Manufacturing and characterization of a 3D printed lithium disilicate ceramic via robocasting: A pilot study.

Objective: The objective of this study was to manufacture and to evaluate the physico-mechanical properties of the Lithium disilicate (LiOSi) ceramic structures fabricated using additive manufacturing (3D printing).

Methods: LiOSi samples were divided into (n = 30/group): SM (subtractively manufactured) and AR (additive/robocasting). For the AR group, LiOSi powder was combined with ammonium polyacrylate, hydroxypropyl methylcellulose, and polyelectrolyte to create a colloidal gel, which was then used for printing. A digital CAD model of a disc was designed, and the G-code transferred to a custom built DIW 3D printer. The control group samples were prepared using pre-crystallized ceramic blocks, which were cut to obtain discs with same dimensions as the AR group. Disc-shaped specimens from both groups were crystallized at 840 °C. Mechanical properties were evaluated using biaxial flexural strength test (BFS) and Vickers hardness test. Representative fractographic images of the specimens were acquired using scanning electron microscopy (SEM) to analyze the fracture origin and crack propagation. Energy-dispersive X-ray spectroscopy (EDS) and attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) were used for chemical analysis, and X-ray diffractometry (XRD) was performed to analyze the crystalline phases.

Results: AR group yielded lower values of BFS (120.02 MPa ±33.91) and hardness (4.07 GPa ±0.30), relative to the SM group, (325.09 MPa ±63.98) and (5.63 GPa ±0.14), respectively. For EDS analysis, AR and SM groups showed similar elemental composition. In FTIR-ATR analysis, higher peaks referring to the crystalline structure were found for SM group. XRD analysis indicated a decreased formation of LiOSi from Lithium metasilicate (LiO-SiO) in the AM group. SEM micrographs showed a more porous microstructure associated with the 3D printed samples.

Significance: The viability of fabricating LiOSi ceramic constructs using the Robocasting technique was successful. However, the samples prepared using subtractive manufacturing presented higher mechanical properties compared to the 3D printed constructs. The difference in properties between the manufacturing may be correlated to the decreased formation of LiOSi crystals and higher degrees of porosity.