seminar - tbc
TRANSCRIPT
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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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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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