1. Oxidation behavior of RuAl alloys Manuel Acosta MSE/REU 2004 Adv. Dr. David R. Johnson August 5, 2004

2. Agenda Introduction Procedure Results Conclusions Recommendations

3. Introduction What is RuAl? Intermetallic compound often considered a good candidate for high temperature applications. RuAl has a B2 structure and melts at approximately 2060ºC. Combines good ductility, oxidation, strength and thermodynamic properties B. Tyron RuAl Eutectic

4. Main applications http://www.matcoinc.com/newsletters/high_temperature_materials.html Characteristics of high temperature alloys (260°C-1205°C) High fracture toughness High temperature strength Good oxidation resistance High temperature alloys have been used generally in the presence of combustion from heat sources such as turbine engines, reciprocating engines, power plants, furnaces and pollution control equipment.

5. Materials Binary RuAl “Brittle” Ru-Al-Mo alloys Ru-Al-Cr alloys “Better fracture toughness”

6. Microstructure AlloyMicrostructure Binary RuAl (Brittle) B2 + eutectic Ru-Al-Mo (K IC ≈30MPa√m) HCP solid solution+B2 eutectic Ru-Al-Cr (K IC ≈40MPa√m) HCP solid solution+B2 precipitates RuAl Eutectic B2 HCP B2

7. Project objectives Mo and Cr samples have a better fracture toughness than binary RuAl. Now we need to describe and compare the oxidation behavior of alloys containing Ru, Al, Mo and Cr produced in different compositions by the tri- arc, arc-melting, floating and induction methods. Study the type of oxide formed and its oxidation resistance

8. Procedure Cut and polish Samples Place samples in to the Lindbergh furnace to run cyclic oxidation process at 1100°C Sample # Composition (at %) Process Volume Fraction RuAlRuPrimary RuAl 1Ru-20Al-25MoTri-arc346619 2Ru-20Al-25MoArc-melted455530 3Ru-20Al-25MoFloat-zone514941 4Ru-10Al-35CrInduction--- 5Ru-7Al-38CrInduction01000 6Binary RuAlArc melted--- Sample polished through.05 micron alumina Characterization XRD SEM

9. What could happen? How do you know if there is good oxidation resistance? –Protective oxide scale Continuous Non-porous Uniform stable –Non-protective oxide scale Porous Cracks easily Non-continuous Non-stable

10. Results Cyclic oxidation @ 1100ºC 0 HR4 HR8 HR12 HR16 HR Ru-Al-Cr Ru-Al-Mo Binary RuAl

11. Results Binary RuAl samples

12. Optical Microscope- RuAl Sample Reaction occurs at eutectic region? Very thin oxide layer RuAl? Ru? Al 2 O 3 ? RuO 2 ? Epoxy mount RuAl Rough interface Oxide scale

13. XRD- RuAl sample (Al 2 O 3 + Ru scale) Ru Al 2 O 3 RuAl XRD Powder Diffractometer scan of the outer surface of RuAl sample after cyclic oxidation tests for 15 hr. at 1100°C

14. SEM/EDS- RuAlsample Al loss near surface (EDS) Layers of Al 2 O 3 and Ru Eutectic regions preferentially attacked 10 μm

15. Results Ru-Al-Mo alloy samples

16. Optical microscope- Mo samples Stacked up layers of oxidation products Al 2 O 3 ? Mo O 3 ? Ru? Mo? RuO 2 ? Scale/matrix interphase What reaction is going on? Cross sectional view of Ru-Al-Mo sample after 4hr of cyclic oxidation tests at 1100°C Scale/matrix int

17. XRD- Mo samples ` ` ` Al 2 O 3 Ru Mo RuO 2 MoO 3 -> Not found (gas at 1100°C) XRD Powder Diffractometer scan of the outer surface of Ru- Al-Mo sample after cyclic oxidation tests for 4hr. at 1100°C

18. SEM/EDS- Mo samples Molybdenum loss in both regions Loss of MoO 3 10 μm B2 HCP B2 HCP

19. Results Ru-Al-Cr alloy samples

20. Optical microscope- Cr samples Green dark thin scale Cr 2 O 3 Protective layer Continuous Uniform Non pourous Ru-Al-Cr Mount Oxide scale

21. XRD- Cr samples XRD Powder Diffractometer scan of the outer surface of Ru- Al-Cr sample after cyclic oxidation tests for 4hr. at 1100°C Cr Cr 2 O 3

22. SEM/EDS- Cr samples Cr lost in the RuAL Region (EDS) A two phase region forms? B2 HCP 10μm

23. Conclusions (operating at 1100°C) Mo samples showed poor oxidation behaivior (non-protective scale) Loss of weight in Mo samples due to MoO 3 vaporization and spoliation Cr samples demonstrated good oxidation behavior (protective scale) Binary RuAl has a good oxidation behavior, but is a brittle material, Oxidation process occurs mainly in the eutectic region forming a thin layer of Ru and Al, Aluminum is lost Cr samples shown the best fracture toughness and oxidation resistance

24. Recommendations Further characterization of the oxide /matrix interphase in the Cr and RuAl samples Make same procedure for distinct temperatures By getting rid of eutectic RuAl oxidation resistance improves.

25. QUESTIONS? THANK YOU