Comparison of HIP and VPS Tungsten Coating Behavior Using Laser Spallation Jaafar El-Awady with significant contributions from H. Kim, J. Quan, S. Sharafat,

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