Superplastic Forming of SiAlON Ceramics

Abstract

Superplastic SiAlON's of the nominal composition Y m /3 ‐Si 12‐( m + n ) AL m + n O n N 16– n are reported in this study using a transient‐phase‐forming approach. They encompass the fields of single‐phase α′‐SiAlON, single‐phase β′‐SiAlON, and their two‐phase mixtures. Excellent formability is obtained at 1550°C for the β’and α’+β’materials, and at 1600°C for the α’material. Typically in the nonequilibrium state before deformation, these fine‐grained materials undergo dramatic phase and microstructure evolutions during superplastic forming. In particular, the stress‐biased α‐Si 3 N 4 →β′‐SiAlON reaction is found to result in elongated and aligned grains with fiber‐strengthening effect and excellent formability.