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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1. Introduction The utilization of high-performance fibers, such as carbon, silicon carbide (SiC), and advanced ceramics, is imperative in various industrial sectors, including aerospace, automotive, energy, and electrochemistry. Their capacity to endure extreme thermal and chemical environments without substantial deterioration of mechanical properties renders them indispensable in high-temperature structural applications. However, these fibers also present critical limitations. Carbon fibers, while exhibiting remarkable mechanical robustness, are susceptible to oxidation when exposed to temperatures exceeding 1300°C. Ceramic fibers, such as SiC or alumina, possess thermal stability; however, they are characterized by brittleness, cost, and manufacturing complexity. Presently, their large-scale industrial production is predominantly concentrated in the USA and Japan. In order to ensure European access to strategic materials and enhance performance under extreme conditions, there is a necessity to develop new fiber technologies that exhibit a combination of high mechanical stability with enhanced oxidation and corrosion resistance. Concurrently, these materials must be cost-effective and environmentally responsible to facilitate large-scale industrial adoption. In this context, the MAXCarbon hybrid fiber has been developed at RWTH Aachen. MAXCarbon integrates the mechanical strength of carbon fibers with the environmental resistance of MAX phases, forming a unique hybrid material. Utilizing a patented reactive synthesis process, commercially available carbon fibers are transformed into a hybrid fiber with a Ti₃SiC₂ boundary layer, thereby providing both oxidation resistance and mechanical durability. This paper presents the development approach, current state of the art, and the synthesis strategy for MAXCarbon fibers, positioning them as a next-generation reinforcement solution for demanding high-temperature applications. 2. State of the Art 2.1. High-Performance Reinforcement Fibres Advanced fibers, including carbon and SiC, demonstrate exceptional strength-to-weight ratios, thermal stability, and chemical resistance. However, their performance under oxidative environments is limited. Oxide fibers, such as alumina or mullite, utilized in oxide matrix composites, exhibit chemical resistance but are susceptible to creep at elevated temperatures. Non-oxide systems, such as C(f)/C or SiC(f)/SiC, offer excellent creep resistance but are highly vulnerable to oxidation. To address these challenges, the utilization of protective coating systems, such as oxide-based environmental barrier coatings (EBCs), has emerged as a common practice. However, the implementation of these systems can introduce processing complexities and interfacial challenges. 2.2. MAX Phases as Functional Materials MAX phases (Mₙ₊₁AXₙ, where M = early transition metal, A = A - group element, X = C and/or N) have recently attracted attention for high-temperature applications. With their unique nano-lamellar structure, MAX phases combine ceramic-like properties—such as high stiffness, creep resistance, and oxidation stability—with metallic attributes including good thermal conductivity, machinability, and thermal shock resistance. Ti₃SiC₂, in particular, forms a stable, self- healing SiO₂ layer under oxidative conditions, offering protection without complete degradation. Recent studies have investigated MAX phases as protective coatings and matrices in composites, yet challenges remain in preserving mechanical integrity when employed as primary structural materials. 2.3. Towards Hybrid Fibre Systems Preliminary research at RWTH Aachen demonstrated that while MAX phases are not ideally suited as composite matrices, they hold strong potential as protective surface layers. Building on this, the MAXCarbon concept was developed: a hybrid fibre system in which a MAX-phase layer is synthesized directly onto carbon fibres. This approach eliminates the need for external coatings, potentially mitigating thermal mismatch issues while leveraging the intrinsic oxidation resistance and defect-healing capabilities of MAX phases.