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

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Šestan,  Andreja
Structure and Nano-/ Micromechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;
Centre for Electron Microscopy and Microanalysis, Jožef Stefan Institute, Ljubljana, Slovenia;

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Sreekala,  Lekshmi
Computational Phase Studies, Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Zavašnik,  Janez
Nano-/ Micromechanics of Materials, Structure and Nano-/ Micromechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;
Centre for Electron Microscopy and Microanalysis, Jožef Stefan Institute, Jamova cesta 39, Ljubljana, Slovenia;

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Liebscher,  Christian
Advanced Transmission Electron Microscopy, Structure and Nano-/ Micromechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Dehm,  Gerhard
Structure and Nano-/ Micromechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Hickel,  Tilmann
Computational Phase Studies, Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;
Federal Institute for Materials Research and Testing (BAM), Richard-Willstätter-Straße 11, 12489, Berlin, Germany;

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Citation

Šestan, A., Sreekala, L., Markelj, S., Kelemen, M., Zavašnik, J., Liebscher, C., et al. (2022). Non-uniform He bubble formation in W/W2C composite: Experimental and ab-initio study. Acta Materialia, 226: 117608. doi:10.1016/j.actamat.2021.117608.


Cite as: https://hdl.handle.net/21.11116/0000-0009-F765-F
Abstract
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 4He+ ions at the fluence of 8 × 1016 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.