Lightweight protection for vehicles, aircraft, and personnel requires materials that can resist local damage and absorb energy without imposing excessive weight. Alumina is attractive for this purpose because of its high hardness and relatively low density, but brittle fracture limits its ability to sustain loading after damage. Combining alumina with a continuous metallic phase can improve load transfer and energy dissipation. In practice, weak ceramic–metal interfaces, residual pores, and limited control over scaffold geometry often prevent these benefits from being fully realized. A three-dimensional interpenetrating network distributes contact between the two phases throughout the component and helps both phases carry load after local ceramic damage. Introducing a high melting point alloy into a designed ceramic structure presents an additional manufacturing challenge.
We fabricated Al₂O₃-FeCoCrNiMn high-entropy alloy (HEA) interpenetrating composites by combining digital light processing (DLP) printing, gel casting, and vacuum hot-press sintering. Reentrant honeycomb skeletons were printed from photosensitive slurries containing 82 wt.% total powders, with HEA additions of 10-30 wt.% relative to the combined ceramic and metal powder mass. An aqueous HEA slurry was then introduced into the designed pores and fixed by gelation. Thermogravimetric measurements guided the removal of resin and gel-derived organic components. The filled structures underwent staged debinding and sintering at 1300 °C for 2 h under 20 MPa. HEA was therefore present both within the printed skeleton and in the filling region, allowing the two regions to connect during sintering.
HEA addition increased light attenuation in the slurry. As the HEA content increased from 10 to 30 wt.%, the fitted penetration depth decreased from 35.69 to 33.89 μm, while the critical exposure energy increased from 0.79 to 1.79 mJ/cm². Increasing the light intensity enabled printing at a layer thickness of 50 μm. Measurements showed that cell lengths and widths were smaller than designed and that walls were thicker, indicating overcuring and the need for dimensional compensation.
Under low vacuum, HEA particles filled defects in the ceramic skeleton and reduced separation at the ceramic/metal boundary. Electron microscopy, elemental mapping, and line scans showed that Cr extended into the alumina-rich region more clearly than the other alloying elements. X-ray diffraction supported the formation of (Al,Cr)₂O₃ in the interfacial region. For the skeleton containing 20 wt.% HEA, changing the sintering vacuum from 10^-2 to 10^-6 Pa increased the relative density from 85.72±1.17% to 95.37±0.69%. The original honeycomb boundaries became less distinct as interdiffusion progressed, and the hardness of the skeleton and interfacial regions increased.
The high-vacuum composite reached a compressive strength of 1218 MPa and a volumetric energy absorption of 7.68 MJ/m³. A nonarchitected control prepared with the same composition and sintering conditions reached 743 MPa and 4.57 MJ/m³, respectively. Fracture observations showed crack deflection near HEA particles, local HEA pullout, and stronger ceramic–metal connections. Increased brittleness under high vacuum was associated with metal volatilization and changes in phase composition. These results show that dense ceramic–metal interfaces can improve compressive performance, while metal retention remains important when developing this route for lightweight protective structures.

Lightweight protective structures,Ceramic–metal interpenetrating composites,High-entropy alloys,Energy absorption