4.7 Article

Non-uniform He bubble formation in W/W2C composite: Experimental and ab-initio study

Journal

ACTA MATERIALIA
Volume 226, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2021.117608

Keywords

tungsten; ditungsten carbide; FAST; helium implantation; density functional theory

Funding

  1. EUROfusion education & training scheme
  2. Euratom research and training programme 2014-2018 and 2019-2020 [633053]
  3. Slovenian Research Agency [10 00-17-0106, P20087-2, J2-8165, P2-0405-5]
  4. Deutscher Akademischer Austauschdienst [BI-DE/19-20-002, 57450885]
  5. MaxPlanck partner group High performance materials
  6. European Union [823717 -ESTEEM3]
  7. Slovenian Research Agency

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This study investigates the effect of helium implantation on the microstructure evolution of tungsten-tungsten carbide composites. It reveals the formation of monomodal helium bubbles in tungsten and larger helium bubbles at the tungsten-carbide interface. Density functional theory calculations suggest that helium migration and accumulation in the composite are influenced by the binding of helium atoms in clusters.
Tungsten-tungsten carbide (W/W2C) composites are considered as possible structural materials for future nuclear fusion reactors. Here, we report on the effect of helium (He) implantation on microstructure evolution of polycrystalline W/W2C composite consolidated by field-assisted sintering technique (FAST), homogenously implanted at room temperature with 1 MeV He-4(+) ions at the fluence of 8 x 10(16) ions cm(-2) and annealed at 1873 K for 20 minutes. Samples were analysed by scanning and transmission electron microscopy to study the presence and size of He bubbles. Monomodal He bubbles in W (30-80 nm) are limited to point defects and grain boundaries, with a considerable void denuded zone (150 nm). Bubbles do not form in W2C, but at the W|W2C interface and are considerably larger (200-400 nm). The experimental observations on He behaviour and migration in W and W2C were assessed by density functional theory (DFT) calculations, suggesting He migration and accumulation in the composite are determined by the effective He-He binding in clusters, which will give rise to decohesion. In the presence of He clusters, the decohesion of bulk W into free surfaces is energetically highly favourable but not sufficient in the W2C; hence bubbles are only observed in W grains and interfaces and not within bulk W2C. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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