The Design of Composition and Mechanical Properties of α-β SiAlON Ceramics Densified with Higher Atomic Number Rare Earths

In addition to the conventionally used yttrium oxide, many studies have been carried out in recent years using rare earth oxides as densification additives for α-β sialon ceramics. Although densification is much easier with these additives, it is difficult to achieve the designed composition and therefore mechanical properties after sintering. This behavior has been explained in terms of the stability region of a-sialon, which decreases as the cation size of rare earth increases. As a result, the use of these oxides as sintering additive is limited. In the present work, α-β sialon starting composition with m=0.8 and n=1.7, which was designed to produce %80 α- and 20% β-sialon, has been densified by capsul free sinter-HIPing using Ln₂O₃, where Ln= Nd, Yb and equimolar mixture of Nd-Yb. The effects of different rare earth oxide additives to achieve the designed composition and properties have been investigated. It has been found that the designed compositions could not be achieved with single dopants as expected. However, by using multi cation doped α-sialon materials, the designed composition and properties were easily achieved.