Damage evolution and domain-level anisotropy in metal/ceramic composites exhibiting lamellar microstructures

Aluminium/alumina composites based on ceramic preforms prepared via freeze-casting are examined. Domains composed of alternating but also interpenetrating ceramic and metallic lamellae are observed. Single-domain samples were extracted from composites processed under different conditions. In situ scanning electron microscopy analyses were carried out to investigate the damage evolution under compressive load. The composite is strong and brittle when loaded along directions parallel to the freezing direction. When compressed in other directions, the behavior is controlled by the soft metal. The plastic anisotropy is less pronounced than theoretical predictions for laminates, which is explained by the presence of bridges between the ceramic lamellae. Coating the preform with Cu or Cu ₂O prior to melt infiltration reduces the compressive strengths of the composites. Transmission electron microscopy analysis shows that even in the case of a Cu coating a Cu ₂O layer is formed during processing, weakening the interface and preventing the dissolution of Cu in the aluminium alloy.