RHEPP Tungsten Update

RHEPP Tungsten Update

Tim RenkSandia National Laboratories

Beam Applications & Initiatives Department

HAPL Program WorkshopAtlanta, GA

February 6, 2004

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy under contract DE-AC04-94AL85000.

Supported by NRL by the HAPL program by DOE NNSA DP

• Polished W exposed to 400 shots N beam: 1.0 < fluence < 3.7 J/cm2

• Room Temp (RT) exposure• Roughening occurs above 1.25 J/cm2,

consistent with single-shot reflectometer roughening threshold

• Powder Met Mo (one point at 2.5 J/cm2 ): roughness stays near unexposed value

• Above threshold, roughening is a severe function of fluence. Maximum Ra exceeds 22 µm, with P-V height above 70 µm

400 shot Map N shots on Tungsten (Room Temperature):Roughening only above threshold

1

10

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Ra W Ra W untreatRa Mo

Fluence (J.cm2)

R a (micr

ons)

Pulsed Power Sciences, Sandia National LaboratoriesTJR 11/25/03

W (Powder Met) roughening: SEM imagesas function of shot number: 60 to 1000X

(N 250X @ 2.5 J/cm2)(N 60X @ 6 J/cm2) He 450X @ 1-1.3 J/cm2)

(N 600X @ 4.0 J/cm2)

(N 1000X @ 2.5 J/cm2)


60-shot exposure of PM W (500C) @ 6 J/cm2: Resolidification from 2-3 µm depth, consistent with

SIM modeling, no cracking

In depth grains (N 1000X @ 2.5 J/cm2)


Hi-Mag image, showing uniform single-xtal (right) and disordered single-xtal (left)

Simulation results:Melt Depth: 2.3 µmMelt Duration: 627 nsMaxTemp: 6648K I.e. above ablation threshold (for 65 ns)Ra = 0.4-0.6 µm

Ablation step: 1-2 µm(165 - 330Å/pulse)

XTEM of 60X-treated PM W (right) show no cracking in depth

Bright-Field TEM image


TEM image from 5 µm depth

• Polished Powder Met W exposed to 100 shots N beam @ 2.25 J/cm2 ave /pulse, ~ melting temperature at surface. No melt layer observed.

• 600°C exposure• Sample cracking horizontally/vertically down to 10 µm depth• Suspect fatigue-cracking

FIB-XTEM of 1000-pulse W at 2.25 J/cm2 (ave):Deep horizontal/vertical cracking without melt

Pulsed Power Sciences, Sandia National Laboratories

TJR 11/25/03

Title: (MML_Logo.eps) Creator: Near-surface 5 - 10 µm depth

FIB-STEM of 1000-pulse W at 2.25 J/cm2 (ave):No melting or recrystallization evident

Pulsed Power Sciences, Sandia National Laboratories

TJR 11/25/03

Title: (MML_Logo.eps) Creator: Near-surface

5 - 10 µm depth

Simulation results:Melt Depth: 0.2 µmMelt Duration: 91 nsMaxTemp: 3752K (from 600C)Ra = 2.3 - 4.5 µm

We may have an alternative ‘Foam’ Supplier

Source: Center for Collaborative Research/Research Center for Advanced Science and technology

(CCR/RCAST) Prof. Tatsuhiko Aizawa

• Type1: W-25Re alloy, cell-structured No carbon, only W-25Re alloyColumn thickness: 50-100 µmPore: < 50 µm

• Type 2: W-25Re Alloy, honeycomb No carbon, only alloycolumn thickness: 100 µm

• Prof. Aizawa to visit SNL March 22, 2004


Summary

• Tungsten: surface roughening excessive (PowderMet), with fatigue cracking below surface maybe even worse. Mitigating: CVD/SingXtal, alloying with Re, heating. Cracking looks like enough to compromise performance as armor coating.

• Roughening occurs over hundreds of shots. Topology may stabilize for W by 1000 shots, looks to increase for other metals beyond this.

• Below the roughening threshold (1.25 J/cm2), W may be topologically stable to repeated ion exposure.

• No W recrystallization below melting temp appears to take place• Both 60X-6J/cm2 and 1000X-2.5J/cm2 sample response consistent

with SIM modeling• Next: treatment of W on SiC, extended treatment of various

samples to 2,000 shots


RHEPP Tungsten Update

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