Toward Integrated Thermal–Tribological Design Framework of WFAAM Functionally Graded Metals for Hypersonic Applications

Hypersonic aerospace components experience multiple extreme conditions (up to 3000°C) due to repetitive and abrupt thermo-mechanical shocks, severe aero-thermal heating and repeated thermal gradients. Existing traditional monolithic alloys or coating solutions are unable to meet such concurrent requirements due to interfacial deterioration and limited thermal and wear protection. Development of functionally graded materials through the wire-feed arc additive manufacturing process (WFAAM) become established as a viable large-scale (deposition rate 3-5 kg/h) solution to mitigate critical challenges through tailored compositions and properties. Existing WFAAM-fabricated multi-material systems have emerged that primarily address thermal management and tribological performance as distinct design goals. Therefore, there is limited research on integrated frameworks due to their concurrent incorporation. This study addresses a hybrid critical review and conceptual design approach for future simulation-driven optimization. It introduces an innovative design framework, the WFAAM-driven FGM system, aimed specifically at hypersonic applications. Significant limitations and knowledge deficiencies are examined critically in existing WFAAM-based FGM studies, with a focus on tribology, alloy development and thermal barrier structures. The major aims are (i) to analyze WFAAM-derived FGMs for thermal regulation, specifically on wear and surface degradation mechanisms, and (ii) to analyze graded thermal transition layers to reduce heat flux and thermal shock durability, which is estimated to reach 25-40% in extreme environments. Particular emphasis is placed on the absence of design approaches that balance dilution control, metallurgical compatibility and functional property gradients in high-temperature gradients and shocks. A structured design framework is proposed to develop WFAAM-driven functional gradient metallic systems for extreme performance in hypersonic applications without depending on distinct coating interfaces. This study underscores the capability of WFAAM-fabricated FGMs to combine thermal, mechanical and tribological properties in one structural multifunctional material, suitable for extreme hypersonic aerospace conditions.