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Anodized samples
Figure 25 shows the XRD patterns of anodized samples of Ti13Nb13Zr alloy in the conditions ND, HPT1GPa, and HPT4.5GPa.
Figure 25: XRD patterns of anodized samples of Ti13Nb13Zr alloy in the ND, HPT1GPa, and HPT4.5GPa conditions.
These XRD patterns indicate that TiO2 nanotubes and nanopores obtained during anodization are amorphous. However, when TiO2 nanotubes and nanopores were heat-treated at 550 °C for two hours, an anatase-rutile mixture was obtained (Figure 26). The indexing of the Bragg peaks indicates the presence of the anatase TiO2 phases (2θ = 25.4 °, 38.3 °, 48.1 °, and 55.2 °) [126] and TiO2 -rutile phases (2θ = 27.4 ° and 36.0 °)[127].
Figure 26: XRD pattern of anodized and annealed samples of Ti13Nb13Zr alloy in the ND, HPT1GPa, and HPT4.5GPa conditions. TiO2 nanostructures were annealed at 550 °C in air.
TiO2 nanotubes morphologies were investigated by SEM. Figure 27 shows the top and lateral views of anodized and annealed samples of Ti13Nb13Zr alloy (a and b) ND; and HPT1GPa in (c and d) and HPT4.5GPa in (e and f).
Figure 27: SEM micrographs of anodized and annealed samples of Ti13Nb13Zr alloy at non-deformed condition, (a) Top and (b) Lateral views, deformed by HPT at 1 GPa, (c) Top and (d) Lateral views and deformed at 4.5 GPa, (e) Top and (f) Lateral views.
Figure 27(a) shows self-organized TiO2 nanotubes formed in the α’ phase and TiO2 nanoporous in the β phase of Ti13Nb13Zr alloy non-deformed. The different nanostructures observed may be explained by the fact that there is a competition between the dissolution and the formation of oxides depending on the chemical composition of both phases. The lateral view of these nanostructures (Figure 27(b)) shows self-organized arrays of nanotubes whose dimensions are described in Table 4.
Table 4: Summary of observed morphologies and dimensions of the formed nanostructures observed in Figure 27 for samples of Ti13Nb13Zr alloy at different conditions.
GPa Nanotubes and 47±10 94±11 1492 ± 73 nanopores
In the same way, the samples deformed by HPT, Figures 27(c) and (e), presented different nanostructures. However, since processing by HPT caused a refinement and spatial redistribution of the α’ and β phases, the deformed samples presented a more homogenous distribution of the nanostructures.
Samples chemically treated by HCl etching and NaOH activation
The surface morphology of samples of Ti13Nb13Zr alloy, chemically treated by HCl etching and NaOH activation, was examined by scanning electron microscopy (SEM). The secondary electron (SE) detection mode with an acceleration voltage of 25 kV was selected for SEM analysis. Figure 28 shows SEM images of Ti13Nb13Zr alloy, chemically treated, at the conditions ND, HPT1GPa, and HPT4.5GPa. Figures 28(b), (d) and (f) are SEM images of higher magnification to show more details of surface morphology.
Figure 28: SEM images of Ti13Nb13Zr alloy, chemically treated by HCl etching and NaOH activation, (a and b) non-deformed, deformed by HPT at (c and d) 1 GPa and deformed by HPT at (e and f) 4.5 GPa.
As shown in the micrographs of Figure 28, the chemically treated by HCl and NaOH, induced the formation of a nano topographic sponge-like morphology on the samples’ surface. Also observed in Figure 28 is that the surface is completely cracked. This behavior has previously been described. For example, Jonášová et al., (2004) reported, that HCl etching of commercially pure Ti leads to the formation of a micro-roughened surface, which after subsequent alkali treatment in NaOH is maintained [128]. Yi et al., (2006) reported, for commercially pure grade 2 Ti treated with H2SO4/H2O2 mixture, a texture characterized by a three-dimensional sponge-like porosity on chemically treated cp Ti surface [129].
On the other hand, in order to obtain an analysis of the surface composition, EDS analysis was performed. The results are shown in Table 5.
Raman spectroscopy was used to identify the crystalline phases present on the surface of samples of Ti13Nb13Zr alloy chemically treated. The results shown in Figure 29 indicate that sodium titanate, anatase, and rutile are the main phases present in all the samples.
Figure 29: Raman spectra of the surface of Ti13Nb13Zr alloy chemically treated by HCl etching and NaOH activation.
Samples chemically treated by H3PO4 etching and NaOH activation
The surface morphology of Ti13Nb13Zr alloy samples, which were chemically treated by H3PO4 etching and NaOH activation, was examined by scanning electron microscopy (SEM). Figure 30 shows SEM images of chemically modified surfaces of Ti13Nb13Zr alloy in the conditions ND, HPT1GPa, and HPT4.5GPa. Figures 30(b), (d) and (f) are SEM images of higher magnification to show more details about the surface morphology.
As observed in the samples treated with HCl, the chemically treated by H3PO4 and NaOH also induced the formation of a nano topographic sponge-like morphology on the samples’ surface, and a surface full of cracks. The etched in different acids, such as HCl, H3PO4 or a mixture of HF+HNO3, and subsequently pretreated in NaOH, were reported for sintered Ti13Nb13Zr alloy by Müller et al., (2008) [130]. The authors also reported a micro-roughened surface as well as microcracks.
Table of contents :
1 INTRODUCTION
2 OBJECTIVES
3 THEORETICAL BACKGROUND
3.1 Titanium: Physical Metallurgy
3.2 Ti13Nb13Zr alloy
3.3 Ti35Nb7Zr5Ta alloy
3.4 Severe Plastic Deformation (SPD)
3.5 Surface modification treatments.
3.5.1 The growth of TiO2 nanostructures by electrochemical anodization
3.5.2 Chemical treatment by acid etching and alkali activation
3.6 Electrochemical characterization
3.6.1 Measurements of open circuit potential (OCP)
3.6.2 The principle of potentiodynamic polarization and extrapolation of Tafel . 24
3.6.3 Electrochemical Impedance Spectroscopy (EIS)
3.6.4 Corrosion of ultrafine-grained materials obtained by severe plastic deformation
3.7 Osseointegration
4 MATERIALS AND METHODS
4.1 Preparation of samples
4.2 High-Pressure Torsion (HPT) deformation
4.3 Surface modification treatments
4.3.1 Electrochemical anodization
4.3.2 Chemical treatment by acid etching and alkali activation
4.4 Electrochemical characterization
4.4.1 Experimental assembly
4.4.2 Protocol and measurement sequence
4.5 Bioactivity assays
4.6 Methods of characterization of samples
4.6.1 Mechanical characterization
5 EXPERIMENTAL RESULTS: Ti13Nb13Zr ALLOY
5.1 Microstructural and mechanical characterizations
5.1.1 Polished samples
5.1.2 Anodized samples
5.1.3 Samples chemically treated by HCl etching and NaOH activation
5.1.4 Samples chemically treated by H3PO4 etching and NaOH activation
5.2 Electrochemistry characterization
5.2.1 Polished samples
5.2.2 Anodized samples
5.2.3 Samples chemically treated by HCl etching and NaOH activation
5.2.4 Samples chemically treated by H3PO4 etching and NaOH activation
5.3 Modeling of impedance spectra for samples of Ti13Nb13Zr alloy
5.3.1 EEC proposed for polished samples
5.3.2 EEC proposed for anodized samples
5.3.3 EEC proposed to samples chemically treatment by HCl etching and NaOH activation
5.3.4 EEC proposed to samples chemically treatment by H3PO4 etching and NaOH activation
5.4 Bioactivity of Ti13Nb13Zr alloy
5.4.1 Bioactivity of polished samples
5.4.2 Bioactivity of anodized samples
5.4.3 Bioactivity of samples chemically treatment by HCl etching and NaOH activation
5.4.4 Bioactivity of samples chemically treatment by H3PO4 etching and NaOH activation
6 EXPERIMENTAL RESULTS: Ti35Nb7Zr5Ta ALLOY
6.1 Microstructural and mechanical characterizations
6.1.1 Polished samples
6.1.2 Anodized samples
6.1.3 Samples chemically treated by HCl etching and NaOH activation
6.1.4 Samples chemically treated by H3PO4 etching and NaOH activation
6.2 Electrochemistry characterization
6.2.1 Polished samples
6.2.2 Anodized samples
6.2.3 Samples chemically treated by HCl etching and NaOH activation
6.2.4 Samples chemically treated by H3PO4 etching and NaOH activation
6.3 Modeling of impedance spectra for samples of Ti35Nb7Zr5Ta alloy
6.3.1 EEC proposed for polished samples
6.3.2 EEC proposed for anodized samples
6.3.3 EEC proposed for samples chemically treated by HCl etching and NaOH activation
6.3.4 EEC proposed for samples chemically treated by H3PO4 etching and NaOH activation
6.4 Bioactivity of Ti35Nb7Zr5Ta alloy
6.4.1 Bioactivity of polished samples
6.4.2 Bioactivity of samples anodized
6.4.3 Bioactivity of samples chemically treated by HCl etching and NaOH activation
6.4.4 Bioactivity of samples chemically treated by H3PO4 etching and NaOH activation
7 DISCUSSION
8 SUMMARY AND CONCLUSIONS:
9 REFERENCES
