Microstructure refinement and strengthening mechanisms of additively manufactured Ti-Zr alloys prepared from pre-mixed feedstock

Abstract

In recent decades, advances in healthcare services have extended life expectancies worldwide and accelerated the demand for orthopedic implants. Accordingly, the development of safe materials for implants has become increasingly critical for minimizing health complications in patients. Herein, additively manufacturable binary titanium-zirconium (Ti-Zr) alloys are investigated as an alternative to the conventionally used Ti-6Al-4V alloys, in which the release of toxic vanadium (V) ions has been identified as a potential health hazard. Using commercially pure (CP)-Ti and pre-mixed blends of Ti 0–10 wt% ZrH2 powders as feedstock, laser powder bed fusion (LPBF) was used to successfully prepare high-density (>98%) Ti–Zr materials with a homogeneous distribution of Zr in the Ti. The presence of Zr was found to promote grain refinement, which reduced the large a/a’ grains in several hundred microns found in the Zr-free samples to a fine acicular grain structure (3.96 µm, 10 wt% ZrH2 addition). Tensile yield strength was also significantly enhanced with increasing Zr content with a remarkable improvement of up to 154% (853.9 MPa, 10 wt% ZrH2 addition) than the Zr-free Ti material, meanwhile retaining acceptable ductility (approximately 10%). To clarify the mechanisms of strengthening, the contributions of grain refinement and solid solution hardening are quantitatively evaluated. Given the excellent performance of the bulk materials, the fabrication of lattice scaffold structures from the Ti-Zr materials was investigated to further evaluate the applicability of the material fabricating lightweight, high-strength, and low-elastic modulus geometries. Ti–Zr scaffolds with different cellular structures are mechanically tested to determine the potential of each design. With compressive performance comparable to Ti-6Al-4V scaffold structures, and no inclusion of harmful elements, this study reveals the strong potential of the use of Ti-Zr scaffolds in orthopedic applications.