Kinetics of rare earth incorporation and its role in densification and microstructure formation of α-Sialon

The reproducible sintering and microstructure formation of α- and α/β-Sialons is a precondition for the production of such materials with reproducible properties.The Rietveld method was used for quantitative analysis of the phase composition and the kinetics of incorporation of the rare earth into the α-Sialon structure. The analysis showed that in the early stages of sintering more rare earth cations were incorporated into the grains than would be expected from the equilibrium conditions. This was observed for all investigated rare earths (Y, Nd and Yb) with different ionic radii. The consequences for sintering and microstructure formation are the fast disappearing of the transient liquid and the formation of polytypes. The use of excess of rare earth in comparison to the stoichiometric Sialon composition results in a stable residual liquid. It allows reproducible densification, anisotropic grain growth and materials with high fracture toughness.

► Investigation of formation of the of elongated grain growth of Sialons.
► Incorporation of rare earth in Sialon was determined by Rietveld method.
► In the starting period of sintering Sialons with high rare earth content are formed.
► An excess of rare earth is an important parameter for elongated grain growth.
► An excess of rare earth is an important parameter for tailored mechanical properties.