27R-SiAlON Reinforced AlN Composite: Synthesis, Sintering and Characterization

Synthesis of powder containing a dual phase mixture of 27R-SiAlON and AlN has been successfully carried out through carbothermal reduction and nitridation route. The probable reaction sequences of formation have been identified through the analysis of transient appearances of intermediate phases associated with parameters like loss of carbon, oxygen and weight as well as nitrogen uptake. Formation of 27R-SiAlON takes place through further reaction of a primary polytype phase, Si 3 Al 7 O 3 N 9 . FTIR spectra provide supplementary evidence for supporting the revealed model of reaction sequences. Particles are agglomerative in nature consisting of fine grains, as low as below 50 nm in size. Spark plasma sintering was applied for an initial densification trial of this bi-phasic powder without externally added sintering aid. The densified samples exhibited elongated grain-reinforced composite microstructure with improved properties over monolithic AlN. Graphic Abstract