STRUCTURAL AND MECHANICAL-PROPERTIES OF FINE COMPOSITES PREPARED BY TI-SI3N4 SOLID-STATE REACTIONS

Mechanical alloying of elemental Ti and Si3N4 powders was conducted by high energy ball milling and solid state reactions were observed to take place during milling. An incubation period for the reaction to begin existed which was related to the critical stored energy during milling. Hot compaction of milled powders could be efficiently conducted at lower temperatures than for conventional sintering of Si3N4. The phases formed after sintering varied with the milling time and sintering temperature and a kinematical model has been proposed for the mechanism of phase formation. The grain size of samples sintered at 1300-degrees-C was about 100 nm and grain growth took place at increasing sintering temperatures preferentially at Ti5Si3 grains. The Vickers hardness decreased monotonically with increasing test temperature, but the bending strength showed an inverse temperature dependence. Substantial plastic deformation took place at over 900-degrees-C and superplastic behaviour was observed.