Formation behavior and microstructure of multi-cation alpha-sialons containing neodymium and ytterbium or yttrium

Multi-cation alpha-sialons containing neodymium and ytterbium, as well as n eodymium and yttrium, were prepared by hot pressing at the temperatures ran ging from 1550 to 1750 degrees C for 2 h with the compositions (Nd0.18Yb0.1 8/Nd0.18Y0.18)Si10.36Al1.62O0.54N15.46. The densification process, reaction sequence, cell dimensions and microstructure were studied in comparison wi th the corresponding single cation alpha-sialon. Experimental results have shown that the samples hot-pressed at 1750 degrees C mainly consist of alph a-sialon phase, whose content (around 95 wt%) is higher than that of counte rpart single rare earth doped alpha-sialon, especially much higher than the one of Nd-alpha-sialon. On the other hand, the multi-cation alpha-sialons compositions are beneficial to lower the eutectic temperature in the system s, thus promoting the dissolution of intergranular crystalline melilite pha se, and facilitating the precipitation of alpha-sialon phase. TEM and EDS r evealed that the amount of Yb3+ or Y3+, which possess relatively smaller io nic radii than Nd3+, is higher than that of the Nd3+ in alpha-sialon grains and more Nd3+ are remained in the grain boundary phase. Small amount of el ongated alpha-sialon grains were observed by TEM and the preferred orientat ion also occurred under hot-pressing for such a low x value composition (x = 0.36) used in this study. (C) 2000 Elsevier Science Ltd. All rights reser ved.