Nuclear Materials and Energy (Aug 2018)

Surface morphology of Tungsten-F82H after high-heat flux testing using plasma-arc lamps

  • K. Ibano,
  • A.S. Sabau,
  • K. Tokunaga,
  • M. Akiyoshi,
  • J.O. Kiggans,
  • C.R. Schaich,
  • Y. Katoh,
  • Y. Ueda

Journal volume & issue
Vol. 16
pp. 128 – 132

Abstract

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F82H reduced activation steel coated with vacuum plasma sprayed (VPS) tungsten is a candidate as a plasma facing material for main chamber components in future fusion reactors. Due to different coefficients of thermal expansion (CTE), significant thermal stresses are expected in these bimetallic materials. Thus, a major uncertainty in the performance of W/F82H components during the operation under high-heat fluxes is the effect of CTE mismatch. In this study, a high intensity plasma-arc lamp was used for high-heat flux cycling tests of W/F82H specimens. While no surface damage was observed for specimens tested for 100–200 cycles at a heat flux of 1.4 MW/m2 pulse when the backside surface temperature was maintained below 550 °C, significant cracking occurred at higher temperatures. A simple analytical model for bimetallic materials indicated that the stress in the VPS-W layer is likely to exceed its failure stress solely due to the bilayer thermal stress. A finite element analysis of the state of stress and deformation confirmed that a significant stress also would occur at the W surface due to the rigid-body like constraint imposed by the clamp, which can be the main cause of the cracking. Keywords: High-heat flux testing, Thermal stress, Bimetallic, Tungsten, Reduced activation steel