Controlling the structure and mechanical properties of porous B4C ceramics with unidirectionally aligned channels using sintering additives

To date, surprisingly few studies about the structure-property correlations in porous B 4 C ceramics with unidirectionally aligned channels have been reported. In this study, bimodally lamellar porous B 4 C ceramics aligned along the freezing direction were produced via freeze casting method using Al 2 O 3 –Y 2 O 3 as the sintering additive. The porosity, pore size distribution , morphology, and compressive strength could be effectively tailored by the addition of Al 2 O 3 –Y 2 O 3 . The volume shrinkage ranged from 1.66 to 2.42%, much lower than the reported values of porous ceramics . A low-melting eutectic liquid was observed to exert significant effects on the sintering and strength of the porous B 4 C ceramics. By varying the contents of the Al 2 O 3 –Y 2 O 3 sintering additive, the preforms displayed a rather high porosity of 78.71–82.01%, a low closed porosity of 0.37–0.86% and an excellent compressive strength of 1.76–3.28 MPa. Meanwhile, the wavelength, lamellar thickness, and pore diameter decreased as the Al 2 O 3 –Y 2 O 3 content increased. Adding Al 2 O 3 –Y 2 O 3 can tailor the structures of porous B 4 C ceramics prepared by freeze casting, which is of great significance for the preforms with low shrinkage, low density, high porosity, and satisfactory mechanical performance.