Sintering behavior, microstructure and mechanical properties of various fluorine-containing Y-SiAlON glass-ceramics

• Various fluorine-containing Y-SiAlON glass-ceramics were prepared by carbothermal reduction.
• XRD and SEM reveal the presence of different crystal phases.
• Addition of fluorine promoted the α-Si3N4 to Y2Si3O3N4 and β-Si3N4 phase transformation.
• By controlling nucleation, enhancement of mechanical properties can be achieved.

Various fluorine-containing Y-SiAlON glass-ceramics from a mixture of Y2O3, α-Si3N4, SiO2, and Al2O3 using AlF3 as the fluorine source were prepared by one-step or two-step carbothermal reduction process. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to study the crystallization behavior of the glass-ceramics. The compositions of the crystals and the glass phase were semi-quantitatively determined by EDX. The final glass-ceramics contained N-containing melilite (Y2Si3O3N4) and β-Si3N4 together with a secondary phase of yttrium aluminum garnet (YAG, Y3Al5O12). The investigated Y-SiAlON glass-ceramics with higher F content showed better sintering properties. Fluorine has important effects on crystallization of glass-ceramics as it affects the crystallization mechanism by reducing the thermal energy barrier for crystallization. By controlling the reaction, the Y-SiAlON glass-ceramics are first held at 1300 °C for 4 h, which contrasts with the samples obtained after direct sintering at 1550 °C, the conversion to Y2Si3O3N4 and β-Si3N4 is promoted and the final microstructure consists of elongated β-Si3N4 grains. These glass-ceramics showed relatively better mechanical properties.