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The use of tungsten fiber-reinforced tungsten composites (Wf/W) has been demonstrated to significantly enhance the mechanical properties of tungsten (W) by incorporating W-fibers into the W-matrix. However, prior research has been restricted by the usage of single fiber-based textile fabrics, consisting of 150 µm warp and 50 µm weft filaments, with limited homogeneity, reproducibility, and mechanical properties in bulk structures due to the rigidity of the 150 µm W-fibers. To overcome this limitation, two novel textile preforms were developed utilizing radial braided W-yarns with 7 core and 16 sleeve filaments (R.B. 16 + 7), with a diameter of 25 µm each, as the warp material. In this study, bulk composites of two different fabric types were produced via a layer-by-layer CVD process, utilizing single 50 µm filaments (type 1) and R.B. 16 + 7 yarns (type 2) as weft materials. The produced composites were sectioned into KLST-type specimens based on DIN EN ISO 179-1:2000 using electrical discharge machining (EDM) and subjected to three-point bending tests. Both composites demonstrated enhanced mechanical properties with pseudo-ductile behavior at room temperature and withstood over 10,000 load cycles between 50–90% of their respective maximum load without sample fracture in three-point cyclic loading tests. Furthermore, a novel approach to predict the fatigue behavior of the material under cyclic loading was developed based on the high reproducibility of the composites produced, especially for the composite based on type 1. This approach provides a new benchmark for upscaling endeavors and may enable a better prediction of the service life of the produced components made of Wf/W in the future. In comparison, the composite based on fabric type 1 demonstrated superior results in manufacturing performance and mechanical properties. With a high relative average density (>97%), a high fiber volume fraction (14–17%), and a very homogeneous fiber distribution in the CVD-W matrix, type 1 shows a promising option to be further tested in high heat flux tests and to be potentially used as an alternative to currently used materials for the most stressed components of nuclear fusion reactors or other potential application fields such as concentrated solar power (CSP), aircraft turbines, the steel industry, quantum computing, or welding tools. Type 2 composites have a higher layer spacing compared to type 1, resulting in gaps within the matrix and less homogeneous material properties. While type 2 composites have demonstrated a notable enhancement over 150 µm fiber-based composites, they are not viable for industrial scale-up unlike type 1 composites. [ABSTRACT FROM AUTHOR]

To overcome the intrinsic brittleness of tungsten (W), a tungsten fiber-reinforced tungsten-composite material (Wf/W) is a possible solution. The introduction of energy dissipation mechanisms like fiber bridging or fiber pull-out by means of an engineered interface between fiber and matrix mitigate the brittleness of tungsten and lead to a pseudo-ductile material behaviour. The push-out test of single-fiber samples is an experimental method to investigate the properties of the interface between fiber and matrix of composite materials. It is widely used for the investigation of ceramic composites. This method was also used to investigate the debonding and frictional properties of the Er2O3 interface region between fiber and matrix of Wf/W single-fiber samples made by CVDand HIP-processes. In this article finite element calculations are used to get a better understanding of the processes acting in the interface during a push-out test of Wf/W. A detailed overview of the debonding progress and of the corresponding stress states of the interface during the different stages of the test is presented. In addition the sensitivity of the push-out behaviour regarding the different interface properties and the plastic flow curve of the tungsten fiber are investigated. [ABSTRACT FROM AUTHOR]

The effect of Ti3SiC2 coatings on the interfacial properties of SiC-fiber reinforced FeSiCr/SiC-filled polymethylsilsesquioxane-derived ceramics was investigated. An electrophoretically deposited Ti3SiC2 coating was prepared on the fiber/matrix interface. Interfacial parameters such as frictional sliding stress and fracture energy were derived from fiber push-out tests and correlated to the thickness of the Ti3SiC2 layer. Compared to uncoated fibers, the Ti3SiC2 interlayer gives rise for a pronounced enhance of interface shear strength, coefficient of friction, and sliding strength but a reduced fracture energy. With increasing Ti3SiC2 coating thickness, thermal mismatch-induced residual compressive stresses at the fiber/matrix interface tend to decrease significantly. [ABSTRACT FROM AUTHOR]

A new coaxial plasma generator has been developed. It provides hypervelocity plasma pulses for aerosol formation purposes. Plasma ignition and acceleration inside the plasma generator strongly determine subsequent particle formation and growth processes and are therefore intended to be studied within the frame of this work. The first part of the paper describes the experimental setup. Special emphasis is drawn to the plasma generator, which basically consists of a coaxial electrode assembly with two high pressure gas injections to supply different reactive and/or inert gases. The plasma is initiated and sustained by the surge current of a capacitor bank (60 μF with charging voltage up to 15 kV). The discharge characteristics (typical several tens of kiloamperes) can be modified by a pulse forming variable inductance and by the settings of the gas injection (e.g., type of gas, pressure of gas, trigger delay). The second part of the paper deals with the experimental investigation of the plasma jet itself. Since plasma ignition and acceleration inside the electrode assembly initiate the whole process chain-including particle formation-special focus is laid on measuring plasma parameters. Standard electrical measurements of current and arc voltage are performed to investigate the energy coupling. Short time photography provides information on arc generation and on acceleration of the jet. Optical emission spectroscopy is carried out to gain information on the composition on the plasma. It permits to derive a first estimation of plasma temperature and of electron density. [ABSTRACT FROM AUTHOR]