Microstructural and diametral tensile strength evaluation of the zirconia-mullite composite

Abstract The purpose of the current research was to investigate the effect of duration of the mechanical activation process of starting materials on Vickers micro-hardness and diametral tensile strength of zirconia-mullite composites. Zirconia-mullite composites with 1:1 M ratio were fabricated by sintering of the mechanically activated kaolinite, gibbsite, and zircon powder mixture as inexpensive and convenient starting materials. Results of dynamic light scattering analysis showed that the mean particle size of the starting powders was reduced from 2.5 µm to 80 nm after 72 h of the mechanical activation process. X-ray diffraction analysis showed that zirconia and mullite were crystallized after 2 h thermal treatment at 1550 °C. Based on the semi-quantification results of X-ray diffraction patterns, increasing the duration of the milling process from 6 to 72 h had a positive effect on improving the amount of tetragonal zirconia in the final matrix. Scanning electron microscopy results revealed a fine and homogeneous distribution of zirconia particles in the mullite matrix after 72 h of the mechanical activation process. Increasing the duration of milling process from 6 h to 72 h had a remarkable effect in increasing the diametral tensile strength values from 30 to 220 MPa. Vickers micro-hardness values were also enhanced considerably from 7.30 to 11.12 GPa by increasing the milling time.