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Optical and Mechanical Properties ofNano-Composite Optical Ceramics
*C. Scott Nordahl, Thomas Hartnett, Todd Gattuso, Richard GentilmanRaytheon Integrated Defense Systems
1Copyright © 2009 Raytheon Company. All rights reserved.
DARPA Distribution Statement “A”Approved for Public Release, Distribution Unlimited
Raytheon Integrated Defense [email protected]
Submicron and Nanostructured Ceramics
10 June, 2009
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4. TITLE AND SUBTITLE Optical and Mechanical Properties of Nano-Composite Optical Ceramics
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13. SUPPLEMENTARY NOTES See also ADM002307. ECI International Conference on Sub-Micron and Nanostructured Ceramics Held inColorado Springs, Colorado on 7-12 June 2009, The original document contains color images.
14. ABSTRACT
15. SUBJECT TERMS
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT
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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18
Introduction
• Background
– Current MWIR transparent materials
– Nano-composite oxides
• Processing/Microstructures
• Optical Properties
2Copyright © 2009 Raytheon Company. All rights reserved.
DARPA Distribution Statement “A”Approved for Public Release, Distribution Unlimited
• Optical Properties
• Mechanical Properties
• Summary
Acknowledgements
Funded by DARPA under Contract N00014-07-C-0337
Sharon Beermann-Curtin / Bill Coblenz, DARPA Program Managers
Raytheon NCOC Project Team
Raytheon IDS - Scott Nordahl
Raytheon RMS - Brian Zelinski
3Copyright © 2009 Raytheon Company. All rights reserved.
DARPA Distribution Statement “A”Approved for Public Release, Distribution Unlimited
Raytheon RMS - Brian Zelinski
Amastan - Kamal Hadidi
CeraNova - Mark Parish
Nanocerox - Todd Stefanik
Rutgers - Bernie Kear
UC-Davis - Amiya Muhkerjee
UConn - Eric Jordon
Maximizing the Optical and Mechanical Performance
The goal is to achieve all of the following simultaneously:
DARPA Goals:
– High Strength - equivalent to Sapphire
– Scaleable Method - able to produce 3” domes
– MWIR Transparent - equivalent to Spinel Raytheon “Stretch Goal”
– MWIR Transparency - equivalent to Yttria
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– MWIR Transparency - equivalent to Yttria
To achieve these goals:
– No pore phase (large ∆n ~ 0.8 = scatter)
– Minimize grain size / grain growth (G.S. < λλλλ/20 for transparency)
– Uniform 2-phase microstructure (small ∆n < 0.2)
– Avoid MWIR absorptions due to Si-O and Al-O bonds
Project Approaches
Raytheon Group
Densify nano-powders to make domes
UConn Group
Direct plasma deposition of dome shapes
Rutgers / UC-Davis Group
Plasma sprayed powders Spark plasma sintering
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• Material test and characterization
• Optical material modeling
Background
– High strength
– Excellent erosion durability (rain/sand)
– High thermal shock resistance
– Low optical scatter
– Intrinsic birefringence
– Lacks full 3-5µm transparency
Sapphire (single crystal Al2O3) is the current MWIR dome material of choice.
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– Lacks full 3-5µm transparency (absorption at 5µm)
– Significant MWIR emission at elevated/operating temperatures
– High temperature mechanical properties degradation
– High cost due to single crystal growth and optical finishing
Objective:Make much stronger dome materials and retain full MWIR transmittance
Absorption ScatterOptical
Isotropy
Mech.
Strength
Impact
Resist.
Thermal
Shock
Resist.
Machin-
ability
Sapphire
Spinel
ALON
Y2O3
Optical Properties Mechanical Properties
Excellent
Marginal
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Y2O3
MgO
ZrO2
YAG
Absorption ScatterOptical
Isotropy
Mech.
Strength
Impact
Resist.
Thermal
Shock
Resist.
Machin-
ability
Oxide Nano-
Composites
Marginal
Poor
Maximizing the Optical Performance
Problem: Most durable MWIR dome materials contain Al-O bonds. However, Al-O bonds absorb at λ > 4 microns
Solution: Select nanocomposite systems without Al-O bonds (Y2O3, MgO, ZrO2)
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Nanocomposite Composition
Baseline Material System:Yttria : Magnesia
Y2O3:MgO50:50 Vol%
Y2O3:MgO20:80 Mol%
1 µm
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XRD Y
Y
Y
YM
M
Nanocomposite Optical Ceramics:
A new class of MWIR dome materials
Hk200 = 3040g-1/2 + 730
R2 = 0.98
800
850
900
950
1000
1050
1100
0.02 0.04 0.06 0.08 0.1 0.12
GS-1/2
(nm-1/2
)
Hk
200 (
kg
/mm
2)
900 350 200 150 100 80
Grain Size (nm)Approach: Reduce grain size of transparent polycrystalline ceramics to increase strength: Hall Petch relation: σ σ σ σ ∝∝∝∝ (g.s.)-½
Problem: Processing conditions (high T & P) required to densify to optical clarity promote grain growth
Solution: Use significant volume fractions of two or more mutually insoluble transparent ceramics
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GS-1/2
(nm-1/2
)or more mutually insoluble transparent ceramics (e.g. MgO + Y2O3)
Problem: Refractive index differences between phases cause scattering by the grains
Solution: Reducing the grain size to < λλλλ/20 eliminates scatter and transparency is restored: 4µm/20 = 200 nanometers !
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
100
200
300
400
Difference in Index
Pa
rtic
le D
iam
ete
r (n
m)
Increasing average index, nave
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
100
200
300
400
Difference in Index
Pa
rtic
le D
iam
ete
r (n
m)
Increasing average index, nave
Nanopowder Production via Liquid Flame Spray Pyrolysis
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Process Overview
Powder Process
• Starting powders produced by Flame Spray Pyrolysis
• Densified by Sinter + HIP
• Slip Casting – alternate forming method
• SPS densification – smaller grain size
Slip CastDie Press
Granulate
Filter
De-agglomerate
FSP Powder
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Grind/Polish
Sinter
Hot Isostatic Press
Cold Isostatic Press
Characterization
Spark Plasma Sinter
Nanocomposite Microstructure
50:50 Vol% Yttria:MagnesiaBackscattered electron images.
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MgO
Y2O3
Uniform microstructure with ~150nm grain size.
Optical Properties
In the visible band
MgO:Y2O3 Nanocomposites
MWIR
60
70
80
90
100
Tra
ns
mis
sio
n (
%)
VIS
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In the MWIR band
0
10
20
30
40
50
0 2 4 6 8 10
Wavelength (µm)
Tra
ns
mis
sio
n (
%)
Powder Process Optimization
300
400
500
600
700
Fracture Strength (MPa) 50:50 MgO:Y2O3
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0
100
200
300
1 2 32007 2008 2009
•Fracture strength improved with optimized powders and processing.
•New material systems and/or more energetic processing needed for 1200 MPa!
Material Property Goals
Material Property Metrics for 3-5 micron Nano-Composite Optical Ceramics
Material Property UnitsPhase I Metrics
Achieved Phase II Metrics
Absorption Coefficient (ave, 3-5µm) cm-1 ≤ 0.1 0.05 ≤ 0.1
Optical Scatter (Fwd TIS @ 3.39µm) % ≤ 2.0 0.6 ≤ 0.5
Fracture Strength at 600°C(average of 10 biaxial disks)
MPa ≥ 600 650 ≥ 1200
2350
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Hardness (µ-indent: 50g load) kg/mm2 ≥ 2200 2350 ≥ 2200
Thermal Shock Resistance (requires thermal conductivity measurement)
calculated FoM: R’
- - -1.3 X
Sapphire≥ 2X
Sapphire
Sand Erosion Resistance(blowing sand – conditions TBD)
grams/std test
- - -≥ 2X
Sapphire
Water Drop Threshold Velocity(Marshall SFC – 3mm drop)
m/s - - -≥ 2X
Sapphire
Spark Plasma Sintering
Pyrometer
DC
Pu
lse
Ge
ne
rato
r
Pressure
Powder GraphiteDie
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DC
Pu
lse
Ge
ne
rato
r
VacuumChamber
Joule HeatingJoule Heating
PulsingPulsingElectricElectric
FieldField
Low T,Low T,FastFast
SinteringSintering
Spark Plasma Sintering
Modeling die geometries to improve temperature uniformity in scaled-up process
3” Diameter Disk
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Uniform Microstructure
PrecursorDroplet
Evaporation Pyrolysis Sinter MeltBreakup andPrecipitation
Direct Deposition
Splat Deposit
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100µm
Direct Deposition
50:50 MgO:Y2O3 Polished Cross-section
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3.3mm thick
Microstructure
Summary
• MgO:Y2O3 based nanocomposite ceramics have been developed using traditional ceramic processing routes and demonstrated:
– Sapphire equivalent mechanical durability
– Yttria equivalent MWIR optical transparency
• New nanocomposite material systems show potential for greater mechanical durability with inherently more
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for greater mechanical durability with inherently more durable crystallographic phases.
• More energetic fabrication techniques are showing promise for refined microstructures and improved mechanical properties.