Trans. Nonferrous Met. Soc. China 22(2012) s579−s584 HR-TEM and FIB-SEM characterization of formation of eutectic-like structure from amorphous GdAlO 3 −Al 2 O 3 system Y. H. HAN 1 , Y. HARADA 1 , J. F. SHACKELFORD 2 , Jaehyung LEE 1 , K. KAKEGAWA 3 1. School of Materials Science and Engineering, Yeungnam University, 214-1 Daedong, Gyeongsan, Gyeongbuk, 712-749, Korea; 2. Department of Chemical Engineering and Materials Science, University of California at Davis, CA, USA; 3. Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan Received 21 May 2012; accepted 6 November 2012 Abstract: The crystallization process of the eutectic composition of GdAlO 3 −Al 2 O 3 from the amorphous phase prepared by rapid-quenching of melt that leads to the formation of a cantaloupe skin-like microstructure was investigated using focused ion-beam scanning electron microscopy (FIB-SEM) and high-resolution transmission electron microscopy (HR-TEM). The amorphous films were heat-treated at temperatures between 1000 °C and 1500 °C for up to 30 min to form the eutectic phases of GdAlO 3 and Al 2 O 3 . The GdAlO 3 and Al 2 O 3 crystal phases that formed from the amorphous phase were identified by FIB-SEM and HR-TEM. Both components began to crystallize and grow from the amorphous phase separately at different temperatures. The formation process of these crystal phases was different from that of the ordinary eutectic microstructure solidified from the GdAlO 3 −Al 2 O 3 system. Therefore, the observed structure is termed “eutectic-like” for distinction. The microstructures formed from the amorphous phases at sufficiently high temperatures consisted of ultra-fine microstructures of individually crystallized components and were similar to ordinary eutectic microstructures. By heat-treating the amorphous films at 1500 °C for either 2 min, 8 min or 30 min, the ultra-fine components of GdAlO 3 and Al 2 O 3 were found to crystallize following a eutectic-like stage after 8 min of heat treatment. Key words: eutectic; amorphous; GdAlO 3 −Al 2 O 3 ; eutectic-like; HR-TEM; FIB-SEM; Crystallization 1 Introduction One solution for realizing the higher operating temperatures of the next-generation turbo-blades operating at gas temperatures as high as 1600 °C is by way of an in-situ development of oxide-based ceramic composites by directed solidification of melt having a eutectic composition. The resulting structure is a single-crystal, three-dimensional lattice with no grain boundary, i.e., a material with coherent interfaces and no vitreous phase. This material is known to exhibit a mechanical strength that is nearly constant up to the melting temperature unlike polycrystalline ceramics that gradually looses strength with temperature. It is also known that the rupture stress in this material can be increased by reducing the size of the constituent phases without reducing the creep strength. This is the case of perovskite-structured oxides having a high temperature plasticity in a eutectic system (melting at 1700−1900 °C) that combines alumina with a rare earth oxide having either a perovskite (XAlO 3 ; X: Gd, Eu) or a garnet (Y 3 Al 5 O 12 ; Y: Er, Dy, Yb) structure. Recently, eutectic ceramics have been considered to be a candidate not only as a heat-resistant material but also as a functional material in various other applications, such as thermophotovoltaic (TPV) generation [1−3] and porous materials technology [4−6]. Although the formation process of the ordinary eutectic microstructures by cooling the eutectic melts has been well-known, the formation process of the eutectic-like microstructures from an amorphous phase has not so far been elucidated in our previous work [7,8]. The current study focuses on the focused ion-beam scanning electron microscopy (FIB-SEM) and high- resolution transmission electron microscopy (HR-TEM) characterization of the crystallization process of the GdAlO 3 −Al 2 O 3 binary eutectic system [9−12]. We characterized the ultra-fine eutectic microstructure processed both from the eutectic melt and from the amorphous phase. Corresponding author: Y. H. HAN; Tel: +82-53-810-2539; Fax: +82-53-810-4628; E-mail: yhhanyu@yu.ac.kr DOI: 10.1016/S1003-6326(12)61769-5