Thermal fatigue testing of purified tungsten and plasma sprayed tungsten coatings

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Thermal fatigue testing of purified tungsten and
plasma sprayed tungsten coatings

• X. Liu, L. Yang , F. Zhang , Z. Xu Southwestern
  Institute of Physics, P.O. Box 432, Chengdu
  610041, Sichuan, China

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Outline

• Introduction
• Previous results
• Present experiment
• Results (1, thermal response. 2, IPS coatings. 3,
  VPS coatings. 4, purified tungsten)
• Conclusions

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Introduction

• Tungsten is envisaged as the promising PFM,
  divertor tiles of ITER, W-Cu joint by HIP as
  module.
• At current stage tungsten coated on carbon is
  widely used.
• The results of IPP indicated that VPS-W coatings
  could sustain 1000 cycles but IPS-W coatings
  showed located cracks by 400 cycles under 15.8
  MW/m2 heat load.(Fusion Technology, 32 (1997)
  263.)
• Good thermal shock resistant capability of W-Cu
  joint by HIP

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Previous experiment
Recrystallization temp.
 
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Previous experiment
Table1 Experimental results of VPS-W/CFC coating
(0.5 mm in thickness) by cyclic heat loads
 
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Present experiment

• Sample PM-W, VPS-W/CFC, IPS-W/G, W/Cu, W/Cu (T)
• 10?10?5 mm
• Electron beam
• Gaussian-like spatial distribution, irradiation
  area 15.7 mm2
• Energy 60 keV.
• Power density 35 MW/M2, pulse/interval length
  3/40 s.
• 85 MW/M2,
  pulse/interval length 3/60 s.
• Surface temperature thermocouple, IR-Camera.

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Cross-section micrographs of W coatings
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Results
Thermal response of PM-W and W coatings
The time evoluation of the electric current and
surface temperature of samples
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Results
Surface temperature of IPS-W coatings versus
cycles
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Results
Limited cracks
Crack-arresting mechanism
SEM image of cross-section of IPS-W/G after 300
cycles
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Results
Without transition layer (100 cycles)
With transition layer (200 cycles)
The cross sections of IPS-W/Cu coatings after
about 100 and 200 cycles, respectively.
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Results
SEM images of VPS-W/CFC after 1000 cycles
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Results
SEM images of PM-W after 1000 cycles
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Results under higher load
Irradiated region
Unirradiated region
Surface images of VPS-W/CFC after 60 cycles under
85 MW/m2.
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Results under higher load
Surface SEM photographs of PM-W after 60 cycles
under 85 MW/m2.
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Summary
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Conclusions

• Surface temperature depends on heat load and the
  thermophysical properties of coatings.
• Under electron beam heat load of 35 MW/m2 and 3s
  pulse duration, IPS-W/Cu coatings were failure by
  detachment after 110 and 270 cycles for without
  and with transition layers, respectively. IPS-W/G
  coating was failure by limited cracks due to the
  formation of brittle tungsten carbides after
  about 300 cycles.
• VPS-W/CFC and PM-W can sustain 1000 cycles under
  the heat load above. Only recrystallization was
  found on the surface of PM-W.
• Cracks were not observed on the surface of
  VPS-W/CFC and PM-W after 60 cycles under higher
  heat load with Gassian-like distribution.

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Next work
Why the electron beam of Kyushu University (it is
so called spot-like beam) can induced cracks, why
not for uniform electron beam, even Gassian-like
distribution electron beam?