Microstructure and Superelastic Behavior of Rapidly Solidified Ti-18Zr-12.5Nb-2Sn (at.%) Alloy Fibers

Abstract

Ti-18Zr-12.5Nb-2Sn (at.%) alloy fibers were fabricated by the rapid solidification method. X-ray diffraction analysis showed that the as-spun alloy fibers were composed of beta phase at room temperature. Scanning electron microscopy analysis revealed that the as-spun alloy fiber exhibited a fine-grained beta microstructure with a grain size of approximately 1 similar to 5 mu m. Tensile tests carried out by a dynamic mechanical analyzer showed the as-spun alloy fibers exhibited superelastic behavior in the temperature range of 238 and 318 K. The martensitic transformation start temperature of the as-spun alloy fiber was approximately 180 K, and a large recovery strain of 4.5% was observed for 5% pre-strain at room temperature. The as-spun alloy fiber exhibited a combination of excellent superelasticity and high tensile strength when compared to the conventional solution-treated alloy bulk. The critical stress for slip deformation of the as-spun alloy fiber was higher than that of the solution-treated alloy bulk, which is attributed to the fine-grained structure of the former. The effect of cyclic deformation on superelasticity was also investigated, and a stable superelastic behavior with a narrow stress hysteresis of 35 MPa was observed in the as-spun alloy fiber at room temperature.