In situ formation of LaAl11O18 rodlike particles in ZTA ceramics and effect on the mechanical properties

A small amount of sintering aids, which contain MgO, kaolin and La2O3, was introduced into ZTA ceramics to realize densification at low temperature and to obtain a fine-grained microstructure. On the base of this, different amounts of La2O3 were added and rodlike LaAl11O18 was formed in situ due to its anisotropic growth habit during sintering. The effects of sintering temperature and the amount of rodlike LaAl11O18 were investigated. It was shown that the mechanical properties of ZTA ceramics were improved by the LaAl11O18, with strength over 500 MPa and fracture toughness 7 MPam1/2. As the LaAl11O18 amount increased, part of the t-ZrO2 transformed to m-ZrO2, which is revealed by the decrease in the peak intensity of X-ray diffraction pattern, and which brought about a reduction in hardness and Youngʹs modulus. It is believed that crack bridging and crack deflection were major factors contributing to strengthening and toughening of the materials as revealed through the microstructural observations by SEM and TEM.