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