HR-TEM and FIB-SEM characterization of formation of eutectic-like structure from amorphous GdAlO_3-Al_2O_3 system

The crystallization process of the eutectic composition of GdAlO_3-Al_2O_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 30min to form the eutectic phases of GdAlO_3 and Al_2O_3.The GdAlO_3 and Al_2O_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_2O_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,8min or 30min,the ultra-fine components of GdAlO_3 and Al_2O_3 were found to crystallize following a eutectic-like stage after 8min of heat treatment.

Fabrication of SiCw/Ti3SiC2 composites with improved thermal conductivity and mechanical properties using spark plasma sintering

High strength SiC whisker-reinforced Ti3SiC2 composites(SiCw/Ti3SiC2)with an improved thermal conductivity and mechanical properties were fabricated by spark plasma sintering.The bending strength of 10 wt%SiCw/Ti3SiC2 was 635 MPa,which was approximately 50%higher than that of the monolithic Ti3SiC2(428 MPa).The Vickers hardness and thermal conductivity(k)also increased by 36%and 25%,respectively,from the monolithic Ti3SiC2 by the incorporation of 10 wt%SiCw.This remarkable improvement both in mechanical and thermal properties was attributed to the fine-grained uniform composite microstructure along with the effects of incorporated SiCw.The SiCw/Ti3SiC2 can be a feasible candidate for the in-core structural application in nuclear reactors due to the excellent mechanical and thermal properties.