Severe plastic deformation and different surface treatments on the biocompatible Ti13Nb13Zr and Ti35Nb7Zr5Ta alloys: Microstructural and phase evolutions, mechanical properties, and bioactivity analysis

Ti13Nb13Zr and Ti35Nb7Zr5Ta alloys containing non-cytotoxic elements for bone tissues can be the right choice for replacing Ti6Al4V for orthopedic implant applications. Formation of ultrafine-grained (UFG) structure in metals and alloys by severe plastic deformation (SPD) techniques allows the achievement of unique mechanical properties. Using high-pressure torsion (HPT), UFG microstructures were formed in both alloys resulting in the average size of grains/subgrains of similar to 203 nm and similar to 112 nm for the Ti13Nb13Zr and Ti35Nb7Zr5Ta samples, respectively. After processing by HPT, hardness measurements gave the values of about 390 HV and 320 HV, and Young's moduli of about 60 GPa and 44 GPa, respectively for the Ti13Nb13Zr and Ti35Nb7Zr5Ta alloys, being the last very close to the modulus of the bone. Additionally, surface modifications have been carried out by anodization and by chemical methods aimed to induce specific responses on osteoblastic cells after implantation. The results of bioactivity tests indicated that oxide nanostructures produced after anodization could activate the surfaces of both samples. However, chemical treatment was capable of activating only the Ti13Nb13Zr alloy. The bioactivity of the Ti3Nb13Zr alloy was much higher than the one for Ti35Nb7Zr5Ta alloy and was improved after processing by HPT. (C) 2019 Elsevier B.V. All rights reserved.