# Presentation: 680241

## 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 Division
- Oak Ridge National Laboratory
- Oak Ridge, TN 37831-6069

- ASME Turbo Expo
- Vienna, Austria
- June 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 screen and evaluate 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.)

## ORNL’s 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

- sample holder

- thermocouples

## Temperature distribution along sample holder

- TET=800°C

## Effect of microturbine exposure on tensile properties

## Temperature History for 500-hr test

## Outline

- Background
- Microturbine Test Facility
- Testing Procedure
- Results
- 347 Stainless Steel

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

- 0.089 mm

- 0.089 mm

- 0.089 mm

- 0.089 mm

- A
- 758°C

- B
- 736°C

- C
- 697°C

- D
- 632°C

- 60 psi internal pressure  -> 50 MPa hoop stress

## 347-stainless steel after 500-hr exposure

- ballooning due to creep deformation

## 347-stainless steel after 500-hr exposure

- D

- C

- B

- A

- cool end
- 630°C

- hot end
- 758°C

**air side**

**exhaust side**

- Position D
- 500 h @ ~632°C
- very little corrosion

- Position C
- 500 h @ ~697°C
- thin scale

- Position B
- 500 h @ ~736°C
- ~3 μm scale

- Position A
- 500 h @ ~758°C
- ~20 μm scale

- ballooning due to creep deformation

- “wart”

- cross-sectional analysis

## 347-stainless steel after 500-hr exposure

- 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

## Tensile strength of 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)

## Tensile strength 347-stainless steel

- 500-hr test
- 60 psi internal pressure

## Outline

- Background
- Microturbine Test Facility
- Testing Procedure
- Results
- 347 Stainless Steel
- HR230®

## As-processed HR230®

- 89 μm

- 89 μm

- 102 μm

- 102 μm

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

- 0.089 mm

- 0.089 mm

- 0.102 mm

- 0.102 mm

- A
- 752°C

- B
- 730°C

- C
- 700°C

- D
- 679°C

- 60 psi internal pressure

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

- D

- C

- B

- A

- cool end
- 679°C

- hot end
- 752°C

- Position C
- 500 h @ ~697°C

- Position B
- 500 h @ ~730°C

- Position A
- 500 h @ ~752°C

- cross-sectional analysis

**air side**

**exhaust side**

- Position D
- 500 h @ ~679°C

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

- Foil exposed at 752°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.

## Tensile strength of HR230® after 500-hr exposure

## Outline

- Background
- Microturbine Test Facility
- Testing Procedure
- Results
- 347 Stainless Steel
- HR230®
- HR120®

## HR120® after 500-hr exposure (TET=800°C)

- D

- C

- B

- A

- cool end
- 632°C

- hot end
- 745°C

- Position C
- 500 h @ ~700°C

- Position B
- 500 h @ ~730°C

- Position A
- 500 h @ ~745°C

- cross-sectional analysis

**air side**

**exhaust side**

- Position D
- 500 h @ ~632°C

## HR120® after 500-hr exposure (TET=800°C)

- 10 μm

- Fe

- Ni

- Si

- Cr

- Foil exposed at 745°C
- Limited corrosion (oxides of Cr, Si and and Fe)
- Grain boundaries near surface are poor in Cr but rich in Ni

## Tensile strength of HR120® after 500-hr exposure

## Tensile strength of metallic alloys after 500-hr exposure

## Outline

- Background
- Microturbine Test Facility
- Testing Procedure
- Results
- 347 Stainless Steel
- HR230®
- HR120®
- Summary, Current and Future Work

## Summary, Current and Future Work

- 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 (cont.)

- Evidence of creep 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 chromium from grain boundaries near interface between base metal and oxide layers.
- Carbide precipitation

## Summary, Current and Future Work (cont.)

- Limited corrosion products found on surface but significant cracking along grain boundaries
- Grain boundaries near surface are poor in chromium but rich in tungsten and carbon.

## Summary, Current and Future Work (cont.)

- 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.

## Summary, Current and Future Work (cont.)

- Effect of intermittent operation on durability of candidate materials

## Slide 45