LAUSR

Carbon fiber/carbon fiber‐based (C/C) composites have attracted significant attention in nuclear energy systems. Especially in molten salt reactors (MSRs) for usage of green energy, this material shows exceptional mechanical properties, high‐temperature resistance, and corrosion resistance. However, in molten salt environments, there is lack of structural failure modes of C/C composites under tensile loading. It is crucial to evaluate the rationality of structural design for in‐service MSR. Herein, synergistic effects of molten salt infiltration and thermal stability are explored on mechanical behaviors of C/C composites, employing acoustic emission (AE) and synchrotron radiation grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) to monitor corresponding structure and morphology evolution. AE identified four distinct damage modes of C/C composites: fiber‐matrix debonding, matrix cracking, individual fiber breakage, and fiber bundle fracture, corroborating by scanning electron microscopy, revealing microstructural reduction. Furthermore, the effects of high‐temperature thermal treatment and molten salt infiltration on the crystal structure of C/C composites are confirmed by in situ high‐temperature synchrotron‐based GIWAXS . These findings suggest that both treatments improve the corrosion resistance, mechanical integrity, and thermal stability of C/C composites.