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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.

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.

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]

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]

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]

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.

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 a-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. [ABSTRACT FROM AUTHOR]

In this research, the microstructures and mechanical properties of similar and dissimilar autogenous joints of 3 mm thick commercially pure titanium (CP-Ti) and Ti-6Al-4V welded by ytterbium fiber laser (Yb:YAG) were investigated. Two sets of laser power and welding speed were selected in such a way that the heat input remained constant. Microstructural characterization of the joints was investigated by an optical microscope, and mechanical properties were determined by hardness and tensile tests. The only defects found were porosity and underfill, and no signs of lack of penetration and solidification cracks were observed in any of the joints. Microstructural evaluation of the fusion zone (FZ) showed that in similar Ti-6Al-4V joint, a supersaturated nonequilibrium α′ martensite was formed due to rapid cooling associated with laser welding. In similar CP-Ti, coarse equiaxed grains were observed in the FZ. Unlike the similar joints, a clear interface was observed between the heat-affected zone (HAZ) and the FZ in both the CP-Ti and Ti-6Al-4V sides in dissimilar joints. Among all the joints with different weld parameters, similar Ti-6Al-4V showed the highest strength and the lowest ductility. In similar CP-Ti and dissimilar joints, fractures took place in the CP-Ti base metal, but all the Ti-6Al-4V similar joints failed in the FZ. Significant changes in the strength and hardness with varying laser power and welding speed implied that the mechanical properties of the weld fusion zones were not entirely governed by the heat input but were also affected by individual welding parameters.

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.

316L stainless steel is commonly used in biomedical applications. However, its use is limited because of its insufficient tribological properties. In this study, a duplex surface modification process of laser melting and plasma nitriding is proposed and wear characteristics of coated 316L stainless steel were investigated. Titanium layers were produced on 316L steel samples at laser powers of 20 and 40 W by selective laser melting. The obtained films were plasma nitrided at 650 and 750 °C for 4 h under a gas mixture of 50% N 2 –50% H 2 . The structural, mechanical, morphological and tribological properties of untreated and processed samples were examined. It was observed that the hardness and wear resistance of coated and plasma nitrided samples were higher than the uncoated and Ti coated samples due to the formation of titanium nitride phases during nitridation. Also, the results indicated that wear resistance of Ti coated and plasma nitrided samples improved with increasing plasma nitriding temperature and laser power. [ABSTRACT FROM AUTHOR]

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.

Titanium composite strengthened by Ti3Al precipitations is considered to be one of the excellent materials that is widely used in engineering. In this work, we prepared a kind of Ti-Ti3Al metallic composite by in-situ synthesis technology during the SLM (selective laser melting) process, and analyzed its microstructure, wear resistance, microhardness, and compression properties. The results showed that the Ti-Ti3Al composite, prepared by in-situ synthesis technology based on SLM, had more homogeneous Ti3Al-enhanced phase dispersion strengthening structure. The grain size of the workpiece was about 1 μm, and that of the Ti3Al particle was about 200 nm. Granular Ti3Al was precipitated after the aluminum-containing workpiece formed, with a relatively uniform distribution. Regarding the mechanical properties, the hardness (539 HV) and the wear resistance were significantly improved when compared with the Cp-Ti workpiece. The compressive strength of the workpiece increased from 886.32 MPa to 1568 MPa, and the tensile strength of the workpiece increased from 531 MPa to 567 MPa after adding aluminum. In the future, the combination of in-situ synthesis technology and SLM technology can be used to flexibly adjust the properties of Ti-based materials.

Enhanced cell adherence to the surface of nanocrystallized commercially pure titanium (CP-Ti) was observed by several authors. However, the understanding of the surface modification of Ti in a physiological solution due to nanocrystallized grain size has not been reached. In this work, equal channel angular pressing (ECAP) was applied to manufacturing ultrafine grained CP-Ti. Martensite and Widmanstatten microstructures were also obtained for comparison. The CP-Ti pieces with different microstructures were subjected to soaking tests in a simulated body fluid. Electrochemical impedance spectroscopy (EIS) measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM), energy dispersive spectrometer (EDS) were used to characterize the surfaces. The results show the surface precipitates mainly contain Ti, O, Ca and P. The quantity of precipitates on ECAPed CP-Ti is the largest among different specimens corresponded to the observation of the thickest layer formation on ECAPed CP-Ti found by EIS. EDS results show more CaPO and less Ti are included on ECAPed Ti comparing to the deposits on other two types of specimens. Smaller numbers of precipitates and denser film are produced on the surface of the water-quenched CP-Ti. The regeneration kinetics of the CaP precipitates evaluated by Gibbs free energy is introduced to interpret the precipitating behaviors on different CP-Ti specimens. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]