Abstract
The influence of complex thermo-mechanical processing (TMP) on the mechanical properties of a Ti-Nb-Zr-Fe-O bio-alloy was investigated in this study. The proposed TMP program involves a schema featuring a series of severe plastic deformation (SPD) and solution treatment (STs). The purpose of this study was to find the proper parameter combination for the applied TMP and thus enhance the mechanical strength and diminish the Young’s modulus. The proposed chemical composition of the studied β-type Ti-alloy was conceived from already-appreciated Ti-Nb-Ta-Zr alloys with high β-stability by replacing the expensive Ta with more accessible Fe and O. These chemical additions are expected to better enhance β-stability and thus avoid the generation of ω, α’, and α” during complex TMP, as well as allow for the processing of a single bcc β-phase with significant grain diminution, increased mechanical strength, and a low elasticity value/Young’s modulus. The proposed TMP program considers two research directions of TMP experiments. For comparisons using structural and mechanical perspectives, the two categories of the experimental samples were analyzed using SEM microscopy and a series of tensile tests. The comparison also included some already published results for similar alloys. The analysis revealed the advantages and disadvantages for all compared categories, with the conclusions highlighting that the studied alloys are suitable for expanding the database of possible β-Ti bio-alloys that could be used depending on the specific requirements of different biomedical implant applications.
Highlights
Good biomedical materials for orthopedic implants with long-term service need a combination of a low Young’s modulus, close proximity to the human bone, and high strength to avoid the known “stress shielding effect” [1,2,3,4,5]
In metastable β-type Ti alloys, it is already known that the ω, α’, and α” phases can be produced in the β matrix as a result of cold plastic deformation [52,53,54,55]
The amount of the β-stabilizing alloying elements was sufficient to obtain a single β-phase, without any subsequent generation of the secondary phases that are possible to be formed during complex thermo-mechanical processing (TMP) and can decrease the processability of the alloy
Summary
Good biomedical materials for orthopedic implants with long-term service need a combination of a low Young’s modulus, close proximity to the human bone, and high strength to avoid the known “stress shielding effect” [1,2,3,4,5]. Among many investigated biocompatible materials, non-cytotoxic β-Ti alloys have been developed in recent decades [6,7,8,9,10,11,12,13], as these alloys have the most attractive combination of a low Young’s modulus, high mechanical strength, and high ductility This property combination can ensure good processability (i.e., plastic deformation, machinability, welding, etc.) and good tribological characteristics, all of which are necessary for the long-term dimensional stability of an implant [14]. Efforts have been made to replace Ta with more accessible Fe and O [31,32,33,34,35,36]
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