The effects of composition and cold groove-rolling on Young's modulus were investigated to achieve low Young's modulus in β Ti–Nb–Sn ternary alloys for orthopedic applications, using ...Ti-(27.5–37.5)%Nb-(2.5–11.25)%Sn ternary alloys. Optical microscopy, transmission electron microscopy, and X-ray diffractometry revealed that the constituent phases of quenched and rolled alloys were classified into three regions of β, β(ω)+α” and α” in the Ti–Nb–Sn ternary phase diagram. The β phase was observed to stabilize by the addition of Sn, and the least stable β alloys existed along a line connecting Ti-37.5Nb-2.5Sn and Ti-27.5Nb–11Sn. Low Young's moduli of approximately 50 GPa were achieved by the least stable, quenched β Ti–Nb–Sn alloys, and these further decreased by cold groove-rolling, reducing the cross section by 75%. The lowest Young's modulus of 36 GPa was realized for the cold groove-rolled Ti–35Nb-3.75Sn alloy, in which the textures of 010α” of deformation-induced α” martensite and 011β of the β matrix developed preferentially, parallel to the rolling direction. The lattice deformation strain along the 010α” axis accompanied by β to α” martensitic transformation was observed to depend on the alloy composition and was maximized in Ti–35Nb-3.75Sn.
Thus, the low Young's modulus of the least stable β Ti–Nb–Sn alloys obtained after cold groove-rolling was attributed to the development of 010α” and 011β textures along the rolling direction, and the lowest Young's modulus of the cold groove-rolled Ti–35Nb-3.75Sn alloy was due to a large lattice deformation strain along the 010α” axis accompanied by β to α” transformation.
The wear resistance of TiNbSn alloy surfaces treated by plasma nitriding, TiN sputtering, and anodic oxidation was investigated with the goal of suppressing the release of wear debris that can act as ...abrasive particles. Among the investigated alloys, the anodized alloy exhibited the highest hardness, adhesive strength, surface roughness, and the lowest friction coefficient (COF) under dry conditions as well as in simulated body fluids of Hank’s balanced salt solution. Wear tracks on the treated alloys, other than the anodized alloy, showed well-defined plow contours owing to adhesive galling accompanied by plastic deformation, and a significant amount of debris was observed on the wear surface. In contrast, in the anodized alloy, the wear track was barely visible (grooves were shallow), and only a few debris objects were observed. The COF under wet conditions was found to be the same as that in the dry condition for the treated alloys except for the anodized alloy, which exhibited a reduced COF under wet conditions. Significant amounts of Si originating from the counter-body SiC were observed on the worn surfaces of the treated alloys, except for the anodized alloy, and the surface of the SiC ball was severely damaged. In contrast, for the anodized alloy, no trace of Si was detected and the surface of the SiC ball was not damaged. It is concluded that the high wear resistance of the anodized alloy can be attributed to the reduced damage afforded by the strongly bonded thick oxide with a hardened rough surface, and that the hydrophilic rough surface reduced the COF under wet wear conditions.
Graphical abstract
The mechanical properties of anodized TiNbSn alloy, prepared in an electrolyte of sodium tartrate acid with H2O2 under the application of a high voltage, were investigated in comparison with those of ...Ti6Al4V and pure Ti. The microstructure of anodized TiNbSn contains randomly distributed pores, whereas the anodic oxides on Ti6Al4V and Ti contain alternating layers with abundant and less abundant pores (mille-feuille structure). The hardness, surface roughness, and exfoliation strength of the anodized TiNbSn alloy were the highest among the samples investigated, and its Young's modulus remained unchanged after anodization. The wear resistance of the anodized TiNbSn alloy improved under both dry and wet friction conditions using Hank's balanced salt solution (HBSS). Anodized Ti generated debris on the abraded surface, and Ti6Al4V showed adhesive galling along with plastic deformation. However, no debris or galling appeared on the worn surface of the anodized TiNbSn alloy. The coefficient of friction of the anodized TiNbSn alloy under dry conditions decreased under wet conditions owing to the porous and rough surfaces allowing the penetration of liquid between the sample and abrasive SiC counterpart. We concluded that the anodized TiNbSn alloy exhibits excellent mechanical properties compared to Ti and Ti6Al4V alloy, and it could be utilized as an implant biomaterial.
•Anodized TiNbSn alloy formed porous, hardened, and strongly adhesive TiO2.•Anodized Ti and Ti6Al4V alloy showed a mille-feuille structure and low hardness.•Anodized TiNbSn exhibited high wear resistance and suppressed a release of debris.•High wear resistance of the anodized TiNbSn were due to the hardened and adhesive TiO2.
The photocatalytic properties of anodic oxides on a newly developed TiNbSn and commonly used Ti6Al4V alloys as biomaterials were investigated. The alloys were anodized in an electrolyte of sodium ...tartrate acid with H2O2 at a high voltage and the mechanism of the photocatalytic and antiviral activities was studied. The anodized TiNbSn and Ti6Al4V exhibited highly crystallized rutile TiO2 and poorly crystallized anatase TiO2, respectively. X-ray photoelectron spectroscopy analysis revealed the presence of oxides of the alloying elements in addition to TiO2. The anodized TiNbSn exhibited higher activities than Ti6Al4V, and electron spin resonance spectra indicated that the number of hydroxyl radicals (⋅OH) generated from the anodized TiNbSn was higher than that from the anodized Ti6Al4V. The results can be explained by two possible mechanisms: the higher crystallinity of TiO2 on TiNbSn than that on the Ti6Al4V reduces the number of charge recombination sites and generates abundant ⋅OH; charge separation in the anodic oxide on TiNbSn due to the electronic band structure between TiO2 and the oxides of alloying elements enhances photo activities. The excellent photoinduced characteristics of the anodized TiNbSn are expected to contribute to the safe and reliable implant treatment.
Titanium and its alloys have poor wear resistance, and the biological response to generated wear debris leads to aseptic loosing and pathological bone resorption. In the fretting wear of artificial ...hip joints, a significant part of the wear surface is contacted by elastic deformation, and electrochemical anodization is a promising method to control the mechanical properties of the surface and improve wear resistance. To suppress wear debris generation and metal ions elution from implant materials into body fluids, the tribocorrosion properties of a newly developed anodized TiNbSn implant alloy were evaluated in the presence of simulated body fluid and compared to those of pure Ti. During anodization under high voltage, spark discharge occurred due to dielectric breakdown occurred for the TiNbSn electrode, but not for the Ti electrode. The primary phase of the anodic oxide layer on TiNbSn alloy was rutile TiO2, whereas that on Ti was anatase TiO2. The anodic oxide layer on TiNbSn had a higher thickness, roughness, and surface area than that on anodized Ti. In addition, the hardness and exfoliation strength were higher than those of Ti. The coefficient of friction of anodized TiNbSn in fretting tests was similar or slightly lower than that of anodized Ti, and the open circuit potential remained unchanged for anodized TiNbSn but shifted to a more negative voltage for anodized Ti. The results suggest that the hard and strongly-adhered rutile TiO2 on TiNbSn formed by spark discharge during the high-voltage anodization process improves fretting wear resistance and reduces the generation of wear debris and elution of metal ions.
•Anodization formed thick, hard, and strongly-adhered rutile TiO2 on TiNbSn.•OCP of anodized Ti shifted negatively after start of fretting, while that of TiNbSn did not drop.•The worn surface of anodized TiNbSn was less damaged by adhesive galling.•Anodized TiNbSn improved fretting wear resistance and reduced wear debris generation.
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•Anodization in the electrolyte of sodium tartrate containing H2O2 formed highly crystallized porous TiO2 on TiNbSn.•High voltage application promoted crystallization and ...transformation of the anodic oxide to rutile.•Large amounts of OH radicals were detected in highly crystallized TiO2 on TiNbSn.•Anodized TiNbSn efficiently decomposed MB solution and exhibited superior photoactivity.
A bioactive TiNbSn alloy was anodized in an electrolyte of sodium tartrate containing hydrogen peroxide (H2O2). The photo-induced characteristics of the anodized alloy were explored by focusing on its crystallinity and electrochemical conditions. The electrolysis curve of the anodization exhibited a higher voltage in the TiNbSn substrate than in the pure Ti substrate. Highly crystallized porous rutile-structured TiO2 was formed on TiNbSn, whereas relatively low-crystallized glassy anatase-structured TiO2 was formed on Ti. The absorption spectra of the oxide, formed on TiNbSn, revealed a steep absorption decrease with increasing wavelength while an explicit transition was not observed for the oxide formed on Ti. The anodized TiNbSn alloy exhibited superior photoactivity and generated hydroxyl radicals under ultraviolet (UV) illumination. The photoactivity of the anodized TiNbSn was attributed to TiO2, which was highly crystallized by the application of a high voltage, thus suppressing the recombination of the photogenerated carriers.
Photo-induced properties of titanium dioxide on Ti–Pd alloy, prepared by anodic oxidation in acetic acid electrolytes have been studied and compared with those of the oxide on pure Ti. The ...photocatalytic activity of the anodic oxide on Ti–Pd was superior to that of the anodic oxide on Ti, and the highest photocatalytic activities were found for the anodic oxide prepared in electrolytes with 1 M or 2 M acetic acid. This superiority was attributed to PdO incorporation into the anodic oxide, which facilitates charge separation. Both photocatalytic activity and hydrophilicity of the anodic oxide varied with the acetic acid concentration in the electrolyte, and were related to the surface morphology of the anodic oxides, which is controlled by the electrochemical reaction. It is concluded that photo-induced properties are imparted to the corrosion-resistant Ti–Pd alloy by anodic oxidation in acetic acid aqueous solutions.
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•Anodic oxide on Ti–Pd exhibits superior photocatalytic activity to that on Ti.•Photoactivity and hydrophilicity were varied with the electrolyte composition.•High activity is ascribed to an incorporated PdO retarding charge recombination.•Electrolyte composition controls surface morphology of the oxides.
The microstructure and surface chemistry of titanium dioxide on TiNbSn alloy, prepared by anodic oxidation in acetic acid electrolytes and subsequent hot water (HW) treatment, have been studied to ...determine the effect of HW treatment on bioactivity. HW treatment promotes TiO2 formation and photo-induced properties were observed on the anodic oxide. Cross-section energy dispersive spectroscopy analysis of the implanted anodic TiNbSn treated with HW revealed the penetration of the constituent elements of bone, Ca and P, into TiO2, which was attributed to the high bonding strength between the bone and the implanted alloy. It is proposed that the high bioactivity observed as a result of HW treatment can be ascribed to the evolution of a crystallized anodic oxide TiO2, which promotes incorporation of the primary ingredients of a bone in the oxide.
•TiNbSn alloy was anodized in an acetic acid electrolyte and hot water treatment.•In vitro tests showed hydroxyapatite precipitation on anodized TiNbSn alloy.•In vivo test showed high bonding strength between bone and implant TiNbSn alloy.•Bone constituents of Ca and P are incorporated in the anodic oxide of implant.•Osseointegration originates from crystalline TiO2 formation by hot water treatment.
This study examines the superhydrophilicity and chemical state of boron-doped TiO2 prepared by the ion implantation method and explores the effect of annealing on them. XRD measurements show that the ...implanted sample forms a polycrystalline structure of anatase with no trace of rutile. Their water-contact angles are significantly reduced upon irradiation with ultraviolet light. The Ti 2p XPS spectra of the oxide exhibit a shoulder peak at the lower binding energy side of the main peak, whereas no shoulder is observed in single-crystal and annealed TiO2. This suggests that the titanium ions with lower valences are produced by boron doping and they disappear on subsequent annealing. The SIMS depth profile of boron in the as-implanted TiO2 exhibits a peak at a depth of 15-20 nm, whereas this peak disappears upon annealing. The water-contact angles increased on annealing under ultraviolet light illumination. It is concluded that the improvement in the superhydrophilicity by boron doping is due to the reduction of titanium, and the deterioration of superhydrophilicity with the subsequent annealing is due to the oxidation of reduced titanium and the inward diffusion of boron.
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