Interpenetrating phase composite (IPC) of PEEK-infiltrated alumina gyroid structure: microstructure and mechanical analysis

The Interpenetrating Phase Composite (IPC) of a PEEK-infiltrated alumina gyroid structure combines the stiffness of a continuous ceramic porous structure with the damage tolerance of a polymer phase, providing lightweight structural performance. Here, alumina (Al 2 O 3 ) gyroid structures fabricated by digital light processing (DLP) stereolithography were characterised using scanning electron microscopy (SEM) and X-ray micro-computed tomography (micro-CT) to assess their geometry and pore-network continuity. A custom-designed hot-pressing system was developed to infiltrate dense PEEK into alumina gyroids. Parameter screening identified dominant defect mechanisms (gas-related porosity without pressure, polymer overflow under prolonged pressing, and flow heterogeneity when pressing before thermal stabilisation) and defined an optimised cycle (375 °C, 2.5 MPa, 10 min dwell, 3 min pressing). Dense PEEK exhibited a homogeneous morphology, no detectable internal voids within the micro-CT resolution, and a compressive response consistent with commercial PEEK. Applying the same cycle to the gyroid structure achieved near-complete infiltration (infiltration ratio >99% by micro-CT) and a continuous polymer-ceramic interface. During compression, alumina gyroids exhibited early brittle collapse and serrated post-fracture crushing, whereas the IPC PEEK/Al 2 O 3 displayed stable stress build-up up to 50% strain. Full-field digital image correlation (DIC) confirmed that the IPC PEEK/Al 2 O 3 stabilised the deformation field relative to alumina gyroid, with further improvements expected from enhanced infiltration homogeneity and interface integrity.