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

• Published in: Nuclear materials and energy 2018-08, Vol.16 (C), p.128-132
• Main Authors: Ibano, K., Sabau, A.S., Tokunaga, K., Akiyoshi, M., Kiggans, J.O., Schaich, C.R., Katoh, Y., Ueda, Y.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Bimetallic; High-heat flux testing; MATERIALS SCIENCE; Reduced activation steel; Thermal stress; Tungsten
• ISSN: 2352-1791; 2352-1791
• DOI: 10.1016/j.nme.2018.06.015

•VPS coated tungsten F82H steel specimens were tested by repeating high heat flux (HHF).•Cracking was observed for a specimen which exceeded 600 °C during HHF tests.•The bimetallic thermal stress due to the difference of thermal expansion could exceed the failure strength of F82H.•A FEM analysis indicated a strong stress by a sample clamp can be a major cause of the cracking. 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.