Comparison of HIP and VPS Tungsten Coating Behavior Using Laser Spallation Jaafar El-Awady with significant contributions from H. Kim, J. Quan, S. Sharafat, V. Gupta, G. Romanowski 1 and N. Ghoniem Mechanical and Aerospace Engineering Department University of California Los Angeles 1 Oak Ridge National Laboratory 16 th High Average Power Laser Workshop Princeton Plasma Physics Laboratory Princeton, NJ Aug. 12 – 13, 2006

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady Outline The Laser Spallation Technique HIP’d W-F82H measurements Plasma Spray W-F82H measurements Dynamic vs. Static Loading Fracture Mechanics Calculations Conclusion

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady The Laser Spallation Technique SiO 2 Substrate Nd:YAG Laser 1064 nm Coating Tension Compression Experimental Layout

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady HIP’d W-F82H Joint 1.1 mm W coating F82H 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

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady HIPPED W-F82H Bond Strength Measurements F82H W W Laser Fluence: 1708 mJ W F82H Delemination Crack nucleation Laser Fluence Failure 613 mJ No Failure 1065 mJ No Failure 1329 mJ Some Crack generatin g at the interface 1577 mJ Severe Damage 1708 mJ Severe Damage 1737 mJ Severe Damage 100  m F82H W Laser Fluence: 1577 mJ F82H W Laser Fluence effect on the failure of the bond

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady HIPPED W-F82H Bond Strength Measurements MPa (80% dense W) MPa (Bulk W properties) 95% dense W properties W bulk properties 80% dense W properties 100  m F82H W Laser Fluence: 1329 mJ W F82H Interface Cracking

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady VPS-W coated F82H Powder Feed Plasma Flame Substrate Example of “Complete Delamination” of the VPS-W Coating 1.Powder melts in Plasma Flame 2.Molten droplets are accelerated towards substrate 3.Droplets solidify on substrate 4.A new layer of molten droplets solidifies Porosities Example of “Popped” VPS-W Coating

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady VPS-W coated F82H Failure Strength Laser Fluence: 75.0 KJ/m 2 Laser Fluence: KJ/m 2

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady VPS-W coated F82H Failure Strength 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 interface The failure strength is estimated to be 25~30 MPa Failure strength of the coating is: at 1/3 of the thickness

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady 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% increase s -1 3*10 3 s -1 *Dümmer et. al ~10 8 s -1 ? ~ ~

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady 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: 80% dense W:(Analytic result) MPa E: modulus of elasticity  = specific surface energy a = one half the length of an internal crack (Experimental result) MPa

HAPL meeting Princeton, NJ Dec. 13 th, 2006 Jaafar A. El-Awady 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