Structure and mechanical properties of ZrO₂-mullite nano-ceramics in SiO₂-Al₂O₃-ZrO₂ system

Abstract

ZrO₂-mullite nano-ceramics were fabricated by in-situ controlled crystallizing from SiO₂-Al₂O₃-ZrO₂ amorphous bulk. The thermal transformation sequences of the SiO₂-Al₂O₃-ZrO₂ amorphous bulk were investigated by X-ray diffraction, infrared spectrum, scanning electron microscope and differential scanning calorimetric. And the mechanical properties of the nano-ceramics were studied. The results show that the bulks are still in amorphous state at 900 °C and the t-ZrO₂ forms at about 950 °C with a faint spinel-like phase which changes into mullite on further heating. ZrO₂ and mullite become major phases at 1 100 °C and an amount of m-ZrO₂ occur at the same time. The sample heated at 950 °C for 2 h and then at 1 100 °C for 1 h shows very dense and homogenous microstructure with ball-like grains in size of 20–50 nm. With the increase of crystallization temperature up to 1 350 °C, the grains grow quickly and some grow into lath-shaped grains with major diameter of 5 μm. After two-step treatment the highest micro-hardness, flexural strength and fracture toughness of the samples are 13.72 GPa, 520 MPa and 5.13 MPa·m^1/2, respectively.

Keywords

SiO₂-Al₂O₃-ZrO₂ system amorphous bulk / heat treatment / structural change / mechanical properties

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