NonNon--Contact Methods of MeasuringContact Methods of Measuring

Stresses in High Temperature MaterialsStresses in High Temperature Materials

David R. Clarke

Qing Ma, Jun He, Don Lipkin, John Nychka

Samuel Margueron, Vladimir Tolpygo, Derek Gardiner

Everyone talks about the weather.. but nobody does anything about it

Mark Twain(Samuel Clemens)

Everyone talks about stresses……. but nobody does anything about them

• Introduction to Cr3+ based luminescence and piezospectroscopy (luminescence and Raman).

• Phase transformations during the growth of alumina by thermal oxidation

• Latest developments on piezospectroscopy

• Modes of strain energy relief in oxide films and coatings

• Wrinkling, wrinkling kinetics leading to oxide film failure

• Buckling and buckle growth

• Conditions for spalling by the growth of buckles

• Large scale buckling

• Rumpling

• Monitoring damage evolution in TBCs by piezospectroscopy

• Summary

OutlineOutline

Vibrational piezospectroscopy –Raman piezospectroscopy Luminescence piezospectroscopy

Single crystal silicon Sapphire containing Cr dopant

Principal Types of Piezospectroscopy Principal Types of Piezospectroscopy

Octahedral coordination of Cr3+

Physical Basis of Luminescence Piezospectroscopy: Synopsis Physical Basis of Luminescence Piezospectroscopy: Synopsis

Piezospectroscopy Relation

Ambient pressure transitions in the visible

Electronic Transitions of d 3 Electrons Electronic Transitions of d 3 Electrons

Strain alters ligand length and hence local potential on the electrons.

Ambient pressure transitions in the visible

Electronic Transitions of d 3 Electrons Electronic Transitions of d 3 Electrons

Strain alters ligand length and hence local potential on the electrons.

Cr3+ Piezospectroscopy in SapphireCr3+ Piezospectroscopy in Sapphire

Calibration of piezo-spectroscopy coefficientsCalibration of piezo-spectroscopy coefficients

Analysis for General OrientationAnalysis for General Orientation

Calibration for polycrystalline, randomly oriented aluminaCalibration for polycrystalline, randomly oriented alumina

Uniaxial Compression to tensionHydrostatic stress

Summary of Luminescence ShiftsSummary of Luminescence Shifts

Effect of Stress GradientEffect of Stress Gradient

( )223o

ii

wwtzd

d−

Π=

σ

Stress gradient causes peak broadening

Optical Microprobe ConfigurationOptical Microprobe Configuration

Internal Stress Distribution in Polycrystalline Alumina Internal Stress Distribution in Polycrystalline Alumina

Observation in transmitted light through cross-polarizers of alumna.

Variation in stress made visible through the piezo-optical effect.

Raman PiezospectroscopyRaman Piezospectroscopy

Raman PiezospectroscopyRaman Piezospectroscopy

Active vibrational modesTransverse Optical --- TO1 along [100], TO2 along [010]Longitudinal Optical – LO along [001]

Raman Piezospectroscopy of SiliconRaman Piezospectroscopy of Silicon

Raman PiezospectroscopyRaman Piezospectroscopy

Raman Piezospectroscopy In ElectromigrationRaman Piezospectroscopy In Electromigration

Phase Transformations in Alumina During

High Temperature OxidationPhase Transformations in Alumina During

High Temperature Oxidation

Reported Phase Transformations in Alumina Ceramics, Powders and Films

Reported Phase Transformations in Alumina Ceramics, Powders and Films

0

100

200

300

400

500

600

14000 14200 14400 14600 14800 15000

Inte

nsity

[cp

s]

Frequency [cm -1]

α -Al2O

3

θ -A l2O

3

γ -A l2O

3

Luminescence Identification of Alumina PhasesLuminescence Identification of Alumina Phases

Oxidation Induced Transformation Sequence on MCrAl vs NiPtAlOxidation Induced Transformation Sequence on MCrAl vs NiPtAl

Alumina Transformation Kinetics on NiAlAlumina Transformation Kinetics on NiAl

Grumm and GrabkePhase identification by X-ray diffraction

Nucleation and Growth of α-alumina on NiAlNucleation and Growth of α-alumina on NiAl

Oxidation Temperature 1100oC

Luminescence Mapping For Transformation KineticsLuminescence Mapping For Transformation Kinetics

tBAR log+=

αθ+α

Evolution of Stress in NiAl Single CrystalEvolution of Stress in NiAl Single Crystal

Thermalexpansionstress

NB. Alpha phase is under net tension under transformation is complete. Then oxide is under compression.

Nucleation and Growth of a-Alumina During OxidationNucleation and Growth of a-Alumina During Oxidation

Origin of Transformation StressesOrigin of Transformation Stresses

αθ → transformation is accompanied by a 9.5 % volume decrease.

The transformation is constrained by the surrounding θ oxide, placing theα - islands under tension. This causes “tearing” of islands.

Alpha-island

θ - matrix

Heterogeneous Nucleation and Growth of α-alumina on NiAlHeterogeneous Nucleation and Growth of α-alumina on NiAl

Note the radial cracks in the islands, giving the“star” contrast

1 hour θ ~ 0.5 μm thick 25 hour mixed α + θ

TGO Morphology at 1000oCTGO Morphology at 1000oC

0

200

400

600

800

1000

14300 14400 14500 14600 14700

Inte

nsity

[cp

s]

Frequency [cm -1]

Ar θ -Al2O

3

α-Al2O

3

(σ ~ -3.75 GPa)

0

2000

4000

6000

14350 14400 14450

Inte

nsity

[cp

s]

Frequency [cm -1]

α-Al2O

3

(whiskers)

α-Al2O

3

(layer)

Ar

"transition" c

1 hour at 1100oC 25 hour at 1100oC

Fibrous θ-phase Transforms to α−aluminaFibrous θ-phase Transforms to α−alumina

Recent DevelopmentsRecent Developments

Stress Effects on the Luminescence LifetimeStress Effects on the Luminescence Lifetime

Lifetime varies with crystallographic direction and linearly with stress

Polycrystalline alumina

Use of Polarization to Distinguish Stress ComponentsUse of Polarization to Distinguish Stress Components

FIB cuts create a stripunder uniaxial stress

Luminescence intensitymap around strip

( ) 3/62.72 zzyyxxR σσσν ++=Δ

Frequency shift proportional to meanstress in polycrystalline alumina:

Use of Polarization to Distinguish Stress ComponentsUse of Polarization to Distinguish Stress Components

Imaging under different polarization conditions reveals directions of principal stresses by affecting R2/R1 peak area ratio.

End of Part IEnd of Part I