1. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 1 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 2 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 3 of 39 Outline Background Microturbine Recuperator Testing Facility Test Procedure Steady State Intermittent Operation Results Intermediate-range materials Long-range materials Summary

4. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 4 of 39 Background 200020022004200620082010 higher TIT higher TET advanced materials U.S. DOE Advanced Microturbines Program $500/kW 40% Efficiency 40,000-hr life

5. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 5 of 39 Background (cont.) 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) Main factors to consider for the selection of materials for microturbine recuperators

6. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 6 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 7 of 39 Outline Background Microturbine Test Facility

8. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 8 of 39 Microturbine Test Facility gas compressor shelter housing instrumentation Capstone 60kW microturbine screenevaluate 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

9. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 9 of 39 Microturbine Test Facility (cont.)

10. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 10 of 39 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 air line water lines sample holders

11. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 11 of 39 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

12. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 12 of 39 Temperature distribution along sample holder TET=800°C

13. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 13 of 39 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.

14. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 14 of 39 ORNL’s Microturbine Test Facility (cont.) 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 thermocouples

15. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 15 of 39 ORNL’s Microturbine Test Facility (cont.) insert movie file

16. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 16 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 17 of 39 Outline Background Microturbine Recuperator Testing Facility Test Procedure Steady State Intermittent Operation Results Intermediate-range materials

18. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 18 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 19 of 39 Results: ORNL modified stainless steels Before 500-hr test After 500-hr test Alloy 625 SS18115 & SS18116 SS18115 & SS18116

20. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 20 of 39 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. Results: ORNL modified stainless steels

21. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 21 of 39 10  m Uniform surface scale observed on foil gas-path surface SS18115 (B) Exposed for 500 hrs in MRTF 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)

22. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 22 of 39 10  m Cr Fe Cr and Mn grain boundary depletion observed ~10  m below scale Cr-depletion also observed at grain boundaries in bulk foil due to Cr- carbide formation Scale formed is 3-layer: inner Cr 2 O 3, middle (Fe,Mn) oxide, and outer MnO with silica associated with Cr 2 O 3 SS18115 (B) Exposed for 500 hrs in MRTF 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) Mn Cr Fe MnO (Fe,Mn) oxide Cr 2 O 3 +SiO 2

23. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 23 of 39 10  m 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 SS18116 (B) Exposed for 500 hrs in MRTF 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)

24. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 24 of 39 10  m CrFe Cr and Mn grain boundary depletion observed ~10  m 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 Cr 2 O 3, and outer MnO with silica associated with Cr 2 O 3. (note: no (or very limited) middle (Fe,Mn) oxide layer forms on this alloy) Mn Cr Fe MnO Cr 2 O 3 +SiO 2 SS18116 (B) Exposed for 500 hrs in MRTF 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)

25. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 25 of 39 HR-120

26. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 26 of 39 Results: HR-120 after 500-hr exposure after 1000-hr exposure

27. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 27 of 39 HR-230

28. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 28 of 39 Results: HR-230 after 500-hr exposure after 1000-hr exposure

29. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 29 of 39 Outline Background Microturbine Recuperator Testing Facility Test Procedure Steady State Intermittent Operation Results Intermediate-range materials Long-range materials

30. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 30 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 31 of 39 10  m C C HR-214 after 500-hr exposure in MRTF D 10  m B A 578°C 654°C 705°C 751°C without pre- oxidation treatment

32. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 32 of 39 Outward-growing (dense) Ni (Cr,Fe) Oxide Cr 2 O 3 10  m Al NiFe Cr HR-214 after 500-hr exposure in MRTF Inward-growing Al (Cr,Ni) Oxide

33. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 33 of 39 10  m Outward-growing (porous) Ni (Cr,Fe) Oxide Inward-growing Al (Cr,Ni) Oxide Cr 2 O 3 Al and Cr segregation at grain boundaries HR-214 after 500-hr exposure in MRTF

34. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 34 of 39 Outline Background Microturbine Recuperator Testing Facility Test Procedure Steady State Intermittent Operation Results Mid-range materials Long-range materials Summary

35. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 35 of 39 A test facility is operational to screen and evaluate candidate materials for advanced microturbine recuperators. TET up to 850°C Mechanical stressing Intermittent operation Summary

36. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 36 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 37 of 39 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. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 38 of 39 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 T o, which depends on time of exposure, is a measure of the thermal resistance of the material.

39. O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY Lara-Curzio et al. IGTI-2005. Page 39 of 39 Summary (cont.) Tests are in progress to evaluate the resistance of metallic alloys (alloy 20/25, HR-120) to intermittent microturbine operation.