O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 1 Tungsten Armored Ferritic Steel...
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Transcript of O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 1 Tungsten Armored Ferritic Steel...
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Tungsten Armored Ferritic Steel
Glenn Romanoski & Lance Snead
June 2004
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Phase I : Fabrication Process and RepairTungsten Armored Low Activation Ferritic Steel
Objective: select and optimize methods for bonding tungsten to a Low Activation Ferritic Steel and assess the integrity of these coatings under IFE relevant thermal fatigue conditions.
Approach: - Evaluate methods for applying tungsten coatings to F82H steel substrates.
Fabricate and study adherence and thermal stability. Is this material combination viable? FY-04 Milestone.
- Given W thickness (100μm to 250µ nominal) and thermal boundary conditions, assess the stability and fatigue performance of the underlying LAF. FY-04 Milestone.
- Screen coupon coatings using thermal fatigue facility. Select candidate monolithic armor system or move to “engineered structure.” FY-05 Milestone.
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
IFE Relevant Performance Assessment is Critical to Armor Design and Material Selection
The goal of materials performance assessment is to be relevant if not equivalent.
The goal of materials selection and design is to meet or exceed the operational and durability requirements of the IFE first wall.
How close is our most relevant thermal fatigue test conditions to IFE equivalent conditions?
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
IR Thermal Fatigue Facility
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-200 0 200 400 600 800 1000Time (ms)
Hea
t flu
x (M
W/m
2 )
• Facility has been used for interfacial fatigue of W/LAF
• Previously 20 MW/m2 (time average), 20 msec pulse, 10 Hz, 10 cm2
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Facility Improvements : IR Thermal Fatigue
• Now capable of 100 MW/m2 (time average), 2 msec pulse, 10 Hz, 5 cm2
• Phase 1 goal 1000 MW/m2 (time average), 0.1 msec pulse, 10 cm2
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100
1000
104
0.001 0.01 0.1 1 10 100
Hea
t L
oad
(M
W/m
2 )
Time (milliseconds)
IFE
~104 MW/m2
~ 10 sec
IR upgrade
~102 MW/m2
~ 2 msec
IR Thermal FatigueFacility~20 MW/m2 ~ 20 msec
> 0.1 MJ/m2
~ 0.4 MJ/m2
~ 0.2 MJ/m2
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Simulating HAPL Interface Stresses
The IR heat load cannot duplicate tungsten surface stresses, but it can duplicate the interface stresses
If the tungsten layer is sufficiently thick, preserving the time-averaged heating is sufficient
The key metric is the stress distribution
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Comparison of Stress Distribution
7.2 MW/m2 20 ms pulse
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-100
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100
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0 0.5 1 1.5 2 2.5 3 3.5
HAPL baseline
Infrared heating
Str
ess
(MP
a)
depth (mm)
Armor interface
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
F82H Ferritic Steel with 100µm of Tungsten Armoris the Reference Material/Design Solution
Infrared fusion of tungsten powder
Diffusion bonding of tungsten foil
Vacuum plasma spraying powder
Alternative approaches, e.g., CVD
Processing Method Method of Screening
Thermal stability of the interface
will be assessed under cyclic and
isothermal conditions.
Thermal fatigue performance of the
tungsten armor and substrate will
be assessed with the IR plasma arc
lamp.
Interfacial Strength will be
measured using flexural tests.
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Preliminary Thermal Cycling Test Results Illustrate the Issues Pertinent to Material Selection, Processing and Testing.
Processing Method
Initial tests showed promise -----Coatings adhered after 1000 cycles.
Tensile cracks developed in the substrate due to CTE mismatch and phase changes. Diffusion bonding below the phase transformation temperature will be tried.
Dissolution of carbides in the steel at the interface indicated that the temperature probably exceeded 900ºC. Diffusion of tungsten into the steel could generate brittle phases such as FeW and Fe2W.
Thermal management of the substrate and incident heat flux is critical to a meaningful thermal fatigue test.
Diffusion bonded tungsten foil
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Thermal conductivity of W and F82H defines the interface temperature for fixed geometry and thermal boundary conditions.
Thermal Conducti vi ty versus Temperature
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1 10 100 1000 10000
Temperature (K)
k(W/
mK) Tungsten
F82H Steel
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Microstructural stability of F82H will limit the interface temperature to about 800C
Coarsening of carbides in the F82H steel above 800C and dissolution around 900C will degrade mechanical properties.
The alpha – gamma - alpha phase transformation and CTE mismatch will impart strains at the interface.
A critical thickness of tungsten may be required to dissipate the heat pulses to maintain the interface in an acceptable temperature regime. Will that be adequate?
A thermal model of our experiment and appropriate instrumentation of specimens is the key to running meaningful experiments.
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Alternative Design/Material Approaches
Given the selection of a ferritic steel as the substrate material, the interface temperature is limited to 800ºC. What thickness of W coating and back face heat flux is required to maintain a stable interface? Is 600ºC an appropriate far field temperature?
Given the selection of tungsten as the armor material, are there other substrate materials with higher temperature capability?
Group VA alloys (V, Nb or Va) could serve as an intermediate layer having higher temperature capability. Sensitivity to oxygen would be a consideration.
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
04 Milestone : Go/No Go on tungsten armor. Is tungsten clad F82H steel a viable material option?
!
Where are we ???
• Vacuum plasma sprayed W on F82H is the principal material candidate. A number of material conditions are ready for testing. Additional material conditions exploring the extremes of the W/F82H material option will be produced, e.g., thick tungsten coatings.
• Achieving thermal similitude between our thermal cycling test and the IFE condition is critical. Well modeled and instrumented tests are our goal.
• Long-term stability of interface is required. Is the temperature limits imposed by the current choice of materials and/or design too limiting for the thermal boundary conditions of the IFE first wall?
Do these temperature limits result in desired system efficiency?
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Development of Armor
Fabrication process and repair
He management Mech. & thermal fatigue testing
“Engineered Structures”Ablation
Underlying Structurebonding (especially ODS)
high cycle fatiguecreep rupture
Armor/Structure Thermomechanicsdesign and armor thickness
detailed structural analysiis
thermal fatigue and FCG
Structure/Coolant Interface
corrosion/mass transfer/coating
2003 2004 2005 2006 2007
Development of W/LAF : Phase 1 Effort and Milestones
!!
!
!
} !
scoping optimization scaling
!
!scoping & modeling optimization
! !
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Comparing Data from Different Exposure Experiments It is customary to correlate surface effects with fluence, but exposure
times and deposition depths vary across the different experiments This implies different stresses for the same fluence
If roughening is a thermomechanical phenomenon, then we must compare thermomechanical results across the experiments (peak surface temperature, peak surface temperature gradient, peak stress, plastic strain range, stress intensity factor, etc.)
We intend to use peak surface temperature, stress intensity factor, and plastic strain range for our comparisons
If the correlation across the experiments is consistent, then we will use this as the primary design criterion
It is important that we are able to deduce the damage mechanism as a result of this process
pulse
reft
TT1
Fixed fluence; surface heat
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
RHEPP Simulations (p, N+, N++)
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0 0.5 1 1.5 2 2.5
Fluence (J/cm2)
Ma
x S
urf
ac
e T
em
p (
C)
0
0.5
1
1.5
2
2.5
3
3.5
0 0.5 1 1.5 2 2.5
Fluence (J/cm2)
Su
rfac
e S
trai
nra
ng
e (%
)
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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY
Next Step: Fracture Comparisons
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25 um crack50 um crack75 um crack100 um crack150 um crack
Sre
ss I
nten
sity
(M
Pa
-m1
/2)
Crack spacing (m)