Phase transformations in a heterogeneous Ti-xNb-7Zr-0.8O alloy prepared by a field-assisted sintering technique
Abstract
Biomedical metastable alloy Ti-xNb-7Zr-0.8O with a compositional gradient of Nb was prepared from elemental powders by a field-assisted sintering technique (FAST). The aim was to investigate phase transformations over a wide range of compositions, facilitating the designing of biomedical Ti alloys.
Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) investigations revealed that Nb-rich regions retained the 13 phase, surrounded by transition region consisting of the 13 and to phases, while Nb-lean regions consisted of the a and 13 phases. The Nb concentration, above which formation of the to phase occurs during cooling instead of the a phase, was determined to be 22 wt%, an important parameter for the low-modulus alloy design.
The paper validates the viability of using FAST to prepare heterogeneous Ti alloys permitting to study microstructure over a wide range of compositions. This technique could also be readily used as a high-throughput method for designing other alloy systems.
The experimental results were supplemented by calculation of Gibbs energy curves and schematic phase diagrams, which allowed to explain a competition between a and to formation depending on alloy composition. Such semi-empirical approach can serve as a useful tool for general alloy design, in particular for biomedical Ti alloys. (C) 2020 The Authors.
Published by Elsevier Ltd.