SnO₂-Ag composites with high thermal cycling stability created by Ag infiltration of 3D ink-extruded SnO₂ microlattices

SnO₂-Ag composites with designed architectures with sub-millimeter feature sizes can provide enhanced functionality in electrical applications. SnO₂-Ag composites consisting of a ceramic SnO₂ micro-lattice filled with metallic Ag are created via a hybrid additive manufacturing method. The multistep process includes: (i) 3D extrusion printing of 0/90° cross-ply micro-lattices from SnO₂-7%CuO nanoparticle-loaded ink; (ii) thermal treatment in air to burn the binders and sinter struts of the SnO₂ micro-lattice to ~94% relative density; (iii) Ag melt infiltration of channels of sintered micro-lattices. Densification of the SnO₂ struts during air-sintering is accelerated by CuO liquid phase forming at 1100°C. During the subsequent Ag infiltration, CuO acts as wetting agent between Ag and SnO₂, with liquid Ag infiltrating the open channels of the SnO₂ lattice and the micropores in the SnO₂ struts left from incomplete sintering, thus forming a dense composite. Infiltration time and temperature influence the structure of the SnO₂-Ag interface and the distribution of CuO within the Ag matrix. The resulting anisotropic electrical conductivity of the composite is controlled by the low-conductivity SnO₂ architecture, as determined via finite element (FE) analysis. 3D ink-extruded and infiltrated SnO₂-Ag composites show good structural stability and maintain high conductivity upon thermal shock cycles between 850 and 20°C. FE analysis reveals that thermal expansion/contraction mismatch stresses between the ceramic and metallic phases are mostly concentrated at the contact area between filaments in the SnO₂ microlattices, and that plastic deformation accumulating in the soft Ag phase accommodates these mismatch stresses upon thermal cycling.