α′ phase stability in Nd–Li-sialon systems

The formability and stability of the α-sialon (α′) phase was investigated in multi-cation Nd–Li-sialon systems. Four samples were prepared, ranging from a pure Nd-sialon to a pure Li-sialon, with two intermediate samples being prepared with either lithium or neodymium replacing the other α′-stabilising additive by 20 eq.%, as to maintain an equivalent design composition in all samples. After sintering, all samples were subsequently heat treated up to 192 h at 1450 and 1300 °C. While significant quantities of the β′-sialon (β′ phase were found in most samples, the high-lithium Li–Nd-sialon sample was found to be almost pure α′ phase after sintering. Furthermore, the long-term stability of the α′ phase on heat treatment was also found to be superior in both multi-cation samples than in either of the single-α′-stabilising-cation samples. This is thought to be related to improved retention of the lithium in the multi-cation systems, as much of the lithium was found to volatilise during sintering in the neodymium-free sample.