the Zr content increased Ti-40Nb-xZr alloys. As the Zr content of the Ti-40Nb-xZr alloys increased, the FWHM (full width at half maximum) of x-ray peaks became narrower, which means that the grain size of the alloy increased and the hardness decreased [55]. In addition, as the Zr content increased, the peak shifted to the left, which is a phenomenon that occurs when Zr added, which has a larger atomic radius than Ti and Nb elements, is inserted into a solid solution, increasing lattice parameters [56].
Fig. 15. XRF results of Ti-40Nb-xZr alloys after heat treatment at 1050℃ for 1h in Ar atmosphere, follwed by 0℃ water quenching: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Table 7. XRF results of Ti-40Nb-xZr alloys after heat treatment at 1050℃ for 1h in Ar atmosphere, followed by 0℃ water quenching
Elements (%) Specimen
Ti Nb Zr
Ti-40Nb 60.26 ± 0.52 39.74 ± 0.51
-Ti-40Nb-3Zr 55.96 ± 0.66 40.94 ± 0.61 3.10 ± 0.06 Ti-40Nb-7Zr 53.12 ± 0.66 39.77 ± 0.54 7.11 ± 0.12 Ti-40Nb-15Zr 45.15 ± 0.76 39.68 ± 0.53 15.17 ± 0.23
Fig. 16. Optical micrographs of Ti-40Nb-xZr alloys after heat treatment at 1050℃ for 1h in Ar atmosphere, followed by 0℃ water quenching: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 17. XRD results of Ti-40Nb-xZr alloys after heat treatment at 1050℃ for 1h in Ar atmosphere, followed by 0℃ water quenching: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Ⅳ. 2. Elastic modulus and hardness of Ti-40Nb and Ti-40Nb-xZr alloys
Ⅳ. 2. 1. Ti-40Nb alloys
Figure 18 shows images of the indentation observed with an optical microscope after nano-indentation measurement according to the phase of Ti-40Nb alloy. It can be seen that the degree of ductile and brittle deformation is different depending on the phase of the alloy, and this can be seen by looking at the indentation trace. In the α” phase of the needle structure, the indentation area was small, and in the β phase of the equiaxed structure, a relatively wide and deep indentation was formed. The deeper the indentation trace, the more severe the deformation and the lower the hardness [57].
Therefore, it can be seen that the β phase has a lower elastic modulus and hardness than the α” phase from the indentation in Figure 18.
Figure 19 shows the load-displacement graph of Ti-40Nb alloy obtained after the nano-indentation measurement and the bar graph of the measured values. Figure 19 (a) is the β phase of the Ti-40Nb alloy, (d) is the nano-indentation measurement graph of the α” phase of the Ti-40Nb alloy. From Figure 19 (a) to (d), the alloy phase changes from β to α” phase. As a result of the nano-indentation measurement, the graph shifts to the left as the alloy phase moves to the α” phase, indicating that the nano-indentation hardness and elastic modulus values increase. The nano-indentation hardness was 3.47 GPa in Figure 19 (a) and 5.48 GPa in Figure 19 (d), which showed that the hardness of the α” phase increased by 1.58 times than the β phase hardness.
The elastic modulus in Figure 19 (a) is 89.35 GPa, and the elastic modulus in Figure 19 (d) is 168.17 GPa, showing that the elastic modulus also increases from the β phase to the α” phase. This is consistent with previous studies that the hardness value and the elastic modulus decrease as the β phase increases [31]. The detailed nano-indentation hardness values and elastic modulus values of Ti-40Nb are shown in
Fig. 18. Optical micrographs of Ti-40Nb alloy after nano-indentation measurement according to phase.
Fig. 19. Nano-indentation test results of Ti-40Nb alloy according to phase after heat treatment at 1050℃ for 1h in Ar atmosphere followed by 0℃ water quenching.
Table 8. Elastic modulus and nano-indentation hardness value of Ti-40Nb alloy according to phase
Position
Nano-indentation Hardness
[GPa]
Elastic Modulus [GPa]
Ti-40Nb(a) 3.47 ± 0.12 89.35 ± 6.17
Ti-40Nb(b) 4.13 ± 0.05 98.26 ± 3.93
Ti-40Nb(c) 5.12 ± 0.01 127.72 ± 2.29
Ti-40Nb(d) 5.48 ± 0.11 168.17 ± 17.94
Ⅳ. 2. 2. Ti-40Nb-xZr alloys
After measuring the nano-indentation of Ti-40Nb-xZr alloys according to the Zr content, images of indentations observed with an optical microscope are shown in Figure 20 (a ~ d). Figure 20 (a) shows the indentation trace of Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr. Show the indentation traces, and it can be seen that the size of the area increased as the content of Zr increased.
Figure 21 shows the measured nano-indentation results of Ti-40Nb-xZr alloys as load-displacement graph and bar graph. It can be seen that the Ti-40Nb-xZr alloys are divided into an elastic region and a plastic region through the graph curve shape. In the case of Ti-40Nb-xZr, it can be seen that the amount of plastic deformation is significantly increased when compared with Ti-40Nb. As the content of Zr increased, the graph shifted to the right, which means that the alloy hardness decreased. From the measured nano-indentation hardness values, Ti-40Nb was 4.55 GPa, Ti-40Nb-15Zr was 2.00 GPa, and the nano-indentation hardness of the alloy to which Zr was added decreased by about 0.44 times. Detailed nano-indentation hardness values are shown in Table 9, and it can be seen that the hardness decreases as the Zr content increases.
The elastic modulus also decreased as the Zr content increased, as shown from the slope when the load is removed in Figure 21. The gentler slope of the load-displacement graph when the load is removed, the lower the elastic modulus becomes. As the Zr content increases, the slope becomes gentler when the load is removed. As a result of nano-indentation measurement, the elastic modulus of the Ti-40Nb alloy without Zr was 120.87 GPa, and the elastic modulus of Ti-40Nb-xZr alloys decreased as the Zr content increased. This is due to the effect of the element Zr, Zr added to the alloy can reduce other phase formations, such as the omega (ω) phase, which is known to increase the elastic modulus. Therefore, in the Ti-40Nb-xZr alloys, the ω phase, which appears when the β-type alloy is quenched, was not formed under the influence of Zr. Moreover, the elastic modulus was lowered under the influence of the β-type element [58,59]. The elastic modulus of Ti-40Nb-15Zr is 67.16 GPa, which is reduced by about 0.52 times compared to the elastic modulus (130 GPa)
of Ti-6Al-4V alloy widely used implant material. Ti-40Nb-xZr alloys, which have a low elastic modulus, are expected to reduce the difference in elastic modulus with human bones, preventing the stress shielding effect [4].
Fig. 20. Optical micrographs of Ti-40Nb-xZr alloys after nano-indentation measurement:
(a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 21. Nano-indentation test results of Ti-40Nb-xZr alloys after heat treatment at 105 0℃ for 1h in Ar atmosphere followed by 0℃ water quenching.
Table 9. Elastic modulus and nano-indentation hardness value of Ti-40Nb-xZr alloys
Nano-indentation Hardness
[GPa]
Elastic Modulus [GPa]
Ti-40Nb 4.55 ± 0.79 120.87 ± 30.78 Ti-40Nb-3Zr 2.31 ± 0.48 85.98 ± 4.38 Ti-40Nb-7Zr 2.08 ± 0.28 76.33 ± 5.57 Ti-40Nb-15Zr 2.00 ± 0.30 67.16 ± 10.15
Ⅳ. 3. Surface properties of Ti-40Nb-xZr alloys treated with plasma electrolytic oxidation (PEO)
Figure 22 shows the spark discharge appearing on Ti-40Nb-xZr alloys during the PEO treatment in an electrolyte containing Ca and P ions. Figure 22 (a ~ d) shows spark discharge images Ti-40Nb, Ti-40Nb-3Zr, Ti-40Nb-7Zr, and Ti-40Nb-15Zr, respectively. From 0.0 to 0.1 sec after the start of the PEO treatment, it can be seen that the intensive gas bubbles associated with the appearance of the spark discharge occur, which means that all coatings have the same fracture value regardless of the Zr content of the alloy [60]. Afterward, irregular spark discharges appeared on the entire surface of alloys, and it was confirmed that as the Zr content increased, more elongated sparks were generated on the alloy surface. This spark discharge is thought to affect the pore morphology of the alloy surface. The spark discharge was actively formed before 10 sec but was rarely formed from 10 sec to 180 sec.
As a result of FESEM observation of the pore morphology formed on Ti-40Nb-xZr alloys surface after the PEO treatment, as shown in Figure 23, the pore morphology was formed differently depending on the Zr content. It was also observed that porous and irregularly sized pores were formed on alloys surfaces. As the Zr content increased, the size of the pores gradually increased, and pores in the form of large grooves were formed in Ti-40Nb-15Zr. During the PEO treatment, an extended spark discharge occurred on the surface of Ti-40Nb-15Zr alloys for a long time compared to other alloys. Therefore, it is thought that the large pores are connected to form groove-shaped pores. As a result of magnification around the pores and observation with FESEM, Ca and P ions in the electrolyte were observed on alloys surface [61].
Figure 24 shows the results of analyzing the pores formed on the alloy surface with Image J. Figure 24 (a) shows the small and large pore size, (b) shows the porosity and number of pores, and (c) shows the fraction of large pores. After determining pores with a size of fewer than 1 ㎛ as small pores, the size of the pores was similar regardless of the Zr content. However, as a result of measuring the size of large pores than 1 ㎛, pores size also increased as the Zr content increased. In particular, in
Ti-40Nb-15Zr, pores size increased rapidly, and the proportion of the pores increased as pores size increased. Therefore, From the Figure 24 (a, b), it can be seen that the graphs showing large pores size and the ratio of the pores are measured and drawn similarly. As pores size increased, the number of pores decreased, and the area occupied by large pores increased. This change in pores size is likely to affect the roughness of alloys, and the detailed measured values are shown in Table 10.
The results of EDS analysis of the pore-formed surface are shown in Figure 25.
Figure 25 (a ~ d) is Ti-40Nb, Ti-40Nb-3Zr, Ti-40Nb-7Zr, and Ti-40Nb-15Zr, respectively. In Figure 25 (a), Zr element was not detected with Ti-40Nb alloy, and in 25 (b ~ d), Zr element was detected with Ti-40Nb-xZr alloys. The Zr element peak increased as the Zr content increased, and Ca and P ions in the electrolyte due to the PEO treatment were detected on all alloy surfaces. The detected Ca/P ratios were 1.58, 2.06, 1.98, and 2.32 wt.%, respectively, depending on the Zr content, and it was confirmed that Zr was added alloys had a higher ratio than the Ca/P ratio. The oxide layer, including Ca and P elements formed on the alloy surface, is expected to improve the biocompatibility and increase the bonding force between the bone and the implant [52].
To observe the oxide layer thickness, fine grinding was performed down to 0.3 ㎛ and then analyzed using FESEM and EDS line profiling. As observed from the FESEM image of Figure 26, the coating layer was divided into an inner layer and an outer layer, and large and small pores inside the oxide layer could be observed. As a result of line profiling, it was observed that the boundary between the coating layer and alloys was clearly divided, and the thickness of the coating layer could be confirmed.
In the coating layer, oxygen by the TiO2 layer generated by the PEO treatment was detected, and Ca, and P elements in the electrolyte were detected. Conversely, O, Ca, and P elements were not detected in alloys, and Ti, Nb, and Zr elements, which are alloying elements, were detected. The results of analyzing the oxide layer thickness using Image J are shown in Figure 27 and Table 11. As a result of measuring the average value and standard deviation of the oxide layer thickness by 5 measurements
respectively, but gradually thickened as the Zr content increased, and the oxide layer of Ti-40Nb-15Zr was 3.67 ㎛. It was confirmed that a thicker oxide layer was formed compared to other alloys. In Ti-40Nb-xZr, as Zr increased, a thick oxide layer was formed, which is thought to be related to the spark discharge in Figure 22.
Figure 28 shows the x-ray diffraction diagram of Ti-40Nb-xZr after PEO treatment in an electrolyte containing Ca and P ions. Figure 28 (a) is Ti-40Nb, (b) is Ti-40Nb-3Zr, (c) is Ti-40Nb-7Zr, and (d) is Ti-40Nb-15Zr. Anatase and rutile phases by the TiO2
layer formed on the alloy surface were detected at 2θ = 38.72°, 54.85°, 69.91°, and 82.57°. In addition, Nb and Zr added to the alloy occupied the Ti element site, and Nb2O5 and ZrO2 were formed instead of TiO2. Therefore, as the Nb element was added to the alloy and the Zr content was increased, the formation of TiO2 decreased, and the peaks of anatase and rutile phases decreased, and Nb2O5, ZrO2 peaks increased. 2θ = 69.91°, 69.87°, 69.77°, 69.28°, and PEO-treated alloys, the lattice parameters increased as the Zr content increased, and the peak shifted to the left [56].
Fig. 22. Spark discharges images of Ti-40Nb-xZr alloys with coating time in PEO treatment in a solution containing Ca and P ions:
(a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 23. FESEM images of PEO-treated Ti-40Nb-xZr alloys in a solution containing Ca and P ions: (a) Ti-40Nb, (a-1) high magnification of Ti-40Nb, (b) Ti-40Nb-3Zr, (b-1) high magnification of Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, (c-1) high magnification of
Fig. 24. PEO-treated Ti-40Nb-xZr alloys in a solution containing Ca and Pions: (a) small and large pore size, (b) porosity and number of pore, and (c) fraction of large pores.
Table 10. Pore analysis of PEO-treated Ti-40Nb-xZr alloys in a solution containing Ca and P ions
Specimens
Ti-40Nb-xZr
0Zr 3Zr 7Zr 15Zr
Porosity (%) 7.56 ± 0.30 12.87 ± 0.63 15.85 ± 0.66 38.70 ± 1.08
Large pore size (≥1 ㎛ ) 1.68 ± 0.41 2.74 ± 1.03 3.38 ± 0.68 11.53 ± 0.55 Small pore size (≤1 ㎛ ) 0.40 ± 0.12 0.92 ± 0.42 0.97 ± 0.03 0.49 ± 0.16 Number of pore (2500 ㎛2) 234.50 ± 7.26 99.25 ± 5.40 76.25 ± 5.40 33.75 ± 5.80
Fig. 25. EDS result of PEO-treated Ti-40Nb-xZr alloys in a solution containing Ca and P ions: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 26. FESEM images and EDS line profiling of the coating layer of PEO-treated Ti-40Nb-xZr alloys at 280V in a solution Ca and P ions: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 27. Oxide layer thickness of the coating layer of PEO-treated Ti-40Nb-xZr alloys in a solution containing Ca and P ions.
Table 11. Oxide layer thickness measurements value of Ti-40Nb-xZr alloys after PEO-treatment in a solution containing Ca and P ions
Samples
Ti-40Nb-xZr
0Zr 3Zr 7Zr 15Zr
Thickness of oxide layer (㎛)
7.56 ± 0.30 12.87 ± 0.63 15.85 ± 0.66 38.70 ± 1.08
Fig. 28. XRD results for Ti-40Nb-xZr alloys after PEO-treatment in a solution containing Ca and P ions: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Ⅳ. 4. Surface properties of anodized Ti-40Nb-xZr alloys
Figure 29 shows the observation results of Ti-40Nb-xZr alloys surface with nanotubes using FESEM. Figure 29 (a ~ d) shows Ti-40Nb, Ti-40Nb-3Zr, Ti-40Nb-7Zr, and Ti-40Nb-15Zr, respectively, and nanotubes formed on the alloy surface can be observed.
It was observed that nano-sized pores due to the nanotubes were formed on the surface of the alloy. And the diameter of the nanotube decreased as the content of Zr increased. This result is consistent with previous studies that the nanotube diameter varies according to the alloy composition [18].
The results of observing the alloy surface from which the nanotubes were removed are shown in Figure 29 (a-1 ~ d-1). After the nanotubes were removed, a very small nanomesh surface with nanostructures was formed on the surface, and this structure is known to shorten the initial healing period after implantation into bone [13]. Figure 29 (a-2 ~ d-2) is an image of the bottom surface of the removed nanotube observed by FESEM, and it can be seen that the nanotube diameter size is different depending on the elements of the alloy. After classifying nanotubes with large diameters and small nanotubes based on 0.1 ㎛, the diameter of the bottom of the nanotube was randomly measured 10 times through Image J, and the measured values are shown in Figure 30 and Table 12. When 3 wt.% Zr was added, the bottom diameter of the large nanotube increased from 115.40 nm to 124.07 nm, and the bottom diameter of the small nanotube decreased from 71.69 nm to 71.56 nm. As the Zr content increased, the bottom diameters of large and small nanotubes decreased, forming nanotubes with 117.73 nm and 64.94 nm and showing a regular arrangement. At the bottom of Ti-40Nb-15Zr, nanotubes with large diameters were surrounded by small nanotubes. As a result of microstructure and XRD analysis, the alloy changed to the β phase as the Zr content increased, and stable nanotubes were formed in the β phase rather than the α phase [29]. Therefore, stable nanotubes are formed in the β-phase Ti-40Nb-15Zr alloy, showing a regular arrangement.
To confirm the nanotube thickness according to the alloy composition, the nanotube side surface was observed by FESEM. This is shown in Figure 31, and a change in
the nanotube thickness according to the Zr content was observed. The values of the nanotubes measured by Image J are shown in Figure 32 and Table 13. The nanotube thickness of Ti-40Nb without Zr was 1.80 ㎛, and the nanotube length of Ti-40Nb-15Zr with the highest Zr content was 2.17 ㎛. As a result of comparing the nanotube thickness of Ti-40Nb-xZr to which Zr was added, the nanotube thickness increased as the Zr content increased. Depending on the alloying element composition, the nanotube length can be controlled, and the amount of drug doped on the nanotube surface can be controlled [62].
The x-ray diffraction diagram of Ti-40Nb-xZr with nanotubes is shown in Figure 33.
Anatase and rutile phases were detected by the nanotube layer, and Nb2O5 and ZrO2
peaks were detected under the influence of Nb and Zr elements. The (110) plane of anatase is critically compatible with the (0001) plane of HA. Therefore, HA formation was induced through nanotube formation, and the HA phase was detected [51].
Fig. 29. FESEM images of the nanotube surface formed on the Ti-40Nb-xZr alloys in 1.0M H3PO4 with 0.8 wt.% NaF electrolyte by anodization for 1 h at 20V: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, (d) Ti-40Nb-15Zr, (a ~ d) nanotube surface (a-1 ~ d-1) deleted nanotube surface, (a-2 ~ d-2) bottom of nanotubes.
Fig. 30. The diameter value of the nanotube bottom formed on the Ti-40Nb-xZr alloys:
(a) large nanotube bottom, (b) small nanotube bottom.
Table 12. The diameters of the nanotube bottom formed on the Ti-40Nb-xZr alloys: (a) large nanotube bottom, (b) small nanotube bottom
Samples
Ti-40Nb-xZr
0Zr 3Zr 7Zr 15Zr
Diameter of large nanotube bottom
(nm)
115.40 ± 12.15 124.07 ± 8.40 122.92 ± 13.94 117.73 ± 12.99 Diameter of small
nanotube bottom (nm)
71.69 ± 7.74 71.56 ± 12.25 65.50 ± 9.35 64.94 ± 8.24
Fig. 31. FESEM images of the nanotube thickness formed on the Ti-40Nb-xZr alloys in 1.0M H3PO4 with 0.8 wt.% NaF electrolyte by anodization for 1 h at 20V: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 32. Nanotube thickness formed on the Ti-40Nb-xZr alloys according to Zr contents.
Table 13. Nanotube thickness formed on the Ti-40Nb-xZr alloys according to Zr contents
Samples
Ti-40Nb-xZr
0Zr 3Zr 7Zr 15Zr
Thickness of
Nanotube (㎛) 1.80 ± 0.12 1.91 ± 0.17 1.92 ± 0.07 2.17 ± 0.10
Fig. 33. XRD results of the nanotube surface formed on the Ti-40Nb-xZr alloys in 1.0M H3PO4 with 0.8 wt.% NaF electrolyte by anodization for 1 h at 20V: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Ⅳ. 5. Surface properties of Ti-40Nb-xZr alloys coated with hydroxyapatite (HA) by RF-magnetron sputtering
Ⅳ. 5. 1. Surface properties of Ti-40Nb-xZr alloys coated with HA by RF-magnetron sputtering after polishing
Figure 34 shows the FESEM image of the surface of the alloy (Bulk+HA) on which the HA coating layer was formed using RF-magnetron sputtering after polishing up to
#2000 using SiC paper. Figure 34 (a ~ d) show the surfaces of Ti-40Nb, Ti-40Nb-3Zr, Ti-40Nb-7Zr, and Ti-40Nb-15Zr alloys, respectively parallel lines appearing on the alloy surface are scratch generated by polishing before coating. It could be seen that the HA coating layer formed on the alloy surface covered the scratch, and it was confirmed that the HA coating was uniformly well formed on the alloy surface. In addition, HA particles were observed on the alloy surface when the HA-coated Ti-40Nb-xZr alloys surface was observed at high magnification using FESEM.
As a result of analyzing the surface of the HA-coated alloy with EDS, elements, as shown in Figure 35, were detected. Alloying elements Ti, Nb, and Zr, were detected, and Ca, P, and O elements were detected by the HA coating layer. It can be seen that a uniform HA coating layer is formed on the alloy surface due to the detection of Ca, P, and O elements. Most of the peaks were similarly detected regardless of the alloy composition, but as the Zr element content increased, the Zr peak was stronger, and the Ti peak was weakly detected.
Figure 36 shows the XRD analysis results of Ti-40Nb-xZr alloys coated with HA by RF-magnetron sputtering. As a result of analyzing the XRD diffraction peak compared to the JCPDS file, a peak of HA crystallized by the coating layer was observed.
Compared to bulk Ti-40Nb-xZr alloys without HA coating (Figure 17), broad and weak peaks were detected. The HA particle size was very small, 24.29 ± 2.46 nm and abroad, and a weak peak was detected when the HA particle size was extremely small,
Fig. 34. FESEM images of HA-coated surface by RF-magnetron sputtering on Ti-40Nb-xZr alloys: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 35. EDS result of HA-coated surface by RF-magnetron sputtering on Ti-40Nb-xZr alloys: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 36. XRD result of HA-coated surface by RF-magnetron sputtering on Ti-40Nb-xZr alloys: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Ⅳ. 5. 2. Surface properties of Ti-40Nb-xZr alloys coated with HA by RF-magnetron sputtering after PEO treatment
After PEO treatment, HA coating (PEO+HA) was deposited on the alloy surface for 30 minutes using RF-magnetron sputtering, and the image observed with FESEM is shown in Figure 37. Comparing the FESEM images observed at high magnification in Figure 37 and Figure 23, it can be observed that HA particles generated by the RF-magnetron sputtering treatment are formed on the alloy surface. HA particles by PEO treatment were rarely seen even before HA coating, but after coating, even and uniform HA particles were observed on the entire surface. As a result of measurement using image J, the diameter of the spherical particles was 5 to 10 nm, which was smaller than the HA particle size of Bulk+HA.
As a result of EDS analysis, many Ca and P ions were detected on the alloy surface by PEO treatment and HA coating. These results show that the HA coating is uniformly formed on the surface of Ti-40Nb-xZr alloys, and the coating layer formed on the implant's surface is expected to improve osseointegration and shorten the initial healing period of the implant. In addition, the corrosion resistance is increased due to the formed HA layer, which is considered suitable for clinical use [51].
The results of the XRD analysis of PEO+HA alloy are shown in Figure 39; Figure 39 (a ~ d) shows x-ray diffraction diagram of alloys Ti-40Nb, Ti-40Nb-3Zr, Ti-40Nb-7Zr, and Ti-40Nb-15Zr, respectively. As seen from the XRD, anatase and rutile phases of TIO2 generated by PEO layer treatment were detected. In addition, the HA phase was detected by ions Ca and P in the electrolyte and HA coating layers.
Compared with the XRD of Ti-40Nb-xZr alloys after PEO treatment without HA coating (Figure 28). After HA coating, an additional HA phase was detected at 2θ = 68.42°, 84.71°. This seems to be the effect of HA particles uniformly forming on the PEO pores after HA coating.
Fig. 37. FESEM images of HA-coated surface by RF-magnetron sputtering on PEO-treated Ti-40Nb-xZr alloys in solution containing Ca and P: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 38. EDS result of HA-coated surface by RF-magnetron sputtering on PEO-treated Ti-40Nb-xZr alloys in solution containing Ca and P: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Fig. 39. XRD result of HA-coated surface by RF-magnetron sputtering on PEO-treated Ti-40Nb-xZr alloys in solution containing Ca and P: (a) Ti-40Nb, (b) Ti-40Nb-3Zr, (c) Ti-40Nb-7Zr, and (d) Ti-40Nb-15Zr.
Ⅳ. 5. 3. Surface properties of Ti-40Nb-xZr alloys coated with HA by RF-magnetron sputtering after anodizing
Figure 40 is an FESEM image of the HA-coated nanotube surface (Nano+HA) by RF-magnetron sputtering after anodization in 1M H3PO4 and 0.8 wt.% NaF electrolyte.
As a result of coating simultaneously, the HA coating was better on the nanotube surface with nano-sized pores than on the polished surface and the PEO-treated surface.
It was confirmed that the HA coating layer was blocking the nanotube pores, and as the Zr content increased, regular nanotubes were formed, confirming that the HA coating was well performed. As a result of observing the nanotube side surface, it was observed that the HA coating layer was formed over the nanotube pores. Coating using RF-sputtering is clinically applied to dental implants by forming an HA coating layer with high bonding strength on the alloy [63]. Therefore, it is considered that the HA coating layer with high bonding strength formed on the nanotubes is not easily peeled off. As a result of analyzing the surface of the Nano+HA alloy using EDS, Ca and P elements were detected by the coating layer, and the formed HA coating layer is expected to promote biocompatibility and bone formation by improving biocompatibility [64].
As a result of comparative analysis of the XRD results of Ti-40Nb-xZr alloys with nanotubes (Figure 33) and Nano+HA (Figure 42), a peak caused by HA coating was additionally detected at 2θ = 38.19°. A broad and weak peak was formed by the HA coating layer formed on the nanotube, and overall weak peaks were detected compared to Bulk+HA and PEO+HA. This is a phenomenon caused by the HA coating layer covering the nano-sized pores, and it can be confirmed from the FESEM observation that the HA coating was most uniformly formed on Nano+HA. Also, the influence of the HA coating layer uniformly formed on the nanotubes, the Nb2O5 peaks found at 2 θ = 47.17° and 48.22°.