Powder development of lead-free piezoceramics material for additive manufacturing technology

In the last decades, 3D printing additive manufacturing has attracted the attention of the scientific and engineering community. In fact, these new technologies have emerged as one of the most interesting technologies for designing and production of innovative materials. Additive manufacturing 3D printing of different types of materials (from metals and plastics to ceramic) has allowed a versatility in design and realization never seen before. Today, 3D printing is one of the most promising technology able to change production paradigms and transform the manufacturing industry. The production process starts from a 3D model CAD design file with the consequent conversion to STL format (stereolitography), which consists in the object slicing into virtual layers printable in 2D, with different techniques, by the 3D printers. Binder Jetting 3D printing is one of the emerging additive manufacturing technologies, in which the object is printed with the aid of a chemical binder and then heat-treated for densification. With respect to ceramic materials and more precisely piezoelectrics, additive manufacturing technology offers new possibilities of part designing and thus innovative applications. For instance, just think on the next internet of things (IoT) industrial revolution and the new needs and challenges that we will have to face from the manufacturing point of view. Piezoelectric materials are the basis for a large number of devices including sensors (pressure, force and vibration), accelerometers, actuators and transducers but only few of them are used in applications as piezoelectric devices. Nowadays, the most important piezoelectric material applied in the practice is Lead Zirconate Titanate (PZT). In fact, this ferroelectric ceramic material guarantees excellent performances thanks to its high piezoelectric properties and high Curie temperature. Nevertheless, Pb represents a serious hazard for human health leading scientific community to develop alternative lead-free piezoelectric materials. Among the others, Potassium-Sodium Niobate (KNN) system is one of the most promising, due to its high piezoelectric constant and high Curie temperature although its piezoelectric properties are not still comparable with those of PZT. The aim of the PhD project was to study the 3D printing feasibility of lead-free piezo-electric ceramic powder using binder jetting technology. This challenging target was achieved through a dual pathway: lead-free piezoelectric powder synthesis and study of the most important parameters in binder jetting 3D technology. First, K0.5Na0.5NbO3 (KNN) was synthetized by solid-state reaction through mechano-chemical activation and sol-gel method. Second, stainless steel (316L) and alumina (Al2O3) were used as powder testing materials for studying binder jetting 3D printer technology and its fundamental parameters. Finally, a KNN sample was 3D printed, poled and tested obtaining a working piezoelectric disc proving the usability of binder jetting technology even for advanced ceramics.