Oxidation behavior of Dy-melilite and Dy-α-Sialon with melilite as the grain boundary phase

Four compositions of nitrogen-containing Dy-melilite solid solutions Dy2Si3-xAlxO3+xN4-x (Dy-M', x=0, 0.3, 0.6 and 1.0) were prepared by hot-pressing and oxidized at 1000 degrees C for 20h in air in a TG unit. The weight gains per area of Dy-M' samples decreased with increasing the Al substitution, indicated that the oxidation resistance of Dy-M', especially for Dy-M'(x=0.6), became better comparing the one of Dy-M. A composition of Dy-alpha-Sialon with Dy-M' as the grain boundary phase prepared by hot-pressing was exposed to air at 1000 degrees C and 1300 degrees C for 20h. No catastrophic oxidation behavior was observed in the first situation. When the sample was oxidized at 1300 degrees C for 20h, crystals of alpha-Dy2Si2O7 were observed in preferred orientation on the oxidized surface of Dy-alpha'-M' sample.