ELABORATION OF ALUMINA-YAG NANOCOMPOSITES FROM PRESSURELESS SINTERED Y-DOPED ALUMINA POWDERS

The elaboration of 95 vol.% Al2O3 - 5 vol.% YAG (Y3Al5O12) nanocomposites was pursued by a novel processing route. A commercial nanocrystalline transition alumina powder was doped by using a yttrium chloride solution. After drying, salt decomposition and final phases development were obtained by performing a high-temperature treatment, leading to a composite powder made of a-alumina and YAG. The as-dried material as well as some powders calcined at some selected temperatures were characterized by means of HR-TEM to follow the morphology and crystallography evolution as a function of the calcination temperature and time. In addition. the yttrium distribution was investigated by systematic EDX analyses performed on both bulk and surface of the alumina particles. Differently calcined powders were uniaxially pressed in bars and the influence of the precalcination treatment on the pressureless sintering behaviour was investigated by dilatometric analyses performed up to 1500 degrees C for 3 hours soaking time. SEM and ESEM observations, performed on fracture surfaces of sintered bodies. allowed to characterize the final microstructure of the micro-nano composites, made of equiaxial YAG particles with a mean size of 250 nm, uniformly dispersed into a submicronic-grained alumina matrix.