Advanced Alloy Interconnect Development

Advanced Alloy Advanced Alloy Interconnect DevelopmentInterconnect Development

Z. Gary Yang, Matt Walker, Gordon Xia,

Prabhakar Singh, and Jeff Stevenson

Presented at the SECA CTP Review MeetingAlbany, NY

September 30, 2003

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Interconnect DevelopmentInterconnect DevelopmentInterconnect DevelopmentObjectives:Objectives:

Develop cost-effective, optimized materials for intermediate temperature interconnect and its interface applications.Identify and understand degradation processes in candidate alloys.

ApproachApproach:Screen testing of conventional and newly developed alloys (chemical, electrical, mechanical properties, cost).Investigation of oxidation/corrosion behavior of alloys and scale stability under SOFC operating conditions. Materials development.

! Surface modification (surface doping, overlay coatings, cladding).! Bulk modification or alloy development.! Cathode/interconnect interfaces.

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Highlights of AchievementsHighlights of AchievementsHighlights of AchievementsDeveloped standardized testing capability for evaluation of SOFC interconnect alloysIdentified and evaluated suitable candidate alloys using systematic screening techniques.Developed conductive oxide coated alloy interconnects for improved stability.Evaluated newly developed alloys, including Crofer22 APU and ZMG232.Examined oxidation/corrosion behavior of steels and superalloys.

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Evaluation of Newly Developed Alloys

Evaluation of Newly Evaluation of Newly Developed AlloysDeveloped Alloys

0.06La0.0020.016--0.08--0.50.00522.0Bal.Crofer22 APU

0.04La0.02Zr

0.21--0.400.50.0222.0Bal.ZMG232

SP REAlTiSiMnCCrFeFSS

Crofer is a trade mark of ThyssenKrupp; ZMG is a trade mark of Hitachi Metals, Ltd.

"" Thermal expansion;" Scale growth and oxidation resistance;" Scale electrical conductivity;" Scale evaporation;" Compatibility with seals;" Scale adherence and seal bonding strengths.

Properties relevant to SOFC applications:Properties relevant to SOFC applications:

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Crofer22 APU: Crofer22 APU: Thermal ExpansionThermal Expansion

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

0 100 200 300 400 500 600 700 800

Temperature (C)

∆L/

L

AL453Crofer 22EbriteReduced anode

Some Fe-Cr ferritic compositions (including Crofer22 APU) demonstrate good CTE matching to the Ni/YSZ anode.

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Oxidation ResistanceOxidation Resistance

( )ttk gp 2

2

χρκ

ξ ==

Crofer22 APU

Crofer22 APU

0

2

4

6

8

10

12

14

16

18

20

Par

abol

ic ra

te c

onst

ants

(x10

-14 g

2 .cm

-4.s

-1)

800oC 35 7 19.84 13.32 3.53 0.35 0.88700oC 2 1.28 0.88 0.61 0.04 0.15

430 Crofer22 APU AL 453 446 E-brite Fecralloy Alpha-4

Crofer22 APU

Chromia former Alumina former

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Formation of (Formation of (Mn,CrMn,Cr) ) SpinelSpinelTop LayerTop Layer

Fe-Cr substrateDiffusion and internal oxide formation zone

Cr2O3 rich sub scaleMnCr2O4 rich top layer

Cr

Al Mn

(Al,Ti)xOyCrofer22 APU was heat treated at 800oC for 1,200 hours in air

8

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0 50 100 150 200 250 300 350 400 450 500Time (hours)

AL453Crofer22 APUE-briteCrofer22APU (700ºC)

AL453, 800oC

E-brite, 800oC

Crofer22 APU, 800oC

Crofer22 APU, 700oC

800oC, air

Crofer22 APU Crofer22 APU

Scale Scale

Pt

Crofer22 APUScale Electrical Conductivity

Scale Electrical Conductivity

Extrapolation of the 2,000 h test gives an ASR of about 200 mΩ.cm2 after 40,000 h.

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Chromia Scale EvaporationChromia Scale EvaporationChromia Scale Evaporation

0,0

5,0

10,0

15,0

20,0

351 338 346 255 160

Exposure time / h

Cr5Fe1Y2O3

X10CrAl

Fe20Cr5Al Crofer 22 APU

Fe20Cr5Al

FeCrMnCr-

Rel

ease

Rat

e 10

-11

kg s

-1m

-2

Chromium Release Rate at 850oC**After Hilpert, et al.

Chromium Release Rate at 850oC**After Hilpert, et al.

-6

-5

-4

-3

-2

-1

0

6.5 7 7.5 8 8.5 9 9.5 10 10.5

Cr2O3(s) + 1.5O2 + 2H2O= 2CrO2(OH)2 (g)

CrO3

CrO2(OH)

750oCPH2O=2.0×103 Pa

PO2=2.13×104 Pa-6

-5

-4

-3

-2

-1

0

6.5 7 7.5 8 8.5 9 9.5 10 10.5

Cr2O3(s) + 1.5O2 + 2H2O= 2CrO2(OH)2 (g)

CrO3

CrO2(OH)

750oCPH2O=2.0×103 Pa

PO2=2.13×104 Pa

The chromia evaporation rate is relatively low, compared with other alloys.

Is this low enough?

PlanseeDucralloy

Fecralloy

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Evaluation of ZMG232Evaluation of ZMG232

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 50 100 150 200 250 300 350 400 450 500

Time (hours)

ASR

(ohm

.cm

2 )

Crofer22 APU, 800oCCrofer22 APU, 700oCZMG232, 800oCZMG232, 700oC

ZMG232, 800oC

ZMG232, 700oC

Crofer22 APU, 800oC

Crofer22 APU, 700oC

Fe

Cr

Mn

Si

SiO2 scalePt contact

0.06La----.522Bal.Crofer22 APU

0.04La0.22Zr

.210.40.522Bal.ZMG232REAlSiMnCrFeFSS

The Si level in ZMG232 is enough to form a silica layer that leads to an increased electrical resistance.

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SummarySummarySummary

Newly developed Newly developed ferriticferritic stainless steels demonstrate:stainless steels demonstrate:Good CTE matching;

Reduced scale electrical resistance;

Increased scale adherence;

Decreased chromia evaporation.

For >700oC applications

There is HOWEVER, a need for further improvement in:There is HOWEVER, a need for further improvement in:Scale electrical conductivity in the long term;

Scale evaporation;

Scale adherence and sealing effectiveness;

Corrosion resistance under dual environments.

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Dual Atmosphere Study

14

--

--

--

W

Bal.

--

--

--

Ni

0.06La--0.08----0.50.00522.0Bal.Crofer22 APU

0.02La.005B

0.3--1.40.40.50.1022.01.5Haynes 230

--------0.0250.010.00126.0Bal.E-brite

--------1.01.00.116.0Bal.AISI430

REAlTiMoSiMnCCrFeFSS

{FeSS{NiBS

Air Air

T/C

xxxx

x

xxxx

x

Seal

FuelAirAir

T/C

Stainless steel

Variables: Temperature, 700~800oCTime, 300 hoursFuel, H2+3% H2OHeating, isothermal and cycling.

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Crofer22 APU: Structure of ScalesGrown on the coupon in air only and on the air side of the coupon that was ISOTHERMALLYISOTHERMALLY heat-treated at 800oC, 300 hours.

Fe

Cr

Mn

Air exposure at both sides

M = Fe-Cr SubstrateC = Cr2O3S = (Mn,Cr,Fe)3O4

Air exposure on both sides of the tested coupon.

Air side of dual exposures.

Fe

Cr

Mn

Air-side of dual exposures

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Crofer22 APU: Structure of Scales

Cr

Mn

Fe

Fuel exposure at both sidesGrown on the coupon in fuel (H2+3%H2O) only and on the fuel side of the coupon that was ISOTHERMALLYISOTHERMALLY heat-treated at 800oC, 300 hours.

(H2+3%H2O) side of the dual atmosphere exposure.

M = Fe-Cr SubstrateC = Cr2O3S = Mn(Cr,Fe)2O4

2θ

Both sides exposed to (H2+3%H2O).

Fe

Cr

Mn

Fuel side of dual exposures

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Crofer22 APU: Structure of ScalesGrown on the coupon in air only and on the air side of the coupon that was heat-treated at 800ºC for 300 hours, with three thermal cycles.

Air-side of dual test

Fe2O3

Mn

Cr

Fe

Cross-section: airside of dual test

Airside of the dual exposures.

Air exposure at both sides.M = Fe-Cr Substrate

C = Cr2O3S = (Mn,Cr,Fe)3O4O = Fe2O3

2θ

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AISI430: Scale MicrostructuresAir-side of dual exposuresAir exposure at both sides

Fe2O3

Surf

ace

mic

rost

ruct

ures

Cro

ss-s

ectio

ns Cr

Mn

Fe Fe

Cr

Mn

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E-brite: Scale Microstructures

Cr2O3

Air side of dual exposuresAir exposure at both sides

Cr2O3

(H2+3%H2O) at both sides

Cr2O3

Fuel side of dual exposures

Cr2O3

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Air side of dual exposures

0

200

400

600

800

1000

1200

30 35 40 45

2θ

Rel

ativ

e In

tens

ity (A

. U.)

Air of Dual

Air/Air Cr2O3 (Mn,Ni,Cr)3O4 NiO

NiO

Haynes230: Structure of ScalesGrown on the coupon in air onlyair only and on the air sideair side of the coupon that was isothermallyisothermally heat-treated at 800oC, 300 hours.

Air exposure at both sides

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Haynes230: Cross-SectionsGrown on the coupon in air onlyair only and on the air sideair side of the coupon that was isothermallyisothermally heat-treated at 800oC, 300 hours.

Ni

Cr

Mn

Air exposure at both sides

Air side of dual exposuresNi

Cr

Mn

20

(H2+3%H2O) at both sides

Fuel side of dual atmospheres

0

200

400

600

800

1000

1200

30 35 40 45

2θ

Rel

ativ

e In

tens

ity (A

. U.)

H2 of Dual

H/H Cr2O3 (Mn,Ni,Cr)3O4

Haynes230: Structure of ScalesGrown on the coupon in fuel onlyfuel only and on the fuel sidefuel side of the coupon that was isothermallyisothermally heat-treated at 800oC, 300 hours.

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Haynes230: Cross-SectionsGrown on the coupon in fuel onlyfuel only and on the fuel sidefuel side of the coupon that was isothermallyisothermally heat-treated at 800oC, 300 hours.

Fuel exposure at both sides

Ni

Cr

Mn

Ni

Cr

Mn

Fuel side of dual atmospheres

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SummariesSummariesSummariesThe Dual Atmosphere exposure can lead to an anomalous The Dual Atmosphere exposure can lead to an anomalous oxidation/ corrosion behavior of oxidation resistant alloys:oxidation/ corrosion behavior of oxidation resistant alloys:

For ferriticferritic stainless steelsstainless steelswith relative low chromium level, dual exposure enhances the iron transport in scale on the airside, leading to hematite formation and a locallized attack.

For NiNi--based based superalloyssuperalloys, e.g. Haynes230 with 22% Cr, dual exposure facilitates the formation of a uniform chromiadominated scale.

H+

H+

Oxide scale Oxide scale

FuelAir

2HpH2

Metal substrate2H

p

O2

H

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ComparisonComparisonComparisonHaynes230Haynes230NiNi--base base superalloysuperalloyNiNi--22Cr22Cr--14W14W--2Mo2Mo--.5Mn

Crofer22 APUCrofer22 APUStainless steelStainless steelFeFe--22Cr22Cr--.5Mn.5Mn.5Mn

0.360.36, 800oC0.050.05, 700oC

InexpensiveFairly expensive

Fairly easyVery easy

443443, RT

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Future Work

Identifying Issues and Identifying Issues and UnderstandingUnderstanding! Continue the systematic screening studies, with emphasis on dual atmosphere studies, including extension of dual atmosphere studies to air vs. reformate invironments.

! Study scale evaporation.

Materials Materials DevelopmentDevelopment! Modifications (bulk and/or surface) to Fe and Ni based alloys

! Cathode/interconnect interfaces.

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AcknowledgementsAcknowledgementsAcknowledgements

The authors wish to thank Wayne Surdoval, Lane Wilson, and Don Collins (NETL) for their helpful discussions regarding this work. This work was funded by the U.S. Department of Energys Solid-State Energy Conversion Alliance (SECA) Core Technology Program.

Advanced Alloy Interconnect DevelopmentInterconnect Development