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Oxidation behavior of RuAl alloys
Manuel AcostaMSE/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
B. Tyron
RuAl
Eutectic
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.
Materials
• Binary RuAl “Brittle”
• Ru-Al-Mo alloys
• Ru-Al-Cr alloys
“Better fracture
toughness”
MicrostructureAlloy Microstructur
e
Binary RuAl(Brittle)
B2 + eutectic
Ru-Al-Mo(KIC≈30MPa√m)
HCP solid solution+B2
eutectic
Ru-Al-Cr(KIC≈40MPa√m)
HCP solid solution+B2 precipitates
RuAl
Eutectic
B2
HCP
HCP
B2
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 #
Composition(at %)
ProcessVolume Fraction
RuAl Ru PrimaryRuAl
1 Ru-20Al-25Mo Tri-arc 34 66 19
2 Ru-20Al-25Mo Arc-melted 45 55 30
3 Ru-20Al-25Mo Float-zone 51 49 41
4 Ru-10Al-35Cr Induction - - -
5 Ru-7Al-38Cr Induction 0 100 0
6 Binary RuAl Arc melted - - -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
ResultsCyclic oxidation @
1100ºC
0 HR4 HR8 HR12 HR16 HR
dm/A PER HOUR (g/mm^2-hr)
-0.0007
-0.0006
-0.0005
-0.0004
-0.0003
-0.0002
-0.0001
0
0.0001
0 2 4 6 8 10 12 14 16 18
Time (hr)
dm/A
(g/m
m^2
)
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Ru-Al-Cr
Ru-Al-Mo
Binary RuAl
Results
Binary RuAl
samples
Optical Microscope- RuAl Sample
•Reaction occurs at eutectic region?
•Very thin oxide layer
•RuAl?
•Ru?
•Al2O3?
•RuO2?
Epoxy mount
RuAlRough interface
Oxide scale
XRD- RuAl sample (Al2O3 + Ru scale)
XRD Binary RuAl
0
500
1000
1500
2000
2500
3000
3500
2 theta
Lin
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
•Al loss near surface (EDS)
•Layers of Al2O3 and Ru
•Eutectic regions preferentially attacked
10 μm10 μm
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?
Cross sectional view of Ru-Al-Mo sample after 4hr of cyclic oxidation tests at 1100°C
Scale/matrix int
XRD Ru,Al,Mo
0
100
200
300
400
500
600
2 theta
Lin
XRD- Mo samples
``
`
Al2O
3
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
•Molybdenum loss in both regions
•Loss of MoO3
10 μm 10 μm
B2
HCP
B2
HCP
Results
Ru-Al-Cr alloy samples
Optical microscope- Cr samples
•Green dark thin scale Cr2O3
•Protective layer
•Continuous
•Uniform
•Non pourous
Ru-Al-Cr
Mount
Oxide scale
XRD- Cr samples
XRD Ru, Al, Cr
0
200
400
600
800
1000
1200
1400
1600
1800
2 theta
Lin
XRD Powder Diffractometer scan of the outer surface of Ru-Al-Cr sample after cyclic oxidation tests for 4hr. at 1100°C
Cr
Cr2O3
SEM/EDS- Cr samples
•Cr lost in the RuAL Region (EDS)
•A two phase region forms?
B2
HCP
10μm
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.
QUESTIONS?
THANK YOU