Cryogenic 3D printing of damage tolerant hierarchical porous ceramics

Fabricating damage tolerant porous ceramics with efficient energy absorption and impact-resistant capability has been a challenge because of the brittle nature of ceramics. In nature, mineralized tissues or organisms such as cuttle bones and diatoms have been evolved with hierarchical pores to overcome this difficulty. A bioinspired design of ceramic lattice structure with pores at multiple length-scales, ranging from few nanometers to hundreds of micrometers, is proposed in the present work. These ceramic lattices with hierarchical porous structures were successfully fabricated via cryogenic 3D printing. The printed ceramic lattices showed an unprecedented long plateau strain (~60%) and a specific energy absorption of ~10 kJ/kg with a porosity of ~90%. The resulting energy absorption capability was comparable with most composites and metals. This was attributed to the delayed destruction of the lattice structure, as well as the gradual collapse of pores at multiple length-scales. Similar trends have also been observed under split Hopkinson pressure bar tests, indicating excellent energy absorption under high strain-rate impacts. The proposed 3D printing technique was also demonstrated to apply to other functional materials, such as silicon carbide, barium titanate, hydroxyapatite and even titanium alloy, and thus opens up new possibilities for fabricating bioinspired hierarchical porous structures.