Mechanical and microstructural evaluation of solid-state foamed Ti6Al4V-ELI alloy

Abstract

Metallic materials adopted in biomedical applications play a key role in the replacement of so-called "hard tissues" (the human bone). Titanium (Ti) alloy prostheses are considered the best among all metallic implants due to their mechanical performance, corrosion resistance and biocompatibility. In particular, Ti foams are characterized by properties very similar to those of human bone since the typical cell structure obtained by a foaming process is very similar to the microstructure of a trabecular bone. Therefore, foaming processes allow for obtaining less stiff prostheses than those composed of a bulk material, leading to reduced stress shielding. In this work, strictly related to the national project FabriCARE, Ti-6Al-4V-ELI foam-based structures were investigated. Unlike those made of other alloys, Ti foams cannot be obtained directly from the liquid phase due to the excessive reactivity of this material with the environment. Thus, a Ti-based foam structure can be more conveniently produced by the solid-state process, which also allows to conveniently set the specific level of porosity, thus customizing the implant even from this point of view. Ti powders were processed via Hot Isostatic Pressing (HIP) to obtain billets. Samples were then extracted via EDM from the billets, and then subjected to foaming process at different temperatures exploiting the physical simulator Gleeble system 3180. Foamed samples were properly prepared and subjected to microstructural and mechanical investigations to investigate the level of porosity and their dimensions along with the changes in mechanical properties.