Crystallization and Microstructure Development of Si3N4-Ti(C,N)-Y2O3 Ceramics Derived from Chemically Modified Perhydropolysilazane.

Abstract

[Si-Y-Ti-O-C-N] multicomponent amorphous powders were synthesized by pyrolysis at 1000°C, in NH3 flow, of chemically modified PHPS using Y(OCH(CH3)2)3 and Ti(N(CH3)2)4. The crystallization and microstructure de velopment were studied by comparison with [Si-Y-O-C-N] amorphous powders derived from PHPS chemically modified with Y(OCH(CH3)2)3.(1) Amorphous Si3N4 in the [Si-Y-Ti-O-C-N] powders was rather stable below 1400°C in N2. Above 1600°C, Si-Ti-Y-O-N liquid phase accelerated the α-/β- phase transformation of Si3N4 and the [Si-Y-Ti-O-C-N] powders yielded β-Si3N4-Ti(C, N)-Y2O3 ceramics at 1800°C.(2) Fully dense β-Si3N4-Ti(C, N)-Y2O3 ceramics were also synthesized by hot pressing at 1800°C in N2. The resulting ceramics exhibited a uniform and fine-grained micro structure.(3) Ti(C, N) phase was dispersed as particles having a size range of 10nm to 1.6μm and the large Ti(C, N) particles with diameters larger than 0.5μm were located at the β-Si3N4 matrix boundaries.(4) Titanium in the [Si-Y-Ti-O-C-N] powders could act as a catalyst to accelerate α-/β-Si3N4 phase transformation as well as an in-situ source for nano/micro Ti(C, N) particles, which lead to microstructure uniformity and refinement of β-Si3N4-Ti(C, N)-Y2O3 ceramics.