Crack bridging in as-fabricated and embrittled tungsten single fibre-reinforced tungsten composites shown by a novel in-situ high energy synchrotron tomography bending test

Due to a unique property combination, tungsten is a promising candidate for highly loaded areas in advanced fusion reactors. However, tungsten suffers from its inherent brittleness at low temperature and its susceptibility to operational embrittlement. In tungsten fibre-reinforced tungsten composites (W-f/W) the toughness is enhanced by extrinsic mechanisms of energy dissipation allowing toughening in the absence of any plasticity. In the here presented work active extrinsic mechanisms of toughening were shown on a model system for as-fabricated and embrittled samples. The mechanisms were evaluated by means of mechanical bending tests in combination with high energy synchrotron tomography. For that a novel 4-point bending test for the in-situ use with high energy synchrotron tomography was developed. Despite the high X-ray attenuation in tungsten a sufficiently high resolution was achieved and clear images of crack extension and crack-fibre interaction were obtained. Several active toughening mechanisms were observed and quantified for the as-fabricated state and, in the case of a stable fibre-matrix interface, also in the embrittled state. The toughening contribution of the individual mechanism was estimated using the mechanical test results and compared with analytically derived values. Using the determined values a high toughening was estimated for as-fabricated and for embrittled bulk Wf/W. The results give hope that the composite material will retain toughness even if experiencing operational embrittlement when used in a future fusion reactor.