PSI - Issue 77

Fabian Jung et al. / Procedia Structural Integrity 77 (2026) 308–315 Fabian Jung / Structural Integrity Procedia 00 (2026) 000–000

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3.1. Microstructural and Phase Verification via Radiological Examination The successful synthesis of the Ti₃SiC₂ MAX -phase within the hybrid fibre semi-finished products was verified at the Institute of Mineral Engineering (GHI), RWTH Aachen University. Scanning electron microscopy (SEM) using a Zeiss GeminiSEM 500, combined with energy-dispersive X-ray spectroscopy (EDX, Bruker D8 Advance), was performed at an acceleration voltage of 15 kV in high-vacuum mode. SEM imaging revealed the lamellar microstructure typical of Ti₃SiC₂, characterised by elongated, leaf -like grains. This morphology is a well-documented feature of MAX-phase materials and demonstrates the targeted conversion of the fibre surface. The complementary EDX spectra confirmed the elemental composition (Ti, Si, and C) in stoichiometric ratios consistent with Ti₃SiC₂, while no significant secondary phases or impurities were observed. These findings indicate a successful and phase-pure conversion of carbon fibres into MAXCarbon hybrid fibres. 3.2. Mechanical Characterization The mechanical performance of the samples was evaluated through single filament tensile tests, which were conducted on isolated hybrid fiber filaments. Filaments with diameters of 7 ± 0.3 µm were extracted from converted fiber strands and tested on a FAVIMAT+ system (Textechno Herbert Stein GmbH & Co. KG, Mönchengladbach) under standard laboratory conditions (21 °C, 65% relative humidity). Tests were conducted at a gauge length of 20 millimeters and a crosshead speed of 2 millimeters per minute. A series of n = 50 fibers was analyzed, yielding a fiber fineness of 0.66 dtex and a density of 1.77 g/cm3. These results initially offered insights into the mechanical properties of MAXCarbon and facilitated a comparison with standard carbon fibers. 3.3. Thermal Stability Assessment Thermal Stability Assessment A series of preliminary trials were conducted in order to provide evidence regarding the oxidation resistance of MAXCarbon fibers. A heating microscope setup (Figure 3.1) was utilized to compare a converted MAXCarbon hybrid nonwoven with an unmodified carbon nonwoven. Both samples were exposed to a furnace treatment in ambient air. The MAXCarbon fibers demonstrated a substantial enhancement in resistance to oxidative degradation, thereby substantiating the protective effect of the Ti₃SiC₂ interfacial layer. While these results validate the fundamental concept, further investigation is necessary. Specifically, extended investigations on continuous fibre textiles (woven and non-crimp fabrics) are currently ongoing. 3.4. Process Optimization and Limitations The synthesis of MAXCarbon fibres is highly dependent on the control of process parameters such as temperature, heating rate, and gas atmosphere composition. Small deviations can lead to incomplete formation of Ti₃SiC₂ or the development of secondary phases that compromise performance. Furthermore, the mismatch in thermal expansion between the carbon core and the Ti₃SiC₂ boundary layer requires precise tuning of processing conditions to avoid interfacial stresses and fibre damage. While preliminary results confirm the feasibility of producing MAXCarbon with high phase purity, scaling the process to continuous fibre textiles introduces additional challenges, including uniform coating thickness, defect control, and reproducibility across large volumes. Ongoing optimisation efforts therefore focus on refining synthesis conditions, improving scalability, and integrating the process into textile-relevant formats suitable for industrial applications.