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Tungsten (W) is a promising candidate material for the plasma-facing components in future fusion reactors. However, it has issues regarding the intrinsic brittleness as well as operational embrittlement. Tungsten fiber reinforced tungsten (Wf/W) composites overcome these issues by using extrinsic toughening mechanisms. Due to neutron irradiation and high-temperature recrystallization during fusion operation, the ductility of the fibers may degrade over a long period of service. Therefore, it is necessary to investigate the fracture behavior of Wf/W composites with brittle fibers. In the present work, the tungsten fibers were embrittled by carbonization. Subsequently, the continuous brittle Wf/W composite with yttrium oxide (Y2O3) interface was fabricated by the field-assisted sintering technology process. The microstructure of the prepared Wf/W composites was characterized. The fracture behavior and toughening mechanisms were discussed in detail based on the experimental results of 3-point bending tests and the corresponding finite element simulation. The composites show a pseudo-ductile fracture behavior. Cracks are hindered and deflected by the de-bonded fiber-matrix interface. The extrinsic toughening mechanisms of interface de-bonding, crack bridging, and fiber pull-out are active. This indicates the reinforcement concept still works even though all components in the Wf/W are brittle.

The composite material tungsten fiber-reinforced tungsten (Wf/W) addresses the brittleness of tungsten by extrinsic toughening through introduction of energy dissipation mechanisms. These mechanisms allow the release of stress peaks and thus improve the materials resistance against crack growth. Wf/W samples produced via chemical vapor infiltration (CVI) indeed show higher toughness in mechanical tests than pure tungsten. By utilizing powder metallurgy (PM) one could benefit from available industrialized approaches for composite production and alloying routes. In this contribution the PM method of hot isostatic pressing (HIP) is used to produce Wf/W samples. A variety of measurements were conducted to verify the operation of the expected toughening mechanisms in HIP Wf/W composites. The interface debonding behavior was investigated in push-out tests. In addition, the mechanical properties of the matrix were investigated, in order to deepen the understanding of the complex interaction between the sample preparation and the resulting mechanical properties of the composite material. First HIP Wf/W single-fiber samples feature a compact matrix with densities of more than 99% of the theoretical density of tungsten. Scanning electron microscopy (SEM) analysis further demonstrates an intact interface with indentations of powder particles at the interface-matrix boundary. First push-out tests indicate that the interface was damaged by HIPing.