Resistência a corrosão em ligas de TiNiNb resultantes do processo de fusão a Plasma-Skull para aplicações como biomateriais.

Abstract

Titanium is a metal that is very resistant to corrosion in most environments. However, it has a low chemical bonding capacity with bone, which can result in its encapsulation by fibrous tissue and, consequently, in loosening and loss of implant correction. To improve this chemical bonding capacity, we carry out studies with the objective of obtaining titanium alloys to be used as biomaterials in different areas due to their low modulus of elasticity, tensile strength, biocompatibility and greater resistance to corrosion when compared to other alloys metal used in implants. It is known that all the properties of this alloy can still be improved and adjusted for various purposes in the medical field and many studies are still being carried out around the world. Given the above and the great interest in expanding the Ni-Ti alloy usage, merging this material with other elements looks like a research alternative with innovative characteristics in the field of biomaterials. Niobium, among the metals considered inert, is the main stabilizer of the β-phase of titanium. Thus, this work aimed to obtain a TiNiNb alloy by varying the niobium contents to verify its influence on the phase transformations and on the physical, chemical and biological properties of the alloy. We produced TiNiNb alloys thorugh the Plasma-Skull Push-Pull (PSPP) fusion process, which was followed by injection molding in a metal mold. The study was carried out with these alloys in five different compositions, with the addition of 0; 5.0; 10.0; 15.0 and 20.0 at.% Nb. The addition of Nb in different percentages in the binary Ni-Ti alloy caused modifications in the microstructure of the ternary alloy, with the emergence of intermediate phases, TiNi2 and Ni4Ti3 precipitates and βNb. The XRD analysis revealed that the βNb phase volume fraction increases with the increasing Nb addition in the range of 5 to 20% to the alloy, as well as the number of precipitates in the alloy increases with increasing niobium content. With the thermal analysis performed by DSC tests we could not establish a direct relationship between the variation of niobium in the composition of the alloys with the manifested thermal behavior. Regarding the emergence of the R intermediate phase, the increase in the niobium content caused an increase in the Ri and Rf temperature. The microhardness and modulus of elasticity results showed that the increase in the niobium content caused a decrease in these values. The corrosion analysis revealed that the alloy with the lowest niobium content was the most resistant to corrosion, a behavior that was observed in the Linear Potentiodynamic Polarization (PPL) and the Electrochemical Impedance Spectroscopy (EIE) measurements and is related to the presence of Ni2Ti4O oxides. The cytotoxicity assay proved the biocompatibility of the studied alloys. The results obtained through the studies carried out were significantly influenced by the non-uniformity of the mixture. Therefore, we conclude that it was possible to obtain a ternary alloy of biocompatible TiNiNb by varying the niobium contents to verify their influence on phase transformations, properties of metallic biomaterials and alloy microstructure.