the effect of high-temperature exposure on the interfacial microstructure of co-based coatings (1)
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8/9/2019 The Effect of High-temperature Exposure on the Interfacial Microstructure of Co-based Coatings (1)
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Materials Sci ence & Technolog y
The effect of highThe effect of high--temperature exposure on thetemperature exposure on the
interfacial microstructure of Cointerfacial microstructure of Co--based coatingsbased coatingson a 9%on a 9% --Cr steel for steam turbineCr steel for steam turbine
applicationsapplications
Reinhard Hitzek, Andrea Al-Badri, Dr. Christian Leinenbach
Power Gen India & Central Asia 2012
19.-21. April 2012
Hilfe2
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Slide 1
Hilfe2 Diese Folie enthält zwei Mastergruppen (Master und Titelmaster), welche den Corporate-Design-konformen Auftritt definieren. Der jetztzugewiesene Empa-Master 1 sieht für die Titelfolie das Empa-Logo vor. Den weiteren Folien ist kein Logo zugewiesen. Für längere
Vorträge mit Zwischentiteln empfehlen wir, den Folien mit Zwischentiteln den Empa-Master 2 (mit Logo unten rechts) zuzuweisen. Dazuöffnen Sie via Ansicht > Aufgabenbereich > Foliendesign-Entwurfsvorlage rechts die Masterauswahl. Nun markieren Sie im linken Ansichtsfenster die Folien, denen Empa-Master 2 zugewiesen werden soll (mindestens zwei, ansonsten für den ganzen SatzEmpa-Master 1 verwendet wird). Weitere Hilfe erhalten Sie bei Monika Ernst, 4995 (Empa, Dübendorf)M. Ernst, 2/4/2005
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Stellba, Power Gen India & Central Asia 2012 2
OutlineOutline
Introduction Stellba History of materials
- From steel to nickel based materials
Why special treatments are necessary
- High temperature exposure
- Failure of coatings occurring at these temperature
Materials and Method
- Base and coating materials
- Coating technique and heat treatment
Material Characterisation
Results
- SEM investigations, element distribution,
hardness measurements, TEM investigation
Phase diagram and thermodynamic calculations
Conclusions
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Founded 1957 in SwitzerlandCertified ISO 9001, 14001, 3834-2
GTS Certification for Thermal Spraying
Address:
Stellba Schweisstechnik AGWohlerstrasse 51
5605 Dottikon / Switzerland
Phone +41 56 201 43 43
Fax +41 56 201 43 41
[email protected], www.stellba.ch
Introduction of company StellbaIntroduction of company Stellba
3Stellba, Power Gen India & Central Asia 2012
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History of materialsHistory of materials
Steam turbine valves and materials
Year Temp. °C Materials / Coatings HP-control HP-stop IP-control IP-stop
1960 460°C -Low alloy steels-Nitrided
-Some Stellit
X X X X
538°C -Low alloy creep resistant steels-Stellit
X X X X
565°C -High alloy creep resistant steels(12%Cr)
-Stellit-Chromium carbide
X X X X
585°C -High alloy creep resistant steels(9-12%Cr)
-Stellit-Chromium carbide
X X X X
600°C + -High alloy creep resistant steels(9-12%Cr)
-Nickel based materials-Special coatings
X X X X
2020 700°C -Nickel based materials-Special coatings
R&DParticipate in
Comtes 700project
R&DParticipate in
Comtes 700project
R&DParticipate in
Comtes 700project
R&DParticipate in
Comtes 700project
X = produced by Stellba X = produced by Stellba
HP = high pressure IP = intermediate pressure /reheat
Remarks:All type of valves including actuators and casings can be produced at Stellba
Our Customers are all major OEM’s world wide
4Stellba, Power Gen India & Central Asia 2012
8/9/2019 The Effect of High-temperature Exposure on the Interfacial Microstructure of Co-based Coatings (1)
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Stellba, Power Gen India & Central Asia 2012 5
Why special treatments are necessaryWhy special treatments are necessary
SIEMENS AG
Alstom
- Reduction of CO2 emission into atmosphere- Therefore improvement of efficiency of steam power plants
- One important parameter is the working temperature in turbines(efficiency increase 1% per 20°C increase of steam temperature)
- valve seat coatings are used for temperatures up to 550°CProblems at temperatures T > 600°C: • Delaminating of Stellite coatings on
stainless steel on valve seats
WHY SO?WHY SO?
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Stellba, Power Gen India & Central Asia 2012 6
Materials and MethodMaterials and Method
Base and coating material
Base: 9% Cr-steel X10CrMoVNb 9-1
Coating: Co-based hardfacing alloys
Stellite 6 (Co-29Cr-4W-1C)
Stellite 21 (Co-27Cr-5Mo-0.3C)
Ultimet (Co-26Cr-9Ni-5Mo-0.04C)
Coating technique and heat treatment
X10CrMoVNb9-1 - Co-based alloy → Plasma Transferred Arc (PTA) welding
After coating process→
heat treatment at 690°C for 4 h to minimize residual stress
Heat treatment was performed at 650°C, respectively for 1’000, 3’000 and
10’000 hours in a furnace in standard air atmosphere.
8/9/2019 The Effect of High-temperature Exposure on the Interfacial Microstructure of Co-based Coatings (1)
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Stellba, Power Gen India & Central Asia 2012 7
Material CharacterisationMaterial Characterisation
Microstructural characterisation
- analysed by scanning electron microscopy (SEM) in BSE mode
Element distribution
- taken perpendicular to the interface by energy dispersive spectrometry (EDS)
- three spot measurements at a defined distance from Steel- Co-based-
interface were taken and averaged
Hardness measurement
- a Fisherscope HM 2000 with WIN- HCU ® - software was used for micro
hardness measurements
- Vickers hardness was measured perpendicular to the interface on 5 different
spots at a defined distance and averaged
8/9/2019 The Effect of High-temperature Exposure on the Interfacial Microstructure of Co-based Coatings (1)
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Stellba, Power Gen India & Central Asia 2012 8
TEM investigation
a transmission electron microscopic (TEM) image was taken in the interlayer
region with the assumed interface between steel and Stellite 6
preparation of a thin semicircular disc with 3mm diameter and 80 µm thickness
thinned to approx. 30 µm thickness by grinding
and polishing
a section with a width of 20 µm across the
interface was thinned by Focus IonBeam (FIB) milling, using a gallium ion beam
Thermodynamic simulations
CALPHAD based software ThermoCalc version S
database TCFE3 including thermodynamic data on Co-Cr and
Co-Cr-C systems
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Stellba, Power Gen India & Central Asia 2012 9
ResultsResults
1’000h
3’000h
SEM Investigations
10’000h
as-coated
X10CrMoVNb 9-1 – Stellite 6
Stellite 6
Steel
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Stellba, Power Gen India & Central Asia 2012 10
3’000h 10’000has-coated
X10CrMoVNb 9-1 – Stellite 21
as-coated 1’000h 3’000h
X10CrMoVNb 9-1 – Ultimet
Stellite 21
Steel
Ultimet
Steel
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Interlayer thickness as function of annealing time
20 30 40 50 60 70 80 90 100 1100
5
10
15
20
25
30
35
Stellite 6
Stellite 21
Ultimet
d i n t e r l a y e r
[ µ m ]
t
0.5
[h
0.5]
]
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Element DistributionX10CrMoVNb 9-1 – Stellite 6
-20 -10 0 10 200
10
20
30
40
50
60
70
80
90
100as-coated
Stellite 6X10CrMoVNb9-1
Fe
Cr
Co
Ni
W
c [ m a . -
% ]
d [µm]
-20 -10 0 10 20 30 40 500
10
20
30
40
50
60
70
80
90
1003'000h
Stellite 6InterlayerX10CrMoVNb9-1
Fe
Cr Co
Ni
W
c [ m a . -
% ]
d [µm]
-30 -20 -10 0 10 20 30 40 50 600
10
20
30
40
50
60
70
80
90
100Interlayer
10'000h
X10CrMoVNb9-1 Stellite 6
Fe
Cr Co
Ni
W
c [ m a . -
% ]
d [µm]
0
Stellite 6
Steel
0
10
20
-10
-20
Stellite 6
Steel
-10
-20
10
20
30
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Stellba, Power Gen India & Central Asia 2012 13
Hardness measurement
-60 -40 -20 0 20 40 60250
300350
400
450
500
550
600
650
700
750
Interlayer Stellite 21X10CrMoVNb9-1
as-coated 1'000h
3'000h
10'000h
M
i c r o h a r d n e s s
H V
d [µm]-60 -40 -20 0 20 40 60
250
300350
400
450
500
550
600
650
700
750
InterlayerX10CrMoVNb9-1
Stellite 6- 10'000h
Ultimet- 3'000h
M
i c r o h a r d n e s s
H V
d [µm]
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TEM investigation
Stellite 6 annealed at 625°C
EDS mapping:
Cyan: Cobalt, Co
Green: Iron, Fe
Purple: Chromium, Cr
Yellow: Tungsten, W
point Fe Co Cr W C possible phase
1 28.2 38.7 32.0 0.8 <0.3
2 45.8 45.6 7.5 0.8 <0.3 α‘ – ordered bcc
3 8.4 7.3 71.7 8.1 5.1 M23C6
4 7.7 25.6 42.0 20.0 4.7 M23C6
spot measurement [wt%]
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Phase diagramPhase diagram
Massalski
point Fe Co Cr W C possible phase
2 45.8 45.6 7.5 0.8 <0.3 α‘ – ordered bcc
αα‘‘ (B2(B2--type):type): believed to
result in intergranular brittlefracture
E.P. George, A.N. Gubbi, I. Baker, L.Robertson, Material Science
Engineering A329-331 (2002) 325-333
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Thermodynamic calculationsThermodynamic calculations
Thermodynamic simulations
Stellite 6 at 650°C
44Fe-42Co-9Cr-1Ni-0.45Mo-3W-1C
Average composition at 20 µmfrom 0-point in the interlayer:
0
Possible phases:• M23C6
• µ- phase
• M7C3
• α
- phase
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ConclusionConclusion
Failure of Co-based coatings on 9% Cr – steel attemperatures >600°C:
development of a thin interlayer with a high hardness
interlayer thickness depends on the annealing time
Fe diffuses into the Co-based coating
TEM investigations assume the development of abrittle B2 interlayer and M23C6-carbides
thermodynamic simulations support the developmentof M23C6-carbides and α-phase, as well as thedevelopment of µ precipitates
but development of µ precipitates could not directlyobserved
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Thank you for your attention!
The project (N°8523.2 E) is financially supported by