Lead zirconate titanate (PZT) piezoelectric ceramics are widely used in electronic components. With the continuous development of intelligent, integrated and lightweight piezoelectric devices, the shape and structure of piezoelectric ceramic components become more complex. 3D printing technology has potential advantages in the personalized manufacturing of complex ceramic parts, especially the fused deposition modeling (FDM) method, which has the advantages of high efficiency, low cost, and wide material adaptability. This paper was to prepare PZT piezoelectric ceramics by FDM. In addition, the process optimization, printing performance, sintering behavior, and electrical properties were also investigated.

A PZT powder with an average particle size of 2.85 μm was used. An organic binder was composed of 58% paraffin wax (PW, purity: 99% in mass fraction, the same below), 5% stearic acid (SA, 98%), 20% Polyethylene (PE, 99%), and 17% ethylene-vinyl acetate copolymer (EVA, 98%). The ceramic powder and organic binder were thoroughly mixed by a double-roller mixing machine at 130 ℃ for 60 min, and then crushed into granules of less than 5 mm. The solid loading of the feedstock was set to 83%, 85%, 87%, and 89%. A commercial extrusion printer (UP-R200, Shenzhen Uprise 3D Technology Co., Ltd., China) with the extrusion nozzle diameter of 0.5 mm, and the layer thickness of 0.2 mm for FDM was used in this study. The printing condition was printing temperature of 120 ℃, print speed of 40 mm/s, and printing platform temperature of 85 ℃. Some complex shaped parts like ring array, rectangular array, and thin-walled cylindrical structures were printed. The printed green bodies were firstly placed in kerosene for solvent debinding at 40 ℃ for 20 h and then dried in an oven at 40 ℃ for 15 h. The dried parts were heated at 600 ℃ for 2 h. After thermal debinding, the samples were put into a crucible with a lid, buried on PZT powder, and sintered in the furnace at 1 100 ℃ for 2 h. The PZT ceramics coated with silver electrodes were polarized in an electric field of 2.5 kV/mm in silicone oil at 120 ℃ for 20 min. The phase composition and structure of the sample were determined by a model D8 Advance X-ray diffractometer (XRD, Germany) with detect angles ranging from 10° to 80°. The rheological properties of the printing consumables were tested at 180 ℃ by a model Rosand RH2000 capillary rheometer (Malvern Co., UK). The microstructures of samples were analyzed by a model JSM-6700F field emission scanning electron microscope (SEM, JEOL Co., Japan). The density of the samples was measured by a drainage method. The dielectric constant ε_r and dielectric loss δ were measured by a model Agilent-4294A impedance analyzer (USA). The ferroelectric properties were analyzed by a model aix ACCT-TF Analyzer 2000 ferroelectric tester (Germany). The piezoelectric constant of the polarized sample was measured by a model ZJ-3AN quasi-static d₃₃ meter (Institute of Acoustics, Chinese Academy of Sciences, China).

At a constant solid loading, the shear viscosity of the feedstock at 180 ℃ decreases with the increase of shear rate, and has obvious shear thinning characteristics, which is beneficial to the extrusion process. At a constant shear rate, the higher the solid loading is, the higher the measured shear viscosity will be. At a shear rate of 100 s^-1, the shear viscosity is 30.30, 45.07, 47.08 Pa·s and 655.21 Pa·s respectively as the solid loading increases. Annular arrays with a wall thickness of 1 mm, rectangular arrays with an element spacing of 0.25 mm, and annular thin-wall blank samples with an inclination angle of 30° are printed, indicating that the prepared feedstock has a good printing performance. The SEM images show that the prepared PZT ceramic samples have a good interlayer bonding. Each layer is straight, uniform and continuous. After debinding and sintering, the interior of the material is uniform and dense without obvious pore defects, which shows that PZT ceramics with a good interlayer bonding can be obtained by the FDM method. The density of both green body and sintered body increases with the increase of solid loading, and the density of sintered body increases from 7.55 g/cm³ to 7.84 g/cm³. The results show that the sintering shrinkage in the Z direction is higher than that in the X-Y direction. The SEM images of PZT samples at each stage show that the two-step debinding process of solvent debinding + thermal debinding is beneficial to eliminating organic binders without causing defects. PZT piezoelectric ceramic sheets with a diameter of 17.5 mm and a thickness of 1.35 mm are prepared using a feedstock with a solid loading of 87%. The electrical property analysis indicates that the Curie temperature reaches 295℃, the coercive electric field E is 7.57 kV/cm, the remnant polarization P_r reaches 3.66 μC/cm², and the piezoelectric constant d₃₃ reaches 316 pC/N.

The prepared feedstock with a high solid content and a low viscosity exhibited a typical shear thinning rheology and an excellent printing performance. A PZT spherical shell structure without support was prepared. The PZT ceramic samples had good interlayer bonding and no interlayer cracks. The density of PZT ceramics increased with increasing the solid loading. At a solid loading of 87%, the density of PZT ceramic reached 7.82 g/cm³, and the piezoelectric constant d₃₃ was 316 pC/N. This study provided an effective approach for the preparation of complex structure PZT piezoelectric ceramics.