Ni-Al2O3 nacre-like composites through hot-pressing of freeze-cast foams

A multi-step process is developed to create a nacre-like ceramic/metal composite. First, a slurry of Ni-coated alumina platelets and NiO nano-particles is directionally freeze-cast and the ice is sublimed, creating a foam with aligned lamellar walls containing the two solid phases. Second, the foam is sintered under hydrogen to reduce the NiO phases to metallic Ni micro-particles. Third, hot pressing densifies both the channels between the aligned walls and some of the porosity within the walls, resulting in a brick-and-mortar composite with partially-aligned alumina platelets and 30 vol% Ni. Evidence of various toughening mechanisms - crack deflection, branching and bridging, as well as metal plasticity - is observed during three-point bending tests of double-edge notched beams.