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The growth process of α phase in β-type bio-Titanium alloy TNTZ during aging at 723 K is investigated. The results show that acicular α phase has a Burgers orientation relationship with β matrix of {1−10}β//(0001)α, 〈111〉β//〈11−20〉α. The kinetics equation of acicular α phase length meets l = 333(t-3.95)^0.0764, while the kinetics equation of diameter meets d = 7.50(t-2.83)^0.353. The growth process of α phase can be divided into three stages. During stage I, α phase grows rapidly along both the long direction and the diameter. At beginning of stage I, fine acicular α phase grows with the long direction parallel to each other. Subsequently, α phase grows with another long direction beside the former one in a ‘V-shape’ or in a ‘near perpendicular shape’. During stage II, α phase grows slowly along the diameter, while, the growth along long direction will be gradually restricted with the other α around it. The phase distributes more homogeneously, and present 5 classic possible orientations between α variants. During stage III, α phase grows slowly along the diameter, and stops growing along long direction. The growth of α phase is affected by distortion energy, interface energy and diffusion anisotropy, and it is mainly controlled by Nb diffusion through the ledge riser of the interface between α and β phases.

In this study, Ti3.6Nb1.0Ta0.2Zr0.2 based coatings were deposited on anodized and non-anodized aluminum surfaces by PVD. For this purpose, a target for the magnetron sputtering PVD system was prepared from a β-type Ti–29Nb–13Ta–4.6Zr bulk alloy via hot-forgings. Surface morphologies and elemental composition analysis of the TNTZ-based PVD coatings were conducted using scanning electron microscopy attached with an energy dispersive spectroscopy incorporated (SEM-EDS). A micro-scratch and hardness tester was used to evaluate the adhesion and mechanical properties of the deposited coatings. The contact angle and electrochemical corrosion measurements were applied to assign the wettability levels and potential usability of the coated surfaces under in-vitro conditions. Also, the corrosion resistance of the coatings was compared with commercial Ti and Ti6Al4V alloys. The results showed that the coated surfaces were exhibited a hydrophilic behavior and adequate in-vitro resistance in simulated body fluids (SBF). Besides, the TNTZ coatings on anodized surfaces were presented different cracking mechanisms and higher adhesion resistance than that of their non-anodized surfaces. The reason for the behavior has been discussed in the present study.

Good ductility, low magnetic susceptibility, and tunable Young’s modulus are highly desirable properties for materials usage as spinal fixation rods. In this study, the effects of niobium content on the microstructure, magnetic susceptibility, and mechanical properties of Zr– x Nb (13 ≤ x≤23 wt%) alloys were investigated. For the Zr–15Nb and Zr–17Nb alloys, a remarkable increase in Young’s modulus was achieved due to the occurrence of deformation-induced ω phase transformation. This was the result of the competition of two factors associated with the Nb content: an increase of the stability of β phase and a decrease of the amount of athermal ω phase with increasing Nb content. When the Nb content was 15% or 17%, the amount of deformation-induced ω phase was maximum. Moreover, the magnetic susceptibility decreased with the deformation-induced β → ω phase transformation, and the Zr–17Nb alloy with apparent kink bands exhibited a smaller amount of springback than the Zr–15Nb alloy with {3 3 2} 〈1 1 3〉 mechanical twins. Furthermore, the ions released from the Zr– x Nb alloys in accelerated immersion tests were at a very low level. The combination of low initial Young’s modulus, and its remarkable variation induced by deformation, low magnetic susceptibility, good ductility, and smaller springback make the Zr–17Nb alloy a potential candidate for spinal fixation rods. Statement of Significance For the rods of spinal fixation devices, it is important but difficult to lower the springback for bending formativeness while keeping the low initial Young′s modulus for biocompatibility and lower the magnetic susceptibility for postoperative examination simultaneously. In this study, Zr–17Nb alloy was successfully developed via deformation-induced ω phase transformation during loading, simultaneously meeting the abovementioned properties for spinal fixation rods.

Deformation-induced ω-phase transformation during tensile deformation was investigated in the developed spinal-support alloy, Ti-9Cr-0.2O. Both preferential single-variant ω transformation along its [0001] direction and growth and/or assembling of uniformly distributed ω particles undergo in the alloy during tensile deformation. It is confirmed that this deformation-induced ω-phase transformation can be triggered by elastic strain or stress without plastic deformation. Furthermore, a re-orientation process works for this transformation; that is, the ω1 variant may re-orientate into the ω2 variant via {001} ⟨110〉 twinning-type mechanism probably related to the external loading condition and the orientations of ω and β phases.

Ti-29Nb-13Ta-4.6Zr (TNTZ), which is one of metastable beta-type Ti alloys, has developed as one of representative biomedical and dental Ti alloys in Japan. TNTZ subjected to solution treatment shows Young’s modulus of 60 GPa, which is close to that of cortical bone. In addition, TNTZ has very low cytotoxicity and good bone biocompatibility as well. Heat treatment like solution treatment and aging (STA) is mainly used for improving the mechanical properties of metastable beta-type Ti alloys because of alpha precipitates, while Young’s modulus also rises drastically. This study was investigated the effects of mechanical surface modifications such as fine particle bombarding (FPB) with steel and hydroxyapatite particles or friction stir processing (FSP) on the mechanical strength of TNTZ in order to maintain low Young’s modulus. The relative bone contact ratios between the cancellous bones of Japanese white rabbits and column-shaped TNTZ subjected to FPB of steel particles were also evaluated. Vickers hardness (HV) of TNTZ subjected to FPB with fine particles of steel and hydroxyapatite particles increased by HV30 to 200 at the edge of the specimen surface to around 100 to 300 mm in depth as compared with that of TNTZ subjected to solution treatment. The hydroxyapatite layer was formed on the specimen surface by FPB with fine particles of hydroxyapatite particles, although the trend was not significant by FPB with steel particles. Furthermore, the fatigue strength in high cycle fatigue region of TNTZ subjected to FPB with steel particles was improved and the fatigue limit showed around 400 MPa, although that of TNTZ subjected to FPB with fine particles of hydroxyapatite particles were around 60 MPa higher than that to TNTZ subjected to solution treatment (230 MPa). TNTZ with a rough surface texture (Ra: 0.65 μm) showed a relative bone contact ratio of more than 80% after undergoing FPB with fine particles of steel particles; this value was significantly higher than that of TNTZ with a surface texture (Ra: 0.07 μm). Lastly, the microstructure of TNTZ subjected to FSP showed the recrystallization area by the frictional heating with very fine equiaxed beta phase with an average grain diameter of 3.0 μm. The change in Vickers hardness of TNTZ subjected to FSP was almost identical to that of Young’s modulus and showed the almost same trend of FPB.

The microstructural evolution and its effect on biocompatibility of TNTZ through HPT processing were investigated systematically in this study. TNTZAHPT shows an enhanced mechanical biocompatibility, which is characterized by a higher tensile strength (1375 MPa) and hardness (450 HV) than those of TNTZST, TNTZAT, and Ti64 ELI while maintaining a relatively low Young’s modulus. In this study, such microstructural refinement of TNTZ and its effect on electrochemical biocompatibility through HPT processing are investigated systematically in this study. The microstructure of TNTZAT consists of randomly distributed needle-like α precipitates in the equiaxed β grains with a diameter of approximately 40 m. The microstructure of TNTZAHPT consists of nanograined (NG) elongated β grains that have subgrains of non-uniform morphologies resulting from distortion by severe torsional deformation. Furthermore, the β grains and subgrains are surrounded by non-equilibrium grain boundaries. The needle-like α precipitates are completely refined to a nanograined. TNTZAHPT exhibits an enhanced combination of excellent corrosion performance and improved cellular response compared to TNTZST, TNTZAT, and Ti64 ELI.

Metastable β-type titanium alloys are highly suitable for use as structural biomaterials applied to hard tissue, i.e., as cortical bone (hereafter, bone) replacing implants. However, their mechanical biocompatibitities, such as the Young’s modulus, strength and ductility balance, fatigue strength, resistance against fatigue crack propagation and fracture toughness, require improvenent for increased compatibility with bone. Through deformation, the metastable β-phase in a metastable β-type titanium alloy is transformed into various phases, such as α’ martensite, α” martensite, and ω-phases with exact phase depending by metastable β-phase stability. In addition, twinning is also induced by deformation. Deformation twinning effectively enhances the work hardening in the metastable β-type titanium alloy, leading to increased strength and ductility. This improvement is accompanied by with other deformation-induced transformations including the appearance of deformation-induced martensite and ω-phase transformation. The enhancement of the mechanical biocompatibility of various materials using the abovementioned deformation-induced transformation is described in this paper, for both newly developed metastable β-type Ti-Mo and Ti-Cr alloys for biomedical applications.

In previous studies, Ti-Mn alloys showed promising performance for biomedical applications, but their elongation required improvement. In this study, Mo was added to Ti-Mn alloys to promote mechanical twinning and improve their ductility. Four alloys for biomedical applications were designed and fabricated by cold crucible levitation melting: Ti-5Mn-3Mo (TMM-53), Ti-5Mn-4Mo (TMM-54), Ti-6Mn-3Mo (TMM-63), and Ti-6Mn-4Mo (TMM-64). The microstructure, mechanical properties, tensile deformation mechanisms, and electrochemical corrosion properties of the alloys were evaluated. Their hardness ranges from 336 to 373 HV. Their Young's modulus ranges from 89 to 100 GPa. Both hardness and Young's modulus tend to decrease with decreasing amount of athermal ω phase, which is caused by increasing alloying elements contents. Mo addition improves the elongation of TMM-53 and TMM-54 by promoting twinning. Conversely, it increases the tensile strength of TMM-63 and TMM-64. Particularly, TMM-54 shows an elongation of 34% with an ultimate tensile strength (UTS) of 935 MPa. TMM-63 shows an elongation of 14% and a UTS of 1220 MPa, associated to the formation of deformation-induced ω phase. Moreover, Mo addition decreases the corrosion rate of the Ti-Mn alloys to a level comparable to that of commercially-pure Ti. Keywords: Ti-Mn-Mo alloys, β phase, Mechanical properties, Deformation mechanisms, Electrochemical corrosion

The surface treatment technology known as ‘cavitation peening’ was employed in this study in order to enhance the durability of spinal implant fixture applications, which are subject to fretting fatigue. Cavitation peening can be realized by a technique in which a high-speed water jet is injected into water through a nozzle. It utilizes a phenomenon by which surface impacts due to collapsing cavitation bubbles induce work-hardening by introducing residual compressive stress near the surface. A fretting fatigue test was conducted on a spinal implant rod made of Ti-6Al-4V ELI in accordance with the ASTM F1717 standard, which is the established method for testing spinal implants after they are treated by cavitation peening. The residual stress was evaluated by using X-ray diffraction analysis. The hardness over the cross-sectional area was also measured using an indentation test. The obtained results show that cavitation peening drastically improves the fretting fatigue properties of spinal implant fixtures by as much as 2.2 times compared to untreated ones. This can be attributed to a significant increase in the hardness from 5.0 to 9.6 GPa and a high compressive residual stress of over 600 MPa induced by cavitation peening.

Li Q., Ma D., Li J., et al. Low young's modulus Ti-Nb-O with high strength and good plasticity. Materials Transactions 59, 858 (2018); https://doi.org/10.2320/matertrans.M2018021., Oxygen was added to Ti-38Nb (mass%) alloys to improve their mechanical properties. Ti-38Nb-xO (x = 0.13, 0.24, 0.46, mass%) alloys were prepared by arc melting, and subsequently subjected to homogenization, hot rolling, and solution treatment. It was found that adding oxygen suppresses the martensite transformation and exhibits strong solution strengthening effect. Single β phase is obtained in Ti-38Nb-0.24O, whereas Ti-38Nb-0.13O is composed of both α′′ and β phases. Both alloys exhibit double yielding phenomena during tension, indicating a stress-induced martensitic transformation. Ti-38Nb-0.46O exhibits a non-linear deformation, a low Young's modulus of 62 GPa, high tensile strength up to 780 MPa, and elongation around 23%, which are promising characteristics for biomedical applications.

Titanium (Ti) and its alloys are currently getting much attention for structural biomaterials, because they are much advantageous as compared with other metallic biomaterials such as biomedical stainless steels and Co-based alloys, and their practical uses in implant devices are widely spreading. In this paper, types of Ti alloys for biomedical applications are first described. Pure Ti, (α + β)-type, and β-type Ti alloys for biomedical applications including general β-type Ti alloys, superelastic and shape-memory β-type Ti alloys, Young’s modulus self-adjustable β-type Ti alloys, and β-type Ti alloys for reconstructive implants are then described.

Metallic materials are mainly employed for the orthopaedic and dental implants because of high strength and appropriate ductility. Further, the implants are used for long term so that high fatigue strength is one of the most important properties in practical use. In addition, these implants are exposed to human body fluid, which is composed of corrosive liquid for metallic materials. In the case of metallic materials, corrosion sometimes accelerates the fatigue failure, that is, corrosion fatigue. Therefore, the effect of testing environment on fatigue strength should be also considered. In this chapter, the mechanical properties such as tensile properties and fatigue properties of the representative metallic materials for biomedical applications such as stainless steels, cobalt–chromium alloys, and titanium alloys in air and simulated body fluid are reviewed.

Young’s moduli of metallic biomaterials for implant devices such as artificial hip joints, bone plates, intramedullary rods, and rods for spinal fixation devices should be similar to that of cortical bone to prevent stress shielding [1].

Mouthpieces made for brass instruments cause allergic problems to the user, because the ions of the harmful metallic elements are dissolved into the blood via saliva due to corrosion. Therefore, mouthpieces made of nontoxic and allergy-free elements are required. Ti and its alloys are expected to efficiently solve this problem, because they are nontoxic and allergy-free metallic materials. For instance, Ti-Nb and Ti-Ta alloys are selected for making the mouthpiece of the trumpet. Herein, their vibration and sound-damping characteristics are discussed and compared with those for mouthpieces made of pure Ti and brass. Subsequently, the vibration and sound characteristics of the trumpet mouthpiece, with the practical size made of Ti-10Nb by precision casting, are compared with mouthpieces made of pure Ti and brass. Brass instruments, acoustic characteristics, generation principle of sound and role of mouthpiece, development of Ti alloys for trumpet mouthpieces including Young’s modulus (E) and density (ρ), resonant frequency and internal friction, relationship between E/ρ and resonant frequency, and corrosion resistance are discussed in this chapter. Furthermore, fabrication of trumpet mouthpieces using the developed Ti alloys for brass and sound characteristics of the trumpet mouthpiece made of Ti alloy are also discussed in this chapter.

In this chapter, three functional materials developed in IMR are introduced. The first one is nanoporous metals produced by dealloying Ti-based amorphous alloys. Its process and surface analyses are briefly described. Moreover, Zr-based Zr–Ti gradient material as a biocompatible material is introduced and its microstructure and mechanical properties are summarized. Finally, the Fe–Co alloy thin films were prepared to apply for energy harvesters and their magnetostriction is briefly summarized.

Titanium (Ti) and its alloys are superior to many other biomaterials in mechanical properties and biocompatibility. They are widely used in biomedical devices and components because of their desirable properties, such as relatively low Young's modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, they cannot meet all of the clinical requirements needed for biomedical devices. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. This chapter reviews the various surface modification technologies pertaining to Ti and its alloys, including mechanical treatment, thermal spraying, sol-gel, chemical, and electrochemical treatment, and ion implantation from the perspective of biomedical engineering. Recent work has shown that the wear resistance, corrosion resistance, and biological properties of Ti and its alloys can be improved using appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained. Some recent applications are also discussed in this chapter.

In this chapter, the general behavior of titanium and its alloys is described, with an emphasis on strength level and corrosion resistance. This is followed by a brief discussion of the consumer applications of titanium alloys. Consumer uses are defined as automotive use, sporting applications, backpacking, architecture, firearms and laptops, tools and jewelry, as well as watches and drones.

A non-toxic and non-allergic β-type Ti–29Nb–13Ta-4.6Zr (hereafter abbreviated as TNTZ) target material was prepared by the vacuum arc-melting process and then hot-forged, successfully. The TNTZ target has been deposited on the pure magnesium (Mg) and AZ31 Mg alloys by the physical vapor deposition (PVD) method. The characterization of the coatings was carried out by using SEM, EDS, AFM, and XRD techniques. The coating adhesion and its hardness were determined by scratch and Vickers tests, respectively. The corrosion resistance of the coatings was analyzed in simulated body fluid (SBF) under in-vitro conditions. Also, the coating wettability was compared by contact angle measurements. The results showed that the coatings had a very dense columnar and compact microstructure. The grain sizes were calculated between 20 and 40 nm, and the porosity of the coating was about 8.5% (±1.5). The hydrophilicity of the Ti-based PVD coating was better than the uncoated Mg. The failure mechanism of the coating during the scratch test was formed as conformal cracks. The in-vitro corrosion tests indicated that the Ecorr values of the TNTZ coated pure Mg and AZ31 alloy were nobler about 400 mV than the uncoated Mg-based samples. At the intensive stage of the corrosion, remarkable corrosion products, grown pits, and deep cracks were also observed on TNTZ-based coating layers due to the heavy corrosion attacks in SBF.

Hydroxyapatite (HA) extracted from bovine bones (called as natural HA) was used to coat a relatively new developed titanium alloy, Ti-12Cr, by using the electrophoretic deposition (EPD) method. This is to improve biocompatibility and bioactivity properties of the material to achieve optimal osseointegration in orthopaedic implant applications. There are three particle sizes of the natural HA used in this study (25 μm, 63 μm, and 125 μm) which aims to determine their effect on morphology, structure, and the strength of the resulting coating adhesion. The coating process was carried out at a voltage of 5 Volt for 5 minutes. The resulting layer morphologies and surface coverage were observed using an optical microscope. The increase in sample mass was measured using digital scales to determine the amount of the particles deposition. The coating thickness was measured using coating thickness gauges, and adhesion strength the coating layer was measured by using the cross-cut tape test method. The results of this study indicate that the HA particle size influences significantly on the quality of the coating produced after the EPD process. It is found that the coated Ti-12Cr with a small particle size has better surface properties as compared to the coarse one. Therefore, small size natural HA particles seemmore suitablefor implant applications.

Oxygen was added to the biomedical β-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ, mass pct) in order to improve its strength, while keeping its Young’s modulus low. Conventionally, with an increase in the oxygen content, an alloy’s tensile strength increases, while its tensile elongation-to-failure decreases. However, an abnormal deformation behavior has been reported in the case of oxygen-modified TNTZ alloys in that their strength increases monotonically while their elongation-to-failure initially decreases and then increases with the increase in the oxygen content. In this study, this abnormal tensile deformation behavior of oxygen-modified TNTZ alloys was investigated systematically. A series of TNTZ-(0.1, 0.3, and 0.7 mass pct)O alloy samples was prepared, treated thermomechanically, and finally solution treated; these samples are denoted as 0.1ST, 0.3ST, and 0.7ST, respectively. The main tensile deformation mechanisms in 0.1ST are a deformation-induced α″-martensitic transformation and {332}〈113〉 mechanical twinning. The large elongation-to-failure of 0.1ST is attributable to multiple deformation mechanisms, including the deformation-induced martensitic transformation and mechanical twinning as well as dislocation glide. In both 0.3ST and 0.7ST, dislocation glide is the predominant deformation mode. 0.7ST shows more homogeneous and extensive dislocation glide along with multiple slip systems and a higher frequency of cross slip. As a result, it exhibits a higher work-hardening rate and greater resistance to local stress concentration, both of which contribute to its elongation-to-failure being greater than that of 0.3ST.

The effect of oxygen on stability of isothermal omega precipitates in Ti-29Nb-13Ta-4.6Zr was examined using X-ray powder diffraction, transmission electron microscopy, and atom probe tomography. Two alloys with 0.1 and 0.4 mass% oxygen were subjected to single step, and two-step annealing heat-treatments to respectively promote omega and alpha formation. After second step annealing, large volume fraction of omega precipitates was retained in 0.4 mass% O alloy while mainly alpha phase was observed in TNTZ-0.1O. The enhanced stability of omega in the higher oxygen containing TNTZ alloys questions the conventionally accepted understanding that oxygen destabilizes the omega phase in titanium alloys.

Bioactive oxide layers were fabricated on Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) by three different alkali solution treatments: hydrothermal (H), electrochemical (E), and hydrothermal-electrochemical (HE). The adhesive strength of the oxide layer to the TNTZ substrate was measured to determine whether this process achieves sufficient adhesive strength for implant materials. Samples subjected to the HE process, in which a current of 15mA/cm(2) was applied at 90°C for 1h (HE90-1h), exhibited a comparatively higher adhesive strength of approximately 18MPa while still maintaining a sufficiently high bioactivity. Based on these results, an oxide layer fabricated on TNTZ by HE90-1h is considered appropriate for practical biomaterial application, though thicker oxide layers with many cracks can lead to a reduced adhesive strength.

Nanostructured hydroxyapatite (HA)–graphene nanosheet (GN) composites have been fabricated by spark plasma sintering consolidation. Nanostructual evolution of the bioceramic-based composites during further high temperature heat treatment is characterized and enhanced mechanical strength is assessed. GN keeps intact after the treatment and its presence at HA grain boundaries effectively inhibits HA grain growth by impeding interconnection of individual HA grains. Microstructural characterization discloses strong coherent interfaces between GN and the (300) plane of HA crystals. This particular matching state in the composites agrees well with the competitive theoretical pull-out energy for single graphene sheet being departed from HA matrix. The toughening regimes that operate in HA–GN composites at high temperatures give clear insight into potential applications of GN for ceramic matrix composites.

Centimeter-sized Mg65Zn30Ca5 bulk amorphous alloys were fabricated by the spark plasma sintering process from the amorphous powders with a size smaller than 5 μ m prepared by ball-milling. The sintered Mg65Zn30Ca5 samples were in an amorphous state when the spark plasma sintering was performed at a temperature of 383 K under a pressure of 600 MPa. The data of polarization curves presented that the sintered Mg65Zn30Ca5 bulk amorphous alloys exhibited higher corrosion resistance than pure Mg and AZ31B alloy owing to high content of Zn and homogeneous structure. A calcium phosphate compound layer was formed on the sintered Mg65Zn30Ca5 bulk amorphous sample after immersion in Hanks’ solution, which is effective in improving corrosion resistance and bioactivity. The sintered MgZnCa bulk amorphous alloys with large dimensions broaden the potential application of bulk amorphous alloys in the biomedical fields.

Titanium and its alloys are suitable for biomedical applications owing to their good mechanical properties and biocompatibility. Beta-type Ti–Mn alloys (8–17 mass% Mn) were fabricated by metal injection molding (MIM) as a potential low cost material for use in biomedical applications. The microstructures and mechanical properties of the alloys were evaluated. For up to 13 mass% Mn, the tensile strength (1162–938 MPa) and hardness (308–294 HV) of the MIM fabricated alloys are comparable to those of Ti–Mn alloys fabricated by cold crucible levitation melting. Ti–9Mn exhibits the best balance of ultimate tensile strength (1046 MPa) and elongation (4.7%) among the tested alloys, and has a Young’s modulus of 89 GPa. The observed low elongation of the alloys is attributed to the combined effects of high oxygen content, with the presence of interconnected pores and titanium carbides, the formation of which is due to carbon pickup during the debinding process. The elongation and tensile strength of the alloys decrease with increasing Mn content. The Ti–Mn alloys show good compressive properties, with Ti–17Mn showing a compressive 0.2% proof stress of 1034 MPa, and a compressive strain of 50%.

ZrAlCoNb bulk metallic glasses with different Nb contents were fabricated by copper mold casting. Corrosion behavior, mechanical properties and cell cytotoxity were investigated. The investigated Zr-based bulk metallic glasses exhibit high corrosion resistance due to the enrichment of Zr and Al in the oxide layer. The yield strength of 1975 MPa and a plastic strain of 3.5% for Zr56Al16Co23Nb5 BMG are obtained. The cell viability is improved with increasing of Nb content.

In order to develop new low-cost and high-strength β-type titanium alloys, a Ti–13Mn was fabricated by metal injection molding. For improving its tensile strength, Ti–13Mn was subjected to cold-rolling at reduction ratios of 60% and 90%, respectively. The solutionized Ti–13Mn has pores and titanium carbide (Ti carbide) precipitates and consists of a β phase and an athermal ω phase. The porosity of the alloy decreases from 6.1% to 0.01% after cold-rolling at a reduction ratio of 90%. Moreover, during cold-rolling, the Ti carbides are fragmented and a deformation-induced ω phase is formed. The ultimate tensile strength, 0.2% proof stress, Vickers hardness, and Young's modulus of Ti–13Mn increase from 888 MPa to 1852 MPa, from 827 MPa to 1823 MPa, from 279 Hv to 461 Hv, and from 96 GPa to 108 GPa, respectively, after cold-rolling at a reduction ratio of 90%. On the other hand, the elongations of both the solutionized and cold rolled Ti–13Mn are less than 2%. Although the elongation of Ti–13Mn is less than 2%, the tensile strength of the cold rolled Ti–13Mn is extremely high compared with that of existing titanium alloys. This large-improvement in the tensile strength of the cold rolled Ti–13Mn is attributed to the increase in the dislocation density, decrease in grain size, decrease in porosity, and formation of a deformation-induced ω phase.

The alloy Ti–9Cr–0.2O has been developed as a potential material for implant rods used in spinal fixation applications, since it exhibits good mechanical properties and a remarkably “changeable Young's modulus”, which is achieved by suppressing the athermal ω-phase formed upon quenching and enhancing the deformation-induced ω-phase transformation. In this study, athermal and deformation-induced ω-phase transformations in Ti–9Cr–0.2O were investigated systematically by transmission electron microscopy. This was done in order to understand the nature of these ω-phase transformations, as well as the specific functionality—the “changeable Young's modulus”—resulting from them. In solution-treated alloy samples, in addition to ideal ω-structures, structures considered as initial ω-structures associated with incommensurate ω-phase were observed. This might be attributed to the composition heterogeneity, heterogeneity of oxygen distribution, and/or the inhomogeneous distribution of defects such as vacancies and locally strained areas. Following cold rolling, some of the selected area electron diffraction patterns of the alloy showed that the reflections of one ω-variant had increased significantly in intensity while those of the other ω-variant had decreased sharply. This vanishing of one type of variant ω-structures is attributable to two possible mechanisms: (i) a reversal mechanism, under which the particular partial dislocations transform the corresponding ω-variants back into β-phase or (ii) a re-orientation mechanism, according to which the ω-variants unfavorable with regard to the loading direction re-orient and turn into the preferred ω-variants.

Biomedical titanium alloys with Young’s moduli close to that of cortical bone, i.e., low Young’s modulus titanium alloys, are receiving extensive attentions because of their potential in preventing stress shielding, which usually leads to bone resorption and poor bone remodeling, when implants made of their alloys are used. They are generally β-type titanium alloys composed of non-toxic and allergy-free elements such as Ti–29Nb–13Ta–4.6Zr referred to as TNTZ, which is highly expected to be used as a biomaterial for implants replacing failed hard tissue. Furthermore, to satisfy the demands from both patients and surgeons, i.e., a low Young’s modulus of the whole implant and a high Young’s modulus of the deformed part of implant, titanium alloys with changeable Young’s modulus, which are also β-type titanium alloys, for instance Ti–12Cr, have been developed. In this review article, by focusing on TNTZ and Ti–12Cr, the biological and mechanical properties of the titanium alloys with low Young’s modulus and changeable Young’s modulus are described. In addition, the titanium alloys with shape memory and superelastic properties were briefly addressed. Surface modifications for tailoring the biological and anti-wear/corrosion performances of the alloys have also been briefly introduced.

Although Electron Beam Melting (EBM) is an innovative technology, the fatigue properties of materials manufactured by EBM may be lower than those of casted and wrought materials due to defects and surface roughness. In order to enhance the fatigue life of components or structures manufactured by EBM, a mechanical surface treatment technology, e.g., peening, would be effective because peening introduces high compressive residual stress at the surface which can extend the fatigue life considerably. In the present study, specimens were manufactured by EBM using titanium alloy Ti-6Al-4V powder. Two types of specimens were prepared: as-built and as-machined specimens. Specimens of each type were treated by cavitation peening or shot peening. The fatigue lives of the specimens were evaluated by a plate bending fatigue tester. The residual stress and surface roughness were also evaluated. The results obtained showed that the fatigue strength of as-built specimens can be improved by 21% by cavitation peening or shot peening, and the fatigue life under particular applied stresses can also be extended by 178% by cavitation peening.

Proper surface characteristics for a titanium implant are crucial for the formation of different cellular protrusions known as filopodia and lamellipodia, both of which have a significant impact on cell attachment, spreading, migration, and proliferation. Microstructural features such as grain boundaries and defects of implant surface can modulate the cellular components and structure at the leading edge of cells. Here, a nano-grained Ti–29Nb–13Ta–4.6Zr (NG TNTZ) substrate was produced by high-pressure torsion (HPT) for improved biofunctionality. Cellular response of human osteoblast cells on nano-grained TNTZ substrates is evaluated and compared with the cellular response of those on coarse-grained TNTZ. High wettability, which depends on high internal energy due to the nano-sized grains that are full of boundaries, interfaces, and high dislocation density, influenced the hOBs cells on NG TNTZ to form highly developed cellular protrusions. Large number of filopodia protrusions resulted in excellent cell attachment as consistent with high level of vinculin and superior cell proliferation. This study demonstrates the advantages of nanocrystalline surface modification using HPT for processing metallic biomaterials that are proper for orthopedic implants.

Bioactive surface modification of Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) was performed through three different alkali solution treatments, including the electrochemical (E), hydrothermal (H), and hydrothermal-electrochemical (HE) processes; all of the processes lead to the formation of sodium-contained amorphous titanium oxide layers on TNTZ samples. The TNTZ samples subjected to the E, H, and HE processes exhibit a flat surface, smooth and fine mesh-like structure surface, and rough mesh-like structure surface, respectively. In the bioactive test, namely, simulated body fluid test, apatite inductivity increases as the surface morphology becomes rough. The order of inductivity for the three processes was HE>H>E. The surface chemical composition also affects the apatite induction ability. The surface with fewer niobium species exhibits better apatite inductivity.

Microstructure dependence on mechanical properties were investigated for Ti-17 forged at temperatures between 700 and 850 ˚C with deformation ratio from 33 to 80 %, and solutiontreated at 800˚C for 4 hours and aged at 620 ˚C for 8 hours. The microstructure was observed after solution and aging treatments. The volume fraction and the size of the primary alpha phase was controlled by solution treatment temperature, not forging temperature and deformation ratio. Forging temperature affected the morphology of grain boundary (GB) alpha phase. Deformation ratio affected the grain size and the aspect ratio of the horizontal and vertical grain size of the prior beta phase. The tensile strength was investigated at room temperature, 450, and 600 ˚C. Forging temperature and deformation ratio did not affect the tensile strength because there is no large difference of the volume fraction of the alphaphase. On the other hand, the elongation and the reduction of area increased with increase of the aspect ratio of the prior beta grains; that means, increase of the deformation ratio. Raising of forging temperature also increased elongation and reduction of area due to the film-like GB alphaphase.

The authors proposed an oxide coating on Ti alloys for the dental abutment tooth, and they had reported that Ti–29Nb–13Ta–4.6Zr (TNTZ) alloy forms a dense oxide layer by high-temperature oxidation. On the other hand, CP Ti forms a multilayered oxide consisted of rutile monolayers and the void layer. This morphological change by alloying is supposed to be mainly caused by Nb addition in Ti since the dense oxide layer of TNTZ mainly consists of rutile TiO2and TiNb2O7.Therefore, in this study, oxidation behaviors of various range of Nb content of Ti-xNb alloys (x = 1 ~ 32 mol%) were investigated, and exfoliation resistance was evaluated. And in this paper, the oxide/metal interfacial microstructure of oxidized CP Ti, TNTZ alloy, and Ti-Nb alloy was studied by a transmission electron microscopy (TEM) and by a scanning transmission electron microscopy with an electron dispersive spectroscopy (STEM-EDS).The cross-sectional observations suggested that the substrate was gradually oxidized during heat treatment, and nucleation and grain growth of TiO2and TiNb2O7proceed at the metal/oxide interface. Consequently, the gradual oxidation process in TNTZ and Ti-Nb alloys could lead to its continuous interfacial microstructure and dense oxide structure, which can achieve high exfoliation resistance.

In this study, beta( )type Ti-29Nb-13Ta-4.6Zr alloys coated with biphasic calcium phosphate (BCP) reinforced with rutile-TiO2 compounds by sol-gel technique to evaluate its possible usage in biomaterial science. Calcium nitrate tetrahydrate (Ca(NO3)(2)center dot 4H(2)O), di-ammonium hydrogen phosphate (NH4)(2)HPO4), ammonium hydroxide (NH4OH), and titanium (IV) propoxide (Ti(OC3H7)(4)) (Merck, Germany) were used as precursors for producing the BCP-only and BCP/TiO2 composite coatings. Synthesis and coating procedure, surface morphology, adhesion strength, and corrosion results of the coated samples have been investigated in details. XRD technique has been used in order to characterization of BCP phases. The morphological observations of coatings were determined by using a scanning electron microscopy (SEM). In-vitro corrosion behaviors of the coatings have been determined with polarization method in Ringer's electrolyte at body temperature. It was found that the BCP/TiO2 coating synthesized on TNTZ alloy has higher scratch resistance than BCP-only coating due to its containing rutile-TiO2 compounds. In addition, it can be said that the BCP/TiO2 coated sample was less susceptibility to corrosion than the BCP-only coatings and uncoated TNTZ sample in simulated body fluid. In this study, β type Ti?29Nb?13Ta?4.6Zr alloys coated with biphasic calcium phosphate (BCP) reinforced with rutile-TiO2 compounds by sol-gel technique to evaluate its possible usage in biomaterial science. Calcium nitrate tetrahydrate (Ca(NO3)2•4H2O), di-ammonium hydrogen phosphate (NH4)2HPO4), ammonium hydroxide (NH4OH), and titanium (IV) propoxide (Ti(OC3H7)4) (Merck, Germany) were used as precursors for producing the BCP-only and BCP/TiO2 composite coatings. Synthesis and coating procedure, surface morphology, adhesion strength, and corrosion results of the coated samples have been investigated in details. XRD technique has been used in order to characterization of BCP phases. The morphological observations of coatings were determined by using a scanning electron microscopy (SEM). In-vitro corrosion behaviors of the coatings have been determined with polarization method in Ringer’s electrolyte at body temperature. It was found that the BCP/TiO2 coating synthesized on TNTZ alloy has higher scratch resistance than BCP-only coating due to its containing rutile-TiO2 compounds. In addition, it can be said that the BCP/TiO2 coated sample was less susceptibility to corrosion than the BCP-only coatings and uncoated TNTZ sample in simulated body fluid.