Kinetics of rare earth incorporation and its role in densification and microstructure formation of alpha-Sialon
Kinetik der Seltenerden-Einlagerung und seine Rolle bei der Verdichtung und Mikrogefügebildung von alpha-Sialon
The reproducible sintering and microstructure formation of alpha- and alpha/beta-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 previous termrarenext termprevious termearthnext term into the alpha-Sialon structure. The analysis showed that in the early stages of sintering more previous termrarenext termprevious termearthnext term cations were incorporated into the grains than would be expected from the equilibrium conditions. This was observed for all investigated previous termrarenext term earths (Y, Nd and Yb) with different ionic radii. The consequences for sintering and microstructure formation are the fast disapp earing of the transient liquid and the formation of polytypes. The use of excess of previous termrarenext termprevious termearthnext term 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.