Phase Assemblages of Pr α-sialon Derived from SHS-ed Powders and TEM Study on the Nucleation of Pr α-sialon.

The Pr α-sialon powders prepared by self-propagating high-temperature synthesis (SHS), consisting of 55 wt% Pr α-sialon and 45 wt% of β-sialon (abbreviated as α′ and β′), were hot-pressed at 1800°C for 1 h. The results showed that Pr α′ phase would transfer to β′ with the appearance of JEM phase (Pr(Si_6-zAI_z)(N_10-zO_z)) after sintering., thus resulting in the increase of β′ phase to 86 wt%. The addition of Y₂O₃ into SHS-ed Pr α′ powders as the starting materials restrains the transformation of α′ to β′ and prevents the formation of JEM phase as well. The nucleation mechanism of Pr α′ grain during hot-pressing was investigated in terms of transmission electron microscope and energy-dispersive spectrometer analysis. Two nucleation modes of Pr α′ grains were found, i.e., nucleating on the undissolved Pr α′ grains and on the nuclei of (Pr, Y) α′ grains precipitated from liquid phase. [ABSTRACT FROM AUTHOR]