comparison of hip and vps tungsten coating behavior using laser spallation jaafar el-awady with...
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Comparison of HIP and VPS Tungsten Comparison of HIP and VPS Tungsten Coating Behavior Using Laser SpallationCoating Behavior Using Laser Spallation
Jaafar El-Awadywith significant contributions from
H. Kim, J. Quan, S. Sharafat, V. Gupta, G. Romanowski1 and N. Ghoniem
Mechanical and Aerospace Engineering DepartmentUniversity of California Los Angeles
1Oak Ridge National Laboratory
16th High Average Power Laser WorkshopPrinceton Plasma Physics Laboratory
Princeton, NJAug. 12 – 13, 2006
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
Outline
• The Laser Spallation Technique
• HIP’d W-F82H measurements
• Plasma Spray W-F82H measurements
• Dynamic vs. Static Loading
• Fracture Mechanics Calculations
• Conclusion
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
The Laser Spallation Technique
SiO2
Substrate
Nd:YAG Laser1064 nm
Coating
Tension
Co
mp
ress
ion
Experimental Layout
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
HIP’d W-F82H Joint
1.1 mm
W coatingF82H substrate
D = 20 mm
50 m
HIP (Hot Isostatic Pressure):
W-F82H joint is fabricated with HIP conditions of 1243K, 143MPa and 2 hour holding time.
Akiba and Hirose (JAEA)
Time
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
HIPPED W-F82H Bond Strength Measurements
F82H
W
F82H
W
Laser Fluence: 1708 mJ
W
F82H
Delemination
Crack nucleation
Laser Fluence
Failure
613 mJNo
Failure
1065 mJNo
Failure
1329 mJ
Some Crack
generating at the
interface
1577 mJSevere
Damage
1708 mJSevere
Damage
1737 mJSevere
Damage
100m
100m
F82H
W
Laser Fluence: 1577 mJ
F82H
W
Laser Fluence effect on the failure of the bond
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
HIPPED W-F82H Bond Strength Measurements
1050
450
BOND
BOND
MPa (80% dense W)
MPa (Bulk W properties)
95% dense W propertiesW bulk properties80% dense W properties 100m
F82H
W
Laser Fluence: 1329 mJ
W
F82H
Interface Cracking
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
VPS-W coated F82H
Powder Feed
Plasma Flame
Substrate
Example of “Complete Delamination”of the VPS-W Coating1. Powder melts in Plasma Flame
2. Molten droplets are accelerated towards substrate
3. Droplets solidify on substrate4. A new layer of molten droplets
solidifies
Porosities
Example of “Popped”VPS-W Coating
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
VPS-W coated F82H Failure Strength
Laser Fluence: 75.0 KJ/m2 Laser Fluence: 110.4 KJ/m2
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
VPS-W coated F82H Failure Strength
150 200 250 300
-1000
-800
-600
-400
-200
0
200
400
600
800
Str
ess
(MP
a)
Time (ns)
WVPS
properties W
pure properties
550
450
BOND
BOND
MPa (80% dense W (VPS))
MPa (Bulk W properties)
Static test results (Greuner et. al. 2005): Failure occurs in the coating and not at the interfaceThe failure strength is estimated to be 25~30 MPa
Failure strength of the coating is:
at 1/3 of the thickness
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
WHY? Dynamic vs. Static Loading
• The material undergoes a ductile-to-brittle transition as the strain rate is increased.
• The yield stress increases significantly and the work-hardening rate decreased as the strain rate increases.
• In dynamic loading the fracture toughness is independent of any plastic deformation and geometry effects on the contrary with static loading.
annealed
90% increase10-3s-1
3*103s-1
*Dümmer et. al. 1998
105~108 s-1?
~~
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
Back of the Envelop Calculations of the Required Stress for Fracture (Fracture Mechanics)
• The stress required to propagation a crack in a brittle material can be calculated using an elastic strain energy model:
• For a 1 m initial size crack in an 80% dense coating:
a
E
aaE
8
42
22
300frac80% dense W: (Analytic result)MPa
E: modulus of elasticity = specific surface energy a = one half the length of an internal crack
550frac (Experimental result)MPa
Dec. 13th, 2006 Jaafar A. El-AwadyHAPL meetingPrinceton, NJ
Conclusions
• We have successfully tested VPS and HIP’d Tungsten coated ferritic steel samples
• HIP’d samples fail at the W-F82H interface while VPS samples fail in the W-coating itself
• Failure strength in HIP’d samples is found to be about twice that in VPS samples
• For VPS W-F82H the static strength is 25~30 MPa while the dynamic strength is about 450~550 MPa
• Fracture mechanics gives similar results to our current experimental results
• We are proposing the use of Fracture toughness instead of tensile properties