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Copyright of Gazi Üniversitesi Fen Bilimleri Dergisi Part C: Tasarım ve Teknoloji is the property of Gazi University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. Whereas many papers have reported on creep studies of CP-Ti as well as on FSW of CP-Ti, no paper has investigated the creep behavior of a CP-Ti FSW'ed joint. Consequently, the current study focuses on this topic. The current paper, which is part of a broader research project, focuses on the metallurgical processes occurring during the creep of a FSW'ed CP-Ti joint at the temperature range of 550-650 °C. Based on the current study and previous results obtained by the authors, it can be concluded that the weld is not the weakest link. In every case, necking and creep fracture occurred in the parent material (PM), rather than either the thermomechanically affected zone (TMAZ) or the stir zone (SZ), indicating that both zones are more creep-resistant than the parent material. Fractography showed that the fracture surface was typical of creep fracture and that the fracture mechanism was microvoid coalescence and also ruled out any preexisting defect. TEM study of broken crept specimens revealed randomly distributed dislocations but no evidence of grain refinement, hence leading to the conclusion that dislocation glide was the dominant creep mechanism. The technological implication of the current study is that the welding process is safe for use as far as its creep properties are concerned. [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP), a severe plastic deformation process, was applied on commercially pure Ti to obtain an improved microstructure. The process yielded a refined microstructure and higher mechanical properties at room temperature (RT). Yet the microstructure was found to contain bright bands demonstrating high hardness values of about 500 HV. High-resolution scanning electron microscopy (HRSEM) as well as electron backscattering diffraction (EBSD) analysis indicated that these bands were composed of extra-fine equiaxed α-Ti grains with an average radius of 1–2 microns. In addition, a retained β phase was detected at the boundaries of these α-Ti grains, together with a small quantity of separate β grains. The results of a fractography study conducted on broken tensile specimens showed that the material that underwent FSP was free of defects and that the fracture started at these bands. It is proposed that these bright bands are due to excessive deformation occurring during the processing stage, leading to an accelerated dynamic recrystallization (DRX) process. In turn, these heavy deformation regions act as a strengthening constituent, making the material superior to the parent material as far as its mechanical RT properties are concerned. Consequently, this means that the FSP of CP-Ti has the potential to serve as an industrial means of improving the mechanical properties of the material. [ABSTRACT FROM AUTHOR]

In this work, the results of an investigation of electron-beam-welded samples of commercially pure titanium (CP-Ti) and the titanium alloy Ti6Al4V (Ti64) using fillers of various beta-stabilizing elements (Nb, V, Cu) are presented. The fillers were in the form of deposited layers on each of the two specimens via DC magnetron sputtering. The specimens were then subjected to electron-beam welding (EBW) under the same technological conditions. The structure of the obtained welded joints was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) was used to investigate the phase composition of the fusion zone (FZ). The study of the mechanical properties of the samples was carried out via tensile tests and microhardness measurements. The results showed a different influence of the used fillers on the structure and properties of the obtained joints, and in all cases, the yield strength increased compared to the samples welded using the same technological conditions without the use of filler material. In the case of using Nb and V as a filler, the typical transformation of titanium welds into elongated αTi particles along with α'-Ti martensitic structures was observed. The addition of a Cu filler into the structure of the welds resulted in a unification and refining of the structure of the last, which resulted in the improvement of the mechanical properties of the weld, particularly its ductility, which is a known issue where electron-beam welding is concerned. [ABSTRACT FROM AUTHOR]

Laser powder bed fused (LPBFed) metal alloys, such as titanium, aluminium, and steel exhibit high specific strength and hold great potential for utilization in the automotive and aerospace sectors. Since automotive and aerospace structures require the materials to withstand dynamic impacts, accurately predicting the flow behavior of LPBF-based alloys under high strain rates becomes critical. In this paper, the dynamic behavior of LPBFed CPTi, AlSi10Mg, and 316L stainless steel under strain rates of approximately 500–3000 s−1 was investigated using a Split Hopkinson Pressure Bar (SHPB). The study compared the stress-strain response and strain rate sensitivity of LPBFed alloys to those of conventionally produced counterparts. Furthermore, Johnson-Cook constitutive model was adopted to predict the flow behavior. The results showed that all alloys exhibit positive strain rate sensitivity under the tested strain rate range, with LPBFed CPTi demonstrating higher flow stress than conventionally built counterparts due to the fine grain size resulting from the additive manufacturing method. Additionally, differences in the performance of AlSi10Mg observed in this study, as compared to the literature, are attributed to differences in building direction and post-processing. Finally, it was demonstrated that the Johnson-Cook model accurately predicts flow behavior for the selected alloys with relatively low error.

Friction surface stirring (FSS) was employed to enhance the tribological properties of commercially pure Ti (CP-Ti). Applying FSS under the optimised process parameters (i.e. rotation and traverse speeds of 100 rpmand 8mm/min, respectively) was found to increase the surface hardness of as-received CP-Ti from about 200--630 HV. The sliding wear resistance was therefore increased by 76, 76, and 85% under applied loads of 5, 10, and 20 N, respectively. The average friction coefficient (AFC) of CP-Ti also reduced considerably by the FSS. For instance, the AFC was reduced from 0.67±0.07 and 1.04±0.14 to about 0.33±0.03 and 0.45±0.04 at the applied loads of 5 and 20 N, respectively. The wear and friction mechanisms were also discussed. [ABSTRACT FROM AUTHOR]

The porous hydroxyapatite coatings with a spherical structure were formed on commercially pure titanium (CP-Ti) by the micro-arc oxidation (MAO) in an alkaline electrolyte (hydroxyapatite + 1 M potassium hydroxide) at the applied voltage of 140, 160, 180 V and deposition time of 1 and 2 min. It was determined that by increasing voltage from 140 to 160 V the Ca/P ratio increases from 1.54 to 1.69, i.e., the composition of hydroxyapatite (HA) approaches to the biological one that accelerates formation of the interfacial bond between the implant and bone tissue. It was shown that increasing deposition time from 1 to 2 min at the voltage of 140 V promotes increasing Ca/P ratio. The corrosion resistance of CP-Ti with HA coatings was studied in Ringer's solution at a temperature of 37 °C. The best corrosion protection was observed for the coating deposited at 160 V, 1 min, when the thickness of the coating and HA formation is the highest. [ABSTRACT FROM AUTHOR]

The joining of Ti to stainless steel would allow cost-effective and light weight designs for many applications. For friction stir spot welding of Ti to steel with lap configuration, dwell time is an important process parameter. The higher dwell time promotes higher heat generation, which helps material movement and mixing for joint creation. However, higher dwell time also leads to higher peak temperature and incubation time, which encourage undesirable IMC formation. This research focuses on the impact of dwell duration on the elemental diffusion and IMC growth during FSSW of CP-Ti and SS 304. This research numerically and experimentally analyzes the diffusion of elements, intermetallic compound formation, and shear strength of stainless steel 304 and titanium dissimilar friction stir spot welds. The temperature profiles from numerical thermal model show that the peak temperatures at the dissimilar joint interface increases as dwell time increases. The diffusion model and characterization results reveal that Ni, Fe, and Cr diffuse across the dissimilar joint interface from steel to titanium side. Since Ni, Fe, and Cr are β-Ti stabilizers, the β-Ti stabilizes next to the dissimilar interface. The α-β Ti needles are observed between the stabilized β-Ti and α-Ti region towards base material. The numerical predictions of β-Ti and Fe-Ti IMC compare well against the experimental results. From shear strength (tensile) tests, the maximum shear strength (tensile) of ~ 8 kN is achieved from the SS 304-CP-Ti joint performed with 10 s dwell time. At the joint interface, the presence of β-Ti strengthens the joint and the presence of Fe-Ti IMCs encourages abrupt brittle failure and reduces strength. With dwell times less than 10 s, the Fe-Ti IMC thickness is less than 1 μm, which leads to higher shear strength (tensile) with higher β-Ti thickness as dwell time increases. With 20 s dwell time, the Fe-Ti IMC thickness of about 1 μm leads to reduced shear strength (tensile). The EDS analysis of the fracture surfaces reveal that dissimilar SS 304-CP-Ti joints failed from the dissimilar interface containing Fe-Ti IMC. [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP), a severe plastic deformation process, was applied on commercially pure Ti to obtain an improved microstructure. The process yielded a refined microstructure and higher mechanical properties at room temperature (RT). Yet the microstructure was found to contain bright bands demonstrating high hardness values of about 500 HV. High-resolution scanning electron microscopy (HRSEM) as well as electron backscattering diffraction (EBSD) analysis indicated that these bands were composed of extra-fine equiaxed α-Ti grains with an average radius of 1–2 microns. In addition, a retained β phase was detected at the boundaries of these α-Ti grains, together with a small quantity of separate β grains. The results of a fractography study conducted on broken tensile specimens showed that the material that underwent FSP was free of defects and that the fracture started at these bands. It is proposed that these bright bands are due to excessive deformation occurring during the processing stage, leading to an accelerated dynamic recrystallization (DRX) process. In turn, these heavy deformation regions act as a strengthening constituent, making the material superior to the parent material as far as its mechanical RT properties are concerned. Consequently, this means that the FSP of CP-Ti has the potential to serve as an industrial means of improving the mechanical properties of the material.

In this work, the results of an investigation of electron-beam-welded samples of commercially pure titanium (CP-Ti) and the titanium alloy Ti6Al4V (Ti64) using fillers of various beta-stabilizing elements (Nb, V, Cu) are presented. The fillers were in the form of deposited layers on each of the two specimens via DC magnetron sputtering. The specimens were then subjected to electron-beam welding (EBW) under the same technological conditions. The structure of the obtained welded joints was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) was used to investigate the phase composition of the fusion zone (FZ). The study of the mechanical properties of the samples was carried out via tensile tests and microhardness measurements. The results showed a different influence of the used fillers on the structure and properties of the obtained joints, and in all cases, the yield strength increased compared to the samples welded using the same technological conditions without the use of filler material. In the case of using Nb and V as a filler, the typical transformation of titanium welds into elongated αTi particles along with α’-Ti martensitic structures was observed. The addition of a Cu filler into the structure of the welds resulted in a unification and refining of the structure of the last, which resulted in the improvement of the mechanical properties of the weld, particularly its ductility, which is a known issue where electron-beam welding is concerned.

Tribocorrosion of titanium alloys improves by thermal oxidation which results in formation of an oxygen diffusion layer (ODL). However, the formation of ODL decreases the biocompatibility of titanium. The main goal of this paper was to remove this drawback by generation of a more bio-active layer of porous anodic oxide on ODL. Effects of normal load and sliding distance on the tribocorrosion behavior of anodic oxide layers produced by an anodizing process on an ODL were investigated. The ODL layer was formed on CP-Ti by thermal oxidation process in an atmospheric furnace at 850 °C followed by the anodizing process performed at voltages of 150 and 175 V in sulfuric acid solution. Cell viability tests revealed higher biocompatibility for the anodized samples compared to the ODL and titanium. Tribocorrosion tests were carried out under normal loads of 0.5, 1 and 1.5 N at sliding distances of 5–300 m in a phosphate saline buffer solution (PBS) using a pin-on-disk tribometer. The results showed that the anodized layers were durable enough to resist tribological stresses at sliding distances of 5 and 25 m. Further increase in the sliding distance, however, resulted in local damages on the oxide layers followed by a complete removal at a sliding distance of 300 m, especially under the high normal loads of 1 and 1.5 N. The ODL showed the lowest tribocorrosion rate followed by the sample anodized at 150 V and 175 V. Highest hardness and elastic modulus were obtained for the ODL using nano-indentation tests.

Titanium alloys are characterised by poor tribological properties, and a ceramic TiO2 layer formed on the surface can greatly improve its performance. By pre-depositing a gold layer on the titanium surface, the gold particles promoted the outward diffusion of titanium in the ceramic conversion treatment to react with the inward-coming oxygen to form a compact titanium dioxide layer. The surface morphology, microstructure, and phase constituents were characterised by SEM/EDX and XRD. The adhesion of the oxide layers was assessed by a scratch test. The distribution of gold particles in the oxide layer enhanced the surface hardness and reduced the friction and wear against a WC (tungsten carbide) ball in the reciprocal tribological test. The ceramic conversion process was accelerated efficiently at 620–660 °C, and the more gold pre-deposited, the thicker the oxide layer. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The possibility of increasing the hardness to 1420 HV and the corrosion resistance of the CP-Ti surface using a combined plasma electrolytic treatment consisting in anodic plasma electrolytic nitrocarburising in a solution of ammonia, acetone and ammonium chloride at 900 °C and subsequent plasma electrolytic polishing is shown. The morphology, surface roughness, phase composition, structure and microhardness of the modified layer were studied. The corrosion characteristics of the treated surface were studied through potentiodynamic tests and electrochemical impedance spectroscopy. It has been shown that an increase in the surface roughness has a negative effect on the corrosion resistance. The proposed plasma electrolytic polishing makes it possible to remove the outer porous oxide layer, providing increased corrosion resistance. The highest reduction in the corrosion current density, by 13 times compared to CP-Ti and by two orders compared to a plasma electrolytic nitrocarburising sample, is achieved after plasma electrolytic polishing in a solution of ammonium fluoride (4%) at 300 V for 3 min. [ABSTRACT FROM AUTHOR]

A coupled heat source model that combined a Gauss surface heat source with a Gauss cylindrical volumetric heat source was introduced to simulate temperature field distribution and melt pool characteristics using a finite element simulation (FEM) method for the deep and narrow melt pools formed in laser powder bed fusion (L-PBF) aiming at commercial pure titanium (CP-Ti). For comparison, the same simulations using the Gauss surface heat source model and the double ellipsoid heat source model were also performed. The simulated melt pool geometries using the coupled heat source model match well with the measurements, with an average error of 1% for the melt pool depth and 7% for the width. Based on the single-track experimental results, it was found by comparing the simulated results from the three heat source models that the coupled heat source model had better accuracy than the other two. Then, the temperature field and the melt pool geometries of CP-Ti fabricated at different laser power levels from 300 W to 500 W and scanning speeds from 600 mm/s to 4000 mm/s were simulated. According to the simulated maximum temperature and geometries of the melt pool, a suitable process parameters map for CP-Ti was obtained. The reported experimental results agree well with the simulated map. The coupled heat source model is more accurate and applicable for the deep and narrow melt pools formed during L-PBF. [ABSTRACT FROM AUTHOR]

In the process of electron beam cold hearth melting (EBCHM) of commercially pure titanium (CP-Ti), the coarse grain structure of titanium ingots can lead to uneven stress distribution. This increases the tendency for surface cracks, significantly affecting critical properties such as strength and toughness. In this study, the grain growth of CP-Ti ingots during EBCHM was simulated using a combination of microscale cellular automata (CA) and macroscale finite elements (FE) within the ProCAST finite element software. To accurately predict the microstructure growth kinetics and casting conditions, the effect of bulk nucleation parameters on the solidification structure of CP-Ti ingots was investigated. The simulation results were verified by comparing them with metallographic sections of titanium ingots. In addition, the effects of ingot drawing speed and casting temperature on the solidification structure of CP-Ti ingots were examined. The experimental results show that the average grain size decreases and the number of nucleation sites increases as the drawing speed of the ingot and heat transfer film coefficient rises. Conversely, the average grain size increases and the number of nucleation sites decreases as the casting temperature rises. The results of the paper offering theoretical guidance for the stable mass production of high-quality CP-Ti ingots. • The EBCHM is a key process for titanium ingot production. • Built and validated a model describing the EBCHM process based on the CAFE algorithm. • elucidates the growth process and control conditions of the microstructure of CP-Ti ingots. [ABSTRACT FROM AUTHOR]

• Biaxial ratcheting and creep behavior mutually promote each other. • Biaxial fatigue crack propagation is controlled by the maximum principal strain. • Activities of non-prismatic slip and twinning increases with the loading ratio. • A modified model with higher prediction is proposed for biaxial dwell fatigue. This study investigates the biaxial dwell fatigue behavior of commercial pure titanium (CP-Ti) under different load ratios and dwell times. The evolution of mean strain, ratcheting strain, and creep strain was systematically analyzed. The findings reveal that with the decrease of load ratio or the increase of dwell time, both ratcheting and creep strain exhibit an upward trend. The interaction between ratcheting strain and creep strain promotes crack initiation and propagation. The statistical analysis of crack paths by the digital image correlation (DIC) method indicates that crack initiation occurs between 0.7 N f and 0.8 N f , and fatigue failure is governed by the maximum principal strain. Moreover, the electron backscatter diffraction (EBSD) analysis results indicate that as the load ratio increases, the activity of prismatic slip systems decreases, while the activities of other slip systems and twinning modes increases. To enhance predictive accuracy, a modified SWT model by incorporating time-dependent creep damage and anisotropy is proposed for life prediction under biaxial dwell fatigue conditions. [ABSTRACT FROM AUTHOR]

Titanium has been one of the traditional metals used in the medical industry since 1940. This work modeled and simulated a hip-joint replacement implant using Creo 5.0 and DEFORM 3D (v11.0), respectively. Four titanium-based billets were modeled; out of four billets, three billets were coated with a specified thickness, and one was uncoated. Among the three coated billets, one billet was coated with a 500-micron and two billets coated with a 1000-micron thickness. At the end of the simulation, the coating materials formed patches on the surface of the forged parts. The coating material Ti-6Al-4V (high O2) produced excellent mechanical properties in contrast to the CP-Ti material, which displayed low mechanical properties and did not match the core property. Hence, it was suggested to provide a bulk coating of Ti-6Al-4V (high O2) on the billet to improve the physio-mechanical properties and biocompatibility. Four points were selected on the surface of the forged parts at different locations for identifying the property variations concerning forging time. Results found that coating thickness required more on the side surface of the billet material than on the upper and lower surfaces to enhance its properties. [ABSTRACT FROM AUTHOR]

The TA1 welded joints with different heat inputs were obtained by a fiber laser and their microstructure, mechanical properties and corrosion resistance in simulated saliva solution were studied. The results show that the microstructure in fusion zone (FZ) is needle-like α′ martensite and lath-shape α′ martensite, and that of the heat-affected zone (HAZ) is zigzag α phase. With the increase of heat input, the volume fraction of needle-like α′ martensite decrease and the microstructure is coarsened in FZ, but there is almost no change in the microstructure of the HAZ. The order of the corrosion resistance of welded joints with different heat inputs is the same as FZ > HAZ > base material (BM), and the heat input has a more influence on the corrosion resistance of FZ. The binary multiple linear regression relationship between the corrosion current density/charge transfer resistance and the length/width of α′ martensite was established, indicating that the width of α′ martensite is the main factor affecting the corrosion resistance. [ABSTRACT FROM AUTHOR]

During vacuum annealing of C-103 (Nb-10Hf-1Ti) sheets, local melting was noticed at the locations they were in contact with commercially pure titanium (CP-Ti) base sheet. On metallurgical analysis, it was noted that initially CP-Ti sheet reacted with the Inconel 600 tray, forming a series of low melting eutectics, below the annealing temperature of 1175 °C. The weight of C-103 charge experienced at the contact region between the bottom-most C-103 sheet with Inconel 600 gridded tray, where the eutectic reaction between CP-Ti and Inconel 600 occurred initially along with long annealing time, enabled interdiffusion of Ni, Cr, Ti, Nb and Hf, forming a eutectic mixture. Based on detailed metallurgical analysis, the reactions were established and the cause of melting was attributed to improper selection of base tray/sheet combination. Finally, it was recommended to use a Mo tray between Inconel 600 tray and CP-Ti sheet to overcome the problem. [ABSTRACT FROM AUTHOR]

The present work is aimed at developing corrosion-resistant biocompatible coatings on Cp-Ti by anodisation. The coatings were developed by anodising Cp-Ti at a voltage of 60 V over a period of 60 minutes. The coatings were developed by using two different electrolytes, namely ethylene glycol solution of NH4F and an aqueous solution of H3PO4. The developed coatings were annealed at 400 °C. The wettability, surface morphology and phase composition of the samples were evaluated by contact angle goniometry, field emission-scanning electron microscopy (FE-SEM) and X-ray diffractometry (XRD), respectively. The corrosion characteristics of th samples were analysed by potentiodynamic polarisation (PDP) and electrochemical impedance spectroscopy (EIS) in Kokubo's simulated body fluid (SBF) environment to resemble the human blood plasma. Anodisation of the Cp-Ti resulted in the formation of nanoporous structure, which on annealing, resulted in the dwindling of the nanopores. The anodised (A and B) and annealed samples (AH and BH) exhibited better hydrophilic surfaces with enhanced corrosion resistance as indicated by the decrease in current densities of A, AH, B and BH samples by 70.6%, 84.2%, 87.4% and 94.2%, respectively, compared to the substrate, which qualifies them to be corrosion resistant and biocompatible. [ABSTRACT FROM AUTHOR]

It is well known that applying Ni Ti intermetallic coatings on the surface of different alloys can improve their tribological behavior. In this paper, various intermetallic phases of Ni 3 Ti, NiTi, and NiTi 2 and a Ti-rich pearlite-like eutectoid structure were in situ synthesized on the surface of commercially pure (CP) titanium grade 2. Nickel electroplating was performed on titanium samples followed by heat treatment at a temperature of 800 °C for various times up to 8 h. The formation of various phases and structures along the depth were studied using SEM, EDS and XRD. Heat treatment at a temperature of 800 °C for 4 h resulted in the formation of a multi-layered composite of Ni 3 Ti, NiTi, and NiTi 2 intermetallic films with a thickness of 5, 9, and 2 μm, respectively. A nickel diffusion layer (NDL) with a pearlitic structure containing nanolayers of αTi-NiTi 2 was also formed beneath the NiTi 2 layer even after 30 min of heating. Among the different layers formed on the surface of CP-Ti, the titanium-rich NiTi (51–52 at.% Ti) showed the highest hardness of more than 400 HV. Sliding wear tests were performed under a normal load of 10 N and the surfaces of wear tracks were studied using SEM. The results showed higher wear resistance of all intermetallic layers and NDL than the titanium substrate, with the highest wear resistance for Ni 3 Ti top layer. • Raising the heat treatment temperature reduced Ni 3 Ti thickness, increased NiTi, and kept Ni 2 Ti unchanged. • Eutectoid Ti+NiTi 2 and a proeutectoid region with ∼300 HV hardness were detected beneath NiTi 2. • The dense NiTi film had a hardness of 420 HV, while porous Ni 3 Ti measured 250 HV. • Ti-rich NiTi phase (mostly B19') was worn out through plastic deformation. • All developed layers had lower wear than the substrate, with Ni 3 Ti showing the lowest. [ABSTRACT FROM AUTHOR]

• Main crack is perpendicular to the maximum normal stress direction. • Increasing phase angle results in more secondary cracks merging with main cracks. • Crack perpendicular to RD dominated by prismatic slip exhibits faster propagation rates. • Increased activities of non-prismatic deformation modes reduce crack propagation rates. • Chapetti model incorporating Findley equivalent stress demonstrates high prediction accuracy. This study investigates the small fatigue crack propagation behavior of commercially pure titanium (CP-Ti) using thin-walled cruciform specimens under in-plane biaxial loading, considering the effects of biaxial ratio and phase angle. Increasing phase angle results in more secondary cracks merging with main cracks perpendicular to the rolling direction (RD) and transverse direction (TD), a phenomenon attributed to the rise in shear stress that accelerates main crack growth. Higher loading biaxiality or a lower phase angle leads to decreased crack propagation rates and increased biaxial fatigue life. Electron backscatter diffraction (EBSD) analysis reveals that when the maximum normal stress aligns with the RD, prismatic slip primarily governs crack propagation, thereby accelerating crack propagation rates. Conversely, alignment with the TD reduces prismatic slip activity and crack propagation rates. Under equi-biaxial loading, prismatic slip activity decreases further, and crack propagation is dominated by multiple slip and twinning, consequently resulting in the slowest propagation rates. Additionally, a higher proportion of prismatic slip under high phase angle also accelerates crack propagation. Finally, incorporating Findley equivalent stress into the Chapetti model, which considers the crack length-dependent threshold effect, a highly accurate biaxial small fatigue crack propagation rate model is proposed. [ABSTRACT FROM AUTHOR]

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.

Commercial purity titanium (CP-Ti) and a Ti-6Al-4V alloy (Ti64) were processed by high-pressure torsion (HPT) for 10 and 20 turns. The HPT processing produced a nanostructured microstructure and a significant strength enhancement in the CP-Ti and Ti64 samples. After 20 turns, the samples of HPT-processed CP-Ti and Ti64 were subjected to laser surface treatments in an air atmosphere using different scanning speeds and laser powers. The surface roughness of the laser-modified samples increased with increasing laser power and this produced hydrophilicity due to a lower contact angle. After a holding time of 27 days, these samples underwent a hydrophilic-to-hydrophobic transformation as the contact angle increased from 13° to as much as 120° for the CP-Ti sample, and for the Ti64 sample the contact angle increased from 10° to 126°. In addition, the laser surface modification process was carried out with different atmospheres (air, vacuum and O2) on heat-treated but unstrained CP-Ti and Ti64 samples and the contact angle changed due to the surface element content. Thus, as the carbon content increased from 28% to 47% in CP-Ti in a vacuum environment, the surface contact angle increased from 22° to 140°. When a laser surface modification process is conducted under oxygen-less conditions, it is concluded that the contact angle increases rapidly in order to control the hydrophobic properties of Ti and the Ti alloy. [ABSTRACT FROM AUTHOR]

Anodic oxidation of CP-Ti, for production of TiO2 nanotubes, has been extensively described in terms of the electrochemical mechanism of tubular growth or the effect of the parameters on the final tube morphology. Recently, a kinetic growth model was proposed to describe the distinct morphologies of the anodic oxide layer as phases of the nanotubular development process, offering a new perspective for the tuning of nanotube production. In this work, the anodizing behavior of a CP-Ti alloy in an ethylene glycol electrolyte was investigated in light of this new model. The final morphology of the nanotubes was characterized by SEM, considering the effects of electrolyte aging, the microstructure, the applied potential difference and time on the morphological development of nanotubes. Electrolyte aging was shown to lead to a decreased dissolution effect on the oxide. The applied potential difference was shown to lead to an increased dissolution effect and more rapid nanotube growth kinetics, while time resulted in extended dissolution. Moreover, the obtained results were analyzed considering a previous study focused on the anodizing behavior of the α- and β-phases of Ti6Al4V alloy. Overall, the tube morphology resembled that obtained for the Al-containing α-phase of the Ti6Al4V alloy, but the growth kinetics were considerably slower on CP-Ti. [ABSTRACT FROM AUTHOR]

In‐plane biaxial fatigue tests of commercial pure titanium (CP‐Ti) were performed to investigate the effects of load ratio and phase shift on fatigue and ratcheting behavior. The results show that with the decrease of load ratio or the increase of phase shift, biaxial ratcheting strain effect is more significant, leading to the deterioration of fatigue resistance. Analysis of the crack morphology and fracture characteristic reveals that the crack propagation path becomes complex and the fracture morphology changes due to the enhanced non‐proportional hardening effect. Finally, current multiaxial life prediction models are evaluated to compare the applicability in the biaxial fatigue life prediction. Highlights: Effects of load ratio and phase shift on biaxial ratcheting behavior are discussed.Biaxial fatigue life is more sensitive to the variation of the phase shift.The crack morphology and fracture characteristics are analyzed.The applicability of different multiaxial life prediction models is evaluated. [ABSTRACT FROM AUTHOR]

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 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.

A coupled heat source model that combined a Gauss surface heat source with a Gauss cylindrical volumetric heat source was introduced to simulate temperature field distribution and melt pool characteristics using a finite element simulation (FEM) method for the deep and narrow melt pools formed in laser powder bed fusion (L-PBF) aiming at commercial pure titanium (CP-Ti). For comparison, the same simulations using the Gauss surface heat source model and the double ellipsoid heat source model were also performed. The simulated melt pool geometries using the coupled heat source model match well with the measurements, with an average error of 1% for the melt pool depth and 7% for the width. Based on the single-track experimental results, it was found by comparing the simulated results from the three heat source models that the coupled heat source model had better accuracy than the other two. Then, the temperature field and the melt pool geometries of CP-Ti fabricated at different laser power levels from 300 W to 500 W and scanning speeds from 600 mm/s to 4000 mm/s were simulated. According to the simulated maximum temperature and geometries of the melt pool, a suitable process parameters map for CP-Ti was obtained. The reported experimental results agree well with the simulated map. The coupled heat source model is more accurate and applicable for the deep and narrow melt pools formed during L-PBF.

In the present work, pack carburization with rubberwood charcoal and rubberwood ash at 925 °C for 6, 12, and 24 h was carried out to improve the surface hardness of commercially pure titanium (CP-Ti). X-ray diffraction and energy dispersive spectrometer analyses revealed the formation of titanium carbide (TiC) and the existence of oxygen diffusion in the carburized surface. The surface hardness of most optimized conditions has remarkably increased by 481 % as compared to untreated CP-Ti (from 175 HV to 1016 HV) due to the TiC surface layer, while the hardened oxygen diffusion layer a bout 300 um in depth, as clearly seen in the microhardness profiles is useful for increased load-bearing capacity. Consequently, pack carburization with rubberwood charcoal and rubberwood ash is a promising surface modification technique, which can significantly enhance the surface hardness and increase the loadbearing capacity of CP-Ti for biomedical and tribological applications. [ABSTRACT FROM AUTHOR]

• Increasing PEO treatment time promotes the formation of the rutile phase. • Rutile increases the hardness of PEO coating. • Thicker anode coatings can be produced with a longer duration of the PEO process. • Increasing PEO treatment time promotes the formation of more rough coatings. The objective of this study was to develop an oxide coating on commercially pure titanium using the plasma electrolytic oxidation (PEO) technique. During the surface treatment process, the time value was varied for 1, 10, 15, 30, 45, and 60 min. The PEO treatment was carried out at a limited current of 2.5 A and a voltage of 300 V. The coatings exhibit the anatase and rutile crystalline structures of TiO 2. The coating produced for longer treatment times has higher concentrations of rutile, resulting in surface hardening. The thickness and the roughness of the coatings increased with the increase in treatment time, but there was a reduction in the size of the pores per unit area. [ABSTRACT FROM AUTHOR]

• Dynamic response of AM lattices at varied densities was analysed. • Studied the energy absorption of CP-Ti, AlSi10Mg, 316LSS lattices. • Explored the influence of material on the isotropic properties of lattice structures. • Insights on lattice's rate-dependent properties were provided. Lattice structures offer a wide range of tuneable qualities that cannot be achieved with bulk materials. While lattice structures offer a range of tuneable qualities, including isotropic properties achievable in bulk materials, the advent of additive manufacturing (AM) advances research in this domain. Although several studies have characterized the quasi-static mechanical properties of lattice structures, there is limited experimental data available on their rate-dependent behaviour. Additionally, most lattice structures are anisotropic, making them unsuitable for applications where loading directions are unknown. In this study, a topology-optimised unit cell with nearly perfect isotropic stiffness is investigated for its isotropic specific energy absorption under high strain rates. The dynamic response of the structure is evaluated using 3 different materials: CPTi, AlSi10Mg, and 316LSS, and both experimental and numerical methods are employed. The influence of topology and relative density on the mechanical properties of the structure are explored, and the specific energy absorption isotropy is determined by loading the lattices in various orientations numerically. This research fills the gap in knowledge regarding the rate-dependent behaviour of lattice structures and offers insight into the potential for isotropic lattice structures in engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents the study of microstructure and properties of 8 mol% yttrium stabilized zirconia coating fabricated by Plasma Spray Physical Vapor Deposition technique on commercial pure titanium. The coating was characterized by X-ray diffraction, high resolution scanning electron microscope, profilometer, nanoindentation and nanomachining tests. The X-ray phase analysis exhibit the tetragonal Zr0.935Y0.065O1.968, TiO and α-Ti phases. The Rietveld refinement technique were indicated the changes of crystal structure of the produced coatings. The characteristic structure of columns were observed in High Resolutions Scanning Electron Microscopy. Moreover, the obtained coating had various development of surfaces, thickness was equal to 3.1(1) µm and roughness 0.40(7) µm. Furthermore, the production coatings did not show microcracks, delamination and crumbing. The performed experiment encourages carried out us to tests for osseointegration.

The TA1 welded joints with different heat inputs were obtained by a fiber laser and their microstructure, mechanical properties and corrosion resistance in simulated saliva solution were studied. The results show that the microstructure in fusion zone (FZ) is needle-like α′ martensite and lath-shape α′ martensite, and that of the heat-affected zone (HAZ) is zigzag α phase. With the increase of heat input, the volume fraction of needle-like α′ martensite decrease and the microstructure is coarsened in FZ, but there is almost no change in the microstructure of the HAZ. The order of the corrosion resistance of welded joints with different heat inputs is the same as FZ > HAZ > base material (BM), and the heat input has a more influence on the corrosion resistance of FZ. The binary multiple linear regression relationship between the corrosion current density/charge transfer resistance and the length/width of α′ martensite was established, indicating that the width of α′ martensite is the main factor affecting the corrosion resistance.

Titanium has been one of the traditional metals used in the medical industry since 1940. This work modeled and simulated a hip-joint replacement implant using Creo 5.0 and DEFORM 3D (v11.0), respectively. Four titanium-based billets were modeled; out of four billets, three billets were coated with a specified thickness, and one was uncoated. Among the three coated billets, one billet was coated with a 500-micron and two billets coated with a 1000-micron thickness. At the end of the simulation, the coating materials formed patches on the surface of the forged parts. The coating material Ti-6Al-4V (high O2) produced excellent mechanical properties in contrast to the CP-Ti material, which displayed low mechanical properties and did not match the core property. Hence, it was suggested to provide a bulk coating of Ti-6Al-4V (high O2) on the billet to improve the physio-mechanical properties and biocompatibility. Four points were selected on the surface of the forged parts at different locations for identifying the property variations concerning forging time. Results found that coating thickness required more on the side surface of the billet material than on the upper and lower surfaces to enhance its properties.

Commercial purity titanium (CP-Ti) and a Ti-6Al-4V alloy (Ti64) were processed by high-pressure torsion (HPT) for 10 and 20 turns. The HPT processing produced a nanostructured microstructure and a significant strength enhancement in the CP-Ti and Ti64 samples. After 20 turns, the samples of HPT-processed CP-Ti and Ti64 were subjected to laser surface treatments in an air atmosphere using different scanning speeds and laser powers. The surface roughness of the laser-modified samples increased with increasing laser power and this produced hydrophilicity due to a lower contact angle. After a holding time of 27 days, these samples underwent a hydrophilic-to-hydrophobic transformation as the contact angle increased from 13° to as much as 120° for the CP-Ti sample, and for the Ti64 sample the contact angle increased from 10° to 126°. In addition, the laser surface modification process was carried out with different atmospheres (air, vacuum and O2) on heat-treated but unstrained CP-Ti and Ti64 samples and the contact angle changed due to the surface element content. Thus, as the carbon content increased from 28% to 47% in CP-Ti in a vacuum environment, the surface contact angle increased from 22° to 140°. When a laser surface modification process is conducted under oxygen-less conditions, it is concluded that the contact angle increases rapidly in order to control the hydrophobic properties of Ti and the Ti alloy.

Commercially pure Ti (CP‐Ti) was heat treated at 1273 K (1000°C), which was higher than β‐transus temperature, followed by water quenching. The dwell time at 1000°C was changed from 1 to 240 h. The heat treatment at 1000°C resulted in α grain coarsening, whereas martensitic transformation occurred due to the rapid cooling from β phase. The hardness increased by the martensitic transformation, where higher hardness was achieved by longer dwell time at 1000°C. However, the fatigue strengths of the heat‐treated CP‐Ti were lower than that of the as‐received one. The fatigue strength of the specimen with the shortest dwell time of 1 h was the lowest among the heat‐treated samples with different dwell times. Untransformed coarse α grains were seen in the heat‐treated specimens, which resulted in the lower fatigue crack initiation resistance and fatigue strength than the as‐received specimen. [ABSTRACT FROM AUTHOR]

[Display omitted] • The passive film formed at 1 V is the densest. • The passive film formed at 1.8 V possessed the strongest capacity to repeal F–. • The average valences were linear with the applied potentials. • N D appeared to be positively correlated with the applied potential. • The change in ICRs was almost proportional to the variations in O2– content. The correlation between applied potentials and the passive films of commercially pure titanium (CP-Ti) in a simulated proton exchange membrane water electrolysis (PEMWE) environment was investigated. In the first passive region, the passive film formed at 1 V exhibited superior overall performance. The values of N D were positively correlated with the applied potentials. The oxygen vacancy diffusivities were determined to be on the order of 10–17 cm2 s−1. The average valences of the passive films were positively linear with the applied potentials. As further increasing the potential, due to the intense OER and consequent growth, the oxide ratios and average valences of the passive films increased. The corrosion induced by accelerated stress cycle (ASC) tests was slight and crystallographically oriented. After increasing the frequency of potential change, the total Ti oxides were slightly less than those of 2.5 V. [ABSTRACT FROM AUTHOR]

In this study, the electrochemical corrosion properties of commercial pure titanium (Cp-Ti) samples produced by additive manufacturing and forging were compared by plasma oxidizing. Plasma oxidizing processes were carried out at temperatures of 650 °C and 750 °C for 1 h and 4 h. Electrochemical corrosion experiments were carried out in Simulated Body Fluid (SBF) using open circuit potential, cyclic potentiodynamic polarization and electrochemical impedance spectroscopy methods. It was found that the coating thickness of F 750 °C-4 h and S 750 °C-4 h samples was the highest. The corrosion resistance of the samples produced by additive manufacturing is lower than that produced by forging due to the Lack of fusion (LOF) effect. The barrier layer developed by the plasma oxidizing process significantly improved the corrosion performance of additive manufacturing by reducing the LOF effect. The minimum corrosion rate was obtained at S 750°-4 h. While the total material loss due to corrosion was the lowest on this surface, the last corroded surface was F 750°-4 h. The maximum resistance was observed on the plasma oxidized surfaces for the group produced by forging. [ABSTRACT FROM AUTHOR]

Commercially pure(CP) Ti fabricated by 135° ECAP and swaging was annealed at 100, 150, 200, 250, 300, 350, 400, 450℃ and 500℃ for 1h, respectively. The microstructure and properties of annealed commercially pure Ti were investigated by transmission electron microscopy, scanning electron microscopy, uniaxial tensile test and microhardness test. The results show that when annealing temperature is below 400℃, dislocation density reduces gradually and grain boundary becomes clear, no obvious change occurs in the microstructure,ultimate tensile strength and microhardness decrease slightly and no obvious increase occurs in the elongation;when annealing temperature is above 400℃, recrystallization occurs with the increase of annealing temperature, and the grain size increases obviously, the average size is about 5μm, the ultimate tensile strength and microhardness decrease significantly and elongation increases at the same time. The tensile fracture shows the tensile fracture of annealed commercial pure Ti by ECAP and swaging is ductile fracture. With the increase of annealing temperature, the size and depth of dimples increase.

Commercial pure titanium（ CP-Ti） TA2 was pressed 1 pass by equal channel angular pressing（ ECAP） with BC route at room temperature（ RT） and 300℃,respectively. The microstructure and mechanical properties of the samples were investigated to find the influence of ECAP temperature on the mechanical properties of CP-Ti. The experimental results suggested that grains of the samples after ECAP 1 pass were elongated and lath-like and crystal twinning was found,the microhardness and tensile strength of the samples pressed 1 pass at room temperature and 300℃ increased from 179. 5 kgf·mm-2,443 MPa to 234. 2 kgf·mm-2,560 MPa and 213. 5 kgf·mm-2、544 MPa,respectively,while the elongation at break reduced from 21. 5% to 11. 5% and 16. 5%,respectively.

Purpose: This paper aims to investigate the structural, tribological and electrochemical properties of Ag2O, ZnO, NiO coatings and Ag2O/ZnO/NiO nanocomposite films deposited on commercially pure titanium. Design/methodology/approach: Ceramic thin films (Ag2O, ZnO, NiO coatings and Ag2O/ZnO/NiO nanocomposite film) were deposited on commercially pure titanium (CP-Ti) substrate. Surface characterization of the uncoated and coated samples was made by structural surveys (scanning electron microscopic examinations and X-ray diffraction analyses), hardness measurements, tribological and corrosion experiments. Findings: Results were indicated that sol-gel coatings improved the wear and corrosion resistance of CP-Ti, and the best results were seen at the nanocomposite coating. It may be attributed to its small grain size, high surface hardness and high film thickness. Originality/value: This study can be a practical reference and offers insight into the influence of nanocomposite ceramic films on the increase of hardness, tribological and corrosion performance. Also, the paper displayed a promising approach to produce Ag2O/ZnO/NiO nanocomposite coating on commercially pure titanium implants for biomedical applications. [ABSTRACT FROM AUTHOR]

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Phosphorus-incorporated oxide layers were grown on commercially pure titanium during plasma electrolytic oxidation in sodium dihydrogen phosphate dihydrate solution. Microstructure, mechanical and electrochemical behavior of the surface oxides indicated a dominant anatase and rutile structure of TiO 2 with nanocrystallites ranging from 45 to 64 nm and 48–98 nm, respectively as well as Ti2+, Ti3+ and Ti4+ chemical species. Using a combination of process time, applied current and electrolyte concentration, coating thicknesses up to about 10 μm were fabricated. Best mechanical performance was observed for potentiostatic deposited samples yielding a 453 HV 300 hardness, 19 N adhesive failure and 38 N full delamination resistance. All PEO-coated samples in this work exhibit a corrosion current density with one order of magnitude lower than CP-Ti when subjected to Ringer's physiological solution. • Preparation of PEO oxide layers on CP-Ti in an acid electrolyte solution containing NaH 2 PO 4 ∙2H 2 O • Comparison of potentiostatic and galvanostatic regimes on mechanical properties and corrosion resistance of PEO coatings obtained in similar growth conditions • The effect of PEO process time and current intensity during potentiostatic and galvanostatic operation mode on composition, microstructure, mechanical properties and corrosion behavior of oxide coatings • Influence of electrolyte concentration in restricting the growth of anatase - the role of phosphorous incorporation [ABSTRACT FROM AUTHOR]