THERMAL CYCLIC BEHAVIOUR OF AIR PLASMA SPRAYED ZIRCONATE BASED COATINGS BATCH MEMBERS: G. AGORAMOORTHY ( ), M. ASWIN ( ), K. RAMKUMAR ( ), M. SURESH ( ), FINAL YEAR MECHANICAL ENGINEERING, AVCCE-MANNAMPANDAL. PROJECT GUIDE: INTERNAL GUIDE:EXTERNAL GUIDE: Mr. A. Ramprakash, M.E.,Prof. Dr. V. Balasubramanian, Asst Professor,Director, CEMAJOR, Dept of Mechanical Engg,Dept of Manufacturing Engg, A.V.C.College of Engg,Annamalai University, Mannampandal.Chidambaram.

NATURE OF THE PROJECT WORK Project work: Outside the campus. Location: Plasma spraying laboratory, Centre for Material Joining and Research, (CEMAJOR), Dept of Manufacturing Engg, Annamalai University, Chidambaram.

OBJECTIVES The project work is made on a thermal sprayed materials to study and analyze the heat withstanding capacity among the materials. Analyzation involves: Scanning Electron Microscopy (SEM testing) X-ray Diffractometer (XRD testing).

SYNOPSIS Substrate used here: INCONEL 800. Coating materials: Lanthanum Zirconate and Yttria stabilized zirconate. Coating systems: APS plasmatron (Atmospheric Plasma Spray system, 40 kw) And HVOF spray system (High Velocity Oxy Fuel spray system).

ABOUT THE SUBSTRATE The substrate used here is INCONEL 800, which is a super alloy of austenitic nickel-chromium. Composition: –It comprises of Nickel, Chromium, Iron, Molybdenum, Niobium, Cobalt, Manganese, Copper, Aluminium, Titanium, Silicon, Carbon, Sulfur, Phosphorus, Boron. Properties: –Oxidation and corrosion resistant. –When heated, Inconel forms a thick, stable, passivating oxide layer protecting the surface from further attack.

ABOUT THE SUBSTRATE(contd.,) Uses: –It is common in gas turbine blades, seals, and combustors, –Turbocharger rotors and seals, Electric submersible well pump motor shafts, –High temperature fasteners, –Chemical processing and pressure vessels, Heat exchanger tubing, steam generators in nuclear pressurized water reactors.

ABOUT THE CERAMIC COATINGS Ceramic coatings used here are: –Lanthanum Zirconate and –Yttria stabilized Zirconate. Yttria stabilized Zirconate: –Yttria-stabilized zirconate (YSZ) is a zirconium-oxide based ceramic, in which the particular crystal structure of zirconium oxide is made stable at room temperature by an addition of yttrium oxide. These oxides are commonly called "zirconia" (ZrO 2 ) and "yttria" (Y 2 O 3 ).

ABOUT THE CERAMIC COATINGS(contd.,) Applications of YSZ: –It is used : –As a refractory, –As a thermal barrier coating in gas turbines, –As the solid electrolyte, –As a material for non-metallic knife blades, produced by Boker and Kyocera companies., –YSZ doped with rare-earth materials can act as a thermographic phosphor (Phosphor thermometry is an optical method for surface temperature measurement. The method exploits luminescence emitted by phosphor material).

ABOUT THE CERAMIC COATINGS(contd.,) Lanthanum Zirconate: –Lanthanum zirconate (La 2 Zr 2 O 7, LZ) is a newly proposed material for thermal barrier coatings (TBCs). –Compared with the standard TBC material yttria-stabilized zirconia (YSZ), LZ coating has a lower thermal expansion coefficient, which leads to higher stress levels in a TBC system. –Lanthanum Zirconate has been developed as a TBC using Electron Beam Physical Vapour Deposition (EB-PVD).

ABOUT THE CERAMIC COATINGS(contd.,) –TBCs deposited by EB-PVD exhibit a columnar grain microstructure. –It is able to balance the difference in thermal expansion between the base material and TBC during thermal cycle and hence improve the TBC lifetime.

ABOUT THE MACHINING There are two processes involved in thermal barrier coating process. They are: –HVOF (High Velocity Oxy Fuel Spray system). –APS (Atmospheric Plasma Spray system). HVOF: –A mixture of gaseous or liquid fuel and oxygen is fed into a combustion chamber, where they are ignited and combusted continuously.fueloxygen –The fuels can be gases (hydrogen, methane, propane, propylene, acetylene, natural gas, etc.) or liquids (kerosene, etc.).

HVOF (contd.,) - The jet velocity at the exit of the barrel (>1000 m/s) exceeds the speed of sound.speed of sound - A powder feed stock is injected into the gas stream, which accelerates the powder up to 800 m/s. - The stream of hot gas and powder is directed towards the surface to be coated. The powder partially melts in the stream, and deposits upon the substrate. - The resulting coating has low porosity and high bond strength.porositybond strength - it is typically used to deposit wear and corrosion resistant coatings on materials due to oxidation.wearcorrosion

HVOF

Welding torch Substrate

APS Atmospheric Plasma Spraying (APS) has been used to deposit porous partially nano structured ceramic coatings. Initially a bond coating made is NiCrAlY (Nickel- Chromium-Aluminium-yttrium) coating, This is made by HVOF spray system to avoid oxidation and to provide a greater bond strength with the ceramic coatings.

APS

Powder feeder Feed motor

APS Welding electric torch Substrate holding Fixture

APS

OVERALL PROCESS Initially the substrate is prepared by Sand blasting process to remove impurities. Sand blasting is essential to increase bond strength between substrate and coating material. After sand blasting, the substrate is acid treated for removing organic contaminants. The chemical used here is acetylene.

OVERALL PROCESS (CONTD.,) After chemical treatment, a bond coating is made on the substrate by High Velocity Oxy Fuel Spray system. The bond coating applied here is Ni-Cr-Al-Y (Nickel- Chromium-Aluminium-Yttrium alloy powder). This coating increases bond strength with the ceramic coatings and it also reduces oxidation. Then the ceramic coatings are applied on the substrate by six various combinations using Atmospheric Plasma Spray System.

OVERALL PROCESS (CONTD.,) After coating of ceramic materials, Scanning Electron Microscopy is made on the substrates to analyse the bonding structure among the substrates. After SEM testing, the substrates are treated in the furnace at various operating temperatures ( c, c, c) and quenched. This process gets continued until the coating material peeled off from the substrate.

OVERALL PROCESS (CONTD.,) After the coating material get peeled off, the substrates are again tested by Scanning Electron Microscopy. The results are observed and compared with the previous results.

COATING COMBINATIONS µ YSZ µ NiCrAlY + BOND COATING µ LZ µ NiCrAlY + BOND COATING. 3.(175 µ LZ µ YSZ) µ NiCrAlY + BOND COATING. 4.(150 µ LZ µ YSZ) µ (50% NiCrAlY + 50% YSZ) POWDER µ NiCrAlY + BOND COATING.

COATING COMBINATIONS(CONTD.,) µ LZ µ (50% LZ + 50% YSZ) POWDER µ YSZ µ NiCrAlY + BOND COATING µ LZ µ (50% LZ + 50% YSZ) POWDER µ YSZ µ (50% NiCrAlY + 50% YSZ) POWDER µ NiCrAlY + BOND COATING.

RESULTS AND DISCUSSIONS This project work has been carried out for about 3 months. The overall physical work has been finished by our team members and we are at the edge of our analysation work. We are awaiting for the results and conclusions.

FUTURE SCOPE OF THE PROJECT The major factors that influences the future scope of our project work, that we consider are as follows: –Increased life of the material (INCONEL 800), against wear and corrosion. –Enhanced protection from dusts and flying Aerosols. –Enhanced heat resistance and safety of the material (INCONEL 800), such as turbine blades, pressure vessels, high temperature vessels and so on.

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