metallic interconnect systems · 2014. 7. 29. · slide # silicon in stainless steels • silicon...

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Rakowski – Allegheny Ludlum ‐ Project DE‐FC26‐05NT42513

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Solid Oxide Fuel CellSolid Oxide Fuel CellMetallic Interconnect Systems Metallic Interconnect Systems

99thth Annual SECA WorkshopAnnual SECA Workshop55‐‐7 August 2008, Pittsburgh PA7 August 2008, Pittsburgh PAProject Project DEDE‐‐FC26FC26‐‐05NT4251305NT42513J. M. Rakowski, ATI Allegheny LudlumJ. M. Rakowski, ATI Allegheny Ludlum

© 2008 ATI Allegheny Ludlum


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This presentation is intended for general informative use only. The information and data presented are not specific to any given production lot of material and are not applicable for design and specification.


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Overview

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Project DescriptionProject Description• Evaluate materials for use as a basis for interconnect structures– Low‐cost substrates– Functional modifications

• Low cost substrates– Commercially available ferritic stainless steels– Minor alloy modifications within specifications

• Functional modifications include– Coatings– Integral surface treatments

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Project DescriptionProject Description•A large portion of the mass of a SOFC stack is metallic alloys (interconnects)

• The focus of this project is integration of commercially available ferritic stainless alloys (e.g. Type 441) into an interconnect system

•Current community focus on functional coatings (e.g. manganese cobaltite spinel) indicates use of less expensive substrates

•Modified processing designed to have minimal impact on cost

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Technical ApproachTechnical Approach• The goal is to identify materials to serve as the basis for a high‐performance interconnect system

• The deliverable is the selection of an alloy or alloys suitable for such

• The work to‐date has focused on commercially available stainless steels and relies on well‐established technologies such as surface coatings and minor element alloying additions

• Techniques used to identify good candidates include– High temperature oxidation testing – measurement of rate of oxide scale thickening

– In‐situ area specific resistance (ASR) testing


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Materials

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Melting and ProcessingMelting and Processing• Alloy development is done by melting experimental compositions in the laboratory

• Melting is via a 22 kg VIM process

• Processing is done by hot and cold rolling on a variety of small‐scalerolling mills

• Material is comparableto that produced on amill scale

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Melting and ProcessingMelting and Processing• Melted and processed a set of lab heats to thin strip

• Complementary to studies on production alloys(Type 441, E‐BRITE® alloy)

‐‐‐‐1.01.0‐‐‐‐‐‐‐‐Mo

0.30

0.30

0.20

0.05

‐‐

0.3

26.0

580‐5

0.30

0.30

0.20

0.05

‐‐

0.15

23.0

580‐8

0.30

0.30

0.20

0.05

‐‐

0.05

24.0

580‐9

0.30

0.30

0.20

0.05

‐‐

0.15

17.0

580‐6

0.30

0.30

0.20

0.05

‐‐

0.05

17.0

580‐7

0.30

0.30

0.20

0.05

0.10

0.05

17.0

580‐2

0.04

0.20

‐‐

0.05

‐‐

0.3

26.0

E‐BRITE® alloy

0.33

0.46

0.18

0.05

‐‐

0.47

17.6

T441

Si

Ce+La

Mn

Nb

Ti

Al

Cr

Element

® Registered Trademark of ATI Properties, Inc.

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CoatingsCoatings•Manganese cobaltite spinel (nominal Mn1.5Co1.5O4) identified as effective interconnect coating– Electrically conductive–Oxidation barrier

•RE additions to heat‐resistant alloys known to reduce oxide growth and increase oxide adherence

•Spinel was modified by addition of Ce as a surface treatment (based on NETL‐Albany R&D) and then applied as a single‐step coating

•Coated substrates provided by PNNL for testing

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Silicon in Stainless SteelsSilicon in Stainless Steels• Silicon is typically present in most commercially‐produced stainless steels

• By‐product of the EAF/AOD steelmaking process

• Ferritic stainlesssteels generallycontain about0.3‐0.6 % silicon byweight

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Silicon Removal TrialsSilicon Removal Trials• High‐temperature pre‐treatment with optional chemical component

• Tested using a variety of Fe‐Cr stainless steels

0.1

1.0

10.0

100.0

0.00 0.10 0.20 0.30 0.40

Depth (microns)

Enrichmen

t

Si

Fe

Cr

AES analysis with sputter depth‐profiling

Estimated removal of 40% of siliconfrom 0.5 mm thick T430SS

• Formation/removal of an Si‐rich surface oxide layer

• Short‐term results show a 25‐75% reduction in ASR


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Oxidation Testing

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Effect of Water VaporEffect of Water Vapor• Humidified air used to simulate the cathode environment in SOFC

• Dual atmosphere effect commonly noted for high temperature exposures where the plate separates a hydrogen‐bearing atmosphere from an oxidizing atmosphere

• Hydrogen effect– Anomalously rapid oxidation at a given test temperature– Manifested by the formation of mixed iron and chromium oxides

• Two different environments – similar results

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Effect of Water Vapor / HEffect of Water Vapor / H22

Fe‐Cr or Fe‐Cr‐Ni alloy

Cr2O3

air + water vaporor dual atmosphere

Cr is irretrievably lost and

substrate is Cr‐depleted

2Cr2O3(s) + 3O2(g) + 4H2O(g) 4CrO2(OH)2(g)

Cr Cr

mixedFe and Croxides

rapid degradation via the formation

of mixed oxides is possible at high

levels of Cr‐depletion

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Results of Oxidation TestingResults of Oxidation Testing• Strong dependence of oxidation resistance on chromium content

• Effect of silicon– Very low silicon‐content alloys show an added tendency towards rapid oxidation

– Alloys processed to remove silicon do not show an added tendency towards rapid oxidation

• Manganese critical to reduce oxide scale evaporation in air containing water vapor

• Testing informs alloy selection and development

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Results of Oxidation TestingResults of Oxidation Testing

0.0

0.5

1.0

0 1000 2000 3000 4000 5000

Time (h)

WC (m

g/cm

2 )

T441 at 850°C

T441 at 750°C

air + 10% water vapor

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0

10

20

30

0 200 400 600 800 1000

Time (h)

WC (m

g/cm

2 )

alloy 580‐7

T441

air + 10% water vapor750°C

alloy 580‐6

alloy 580‐2

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0.0

0.5

1.0

1.5

0 1000 2000 3000 4000 5000

Time (h)

WC (m

g/cm

2 )

T441alloy 580‐6

alloy 580‐2

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‐0.4

‐0.2

0.0

0.2

0.4

0 1000 2000 3000 4000 5000

Time (h)

WC (m

g/cm

2 )


E‐BRITE® alloy

alloy 580‐9

alloy 580‐8

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‐0.5

0.0

0.5

1.0

1.5

2.0

0 1000 2000 3000 4000 5000

Time (h)

WC (m

g/cm

2 )

E‐BRITE® alloy


alloy 580‐9

alloy 580‐8


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ASR Testing

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Test Stack DetailsTest Stack Details

• LSM separator (Praxair)

• LSM contact ink

• Current density 0.5 A/cm2

• Compaction force 0.2 psi

• Three stacks per fixture

• 800°C test temperature

• Exposed in air

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0

100

200

300

400

500

600

700

800

0 200 400 600 800 1000 1200

Time (h)

ASR

(mΩ∙cm

2 )Bare Alloy SubstratesBare Alloy Substrates

alloy 580‐6alloy 580‐9

alloy 580‐8

E‐BRITE® alloy

alloy 580‐5 T441

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0

20

40

60

80

100

0 200 400 600 800 1000 1200

Time (h)

ASR

(mΩ∙cm

2 )Bare Alloy SubstratesBare Alloy Substrates

alloy 580‐6

alloy 580‐9

alloy 580‐8

T441

alloy 580‐5

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0

5

10

15

20

25

30

35

0 200 400 600

Time (h)

ASR

(mΩ∙cm

2 )Coated SubstratesCoated Substrates

alloy 580‐6

alloy 580‐9

alloy 580‐8

E‐BRITE® alloy

alloy 580‐5


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Summary

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Technical ConclusionsTechnical Conclusions• Commercially available ferritic stainless steels may be viable candidates for PSOFC interconnect applications

• Electrical performance is enhanced by the use of a surface coating (e.g. manganese cobaltite spinel with various modifications as developed at PNNL)

• Minor modifications to alloy chemistry can have value– Bulk (notably Nb, Mn, Si, and Cr)– Ultra‐low Si may not be entirely beneficial– Surface (modified by Si removal)

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Balance of ProjectBalance of Project• Continue oxidation testing to +5,000 hours time at temperature

• Currently working through a matrix of commercial and experimental alloys for ASR testing– Uncoated– Coated (with PNNL)– Desiliconized and other potential surface modifications

• It is expected that the majority of the work will be completed by 31 December 2008

• It is expected that the end result will primarily be guidance on materials selection for SOFC interconnects – potentially Type 441 stainless steel

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Project Team AcknowledgementProject Team Acknowledgement• Allegheny Technologies (ATI)• ATI Allegheny Ludlum

– High Temperature Oxidation Test Laboratory at the Technical and Commercial Center (Natrona Heights, PA)

– J. M. Rakowski, principal technical investigator• ATI Wah Chang

– Responsible for project administration (Albany, OR)– C. Jackson, R. Fletcher, J. Schra

• Significant collaboration with the Pacific Northwest National Laboratory (PNNL), NETL‐Morgantown, and NETL‐Albany

• Ayyakkannu Manivannan, Program Manager


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for additional informationfor additional information……

www.alleghenytechnologies.comwww.alleghenytechnologies.comwww.alleghenyludlum.comwww.alleghenyludlum.com

James M. RakowskiJames M. RakowskiManager, Product TechnologyManager, Product TechnologyMarket & Product DevelopmentMarket & Product Development

[email protected]@alleghenyludlum.com

metallic interconnect systems · 2014. 7. 29. · slide # silicon in stainless steels • silicon...

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