Microstructure formation of Al<sub>2</sub>O<sub>3</sub>–HfO<sub>2</sub> eutectic

Abstract

The microstructure formation of Al2O3–HfO2 eutectic prepared by unidirectional solidification and rapid solidification was examined. The microstructure of the Al2O3–HfO2 eutectic samples showed lamellar structure and the relationship between the inter-lamellar spacing λ and solidification rate R can be expressed by λ2R=constant. A small amount of tetragonal HfO2 phase exists in the sample prepared by rapid solidification. Only monoclinic HfO2 phase can be found in the eutectic samples prepared by unidirectional solidification. A tensile stress was induced in Al2O3 phase during the cooling step due to the transformation of HfO2 from tetragonal to monoclinic phase. The tensile stress of the Al2O3 phase in the eutectic structure was estimated to 420 MPa.