Impacts of yttrium on microstructure and tensile properties of biomedical β Ti-Nb-Zr fabricated by metal injection molding

Abstract

Impurities, particularly oxygen, are a critical issue to address in metal-injection-molding (MIM) processed Ti-Nb-Zr biomaterials. The addition of rare earth (RE) elements such as yttrium is a possible solution to the impurity problem due to their potential for scavenging oxygen. The impacts of added Y on the sinterability, microstructure and mechanical properties of the MIMed Ti-Nb-Zr, however, largely remain unclear. In this study, different sized Y particles with varying weight fractions have been added to the β Ti-Nb-Zr alloy in order to elucidate the aforementioned aspects. It has been found that, although the added Y has an obvious β grain refinement effect, its impacts on the residual porosity, ultimate tensile strength and tensile toughness can be significantly negative, particularly if using large sized Y particles. Small sized (<15 μm), moderate amount (e.g. 0.3 wt%) of Y addition, however, proved to be beneficial, in terms of scavenging oxygen and promoting fracture toughness. Characterization techniques and mechanical testing are employed to understand the above experimental findings with the assistance of sintering theory and existing literature. It is hoped that the present study can provide an important guidance for using Y as an oxygen scavenger to develop low-cost, high-performance MIMed Ti alloys.