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Zirconia-mullite composite ceramics were fabricated by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk.The effects of TiO2 addition on the fabrication of zirconia-mullite composites were investigated.The ultra-fine zirconia-mullite composite ceramics were prepared from the amorphous bulk treated.at 980 ℃ for nucleation and 1 140 ℃ for crystallization.The phase transformation of the ceramics was examined using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD).The microstructural features of the samples were evaluated with scanning electron microscopy (SEM),energy dispersive spectroscopy (EDX) and transmission electron microscopy (TEM).The mechanical properties were also determined using Vickers indentation.The results show that the TiO2 additives with mass fraction of 1％-7％ reduce the formation temperature of t-ZrO2 and mullite.When the mass fraction of TiO2 additives is less than 5％,the phases do not change,and most of TiO2 dissolves in ZrO2.When the mass fraction of TiO2 additives is over 5％,the excessive TiO2 forms a new phase,ZrTiO4.Meanwhile,the results also show that TiO2 additives have a great impact on the microstructure and mechanical properties of zirconia-mullite composites.As the TiO2 content increases from 1％ to 7％ (mass fraction),the grain size and the Vickers hardness of zirconia-mullite composites increase.The composite with 3％ (mass fraction) TiO2 additives attains relatively higher fracture toughness.