O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2004. Page 1...

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY Lara-Curzio et al. IGTI-2004. of 45

Screening and Evaluation of Materials for Advanced Microturbine Recuperators

Edgar Lara-Curzio, R. M. Trejo, K. L. More,P.A. Maziasz, B. A. Pint

Metals & Ceramics DivisionOak Ridge National Laboratory

Oak Ridge, TN 37831-6069

ASME Turbo Expo ASME Turbo Expo Vienna, AustriaVienna, Austria

June 16, 2004June 16, 2004


Acknowledgments

Research sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy,

Office of Power Technologies, Microturbine Materials Program, under contract DE-AC05-00OR22725 with UT-Battelle, LLC


Outline

• Background

• Microturbine Recuperator Testing Facility• Test Procedure

• Results• 347 Stainless Steel

• HR230®

• HR120®

• Summary, Current and Future Work


Outline

• Background


Background

2000 2002 2004

$500/kW

40% Efficiency

40,000-hr life

2006 2008 2010

U.S. DOE Advanced Microturbines Program


Background (cont.)

2000 2002 2004 2006 2008 2010

higher TIT

higher TET

advanced materials

U.S. DOE Advanced Microturbines Program

$500/kW

40% Efficiency

40,000-hr life


Background (cont.)

• Temperature

• Environment (combustion gases can lead to corrosion)

• Mechanical Stress (pressure differential can induce creep deformation)

Main parameters to consider for the selection of materials for microturbine recuperators


Outline

• Background

• Microturbine Test Facility• Testing Procedure


Microturbine Test Facility

gas compressor

shelter housing instrumentation

Capstone 60kW microturbine

As part of the Advanced Materials for Recuperators Program, ORNL established a microturbine test facility to screenscreen and evaluateevaluate candidate materials for advanced microturbine recuperators


ORNL’s Microturbine Test Facility (cont.)

• Modified Capstone C60 microturbine

• Higher TET (850°C)

• Placement of test specimens at the entrance of recuperator.

thermocouples

water-cooled block

pressure transducer

air line

water lines

sample holder


Microturbine Test Facility (cont.)


• Four (4) laser-welded foils in each sample holder

• foil temperatures are monitored using type-K thermocouples

• sample holders are pressurized with air to simulate the pressure differential experienced by recuperator cells

welded foils

ORNL’s Microturbine Test Facility (cont.)

sample holder

thermocouples


Temperature distribution along sample holder

TET=800°C


Effect of microturbine exposure on tensile properties

Foils are removed from the sample holder and miniature test specimens, obtained by electric discharge machining, are evaluated in tension.


Temperature History for 500-hr test


Outline

• Background




347-stainless steel after 500-hr exposure (TET=800°C)

0.0

89

mm

0.0

89

mm

0.0

89

mm

0.0

89

mm

A758°C

B736°C

C697°C

D632°C

60 psi internal pressure -> 50 MPa hoop stress


Significant corrosion and spalling of oxidation products on foil exposed to highest temperature (758°C)

347-stainless steel after 500-hr exposure

ballooning due to creep deformation


D C B A

cool end630°C

hot end758°C

air side

exhaust side

Position D500 h @ ~632°C

very little corrosion

Position C500 h @ ~697°C

thin scale

Position B500 h @ ~736°C

~3 µm scalePosition A

500 h @ ~758°C~20 µm scale


ballooning due to creep deformation

“wart”

cross-sectional analysis



Fe Ni

Nb

O

Cr

Foil A

exhaust side

air side

Foil exposed at 758°C

• Multilayered oxide scale:

• Ni-Cr-O

• Fe-O

• Depletion of Cr at GBs

• Carbide formation


Tensile strength of as-processed 347-stainless steel


Tensile strength of 347-stainless steel


Tensile strength of 347-stainless steel

• Dimples characteristic of plastic deformation.

• Limited ductility

•758°C•500 hrs•50 MPa (hoop stress due to 60 psi of internal pressure)


0.4

0.6

0.8

1

0 200 400 600 800

347-Stainless Steel

HR230®

HR120®

(° )Temperature C

Tensile strength 347-stainless steel

• 500-hr test• 60 psi internal

pressure


Outline

• Background



• HR230®


As-processed HR230®

89 µm 89 µm

102 µm 102 µm

tungsten-rich particles


0.0

89

mm

0.0

89

mm

0.1

02

mm

0.1

02

mm

A752°C

B730°C

C700°C

D679°C

60 psi internal pressure

HR230® after 500-hr exposure (TET=800°C)


D C B A

cool end679°C

hot end752°C



Position A500 h @ ~752°C


air side

exhaust side




Cr

O W Ni

Mo C


•Limited corrosion products found on surface

•Significant cracking along grain boundaries

•Grain boundaries near surface are poor in Cr but rich in W and C.



0.4

0.6

0.8

1

0 200 400 600 800

347-Stainless Steel

HR230®

HR120®

(° )Temperature C

Tensile strength of HR230® after 500-hr exposure


Outline

• Background



• HR230®

• HR120®


D C B A

cool end632°C

hot end745°C



Position A500 h @ ~745°C


air side

exhaust side




10 µm

Fe Ni Si Cr


•Limited corrosion (oxides of Cr, Si and and Fe)

•Grain boundaries near surface are poor in Cr but rich in Ni



0.4

0.6

0.8

1

0 200 400 600 800

347-Stainless Steel

HR230®

HR120®

(° )Temperature C

Tensile strength of HR120® after 500-hr exposure


0.4

0.6

0.8

1

0 200 400 600 800

347-Stainless Steel

HR230®

HR120®

(° )Temperature C

Tensile strength of metallic alloys after 500-hr exposure


Outline

• Background



• HR230®

• HR120®

• Summary, Current and Future Work


• A test facility was designed to screen and evaluate candidate materials for advanced microturbine recuperators.

• TET up to 850°C

• Mechanical stressing

• Foils of 347 stainless steel, HR230® and HR120® alloys have been evaluated

• Foils have been welded to sample holders by laser and e-beam.

Summary, Current and Future Work


• 347 stainless steel347 stainless steel exhibited significant decrease in tensile strength and ductility, and severe corrosion after 500-hr exposure at 758°C.

• Evidence of creepcreep deformation at temperatures above 700°C at 50 MPa.

• Corrosion products at highest temperature are a mixture of oxides of chromium, nickel and iron.

• Depletion of chromiumchromium from grain boundaries near interface between base metal and oxide layers.

• CarbideCarbide precipitation

Summary, Current and Future Work (cont.)


• HR230®HR230® retains 70% of its tensile strength after 500-hr exposure at 752°C.

• Limited corrosion products found on surface but significant crackingcracking along grain boundaries

• Grain boundaries near surface are poor in chromium but rich in tungsten and carbon.



• HR120®HR120® exhibited good retention of mechanical properties (e.g.- 85% of its tensile strength) after 500-hr exposure at 745°C.

• Limited corrosion products in the form of oxide of chromium, silicon and iron.

• Depletion of chromium from grain boundaries close to surface exposed to exhaust gases.



• Tests in progress to evaluate HR120®, HR214®, Tests in progress to evaluate HR120®, HR214®, HR230®, ORNL-modified stainless steels, HR230®, ORNL-modified stainless steels, FeCrAlY alloys and alloy 625.FeCrAlY alloys and alloy 625.

• Effect of intermittent operation on durability of Effect of intermittent operation on durability of candidate materials candidate materials


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