SiC particle reinforced oxynitride glass and glass-ceramic composites: Crystallization and viscoplastic forming ranges

The viscoplastic forming and the crystallization ranges of SiC particle reinforced oxynitride glass composites were characterized. Crystallization starts beyond 1050 degrees C, with MgAl2O4, MgSiO3, z- and delta-Y2Si2O7 as the main phases. A non-Newtonian flow behaviour was observed from 800 to 900 degrees C, i.e. on both sides of Tg (Tg = 863 degrees C), with n approximate to 0.6 (shear thickening). The viscosity versus temperature curves (drawn from creep tests), show that temperature must be higher than 950 degrees C for the viscosity to be lower than 10(10) Pa s. In the light of these results, the feasibility for viscoplastic forming of a 40 vol.% SiC composite was demonstrated by shaping a parabolic shell at 980 degrees C within 30 min.