface. This implies matching the surface properties of a component to its particular operating stresses. The purpose of surface technology is to produce functionally effective surface. This implies matching the surface properties of a component to its particular operating stresses. The aim is to achieve improvement of : - Operating life - Reliability - Economic performance -Safety -Output from products and processes

Thermal spraying consist of: 1- Heating of the powder. 2- Melting of the powder. 3- Acceleration of the particles on to high velocity. 4- Impacting the particles on to the substrate and subsequent bonding.

Flame Spray Coating

Electron Beam Physical Vapor Deposition

An illustrative diagram of one type of PVD setup. Source: Pages/processing.html

Schematic microstructure of a thermal barrier coating (TBC) obtained by electron beam physical vapour deposition (EBPVD). The columnar microstructure considerably enhances the strain resistance and therefore thermal cycling life.

Plasma Spray Coating

Schematic microstructure of a thermal barrier coating (TBC) obtained by air plasma spray (APS). The structure provides much less strain resistance than the EBPVD counterpart, but is preferred for abradable seals (DeMasi-Martin, 1994)

Figure : Typical micrograph of HVOF coating (left) and APS coating (right) Magnification is approx. 300x

Characterization of Plasma Spayed Coatings 1- The high temperature enables almost all materials to be sprayed. 2- Deposits are of high density and strongly bonded to the substrate. 3- It is possible to control the coating thickness or build overlapping layers with different compositions to achieve the desired requirement.

4- Easy to control the cooling rate by heating or cooling the substrate during the process. 5- Cheap base materials can be used as substrate. 6- Expensive materials need only be used for the coating. 7- Little or no dilution occurs between the coating layer and the substrate. 8- Finishing may not be required

Applications of plasma spray coating 1- Wear protection against- abrasion, scuffing and fretting corrosion. 2- Corrosion protection against- oxidation, hot gas corrosion and immersion corrosion. 3- Thermal insulation ( thermal barrier). 4- Repairing parts by adding material on to worn lactations, or reconstituting apart which has been rejected due to faulty material or incorrect machining.

5- Surfaces with special properties such as: 1- Electrically insulating or conducting. 2- Self –lubricating coatings. 3- Active or passive surface coatings. 4- Decorative coatings. 5- Coatings which are highly absorptive or reflective to light. 6- Special applications, such as production of sensors.

Thermal barrier coatings The main advantages of using thermal barrier coatings are summarized below 1- Improving the creep and oxidation resistance by decreasing the temperature of the substrate. 2- Improving the thermal fatigue resistance of the thermal system by decreasing the thermal stress induced by strain.

3- Decreasing maintenance costs. 4-Improving engines components durability. 5- Enhancing reliability and performance of advanced heat engines components. 6- Improving the efficiency of the engine by reducing the volume of air required for cooling.

Laser Surface Sealing of Plasma Sprayed Coatings The main potential applications for laser sealing of coatings are: 1- Sealing porosity: To increase the life of coated components by eliminating the access of corrosive gases and molten salts to the underlying metallic substrate. 2- Modification microstructure : To improve the structural homogeneity of coatings.

3- Producing a smoother surface finish: To reduce the active surface for heat absorption. 4- Increasing surface hardness: Toenhance erosive and wear resistance of the surface. 5- Improving fracture strength:

Figure : 6 kW CO2 laser coating with coaxial powder nozzle at Fortnum Service Oyo Laser Coating Centre

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