Additively manufactured beta-titanium alloy for biomedical applications: effects of process and heat treatment on microstructure and mechanical properties

Titanium alloys are widely used for biomedical applications, especially for joint replacement, thanks to their good mechanical behavior and excellent corrosion resistance. β-titanium alloys can enhance biocompatibility of the implant by reason of a low stiffness, closer to the bone, and absence of harmful elements, such as V. Additive manufacturing has the potential to be applied to such alloys to produce new generation prosthesis with a high degree of customization. However, the process and post processing need to be carefully optimized. Therefore, the experimental work was focused on the characterization and optimization of Ti21S, a metastable β-titanium alloy, processed via Laser Powder Bed Fusion. A comprehensive approach was adopted, beginning with the analysis of the feedstock powder and proceeding through the fabrication of test specimens, the evaluation of their density and microstructure, and the assessment of post-processing heat treatments. Powder characterization was carried out to obtain size and shape descriptors to be discussed and compared to the one declared by the supplier. Then the process optimization considered three sets of printing parameters, covering an energy density range between 66 and 125 J/mm³. Density and porosity analyses, performed through Archimedes’ method and optical microscopy, led to the identification of the optimal condition that was subjected to an in-depth microstructural characterization to reveal microstructural features. Selected samples underwent 2 different heat treatments: Artificial Aging at 590 °C for 8 hours and at 490 °C for 8 hours. Heat treatments were aimed at inducing strengthening of the alloy, as confirmed by hardness test and supported by microstructural analyses. Overall, these findings provide critical insights into the process–structure–property relationships of Ti21S in additive manufacturing contributing to the development of β-Ti alloys for advanced applications, with relevance to biomedical devices