Additive manufacturing of lead-free KNN by binder jetting

Additive manufacturing of lead-free piezoceramics is of great interest, given the large request of application-oriented designs with optimal performances and reduced material consumption. Binder Jetting (BJ) is an additive manufacturing technique potentially suited to the production of ceramic components, however the number of feasibility studies on BJ of piezoceramics is extremely limited and totally lacking in the case of sodium-potassium niobate (KNN). In this work, as-synthesised powders are employed in the BJ 3D printing process. Microstructural properties, such as porosity, grain size distributions, and phase composition are studied by SEM, XRD and MIP (Mercury Intrusion Porosimetry) and compared to die-pressed pellets. Analyses reveal considerable residual porosity (~40%) regardless of the printing parameters, with a weak preferential orientation parallel to the printing plane. The piezoelectric characterization demonstrates an outstanding d value of 80-90 pC N. Finally, Figures of Merits for the employment as porous piezoceramics in the direct mode are presented.