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W-Steel Interfacial Bond Strength, & MC-Simulation of IEC He-Implantation

W-Steel Interfacial Bond Strength, & MC-Simulation of IEC He-Implantation. Shahram Sharafat * , with significant contributions from A. Hyoungil, A. Takahashi 1 , J. El-Awady, Q. Hu, J. Qua, G. Romanowski 2 , and N. Ghoniem, and collaborative interactions with

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W-Steel Interfacial Bond Strength, & MC-Simulation of IEC He-Implantation

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  1. W-Steel Interfacial Bond Strength, &MC-Simulation of IEC He-Implantation Shahram Sharafat*, with significant contributions from A. Hyoungil, A. Takahashi1, J. El-Awady, Q. Hu, J. Qua, G. Romanowski2, and N. Ghoniem, and collaborative interactions with G. Kulcinski3, R. Radel3, S. Gulobov2, N. Parikh4, and L. Snead2 Mechanical and Aerospace Engineering Department University of California Los Angeles 1 Tokyo University of Science 2 Oak Ridge National Laboratory 3University of Wisconsin – Madison 4University of North Carolina at Chapel Hill 15th High Average Power Laser Workshop General Atomics San Diego, CA Aug. 9 – 10, 2006 *shahrams@ucla.edu This work was supported by the US Navy/Naval Research Laboratories through a grant with UCLA.

  2. OUTLINE • W – Steel Interface Bond Strength • Review HIP’d W-F82H • Report on VPS-W • Monte Carlo Simulation of IEC Results • Issues for Low-Energy He Implantation • Survey of Low-E He Implantation • KMC Simulation Results

  3. Photodiode voltage is used to determine the Displacement profile of the coating surface Al Layer Coating Coating surface velocity is calculated by differentiating the displacement profile Nd:YAG Laser 1064 nm Compression The stress can then be calculated using: s = ½(r c v) Finally, tensile failure stress failure is then evaluated using FEM Tension • Al layer melts and rapidly expands • Launching a compressive stress waves through substrate into film layer • Compressive waves are reflected as tensile waves from free surface • If tensile stress is sufficient interface failure will occur. SiO2 Substrate The Laser Spallation: Determine Interface Bond Strength Density and Elastic Properties of both coating and substrate are required to determine accurate failure stresses

  4. D = 20 mm 1.1 mm W coating ~50 um thick F82H substrate Time: } Interfacial Crack 1050 MPa Bond Strength:Depends on Coating Elastic Properties & Density sbond 450 MPa W (HIP) F82H Since Elastic properties of the coating depend on processing in a statistical manner  Predicted interfacial strengths will have statistical variations HIP’d W-F82H Sample (ITER, JAEA) • Hot Isostatic Pressure (HIP) bonded Tungsten to F82H Sample from ITER Development JAEA (Japan) Reported 14th HAPL

  5. TEST MATRIX: VPS W-Coated Steel Samples VPS-W Test Matrix (PPSI/ORNL) • Vacuum Plasma Sprayed (VPS) samples supplied by PPI (S. O’Dell). • W-Coatings were polished to ~50 mm thickness at ORNL(G. Romanoski)

  6. Powder Feed Substrate Plasma Flame Plasma Spray Coating Process • Powder melts in Plasma Flame • Molten droplets are acceleratedtowards substrate • Droplets solidify on substrate • A new layer of molten droplets solidifies Modified from Ghansen Comp. In Phys. COMPUTERS IN PHYSICS, VOL. 12, NO. 1, JAN/FEB 1998

  7. Plasma Spray Coating Process • Powder melts in Plasma Flame • Molten droplets are acceleratedtowards substrate • Droplets solidify on substrate • A new layer of molten droplets solidifies Powder Feed Substrate Plasma Flame Modified from COMPUTERS IN PHYSICS, VOL. 12, NO. 1, JAN/FEB 1998

  8. Plasma Sprayed Micro-composite Thermal Barrier Coatings (TBC)* Al2O3 Al2O3 ZrO2 ZrO2 Substrate – Interface Porosity Pore Pore Interface Pore Interface Pore Substrate 500 X *S. Sharafat, Vacuum 65 (2002) 415 Interface between Substrate & Coating is Porous Simulated Plasma Sprayed Coating Substrate – Interface Porosity Substrate Substrate

  9. Nano-porousVPS-W Deposits1 1S. O’Dell, PPI 2004 Factors Influencing Coating Bond Strengths • Elastic properties of the coating depends on processing: • HIP’ing results in high density (r) high Young’s modulus (E) • Plasma Spray results in low r and low E • Substrate/Coating interface topography: • HIP’ing results in high fraction of interface coverage • Plasma Spray shows reduction of interface coverage • Present analysis based on: • Published VPS-W E*: EVPS = 54 GPa (ESolid= 410 GPa) • Coating Density Range: 80% – 60% • Interface Coverage Range: 100% – 40 % We need coating properties (E, r) and interface topography *Matejicek, 2005; **Estimate

  10. 80% Dense W-Coating 60% Dense W-Coating VPS-Sample #02:r= 11,548 kg/m3 E = 27 GPa * ELaser = 160.6 mJ Preliminary Interfacial Strengths of VPS-W VPS-Sample #02:r= 15,397 kg/m3 E = 54 GPa * ELaser = 160.6 mJ VPS-W Coating Delamination Stress*: 140 MPa – 616 MPa HIP-W Interface Cracking Stress** : 450 MPa – 1050 MPa *Based on 3VPS-W samples and uncertain coating material properties and interface topgraphy **Based on 1 HIP-W sample uncertain E.

  11. 2 mm HIP (avg.) Example of “Popped”VPS-W Coating 80% Dense Coating No Interface Porosity 60% Dense Coating IP: Interface Porosity VPS-W Coating Failure Example of Complete Coating Delamination VPS-W Coating Surface Bonding of Plasma Sprayed Coating is weaker than that of the HIP’d Coatings: May require development of Interface Layer

  12. Future Work • Elastic properties of coatings need to be measured including: • Densities, Young’s modulus, and Interface Bond Coverage • Determine minimum stress for ONSET of interface cracks in VPS-W (reported results are for complete failure of coatings) • Cross section and micrograph tested VPS samples (# 01, 02, 05)  ORNL • Test remaining samples (# 03 – 04 & 06 – 09) • Present/Publish at the TOFE 17(ANS, Nov 13-14, Albuquerque NM)

  13. OUTLINE • W – Steel Interface Bond Strength • HIP’d W-F82H Sample (ITER, JAEA) • VPS W-Steel Sample (PPS/ORNL) • Monte Carlo Simulation of IEC Results • Issues for Low-Energy He-Implantation • Survey of Low-E He Implantation • Simulation Results

  14. Issues for Low-Energy He Implantation • Results can not be explained by conventional rate theory models because pores sizes are too large (X10) and densities are tool low. • Speculations regarding effects of sputtering on surface: • Sputtering increases with decreasing incidence angle (avalanche) • Surface Erosion Via Ion-Sputtering*: From initial ripples morphology to a rough morphology • Surface Temperatures are too low for rapid and large bubble formation (usually occurs above ~0.6 TM; for W: 730 oC ~ 0.26 TM) • Need to measure/calculate the residual trapped Helium. * R. Cuerno, H. A. Makse, S. Tomassone, S. Harrington, and H. E. Stanley, Stochastic Model for Surface Erosion via Ion-Sputtering: Dynamical Evolution from Ripple Morphology to Rough Morphology, Phys. Rev. Lett. 75, 4464-4476 (1995);

  15. OUTLINE • W – Steel Interface Bond Strength • HIP’d W-F82H Sample (ITER, JAEA) • VPS W-Steel Sample (PPS/ORNL) • Monte Carlo Simulation of IEC Results • Issues for Low-Energy He-Implantation • Survey of Low-E He Implantation • Simulation Results

  16. Low Energy He Implantation of Cu* Copper: 30 keV He 1.2-2.4x1016/cm2 annealed 973 K for 1800 s. He range ~130 nm; peak 1.68 at.%. Pinhole Diamavg ~ 150 nm (predicted ~ 14 nm) … surprising result that after annealing at 973 K, 80% of the helium was released and surface pinholes seen, even though the average bubble size predicted from migration and coalescence theory was 14 nm …* *Evans, Nuclear Instruments and Methods in Physics Research B 217 (2004) 276–280

  17. Survey of Low Energy He Implanted Tungsten Survey of Low Energy He Implanted Tungsten

  18. Tungsten 10 – 30 eV Helium (Nishijima, 2004) • Low Energy Helium (~ 10 to 30 eV) on PM Tungsten; high dose 2.6 x 1027 He/m2 X 5000 • Cross section of sample W1 which shows holes or passage to neighboring bubbles. D. Nishijima et al. / Journal of Nuclear Materials 329–333 (2004) 1029–1033

  19. (a) 2mm (b) Tungsten 19 keV Helium (Tokunaga, 2004) • SEM images of surface (a) and cross section (b) taken from the sample irradiated to 3.3 x 1023 He/m2 at the peak temperature of 2600 ℃. • The energy of He is 19 keV. He beam flux and heat flux at the beam center is 2.0 x 1021 He/m2s and 6.0 MW/m2, respectively. Beam duration is 3.0 -3.9 s and interval of beam shot start is 30 s. K. Tokunaga et al. / Journal of Nuclear Materials 329–333 (2004) 757–760

  20. 1 mm 1 mm 1 mm IEC Results (Cipiti & Kulcinski, 2004) : 730 °C 2.2x1015 He/cm2-s 30 min. 990 °C 8.8x1015 He/cm2-s 7.5 min. 1160 °C 2.6x1016 He/cm2-s 2.5 min. Steady State: 40 KeV He 510184He/cm2 Temperature Pore Size Pore Density dave ~15 nm dave ~50 nm dave ~150 nm

  21. Pore Diameter vs. Temperature Pore Diameter vs. Time IEC Results (Cipiti & Kulcinski, 2004) : Time to Pore Temperature 730 C 1160 C 150 s 1800 s

  22. OUTLINE • W – Steel Interface Bond Strength • HIP’d W-F82H Sample (ITER, JAEA) • VPS W-Steel Sample (PPS/ORNL) • Monte Carlo Simulation of IEC Results • Issues for Low-Energy He-Implantaion • Survey of Low-E He Implantation • Simulation Results

  23. MC Simulation of IEC He-Implantation • Migration and Coalescence (M&C) of He-bubbles is based on Brownian bubble motion • Initial bubble density and avg. bubble radius from HEROS code • Differentiate between near surface and bulk processes by calculating He-pressure based on: – Ideal gas law (near surface) – Hard-sphere model (bulk material)

  24. InitializeModel Calculate diffusion probability of He-bubble Sum probabilities: Diffusion, Coalescence & Implantation for each He Examine one event (Diffusion of a bubble or Implantation) Jump with constant distance Grow He-bubbles by implantation Check Coalescence tn+1 = tn + Dt Surface diffusion rate MC – Calculation Procedure Diffusion Migration: Bubble diffusion rate Es: Activation energy, 2.5eV* D0: Pre-expon 1.25x10-2cm2/s Coalescence: Instantaneous Equilibrium Size: Growth by Implantation: R: Uniform random number (0:1) *Evans, 2004

  25. Temperature Bubble Density He-Implantation Init. Radius Simulation Volume730 C 10171/cm3 2.2 x 1015 1/cm2-s 0.5 nm 0.2 x 1.0 x 1 mm3 990 C 1015 1/cm3 8.8 x 1015 1/cm2-s 1.0 nm 0.2 x 2.5 x 1 mm31160 C 1014 1/cm3 2.6 x 1016 1/cm2-s 1.5 nm 0.2 x 5.0 x 1 mm3 GaussianDensity Distribution Front View Side View He Helium 40 keV He – W: Range: 1.6 nm Straddle: 0.63 nm 1 mm 0.2 mm KMC Model for the 730 oC IEC Case: Simulation Volume

  26. Helium Evolution of Bubble Size for the 730 oC IEC Case (~2000 s): Front View ( 1 mm) Side View ( 0.2 mm) Bubble Color:Red = Matrix BubbleBlue= Surface Pore

  27. Time Sequence of Pore Evolution (730 oC IEC) 3e-4 s 1.5 s 68 s 383 s 562 s 2000 s

  28. T = 730 oC t = 1800 s 990 oC 450 s 1160 oC 150 s Pore Diameter vs. Time KMC Simulation of ICE Experiments 1 mm 2.5 mm 5 mm

  29. IEC IEC IEC IEC Surface Pore Evolution • KMC simulates the trend of surface pore size and density

  30. Bubble Size Near Surface vs Bulk * • 1000 appm He Implanted in Ni at RT. • Uniform He implantation using degrader Al-foil (28 MeV He) • Annealing time: 0.5 – 1.5 hr Near Surface Abundance of Near Surface Vacancies promotes rapid and large bubble growth Bulk *CHERNIKOV, JNM 1989

  31. Sub-Surface Break-Away Swelling He He Avg. Bubble Radius Surface Pore Formation Sub-Surface Break Away Swelling Contribution • BREAK-AWAY Swelling (very rapid growth of bubbles) occurs at the subsurface • However, because the bubbles bisect the surface the swelling is stopped by venting He. • Time to BREAK-AWAY swelling DECREASES with higher Temps.

  32. Probable Explanation of IEC Results • Abundance of near surface vacancies allow bubbles to grow rapidly to equilibrium size:  Large bubbles & low He-pressure • Near the surface, Migration & Coalescence (M&C) plus rapid growth results in super-size bubbles. • Super-large bubbles bisect the surface, thus providing a probable explanation for surface deformation and large subsurface bubbles. • A network of deep interconnecting surface pores is rapidly set up which results in drastic topographical changes of the surface

  33. Abstracts Submitted to TOFE 17 • “Surface Roughening Mechanisms for Tungsten Exposed to Laser, Ion, and X-ray Pulses”Michael Andersen and Nasr M. Ghoniem • “Modeling Space-Time Dependent Helium Bubble Evolution in Tungsten Armor under IFE Conditions”Q. Hu, S. Sharafat, and N. Ghoniem • “Measurement of Interface Bond Strength between Tungsten Coatings and Steel Substrates for HAPL FW Armor”Jaafar El-Awady, Jennifer Quang, Shahram Sharafat, and Nasr Ghoniem • “MC Simulation of Tungsten Surface Pores Formed by Low-Energy Helium Implantation”Akiyuki Takahashi, Shahram Sharafat, Nasr Ghoniem, J. Kulcinski, and R. Radel

  34. Backup Slides

  35. VPS Interface Bond Strengths *Matejicek, 2005; **Estimated EW = 410 GPa No Interface Pores r = 15,397 kg/m3 EW = 54 GPa No Interface Pores r = 15,397 kg/m3

  36. Laser Energy HIP Coating:1050 mJ to Onset of Failure 2.00 1.50 1.00 0.50 0 Compr. Stress to Failure (GPa) VPS Coating:167 mJ to Complete Delamination Example of Complete Coating Delamination VPS-W Coating Failure VPS-W Coating Surface 2 mm Example of “Popped”VPS-W Coating Bonding of Plasma Sprayed Coating is weaker than that of the HIP’d Coating

  37. Plasma Sprayed Tungsten Coating Material Properties • H. You, T. Hoschen, S. Lindig, “Determination of elastic modulus and residual stress of plasma-sprayed tungsten coating on steel substrate,” J. Nucl. Mater. 348 (2006) 94–101 • Jirı Matejıcek ,Yoshie Koza, Vladimır Weinzettl, “Plasma sprayed tungsten-based coatings and their performance under fusion relevant conditions,” Fus. Eng. Des. 75–79 (2005) 395–399 • “The aim of this work is to measure Youngs modulus of a plasma-sprayed thick porous tungsten coating deposited on a steel (F82H) substrate.” [1]

  38. Low Energy He on W Experiments: Nishijima(2004) Tokitani (2005) Iwakiri (2003) Tokunaga (2003)

  39. GOAL of STUDY • IEC implants Low-Energy (<110 keV) Helium in Tungsten • All forms of W examined at 730 °C - 1150 °C showed extensive surface deformation (EHe: 30-40 keV). • Both, steady state or pulsed operation show deformation: • Steady state @ 6 mA ≈ 1014/cm2s; • Pulsed mode @ 10Hz, 1 ms, 60 mA ≈ 1013/cm2 per pulse OBJECTIVES: • Provide a potential explanation for the development of MASSIVE Surface Pores (~10 X predicted He-bubble size). • If possible, provide mitigating measures against these MASSIVE surface deformations.

  40. SEM image (High temp./Low fluence) 2μm 20mm Slide from: K. Tokunagaa ICFRM-11, Dec. 7-12, 2003, Kyoto, Japan For HAPL: R=6.5m Chamber: ~8x1022He/m2/day ~2600℃、1.7x 1022 He/m2 3.5s/30s( 8S) 18.7 keV, 6.7x 1020 He/m2s WF-6(20x20x0.1mm) • The color of surface becomes to be white from metallic sliver color by the irradiation up to ～1022 He/m2. • Fine uneven morphology and small holes are observed on the surface.

  41. SEM image (High temp./High fluence) ～2600℃、 3.3x 1023 He/m2 3.5s/30s( 145S) 18.7 keV, 6.7x 1020 He/m2s WF-2(20x20x0.1mm) Slide from: K. Tokunagaa ICFRM-11, Dec. 7-12, 2003, Kyoto, Japan For HAPL: 3.3x1023 He/m2 in ~4.5 day 2μm 20mm • When fluence is beyond ～1023 He/m2, the color of surface becomes to be black • The surface is modified resulting in a fine uneven morphology and holes with a diameter of about 50 nm are observed on the surface. 1μm

  42. SEM image of cross section Surface 20μm 1μm ~2600℃、3.3x 1023 He/m2 3.5s/30s( 145S), 18.7 keV, 6.7x 1020 He/m2s, WF-2(20x20x0.1mm) K. Tokunagaa ICFRM-11 Dec. 7-12, 2003 Kyoto Japan • Grain growth by re-crystallization occurs. • Many horn-like protuberances with a width of about 300 nm and a length of about 1 μm are observed at the surface. In addition, He bubbles with a diameter of about 50 -500 nm are observed near surface. • The surface modification is considered to be formed by the He bubbles and their coalescence, the migration of He bubbles near surface.

  43. Low E-He on Copper UKAEA FUS 499 EURATOM/UKAEA Fusion Kinetics of bubble growth and point defect migration in metals J.H. Evans October 2003

  44. Low E-He on Copper (Evans, 2004) Evans, Nuclear Instruments and Methods in Physics Research B 217 (2004) 276–280

  45. New HEROs code gives information about pore sizes: R ~ 100 nm R ~ 50 nm R ~ 16 nm

  46. Bubble Density …(corrected!) 4E15 5E14 6E13

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