thermal barrier
TRANSCRIPT
KRUPAJAL ENGINEERING COLLEGE
BHUBANESWAR
SEMINAR REPORT ON
THERMAL BARRIER COATING
Submitted by:-
NITISH KUMAR
REGD.NO:-0701223318
ROLL.NO:-07ML079
ACKNOWLEDGEMENT
I express my sincere gratitude to Mr. S.S.PATI of Mechanical Engineering Department for giving me an opportunity to accomplish seminar on Thermal Barrier Coating .Without his active support and guidance, this seminar would not have been successfully completed.
I also thank Prof. B.D. SAHOO Head of Department of Mechanical Engineering for consistent support, guidance and help in this seminar. I am highly indebted for his help.
NITISH KUMAR
Regd.No. -0701223318
Date - Roll No:-07ml079
Branch – Mechanical Engg.
CERTIFICATE
This is to certify that the seminar entitled “THERMAL
BARRIER COATING” presented by NITISH KUMAR bearing registration No. 0701223318 of Department of Mechanical Engineering in Krupajal Engineering College ,Bhubaneswar has been completed successfully.
This is the partial fulfillment of the requirements of Bachelor Degree in Mechanicals Engineering under Biju Pattnaik University of Technology, Rourkela, and Orissa.
I wish her success in all future endeavors.
Signature of H.O.D Signature of Guide
Prof. B.D Sahoo Lect. S.S. Pati
DECLARATION
I hereby declare that seminar entitled “THERMAL BARRIER COATING” submitted to Department of Mechanical Engineering of
Krupajal Engineering College under the affiliation of Biju patnaik University of Technology ,Rourkela ,Orissa is towards partial fulfillment of the requirement of the award of degree in Bachelor of Engineering.
This seminar has not been submitted elsewhere and is an authenticated work of mine.
NTISH KUMAR
Department of Mechanical Engineering
Krupajal engineering College
Regd no:070122331
Roll no:07ML079
ABSTRACT
Thermal barrier coatings are highly advanced material systems usually applied to metallic surfaces, such as gas turbine or aero-engine parts,
operating at elevated temperatures, as a form of Exhaust Heat Management . These coatings serve to insulate components from large and prolonged heat loads by utilizing thermally insulating materials which can sustain an appreciable temperature difference between the load bearing alloys and the coating surface. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications.
CONTENTS
Introduction
Anatomy
Uses
Processing
Conclusion
References
INTRODUCTION
Thermal barrier coatings (TBCs) perform the important function of insulating components, such as gas turbine and aeroengine parts,
operating at elevated temperature. Typical examples are turbine blades, combustor cans, ducting and nozzle guide vanes. TBCs have made possible the increase in operating
temperature of gas turbines. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal
fatigue. In conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications.
ANATOMY
Thermal barrier coatings consist of four layers: the metal substrate, metallic bond coat, thermally grown oxide, and ceramic topcoat. The ceramic topcoat is typically composed of yttria -stabilized
zirconia (YSZ) which is desirable for having very low conductivity while remaining stable at nominal operating temperatures typically seen in applications.
The oxide that is commonly used is Zirconia oxide (ZrO2) and Yttrium oxide (Y2O3). The metallic bond coat is an oxidation/hot corrosion resistant layer. The bond coat is empherically represented as MCrAlY alloy where
M - Metals like Ni, Co or Fe.Y - Reactive metals like Yttrium.CrAl - base metal.
Coatings are well established as an important
underpinning technology for the manufacture of
aeroengine and industrial turbines. Higher turbine
combustion temperatures are desirable for
increased engine efficiency and environmental
reasons (reduction in pollutant emissions,
particularly NOx), but place severe demands on the
physical and chemical properties of the basic
materials of fabrication.
In this context, MCrAlY coatings (where M = Co, Ni
or Co/Ni) are widely applied to first and second
stage turbine blades and nozzle guide vanes,
where they may be used as corrosion resistant
overlays or as bond-coats for use with thermal
barrier coatings.
Recent advancements in finding an alternative for YSZ ceramic topcoat identified many novel
Layers of TBC in a Turbine Blade
ceramics (rare earth zirconates) having superior performance at temperatures above 1200 °C, however with inferior fracture toughness compared to that of YSZ. This ceramic layer creates the largest thermal gradient of the TBC and keeps the lower layers at a lower temperature than the surface.
TBCs fail through various degradation modes that include mechanical rumpling of bond coat during thermal cyclic exposure, especially, coatings in aircraft engines; accelerated oxidation, hot corrosion, molten deposit degradation. There are issues with oxidation (areas of the TBC getting stripped off) of the TBC also, which reduces the life of the metal drastically, which leads to thermal fatigue.
TBCs with dual functionality: protection and sensing
Knowing the temperature of the surface of the TBC and at the interface between the bondcoat and the thermally grown oxide under realistic conditions is highly desirable. As the major life-controlling factors for TBC systems are thermally activated, therefore linked with temperature, this would provide useful data for a better understanding of these phenomena and to assess the remaining life time of the TBC. The integration of an on-line temperature detection system would enable the full potential of TBCs to be realised due to improved precision in temperature measurement and early warning of degradation. The TBC is locally modified so it acts as a thermographic phosphor . Phosphors are an innovative way of remotely measuring temperatures and also other physical properties at different depths in the coating using photo stimulated phosphorescence.
USES OF TBC
When used under-bonnet, these have the positive effect of reducing engine bay temperatures, therefore lessening the intake temperature.
AUTOMOTIVE
Thermal barrier ceramic-coatings are becoming more common in automotive applications. They are specifically designed to reduce heat loss from engine exhaust system components including exhaust manifolds, turbocharger casings, exhaust headers, downpipes and tailpipes.
This process is also known as Exhaust Heat Management.
Although most ceramic-coatings are applied to metallic parts directly related to the engine exhaust system, some new technology has been introduced that allows thermal barrier coatings to applied via plasma spray onto composite materials. This is now commonplace to find on high-performance automobiles and in various race series such as in Formula 1. As well as providing thermal protection, these coatings are also used to prevent physical degradation of the composite due to frictional processes. This is possible because the ceramic material bonds with the composite (instead of merely sticking on the surface with paint), therefore forming a tough coating that doesn't chip or flake easily.
Although thermal barrier coatings have been applied to the inside of exhaust systems, this has encountered problems due to the inability to prepare the internal surface prior to coating.
INDUSTRIAL USES
In industrial applications, where space is at a premium, thermal barrier coatings are commonly used to protect from heat loss (or gain).
PROCESSING
In industry, thermal barrier coatings are produced in a number of ways:
Electron Beam Physical Vapor Deposition: EBPVD
Air Plasma Spray: APS
Electrostatic Spray Assisted Vapour Deposition: ESAVD
Direct Vapor Deposition
Additionally, the development of advanced coatings and processing methods is a field of active research. One such example is the Solution precursor plasma spray process which has been used to create TBCs with some of the lowest reported thermal conductivities while not sacrificing thermal cyclic durability.
ELECTRON BEAM PHYSICAL VAPOUR COATING DEPOSITION
Electron Beam Physical Vapor Deposition or EBPVD is a form of physical vapor deposition in which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum. The electron beam causes atoms from the target to transform into the gaseous phase. These atoms then precipitate into solid form, coating everything in the vacuum chamber (within line of sight) with a thin layer of the anode material.
AIR PLASMA SPRAY
In plasma spraying process, the material to be deposited (feedstock) — typically as a powder, sometimes as a liquid, suspension or wire — is introduced into the plasma jet, emanating from a plasma torch. In the jet, where the temperature is on the order of 10,000 K, the material is melted and propelled towards a substrate. There, the molten droplets flatten, rapidly solidify and form a deposit
ELECTRONIC SPRAY ASSISTED VAPOUR DEPOSTION
Electrostatic spray assisted vapour deposition (ESAVD) is a technique (developed by a company called IMPT) to deposit both thin and thick layers of a coating onto various substrates. In simple terms chemical precursors are sprayed across an electrostatic field towards a heated substrate, the chemicals undergo a controlled chemical reaction and are deposited
on the substrate as the required coating.
DIRECT VAPOUR DEPOSTION
Producing a film of metal on a heated surface, often in a vacuum, either by decomposition of the vapour of a compound at the work surface or by direct reaction between the work surface and the vapour. Also known as vacuum plating.
CONCLUSION
TBC is a very useful technique and has a wide application in industries as well as in automobile manufacturing.
