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 B4C ceramics with unidirectionally aligned channels have been reported. In this study, bimodally lamellar porous B4C ceramics aligned along the freezing direction were produced via freeze casting method using Al2O3-Y2O3 as the sintering additive. The porosity, pore size distribution, morphology, and compressive strength could be effectively tailored by the addition of Al2O3-Y2O3. 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 B4C ceramics. By varying the contents of the Al2O3-Y2O3 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 Al2O3-Y2O3 content increased. Adding Al2O3-Y2O3 can tailor the structures of porous B4C ceramics prepared by freeze casting, which is of great significance for the preforms with low shrinkage, low density, high porosity, and satisfactory mechanical performance.