Synthesis of Mg‐stabilized nitrogen‐rich alpha‐sialons along Si3N4–0.5Mg3N2:3AlN line via field‐assisted sintering

Abstract

AbstractThe present study reports for the first time the synthesis and evaluation of magnesium (Mg)‐doped nitrogen‐rich (N‐rich) sialon ceramics exploring the possible existence of Mg‐stabilized single‐phase alpha‐sialon (on the Mg‐alpha‐sialon plane). Mg‐stabilized N‐rich sialons, with the general formula of MgxSi12−2xAl2xN16 having x value in the range of 0.2–2.2 for the composition laying along the Si3N4–0.5Mg3N2:3AlN line, were synthesized at 1500°C, using nano‐size starting powder precursors and field‐assisted (or spark plasma) sintering technique. Consolidated sialon ceramic samples were characterized for their microstructure, phase stability regime, and physical and mechanical properties. Although a relatively low synthesis temperature was adopted, well densified sialon samples were achieved; however, the densification of the samples became difficult with a higher x value (containing high Mg3N2/AlN content). Contrary to what was expected to take place, a single‐phase Mg‐doped sialon was not obtained near the N‐rich line (on Mg‐alpha‐sialon plane). Such distinctive behavior in Mg‐doped sialons was supposed to be due to the formation of a highly stable Mg‐containing aluminum nitride polytype phase, which consumed most of the high‐temperature transient liquid phase. Mg‐doped N‐rich sialon sample having the maximum amount of alpha phase depicted a remarkable hardness (HV10) of 21.4 GPa and a fracture toughness of 3.5 MPa m1/2.