Morphology-driven Cu gradient distribution induces varied anti-ablation performance in C/C–ZrC composites

Conventional carbon/carbon-zirconium carbide (C/C–ZrC) composites, though promising for ultra-high-temperature applications, often struggle to balance active cooling and passive oxidation protection, as uncontrolled metal redistribution during service leads to structural instability and premature ablation failure. In this study, copper (Cu) gradient-modified C/C–ZrC composites were fabricated via reactive melt infiltration (RMI) using a layered powder-laying strategy with Cu powders of distinct morphologies to achieve programmable Cu distribution. Two opposite gradient architectures were designed: a Cu-decreasing (ZCI) and a Cu-increasing (ZCS) configuration along the infiltration direction. Microstructural and ablation analyses revealed that the Cu gradient markedly altered the infiltration-reaction pathway and ZrC grain evolution. In ZCS prepared with spherical Cu powders, a dissolution-recipitation mechanism generated fine spherical ZrC grains and a Cu-rich basal layer that sustained heat absorption and conduction, forming a dense bilayer ZrO₂ structure that effectively suppressed oxygen diffusion. Benefiting from this architecture, the ZCS composite exhibited the lowest mass ablation rate of −0.39 mg/s under a 4.18 MW/m² oxy-acetylene flame for 30 s, along with superior surface integrity and thermal stability. This work establishes a direct mechanistic link between Cu gradient architecture and ablation resistance, providing a controllable design paradigm for next-generation active-passive synergistic thermal protection systems.