Amorphization, Field Activated Sintering and Superplastic Forming of UHTCs

Abstract

This article reports new events of amorphization, field activated sintering and superplastic forming of ultrahigh temperature ceramics (UHTCs), in order to provide an advanced method of the integrated material design and solid state synthesis on demand in the framework of material system science and technology. Nonequilibrium reaction ball milling can be used to prepare a variety of amorphous powders of covalent-bonding typed ceramics such as SiC, B4C, HfC and ZrB2, a binary system of B4C∙SiC, and ternary system of B4C∙SiC∙ZrB2, when having a judicious selection of reaction routes and process controls based on thermodynamics and kinetics of mechanically driven amorphization. Then, intelligent nanosintering with multi-variable control makes it possible to obtain full densification of amorphous UHTCs powder below nanocrystallization, and in process amorphous and/or nanocrystalline structure control densification. Especially, millimeter wave pressure sintering makes it possible to obtain rapid densification during enhanced non-Newtonian flow under an electric field at the temperature of below glass transition. The full-density amorphous B4C・SiC shows high-strain rate superplastic forming during viscous flow with compressibility of 0.75 around 1400 K prior to crystallization.