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Ti alloys with lattice structures are garnering more and more attention in the field of bone repair or regeneration due to their superior structural, mechanical, and biological properties. In this study, six types of composite lattice structures with different strut radius that consist of simple cubic (structure A), body-centered cubic (structure B), and edge-centered cubic (structure C) unit cells are designed. The designed structures are firstly simulated and analysed by the finite element (FE) method. Commercially pure Ti (CP–Ti) lattice structures with optimized unit cells and strut radius are then fabricated by selective laser melting (SLM), and the dimensions, microtopography, and mechanical properties are characterised. The results show that among the six types of composite lattice structures, combined BA, CA, and CB structures exhibit smaller maximum von-Mises stress, indicating that these structures have higher strength. Based on the fitting curves of stress/specific surface area versus strut radius, the optimized strut radius of BA, CA, and CB structures is 0.28, 0.23, and 0.30 mm respectively. Their corresponding compressive yield strength and compressive modulus are 42.28, 30.11, and 176.96 MPa, and 4.13, 2.16, and 7.84 GPa, respectively. The CP-Ti with CB unit structure presents a similar strength and compressive modulus to the cortical bone, which makes it a potential candidate for subchondral bone restorations., Graphical abstract Image 1, Highlights • Six types of graded lattice structures with different strut radius are designed and simulated by the FE method. • BA, CA, and CB structures exhibit smaller maximum Von-Mises stress among six type structures. • CP-Ti with CB structures exhibits similar mechanical properties to the cortical bone. • Excellent properties make CP-Ti with CB structures an attractive subchondral bone restoration material.

In this study, powder metallurgy was applied in a furnace atmosphere to form titanium boride layers on a commercially pure Ti surface. Experiments were carried out using the solid-state boriding method at 900 °C and 1000°C for 12 h and 24 h. Samples were produced by pressing the commercially pure Ti powders under 870 MPa. The sintering process required by the powder metallurgy method was carried out simultaneously with the boriding process. Thus, the sintering and boriding were performed in one stage. The formation of the boride layer was investigated by field emission scanning electron microscopy, optical-light microscopy, X-ray diffraction, and elemental dispersion spectrometry analyses. In addition, microhardness measurements were performed to examine the effect of the boriding process on hardness. The Vickers microhardness of the boronized surface reached 1773 HV, which was much higher than the 150 HV hardness of the commercially pure Ti substrate. The X-ray diffraction analysis showed that the boriding process had enabled the formation of TiB and TiB2 on the powder metallurgy Ti substrate surface. Consequently, the production of Ti via powder metallurgy is a potentially cost-effective alternative to the conventional method, and the boriding process supplies TiB and TiB2 that provide super-high hardness and excellent wear and corrosion resistance.

Surface modifications of metallic biomaterials can in great merit, improve the properties of the hard-tissue implants and in that way contribute to the success of the surgical implantation process. Coating deposition stands out as one of the many surface-modifying techniques that can be used to improve implant surface properties and, in turn, induce successful osseointegration. Deposition of the TiO2 layer on the surface of the metallic implants has a great potential to enhance not only their osseointegration ability but also their biocompatibility and corrosion resistance. In the present study, the possibility of successful deposition of the TiO2 layer on the surface of commercially pure titanium (CP-Ti), as the most commonly used metallic implant material, by spraying the colloidal nanoparticles aqueous solution in the electric discharge plasma at atmospheric pressure was investigated. To characterize the colloidal TiO2 nanoparticle solution, used for the coating deposition process, transmission electron microscopy (TEM) was utilized, while scanning electron microscopy (SEM) and optical profilometry were used to investigate the deposited surface layer morphology and quality. Estimation of the deposited film quality and texture was used to confirm that the arc plasma deposition technique can be successfully used as an advanced and easy-to-apply method for coating the metallic implant material surface with the bioactive TiO2 layer which favors the osseointegration process through the improvement of the implant surface properties. The TiO2 coating was successfully deposited using the arc plasma deposition technique and covered the entire surface of the CP-Ti substrate without any signs of coating cracking or detachment.

Commercially pure titanium (CP-Ti) plates were friction-stir welded (FSWed) using a welding tool with a tungsten carbide (WC) pin. The bead-on-plate technique was applied to reduce the effects of welding defects, such as incomplete penetration. An X-ray inspection and fractography showed that the FSWed material was free of defects and of WC particles, which may have originated from the welding tool. The appearance of refined equiaxed grains in the thermo-mechanically affected zone (TMAZ) may have been related to dynamic recrystallization (DRX) occurring during the FSW due to the high temperature and intensive plastic deformation involved in the process. Grain refinement, mechanical twinning, and increased dislocation density were detected within the TMAZ, and these microstructural changes were considered to be responsible for the improved mechanical properties of the TMAZ. The TEM study reported in the current paper revealed the presence of nano-sized grains in the FSWed material due to dynamic recrystallization (DRX) occurring during the processing stage. The microstructure obtained during FSW of Ti has been reported in a several publications, yet many discrepancies can be found in these publications. Among these discrepancies are the size and the shape of the grains at the various zones, as well as the presence or non-presence of various zones at the vicinity of the weld. The current study contradicts the argument for correlations between the conditions prevailing at different points across the TMAZ and microstructural changes, which were previously proposed by several researchers.

In this paper, the effect of equal channel angular pressing (ECAP) on microstructure, mechanical, and erosion-corrosion behavior of commercial pure (CP) titanium was investigated through experimental work. Four passes of ECAP processing at 400 ℃ was performed on CP titanium. The results showed that the homogeneous structure and coarse equiaxed grains of the initial annealed sample are transformed into the combination of UFG and NS with an average size of 750 nm and 85 nm, respectively. Also, ECAP pass numbers increase the fraction of high angle grain boundaries which improves the ductility of the processed sample. The highest hardness and strength improvement rate was observed after the first pass. Furthermore, the increasing rate of hardness and strength is gradually decreased at the subsequent passes and reached the steady-state level at the 4th pass. This is due to the balance between hardening by dislocations and twinnings accumulation and softening by recovery mechanisms. As a result, a uniform hardness distribution on both the cross-sectional and longitudinal planes is achieved. It was confirmed that erosion-corrosion resistance of the processed sample is enhanced due to the grain refinement, material homogeneity, and quick formation of a strong oxide bond layer on the surface.

Investigations on the fatigue crack growth of commercial pure titanium are carried out with cruciform specimens under different biaxial load ratios (λ = 0, 0.5, and 1) and crack inclination angles (β = 90°, 60°, and 45°) in this paper. Based on the finite element results, the modified solution of stress intensity factors KI and KII for cruciform specimens containing mixed mode I-II crack is obtained by considering crack size, biaxial load ratio, and crack inclination angles. The experimental results show that the maximum tangential stress criterion is fit for the prediction of crack initiation angles for mixed model I-II crack under uniaxial or biaxial loading condition. When the biaxial load ratio increases, the crack propagation angle becomes smaller, and so does the fatigue crack growth rate of mode I crack or mixed mode I-II crack. Based on an equivalent stress intensity factor, a new valid stress intensity factor is proposed to better describe the biaxial fatigue crack growth behavior, which can demonstrate the contribution of mode I and mode II of stress intensity factor.

In contrast with titanium (Ti) alloys, the α+β region for commercially pure Ti is neglectable. Therefore, its β transus (Tβ) can be regarded as a watershed for β-Ti and α-Ti. Utilizing this characteristic, we fabricated dual-textured Ti extrudates through a powder metallurgy route via manipulating the hot extrusion temperature. The crystallographic texture along extrusion direction (ED) was analyzed. Different from the sole //ED texture throughout the entire extrudate in previous studies, our extrudates exhibited unique dual-textured microstructure. The firstly extruded portion manifested //ED and //ED, whereas the rest extrudate displayed //ED. This was attributed to the realtime extrusion temperature of each location in comparison with Tβ. On the other hand, the last portion of the extrudate contained much more interstitial nitrogen and oxygen, which led to extremely high strength via solid solution strengthening. This was resulted from a combination effect of diffusion-controlled element absorbing and material flow during extrusion. Our findings may open up a new direction in developing high-performance materials with variable microstructure and mechanical properties for medical applications like neoarthrosis.

Commercially pure (CP) titanium samples were subjected to uniaxial tension of 5, 15, 25, 35 and 45 elongation (%) at room temperature (298 K), 673 K and 873 K respectively. The texture and microstructure evolution as a function of temperature and elongation (%) were evaluated in the present study. The following observations were made: (i) twins of both {10 1 ¯ 2} type tensile twins and {11 2 ¯ 2} type compressive twins were significant during deformation at 298 K while at high temperatures, these twins were observed till 15 elongation (%) only; (ii) both the twins were mostly activated in the grains/orientations of high Schmid factor values, although these twins were also activated in some grains with low Schmid factor values; (iii) both grain refinement and misorientation developments as a function of elongation (%) was higher for the samples deformed at 298 K compared to those at 673 K and 873 K; (iv) The initial texture concentrated along (11 2 ¯ 5) 1 ¯ 00> was observed to be strengthened with progressive deformation irrespective of the temperature of deformation. However, the texture intensity was higher during deformation at high temperatures.

Commercially pure titanium (CP-Ti) was subjected to thermal oxidation at different temperatures and times for determining the optimum oxidation conditions to obtain the optimum corrosion resistance. The phase constituents of the samples were determined by X-ray diffraction (XRD), the morphology of the surface was observed by SEM, and the corrosion behavior was investigated using immersion test by exposing the samples in HCl solutions with a concentration of 37%. The results showed that Rutile TiO2 layer was formed on the surface of CP-Ti after thermal oxidation and the thickness of the TiO2 layer increased with the treating temperature. Meanwhile, it was found that the optimum corrosion resistance to HCl was obtained while oxidizing at 700℃ for 330min～500min.

Hardfacing layers developed by tungsten inert gas (TIG) surface melting on commercial purity titanium (CP-Ti) placing with a mixture of Fe, C and Si powders under two different traverse speeds (1 mm/s and 2 mm/s) and energy input of 1080 J/mm in an argon gas environment were investigated in terms of surface condition, microstructure, hardness and wear of the processed tracks. The surface appearance of treated layers was found to be free from any obvious defect. The TIG hardfacing layer produced dendritic structure due to dissolution of preplaced powder in the Ti melt. A maximum microhardness value of 630 HV0.5 was found on the surface layer processed with lower speed which was 2.5 to 3.5 times higher than the base material. Ball-on-plate wear tests exhibited better performance of the hardfacing layer than the untreated CP-Ti which is attributed to the presence of carbides and silicides in the Ti melt.

Prediction of fatigue life has become an interesting issue in biomaterial engineering and design for reliability and quality purposes, particularly for biometallic material with modified surfaces. Commercially pure titanium (Cp-Ti) implanted with nitrogen ions is a potential metallic biomaterial of the future. The effect of nitrogen ion implantation on fatigue behavior of Cp-Ti was investigated by means of axial loading conditions. The as-received and nitrogen-ion implanted specimens with the energy of 100 keV and dose of 2 × 1017 ions cm-2, were used to determine the fatigue properties and to predict the life cycle of the specimens. The effect of nitrogen ion implantation indicated revealed improved the tensile strength due to the formation of nitride phases, TiN and Ti2N. The fatigue strength of Cp-Ti and Nii-Ti was 250 and 260 MPa, respectively. The analytical results show good agreement with experimental results.

The aim of the present work is to investigate the effects of prestrain and subsequent annealing on tensile properties of commercial pure titanium (CP-Ti). According to tensile test results, yield strength and ultimate tensile strength increase with the increase of prestrain. Elongation and uniform strain decrease linearly with prestrain. In the case of prestrain that is higher than 3.5%, the macro-yield of specimens changes from gradual yielding to discontinuous yielding. It is supposed that considerable numbers of dislocations introduced into the material lead to the appearance of yield plateau. The quantitative analysis of the contribution of dislocation hardening to the strain hardening shows that dislocation-associated mechanisms play an important role in strain hardening. Moreover, a modified Fields-Backofen model is proposed to predict the flow stress of prestrained CP-Ti at different strain rates. Both strain rate sensitivity and strain hardening exponent decrease with prestrain. Fracture surfaces of the specimens show that fracture mechanism of all tested specimens is dimple fracture. The more ductile deformation in prestrained CP-Ti after annealing indicates that its ductility is improved by annealing.

Titanium (Ti) and its alloys may be processed via advanced powder manufacturing routes such as additive layer manufacturing (or 3D printing) or metal injection moulding. This field is receiving increased attention from various manufacturing sectors including the medical devices sector. It is possible that advanced manufacturing techniques could replace the machining or casting of metal alloys in the manufacture of devices because of associated advantages that include design flexibility, reduced processing costs, reduced waste, and the opportunity to more easily manufacture complex or custom-shaped implants. The emerging advanced manufacturing approaches of metal injection moulding and additive layer manufacturing are receiving particular attention from the implant fabrication industry because they could overcome some of the difficulties associated with traditional implant fabrication techniques such as titanium casting. Using advanced manufacturing, it is also possible to produce more complex porous structures with improved mechanical performance, potentially matching the modulus of elasticity of local bone. While the economic and engineering potential of advanced manufacturing for the manufacture of musculo-skeletal implants is therefore clear, the impact on the biocompatibility of the materials has been less investigated. In this review, the capabilities of advanced powder manufacturing routes in producing components that are suitable for biomedical implant applications are assessed with emphasis placed on surface finishes and porous structures. Given that biocompatibility and host bone response are critical determinants of clinical performance, published studies of in vitro and in vivo research have been considered carefully. The review concludes with a future outlook on advanced Ti production for biomedical implants using powder metallurgy.

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2006, Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2006, Üstün mekanik ve korozyon özelliklerine rağmen, zayıf sürtünme ve aşınma özellikleri titanyum ve alaşımlarının yaygın kullanımını sınırlamaktadır. Normal koşullarda yüzeyde oluşan ve korozyona karşı direnç sağlayan oksit tabakası, hareketli temasın olduğu durumlarda aşınarak, iş göremez hale gelmektedir. Aşınma ve korozyon titanyum ve titanyum alaşımlarının yüzeylerinde şiddetli hasar oluşumuna sebep olmaktadır. Titanyumun diğer üstün olduğu özelliklerine kıyasla zayıf olan yüzey özellikleri, çeşitli yüzey işlemleri ile giderilmeye çalışılmaktadır. Bu çalışmada, vakum ortamında termal oksidasyon ile CP-Ti ve Ti6Al4V alaşımının yüzey özellikleri geliştirilmesi amaçlanmıştır. Farklı süre ve sıcaklıklarda gerçekleştirilen termal oksidasyon işlemleriyle yüzeyde oluşan oksit tabakasının ve oksijen difüzyon bölgesinin özellikleri incelenmiş ve oksijen difüzyon bölgesi için kinetik hesaplamalar yapılmıştır., Despite their improved mechanical and corrosive properties, the use of titanium and its alloys is restricted by their weak friction and wear characteristics. In the case of rubbing contact, the oxide layer may be destroyed by abrasion and leads vastly damage on the surfaces of titanium and titanium alloys. There are many attempts to improve the wear resistance of titanium and its alloys, through various surface modification techniques. In the present research, it was aimed to modify the surfaces of CP-Ti and Ti6A14V alloy through thermal oxidation. Thermal oxidation was carried out under vacuum environment at different temperatures for different durations. Progress of oxygen diffusion, zone beneath oxide layer was systematically followed by a kinetic approach., Yüksek Lisans, M.Sc.

A commercially pure (CP) Titanium alloy classified as Grade 1, was processed by Equal Channel Angular Pressing (ECAP) up to 4 passes in the temperature range of 450-150 degrees C.; The resulting microstructures were observed by Electron Back-Scattered Diffraction, revealing a bimodal grain size distribution consisting of small recrystallized grains of submicrometer size, with an average value of 0.3 mu m, and elongated bands of 1.4 mu m with different degree of substructure. Additionally the fraction of restored and deformed grains were evaluated as a function of processing temperature following an internal grain misorientation criterion, leading to an overall fraction of recrystallized grains between 40% and 20% in samples ECAPed at 450 and 150 degrees C, respectively.; The strengthening contributions of the grain size, equivalent oxygen content (O-eq) and Low Angle Grain Boundaries (LAGBs) to the yield stress were identified by the Hall Fetch and Taylor equations. The strengthening coefficient k of the Hall-Fetch relation was approximately 5 MPa mm(-1/2), with an increment of 0.44 MPa mm(-1/2) per 0.1 O-eq.-%, while the LAGB strengthening contribution was responsible approximately by half of the experimental yield stress values measured. (C) 2014 Elsevier B.V. All rights reserved.