Influence of sintering temperature and CVI time on mechanical properties of 3D-printed alumina ceramics

Recently, complex-shaped ceramic components are being fabricated by using 3D printing and subsequent chemical vapor infiltration (CVI) processes. The results indicate that both sintering temperature and CVI time significantly influence mechanical properties of 3D-printed ceramic components. At the sintering temperature of <1500 °C, the pores are reduced during sintering and the ceramic components exhibit significant shrinkage, whereas, at the sintering temperature of 1500 °C, the shape of grains is changed from spherical to cylindrical, which increases the pore size and expands the ceramic parts. Moreover, the ceramic parts are severely densified after sintering at >1500 °C due to high sintering temperature. As 3D-printed ceramic parts render low strength after sintering at 1500 °C, the subsequent CVI process is carried out to increase the flexural strength (2 times) by introducing SiC, and in turn, improving the density of ceramics. One should note that the CVI-induced SiC is deposited on the surface of Al₂O₃ grains, improving the strength of the ceramics. The proposed sintering mechanism consists of the deformation of grains and subsequent densification, leading to the deformation of ceramic components.