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Screening and Evaluation of Materials for Advanced Microturbine Recuperators

Screening and Evaluation of Materials for Advanced Microturbine Recuperators. Edgar Lara-Curzio, R. M. Trejo, K. L. More, S. Dryepondt, P.A. Maziasz, and B. A. Pint Metals & Ceramics Division Oak Ridge National Laboratory Oak Ridge, TN 37831-6069. ASME Turbo Expo Reno, NV June 8, 2005.

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Screening and Evaluation of Materials for Advanced Microturbine Recuperators

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  1. Screening and Evaluation of Materials for Advanced Microturbine Recuperators Edgar Lara-Curzio, R. M. Trejo, K. L. More, S. Dryepondt, P.A. Maziasz, and B. A. Pint Metals & Ceramics Division Oak Ridge National Laboratory Oak Ridge, TN 37831-6069 ASME Turbo Expo Reno, NV June 8, 2005

  2. 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

  3. Outline • Background • Microturbine Recuperator Testing Facility • Test Procedure • Steady State • Intermittent Operation • Results • Intermediate-range materials • Long-range materials • Summary

  4. Background $500/kW 40% Efficiency advanced materials 40,000-hr life higher TET U.S. DOE Advanced Microturbines Program higher TIT 2000 2002 2004 2006 2008 2010

  5. Background (cont.) Main factors to consider for the selection of materials for microturbine recuperators • Temperature • Environment(combustion gases can lead to corrosion) • Stresses(resulting from pressure differential across cell walls and from temperature gradients. These stresses can induce creep deformation)

  6. Background (cont.) Activities have been focused on the evaluation and characterization of commercial alloys: • Currently in use • 347 stainless steel • Intermediate-range • ORNL-modified steels, HR120, 20/25, 625, HR230. • Long-range • HR214

  7. Outline • Background • Microturbine Test Facility

  8. Microturbine Test Facility shelter housing instrumentation 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 gas compressor Capstone 60kW microturbine

  9. Microturbine Test Facility (cont.)

  10. ORNL’s Microturbine Test Facility (cont.) thermocouples • Modified Capstone C60 microturbine • Higher TET (850°C) • Placement of test specimens at the entrance of recuperator. sample holders water-cooled block water lines air line

  11. 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

  12. Temperature distribution along sample holder TET=800°C

  13. Foils are removed from the sample holder and miniature test specimens, obtained by electric discharge machining, are evaluated in tension. Effect of microturbine exposure on tensile properties

  14. ORNL’s Microturbine Test Facility (cont.) thermocouples • The effect of microturbine intermittent operation on the durability of recuperator materials is being investigated by placing a sample holder at the end of a pneumatic actuator, which inserts and retrieves the sample holder at regular time intervals pneumatic actuator metallic bellows

  15. ORNL’s Microturbine Test Facility (cont.) insert movie file

  16. ORNL’s Microturbine Test Facility (cont.) Time dependence of temperature distribution along sample holder used for intermittent tests. The three foils under evaluation are of alloy 20/25.

  17. Outline • Background • Microturbine Recuperator Testing Facility • Test Procedure • Steady State • Intermittent Operation • Results • Intermediate-range materials

  18. ORNL-modified stainless steels SS18115 Fe(58.3)-Cr(19.3)-Ni(12.6)-Si(0.36)-Mn(4.55)-Cu(4.0)-Mo(0.25)-Nb(0.37)-C(0.03)-N(0.25) SS18116 Fe(61.1)-Cr(19.3)-Ni(12.5)-Si(0.38)-Mn(1.8)-Cu(4.0)-Mo(0.25)-Nb(0.38)-C(0.03)-N(0.14)

  19. Results: ORNL modified stainless steels Before 500-hr test After 500-hr test Alloy 625 Alloy 625 SS18115 & SS18116 SS18115 & SS18116

  20. Results: ORNL modified stainless steels • After a 500-hr exposure at 654°C and 705°C, ORNL-modified stainless steels retained more than 90% of their as-processed tensile strength. • At these temperatures ORNL-modified stainless steels exhibited better durability than 347 stainless steel.

  21. SS18115 (B) Exposed for 500 hrs in MRTFFe(58.3)-Cr(19.3)-Ni(12.6)-Si(0.36)-Mn(4.55)-Cu(4.0)-Mo(0.25)-Nb(0.37)-C(0.03)-N(0.25) Uniform surface scale observed on foil gas-path surface 10 mm

  22. Fe Cr 10 mm SS18115 (B) Exposed for 500 hrs in MRTFFe(58.3)-Cr(19.3)-Ni(12.6)-Si(0.36)-Mn(4.55)-Cu(4.0)-Mo(0.25)-Nb(0.37)-C(0.03)-N(0.25) MnO • Cr and Mn grain boundary depletion observed ~10 mm below scale • Cr-depletion also observed at grain boundaries in bulk foil due to Cr-carbide formation • Scale formed is 3-layer: inner Cr2O3, middle (Fe,Mn) oxide, and outer MnO with silica associated with Cr2O3 (Fe,Mn) oxide Cr2O3+SiO2 Mn Cr Fe

  23. SS18116 (B) Exposed for 500 hrs in MRTFFe(61.1)-Cr(19.3)-Ni(12.5)-Si(0.38)-Mn(1.8)-Cu(4.0)-Mo(0.25)-Nb(0.38)-C(0.03)-N(0.14) Uniform surface scale observed on foil gas-path surface which was thinner than that observed on SS18115. Bulk foil degradation (formation of grain boundary Cr-carbides) evident 10 mm

  24. SS18116 (B) Exposed for 500 hrs in MRTFFe(61.1)-Cr(19.3)-Ni(12.5)-Si(0.38)-Mn(1.8)-Cu(4.0)-Mo(0.25)-Nb(0.38)-C(0.03)-N(0.14) 10 mm Cr Fe MnO • Cr and Mn grain boundary depletion observed ~10 mm below scale (Mn-depletion is significant due to limited reservoir!) • Cr-depletion also observed at grain boundaries in bulk foil due to Cr-carbide formation • Scale formed is 2-layer: inner Cr2O3, and outer MnO with silica associated with Cr2O3. (note: no (or very limited) middle (Fe,Mn) oxide layer forms on this alloy) Cr2O3+SiO2 Mn Cr Fe

  25. HR-120

  26. Results: HR-120 after 500-hr exposure after 1000-hr exposure

  27. HR-230

  28. Results: HR-230 after 500-hr exposure after 1000-hr exposure

  29. Outline • Background • Microturbine Recuperator Testing Facility • Test Procedure • Steady State • Intermittent Operation • Results • Intermediate-range materials • Long-range materials

  30. Results: HR-214 • HR-214 does exhibit better strength retention than HR-120 and HR-230 at 750°C. • Tests are in progress to assess the effect of pre-oxidation on the mechanical properties of HR-214 after exposure in microturbine recuperator testing facility.

  31. C D 10 mm 10 mm 10 mm 10 mm B A HR-214 after 500-hr exposure in MRTF 751°C 705°C without pre-oxidation treatment 578°C 654°C

  32. HR-214 after 500-hr exposure in MRTF Outward-growing (dense) Ni (Cr,Fe) Oxide Cr2O3 Inward-growing Al (Cr,Ni) Oxide Al 10 mm Fe Ni Cr

  33. HR-214 after 500-hr exposure in MRTF Inward-growing Al (Cr,Ni) Oxide Cr2O3 Outward-growing (porous) Ni (Cr,Fe) Oxide Al and Cr segregation at grain boundaries 10 mm

  34. Outline • Background • Microturbine Recuperator Testing Facility • Test Procedure • Steady State • Intermittent Operation • Results • Mid-range materials • Long-range materials • Summary

  35. Summary • A test facility is operational to screen and evaluate candidate materials for advanced microturbine recuperators. • TET up to 850°C • Mechanical stressing • Intermittent operation

  36. Summary (cont.) • ORNL-modified stainless steels exhibited superior durability than 347 stainless steel at 700°C in ORNL’s MRTF. • It was found that ORNL-modified stainless steels formed oxide scales of manganese, iron, chromium and silicon and that the grain boundaries in a region 10-µm thick underneath the surface had been depleted of chromium and manganese. • ORNL-modified stainless steels with higher manganese concentration led to the formation of thicker and more uniform oxide scales.

  37. Summary (cont.) • 1000-hr exposure tests to temperatures up to 750°C have been completed for HR-120, HR-230 and work is in progress to characterize the microstructural changes resulting from exposure to ORNL’s MRTF. • Tests are also in progress to evaluate the performance of alloy 20/25, which was recently procured from AL. • HR-214 exhibits superior resistance to exposure to ORNL’s MRTF at 750°C. Work is in progress to assess the effect of pre-oxidation on the durability of this material

  38. Summary (cont.) The temperature dependence of the ultimate tensile strength of the metallic foils evaluated in ORNL’s MRTF could be described according to the following empirical model: where To, which depends on time of exposure, is a measure of the thermal resistance of the material.

  39. Summary (cont.) • Tests are in progress to evaluate the resistance of metallic alloys (alloy 20/25, HR-120) to intermittent microturbine operation.

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