A novel experimental approach to quantitatively evaluate the printability of inks in 3D printing using two criteria

Material extrusion enables deposition of filaments with designed structures, and such sub-categories as direct ink writing brings increasing possibilities for the fabrication of multi-material and complex-shaped high-performance fully dense components. It has been well understood that the critical requirement for successful direct ink writing is the printability of inks. To address this challenge, a novel experimental approach that takes advantages of the developed rotational rheology test and capillary rheology test, has been proposed to evaluate the printability of inks that were prepared from the water-based slurries of Al2O3, Y2O3 and Nd2O3 ceramic powders according to the stoichiometry ratio of Y3Al5O12/Y2.982Nd0.018Al5O12 with different additions of hydroxyethyl cellulose. The parameters including the low strain value (0.4%) within the linear viscoelastic region and the high shear rate (85 s-1) of the inks have been determined by the amplitude sweep test and theoretical analysis. Two criteria - storage modulus and extrusion stress - have been first introduced to assess the success of inks applicable in direct ink writing. Using these criteria, the excellent qualities of printable inks have been quantitatively defined with the values in the range of 2300–6000 Pa and 401–430 Pa, respectively. Moreover, results of capillary extrusion experiments have provided a useful insight into the technology development of suppressing the appearance of bubbles. Finally, the correctness of the proposed approach has been further examined by another transparent ceramic ink, and the in-line transmittance (84.4%) of the transparent ceramic at 1064 nm that is close to the theoretical value has been observed.