Effects of Y addition on microstructure and mechanical properties of Ti-25Zr alloys

Abstract

The influences of rare earth element yttrium (Y) on microstructure, mechanical properties and fracture characteristics of Ti-25Zr-xY (x = 0, 0.5, 1, 2, 3, 4, 5, at%) alloy were investigated. Compositional and microstructural characterization of the as-cast material was conducted by XRD, SEM and TEM. XRD analysis showed that no other phase was found in the specimens, which completely consisted of α and α-Y phases. Addition of trace amounts of Y to the Ti-25Zr alloys induced significant changes in the microstructure, including the decrease in sizes of prior β grain boundaries and α platelets size. The constitutional supercooling were responsible for the grain refinement. Owing to the low solubility and segregation of Y element in the Ti-Zr alloy, when the Y content was less than 1 (at%), the fine and uniformly distributed α-Y phases were dispersed within the grains. The refinement of grains and α-lath and dispersion of α-Y within the grains contributed to the desirable compression performance. By contrast, when the content of Y exceeded 1 at%, the grain boundary segregation of Y was more distinct. Consequently, the mechanical properties deteriorated remarkably because of the serious segregation of the brittle α-Y phase at grain boundaries.