Superplastic deformation of nitrogen-rich Ca-α-sialon ceramics

Nitrogen-rich Ca-α-sialon ceramics, prepared with CaH2 as one of the starting powders, were compressively deformed in spark plasma sintering equipment. Compared with the oxygen-rich Ca-α-sialons, increasing onset deformation temperatures (about 150 K higher) were observed for nitrogen-rich Ca-α-sialons deformed at a rate of 2 × 10−3 s−1. High hardness (HV10 = 18–20 GPa) and toughness (KIC = 4–7 MPa m1/2) were maintained after the deformation. Anisotropic grain growth was found to take place during deformation, resulting in anisotropic microstructures, containing coarse and elongated grains. The observed differences in deformation behaviour and properties between nitrogen-rich and oxygen-rich Ca-α-sialons are, as indicated by transmission electron microscopy and electron energy loss spectroscopy analysis, attributed to the presence of reduced amounts of a nitrogen-rich grain-boundary glass phase.