Seminar - TBC

7/27/2019 Seminar - TBC

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ACKNOWLEDGEMENT

I express my sincere gratitude to Mr. M.B. Maisuriaof Mechanical Engineering

Department for giving me an opportunity to accomplish seminar on Thermal Barrier

Coating .Without his active support and guidance, this seminar ould not have !een

successfully completed. I am highly inde!ted for his help.

In addition, I ould li"e to than"s Dept. of Mechanical Engineering, !N"T for

consistent support, guidance and help in this seminar.

MO#AMMED TO"$ MAN%&"

%'(ME')*

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ABT&ACT

Thermal !arrier coatings are highly advance refractory#oxide ceramic coatings usuallyapplied to metallic surfaces, such as gas tur!ineor aero#engine parts, operating at

elevated temperatures, as a form of Exhaust $eat Management. It is adapted to

provide a thermally insulating protective !arrier on a component exposed to large and

prolonged heat loads !y utili%ing thermally insulating materials hich can sustain an

apprecia!le temperature difference !eteen the load !earing alloys and the coating

surface. In doing so, these coatings can allo for higher operating temperatureshile

limiting the thermal exposure of structural components and there!y extending part

life. In con&unction ith active film cooling, TBCs permit or"ing fluid temperatures

higher than the melting point of the metal airfoil in some tur!ine applications.

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http://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Exhaust_Heat_Managementhttp://en.wikipedia.org/wiki/Exhaust_Heat_Managementhttp://en.wikipedia.org/wiki/Operating_temperaturehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Exhaust_Heat_Managementhttp://en.wikipedia.org/wiki/Operating_temperature


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CONTENT

+AGE NO.

'. "NT&OD%CT"ON (

-. ANATOM ()

*. COAT"NG +&O+E&T ''

'.(. $)*D+E

'.-. E*I+ *EIT)+CE

'.'. )D$EI+ T*E+/T$

'.0. T$E*M)1 C+D2CTI3IT4

/. M%LT"$%NCT"ONA"LT '-

. TBC "N A%TOMOB"LE '*

0. +&OCE"NG '/

5.(. EB63CD

5.-. )I* 61)M) 6*)4

5.'. E1ECT*+IC 6*)4 )ITED 3)6* DE6ITI+

5.0. DI*ECT 3)6* DE6ITI+

). TET"NG AND E!AL%AT"ON '1

7.(. 6$4IC)1 6*6E*TIE

7.-. MEC$)+IC)1 6*6E*TIE

7.'. T$E*M)1 /*)DIE+T TETI+/

7.0. T$E*MMEC$)+IC)1 8)TI/2E

7.9. 12MI+ECE+CE E+I+/

7.5. I+8*)*ED IM)/I+/

1. &ECENT DE!ELO+MENT --

2. CONCL%"ON -*

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L"T O$ $"G%&E

Figur

e No.Title

Page

No.

( T$E*M)1 B)**IE* C)TI+/ 9

- E+/I+E :

' CMB2T* ;

0 T2*BI+E ( hich is desira!le for having very lo

conductivity hile remaining sta!le at nominal operating temperatures typically seen

in applications.

The oxide that is commonly used is Airconia oxide =Ar-> and 4ttrium oxide =4-'>.

The metallic !ond coat is an oxidationhot corrosion resistant layer. The !ond coat is

empherically represented as MCr)l4 alloy here

M # Metals li"e +i, Co or 8e.

4 # *eactive metals li"e 4ttrium.

Cr)l # Base metal.

Coatings are ell esta!lished as an important underpinning technology for the

manufacture of aeroengine and industrial tur!ines. $igher tur!ine com!ustion

temperatures are desira!le for increased engine efficiency and environmental reasons

=reduction in pollutant emissions, particularly +x>, !ut place severe demands on the

physical and chemical properties of the !asic materials of fa!rication.

In this context, MCr)l4 coatings =here M Co, +i or Co+i> are idely applied to

first and second stage tur!ine !lades and no%%le guide vanes, here they may !e used

as corrosion resistant overlays or as !ond#coats for use ith thermal !arrier coatings.

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$igure -3

Cutaay vie of Engine )lliance /67- ith thermal#!arrier coating =TBC> from the high#pressure hot

section of an engine, and a scanning electron microscope =EM> image of a cross#

sectionof an electron !eam physical vapour deposited 7 t. yttria#sta!ili%ed

%irconia TBC. Thermally gron oxide.

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$igure *3

=a> 6hotograph of an annular com!ustor ith thermal!arriercoating =TBC> and

=!>Cross#sectional scanning electron microscopy image shoing an air plasma#

sprayed 7 t. yttria#sta!ili%ed %irconia TBC.T/, thermally gron oxide.

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$igure /@ chematic diagram of a tur!ine !lade ith thermal#!arrier coating =TBC>

from the high#pressure hot section of an engine, and a scanning electron microscope

=EM> image of a cross#section of a tur!ine.

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COAT"NG +&O+E&T"E

Depending on the folloing material properties e choose the coating materials.

#ar4ness@

)s for all materials, the hardness of a coating is a measure of the resistance to

plastic deformation. It is idely recogni%ed that the hardness increases ith

increasing density, i.e. decreasing num!er of pores and micro#crac"s. The hardness

as determined from the average length of the diagonals of each diamond shaped

indentation.

Erosion resistance@

TBC degradation !y erosion occurs mainly on tur!ine !lades and vanes, especially

hen the =aircraft> engine operates in a sandy environment =e.g. desert>. $igh erosion

resistance is normally o!tained !y decreasing the porosity. $oever, high thermal

shoc" resistance is o!tained !y increasing the porosity.

A4hesion strength@

Coating thic"ness, !ond coat pre oxidation and isothermal heating =(


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M%LT" $%NCT"ONAL"T3 +&OTECT"ON AND EN"NG

TBCs are also multifunctional@ they must provide thermal insulation to protect the

underlying superalloy engine parts, have strain compliance to minimi%e thermal#

expansion#mismatch stresses ith the superalloy parts on heating and cooling, and

must also reflect much of the radiant heat from the hot gas, preventing it from

reaching the metal alloy. 8urthermore, TBCs must maintain thermal protection for

prolonged service times and thermal cycles ithout failure

)s the ma&or life#controlling factors for TBC systems are thermally activated,

therefore lin"ed ith temperature, this ould provide useful data for a !etter

understanding of these phenomena and to assess the remaining life time of the TBC.

The integration of an on#line temperature detection system ould ena!le the full

potential of TBCs to !e realised due to improved precision in temperature

measurement and early arning of degradation.

The TBC is locally modified so it acts as a thermo graphic phosphor. 6hosphors are

an innovative ay of remotely measuring temperatures and also other physical

properties at different depths in the coating using photo stimulated phosphorescence.

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http://en.wikipedia.org/wiki/Phosphor_thermometryhttp://en.wikipedia.org/wiki/Phosphor_thermometryhttp://en.wikipedia.org/wiki/Phosphor_thermometry


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TBC "N A%TOMOB"LE

When used under#!onnet, these have the positive effect of reducing engine !ay

temperatures, therefore lessening the inta"e temperature.

)lthough most ceramic#coatings are applied to metallic parts directly related to the

engine exhaust system, some ne technology has !een introduced that allos thermal

!arrier coatings to applied via plasma spray onto composite materials. This is no

commonplace to find on high#performance automo!iles and in various race series

such as in 8ormula (. )s ell as providing thermal protection, these coatings are also

used to prevent physical degradation of the composite due to frictional processes. This

is possi!le !ecause the ceramic material !onds ith the composite =instead of merely

stic"ing on the surface ith paint>, therefore forming a tough coating that doesnt chip

or fla"e easily.

)lthough thermal !arrier coatings have !een applied to the inside of exhaust systems,

this has encountered pro!lems due to the ina!ility to prepare the internal surface prior

to coating.

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+&OCE"NG

In industry, thermal !arrier coatings are produced in a num!er of ays@

Electron Beam 6hysical 3apor Deposition@ EB63D

)ir 6lasma pray@ )6

Electrostatic pray )ssisted 3apour Deposition@ E)3D

Direct 3apor Deposition

)dditionally, the development of advanced coatings and processing methods is a field

of active research. ne such example is the olution precursor plasma spray process

hich has !een used to create TBCs ith some of the loest reported thermal

conductivities hile not sacrificing thermal cyclic dura!ility.

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ELECT&ON BEAM +#"CAL !A+O%& COAT"NG

DE+O"T"ON

Electron Beam 6hysical 3apor Deposition or EB63D is a form of physical vapordeposition in hich a target anode is !om!arded ith an electron !eam given off !y a

charged tungsten filament under high vacuum. The electron !eam causes atoms from

the target to transform into the gaseous phase. These atoms then precipitate into solid

form, coating everything in the vacuum cham!er =ithin line of sight> ith a thin

layer of the anode material.

$igure 03 EB63CD

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A"& +LAMA +&A

In plasma spraying process, the material to !e deposited =feedstoc"> F typically as a

poder, sometimes as a li?uid, suspension or ire F is introduced into the plasma

&et, emanating from a plasma torch. In the &et, here the temperature is on the order of

(


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ELECT&ON"C +&A A"TED!A+O%& DE+OT"ON

Electrostatic spray assisted vapour deposition =E)3D> is a techni?ue =developed !y

a company called IM6T> to deposit !oth thin and thic" layers of a coating onto

various su!strates. In simple terms chemical precursors are sprayed across an

electrostatic field toards a heated su!strate, the chemicals undergo a controlled

chemical reaction and are deposited on the su!strate as the re?uired coating.

D"&ECT !A+O%& DE+OT"ON

6roducing a film of metal on a heated surface, often in a vacuum, either !y

decomposition of the vapour of a compound at the or" surface or !y direct reaction

!eteen the or" surface and the vapour. )lso "non as vacuum plating.

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TET"NG AND E!AL%AT"ON O$ TBCs

+h7sical +roperties

Testing thermal#!arrier coating =TBC> systems and evaluating their performance in

service presents ma&or challenges. 8irst and foremost, the conditions under hich theyoperate are often extremely harsh, com!ining high temperatures, steep temperature

gradients, fast temperature transients, high pressures, and additional mechanical

loading, as ell as oxidative and corrosive environments. These are difficult to

reproduce in the la!oratory. The coating system also changes ith time and

temperature as the process occurs.

)s coatings !ecome prime#reliant, meaning that they can !e implemented into the

design of the engine ith relia!le performance criteria, it is also essential to develop

sensors and non#destructive evaluation methods to monitor TBC temperatures, the

extent of su!#critical delamination in service, as ell as identifying manufacturing

flas, hile also creating an artificial intelligence supervisory system that can !e

implemented in the field to provide feed!ac" to the manufacturing and design sectors

for product improvement. everal sensor approaches are !eing explored, including

infrared imaging, *aman spectroscopy, thermography, impedance spectroscopy,

acoustic emission, and luminescence sensing.

Mechanical properties

ne of the fundamental pro!lems in discussing and evaluating the mechanical

properties of coatings is esta!lishing hat the appropriate value of a particular

property should !e and at hat microstructural scale it should !e determined. 8or

simple properties, such as the overall thermal expansion mismatch stresses on thermal

cycling and the availa!le elastic strain energy release rate, the macroscopic !iaxial

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4oungHs modulus, such as determined !y a macroscopic mechanical test, is generally

ade?uate, recogni%ing that it can !e expected to !e different under tension than

compression.

There is intense interest in using local information, such as that o!tained from nano

indentation, together ith tomographic images to predict overall properties using

o!&ect oriented finite element =8> methods, such as the 8 tool.

While this is a very promising methodology, it is less suited to understanding or

predicting crac" groth, since it does not depend on &ust the average mechanical

properties. 8or small crac" lengths, crac" groth rates are mainly controlled !y

intrinsic fracture toughness.

ne of the surprising results of recent measurements has !een that fracture resistance

for long crac"s in TBCs, for instance those associated ith coating de#lamination, is

at least four times higher than the intrinsic toughness,

Ther5al gra4ient testing

Testing coatings under extreme temperature gradients and heat flux conditions

approximating actual engine operation poses special challenges. ne approach has

!een to use a high poer C- laser rig, such as implemented at the +)) /lenn

*esearch Center, and the other is to use a flame rig configuration in hich heat is

applied to one side of a coating !y an oxygenhydrocar!on gas flame. In !oth cases,

the samples are cooled from the !ac" side ith a high#pressure compressed air &et.

used to evaluate fundamental coating properties such as rates of sintering, thermal

cycle lifetimes, thermal conductivities, and to monitor damage evolution under high#

flux conditions of planar TBC systems, such as coated super alloy !uttons. These

configurations also allo for the introduction of particulates =sand, ash>, ater, and

salt

)t high surface temperature, or ith particulate addition, this type of testing typically

results in su!se?uent chipping of surface layers due to the thermal gradient present..

Ther5o5echanical fatigue

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)s ith other high#temperature materials, including super#alloys, thermo#mechanical

fatigue =TM8> can adversely influence coating dura!ility. The origin of TM8 is creep

and plastic deformation in each of the component layers in the TBC system driven !y

the coefficient of thermal expansion =CTE> mismatch, especially the CTE mismatch

!eteen the !ond coat, the super#alloy, and the topcoat under thermal gradient

conditions, as ell as mechanical loads, such as centrifugal force.

Testing under TM8 conditions is essential, !ut the ide variety of possi!le in#phase

mechanical and temperature loadings and out#of#phase loading conditions as ell as

realistic thermal gradient conditions ma"es this a demanding materials engineering

tas" that is only no !eing addressed

*atcheting !ehavior, here the materials are left permanently deformed after each

cycle, is superimposed on the creep !ehavior this !ehavior is consistent with most

of the applied load !eing supported !y the superalloy su!strate. Within creasing

tensile creep strain, crac"ing of the TBC layer initiates, and ultimately, multiple

arrangements occurs. It is found that the crac"s in the TBC layer do not propagate

through the entire thic"ness, and the crac" spacing of the TBC layer .

. )fter crac"ing of the TBC, the life of the system is similar to that of the !are

superalloy. )nother form of damage is large area delamination here the !ond coat

and superalloy are locally exposed to higher temperatures )nisotropic groth and

stress distri!ution in the T/ layer are also o!served and analysed.

ensing an4 Non8Destructi6e e6aluation

Lu5inescence sensing

Concurrent ith developments in testing the mechanical properties of TBC systems,

there have !een explorations of ne sensing approaches. 8or instance, as the

temperatures at the TBC surface and at the T/ are critical parameters, there has

!een an emphasis on non#contact methods of measuring temperature at these

locations. ne method that has shon particular promise is luminescence sensing

!ased on the dependence of photoluminescence lifetime on temperature.

1uminescence is also used to monitor delamination !y detecting the interface

temperature changes and interface luminescence reflectivity.

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In this method, luminescent rare#earth ions are incorporated into the crystal structure

of the 4A coating during deposition of the EB63D coating so that they are locali%ed

During high temperature testing, they are stimulated !y a pulsed laser, and the decay

of the excited luminescence is monitored. In addition to !eing a non#contact method,

therare#earth dopant can also !e locali%ed to a smaller depth than theoptical

penetration depth in optical pyrometry, giving superior depth resolution

"nfrare4 i5aging

The ma&ority of non#destructive methods for this type of monitoring utili%e spectral

variations in the optical properties of 4Ane approach is to image local separations

!eteen the coating and alloy !ased on variations in reflectivity of thermal aves

launched !y pulse heating of the coating surface.

*adiation reaching the detector includes contri!utions from three sources@

=(> *adiation emitted from the surface of the tur!ine component !eing imaged,

=-> *eflected radiation included from particulates in the gas stream, as ell as

='> *adiation emitted from hot gases and particles in the field of vie.

ne exciting development in inspection methods is com!ining thermal imaging ith

ultrasonics. The concept is to induce vi!rations in a component or an array of !lades,

for instance, ith an ultrasonic source and use a highly sensitive focal plane array to

image the locations of frictional heating. Its attri!utes include high sensitivity to tight

interfaces, the a!ility to see defects through coatings, and the a!ility to inspect

components ith minimal preparation. 6ost#processing algorithms are then used to

assist in the identification of defects.

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&ECENT DE!ELO+MENT

*ecent advancements in finding an alternative for 4A ceramic topcoat identified

many novel ceramics =rare earth %irconates> having superior performance at

temperatures a!ove (-


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$igure 23

6rogression of temperature capa!ilities of +i#!ased superalloys and thermal#!arrier

coating =TBC> materials over the past 9< years. The red lines indicate progression of

maximum alloa!le gas temperatures in engines, ith the large increase gained from

employing TBCs.

CONCL%"ON

The present study aimed to understand TBCHs and it as found that Thermal Barrier

coatings consists of four principal layers =ceramic top coat, thermally gron oxide,

!ond coat, !ase metal> and complexities in their interaction ith the each other and!ehaviour under thermal and mechanical loading. Each layer performs different

functions li"e Ceramic coating help in resisting thermal loading and prevents heat to

reach the su!strate. )nd even though TBC promises high temperature !enefits still

their use is limited as the !ehaviour of TBC is not fully understood and it ma"es

difficult for the designer to fully rely on the coatings thatHs hy orldide research is

currently going on to explain some of these !ehaviours and ma"e it possi!le to predict

their failure and hence the designer can rely on TBC and their full potential can !e

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exploited. This study also helped to understand the effect of different processing

methods on the microstructure of the TBCs. The prediction of failure is most critical

aspects of TBC so different testing techni?ues are also understood in this study.

&E$E&ENCE

.i"ipedia.org

.scri!d.com

.google.com

.&ap.aip.org

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Seminar - TBC