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Oxidation behavior of RuAl alloys Manuel Acosta MSE/REU 2004 Adv. Dr. David R. Johnson August 5, 2004
Agenda • Introduction • Procedure • Results • Conclusions • Recommendations
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 RuAl Eutectic B. Tyron
Main applications • 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. http://www.matcoinc.com/newsletters/high_temperature_materials.html
Materials • Binary RuAl “Brittle” • Ru-Al-Mo alloys • Ru-Al-Cr alloys “Better fracture toughness”
Microstructure RuAl Eutectic B2 HCP B2 HCP
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
Procedure • Cut and polish Samples • Place samples in to the Lindbergh furnace to run cyclic oxidation process at 1100°C Sample polished through .05 micron alumina • Characterization • XRD • SEM
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
Results Cyclic oxidation @ 1100ºC Ru-Al-Cr Binary RuAl Ru-Al-Mo 0 HR 4 HR 8 HR 12 HR 16 HR
Results Binary RuAl samples
Optical Microscope- RuAl Sample RuAl Rough interface Oxide scale Epoxy mount • Reaction occurs at eutectic region? • Very thin oxide layer • RuAl? • Ru? • Al2O3? • RuO2?
XRD- RuAl sample (Al2O3 + Ru scale) Ru Al2O3 RuAl XRD Powder Diffractometer scan of the outer surface of RuAl sample after cyclic oxidation tests for 15 hr. at 1100°C
SEM/EDS- RuAlsample 10 μm 10 μm • Al loss near surface (EDS) • Layers of Al2O3 and Ru • Eutectic regions preferentially attacked
Results Ru-Al-Mo alloy samples
Optical microscope- Mo samples • Stacked up layers of oxidation products • Al2O3? • Mo O3? • Ru? • Mo? • RuO2? • Scale/matrix interphase • What reaction is going on? Scale/matrix int Cross sectional view of Ru-Al-Mo sample after 4hr of cyclic oxidation tests at 1100°C
XRD- Mo samples Al2O3 Ru Mo RuO2 ` ` ` MoO3 -> 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
SEM/EDS- Mo samples B2 B2 HCP HCP 10 μm 10 μm • Molybdenum loss in both regions • Loss of MoO3
Results Ru-Al-Cr alloy samples
Optical microscope- Cr samples Ru-Al-Cr Oxide scale Mount • Green dark thin scale Cr2O3 • Protective layer • Continuous • Uniform • Non pourous
XRD- Cr samples Cr Cr2O3 XRD Powder Diffractometer scan of the outer surface of Ru-Al-Cr sample after cyclic oxidation tests for 4hr. at 1100°C
SEM/EDS- Cr samples B2 HCP 10μm • Cr lost in the RuAL Region (EDS) • A two phase region forms?
Conclusions (operating at 1100°C) • Mo samples showed poor oxidation behaivior (non-protective scale) • Loss of weight in Mo samples due to MoO3 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
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.
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