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

Applied Materials Today 2020 Volume 21, Article 100794

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.