Synthesis and characterization of ZrO2 shape memory ceramic fibers

Abstract

Cerium and yttrium stabilized zirconia (CYZ) ceramics in nano or microscales have demonstrated excellent shape memory and superelastic properties. However, how to scale up such small volume ceramics and bring it to engineering applications remains challenging. In this project, we have used electrospinning method to synthesize the small volume shape memory ceramics in nanofiber form and assemble the nanofibers into centimeters long yarns and springs. The shape memory and actuation properties of these macroscopic samples have been characterized and the effect of sintering conditions and dopant concentration on the crystallization of the fibers and the shape memory properties have been studied. Our results show that the sintering temperature/ time and the ceria doping concentration are the important factors controlling the grain size and phase composition of the fibers. Higher temperatures or longer dwelling time results in larger grain sizes but more monoclinic phases, while higher ceria doping concentration can lead to larger grain sizes and at the same time retain the tetragonal phases in fibers. Full cycle of shape memory effect has been successfully demonstrated in the centimeter long CYZ yarns and the specific output force and energy measured on the spring samples can be as high as 1155.90 N/kg and 3.29 J/kg, respectively. The specific energy output/force output are sensitive to the grain size of the fibers. When the grain size is ~150 nm, the output energy can be ~2-3 J/Kg. Out of that range, the energy output is significantly lower. This work paves a way to scale up the small volume shape memory ceramics (SMC) for engineering application and is the first study of the macroscale actuation property of the small-volume SMC and therefore has advanced the understanding of SMCs.