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Titanium and titanium alloys with a medium thickness of 5 to 12 mm are widely used for ocean platforms, military equipment and in other fields because of their light weight, appropriate strength and corrosion resistance. In this study, autogenous laser welding and narrow-gap laser welding processes were researched and compared, and the welding characteristics, weld microstructure and joint strength were analyzed. The results showed that autogenous laser welding had higher efficiency, narrower weld width and higher microstructure uniformity. Autogenous laser welding can achieve the single pass weld penetration at laser keyhole mode. The weld width of narrow-gap laser welded joint was 12.5 mm, which was nearly three times than that of autogenous laser welding. The grain size of autogenous laser welding was obviously smaller and more uniform in depth than that of narrow-gap laser welding. In the weld zone, the coarse columnar α grains grew from the fusion line, while in the heat-affected zone, equiaxed α grains with needle and sawtooth α morphologies were presented. The microhardness of the heat-affected zone was higher than in the weld zone and the base metal due to the denser needle microstructure. The tensile samples all fractured at the base metal, indicating the welded joint strength efficiency was greater than 1. [ABSTRACT FROM AUTHOR]

The deposition of cladding titanium (Ti) alloy layers on aluminum (Al) alloy components via wire-arc additive manufacturing (WAAM) has many attractive properties but is also significantly challenging because the deposition of a molten Ti alloy in a high-temperature state causes Ti and Al alloys to melt and mix. This leads to serious problems such as the formation of brittle intermetallic compounds (IMCs), lower forming dimensional accuracy (the formation of beads with side overhang and hump defects), and the generation of cracks and voids in the dissimilar metal interface. This study aimed to comprehensively investigate these challenges, in particular, the effect of WAAM path strategies on the forming dimensional accuracy. A pure Ti bead equivalent to ERTi-2 was deposited on an Al alloy plate equivalent to 5052 using stringer and weaving strategies. As a result, cladding ERTi-2 multi-beads on a 5052 plate without fusion defects were successfully fabricated using weaving strategies. In addition, the formation mechanisms for hump defects and severe spatter were clarified by observing the behavior of the molten pool. We also examined the formation of brittle IMCs and low mechanical properties. Tensile tests results showed an ultimate tensile strength of 54 ± 18 MPa (average ± standard deviation) at the dissimilar metal interface. According to fractographic analysis, the irregular formation of microcracks at the thicker IMC layer reduces bonding strength. The formation of the IMC layer is a result of the concentrated heat input in the directed energy deposition (DED) process, and is not due to the weaving strategy. [ABSTRACT FROM AUTHOR]

The thermal chemical vapor deposition (CVD) process was utilized to fabricate 6H-structured SiC coating dies with carbon control. The carbon-rich clusters along the SiC grain boundaries acted as a pinning site to suppress irregular crystal growth and to homogenize the fine-grained structure. These massive carbon-supersaturated (MCSed) SiC dies with a thickness of 4 mm were utilized for upsetting pure titanium bars in dry and cold conditions. Under a stress gradient from the contact interface to the depth of the SiC coating, the carbon solute isolated from these carbon clusters diffused through the grain boundaries and formed free carbon agglomerates on the contact interface to the pure titanium bars. These in situ-formed free carbon agglomerates acted as a solid lubricant to sustain the friction coefficient at 0.09 at the hot spots on the contact interface and to protect the dies and bars from severe adhesive wearing. [ABSTRACT FROM AUTHOR]

Pure titanium is a preferred material for medical applications due to its outstanding properties, and the fabrication of its surface microtexture proves to be an effective method for further improving its surface-related functional properties, albeit imposing high demands on the processing accuracy of surface microtexture. Currently, we investigate the fabrication of precise microtextures on pure titanium surfaces with different grid depths using precision-cutting methods, as well as assess its impact on surface wettability through a combination of experiments and finite element simulations. Specifically, a finite element model is established for pure titanium precision cutting, which can predict the surface formation behavior during the cutting process and further reveal its dependence on cutting parameters. Based on this, precision-cutting experiments were performed to explore the effect of cutting parameters on the morphology of microtextured pure titanium with which optimized cutting parameters for high-precision microtextures and uniform feature size were obtained. Subsequent surface wettability measurement experiments demonstrated from a macroscopic perspective that the increase in the grid depth of the microtexture increases the surface roughness, thereby enhancing the hydrophilicity. Corresponding fluid–solid coupling finite-element simulation is carried out to demonstrate from a microscopic perspective that the increase in the grid depth of the microtexture decreases the cohesive force inside the droplet, thereby enhancing the hydrophilicity. [ABSTRACT FROM AUTHOR]

In this study, crystal grain refinement of pure titanium manufactured by electron beam melting through cryogenic rolling was performed. The effect of rolling in a cryogenic atmosphere on average grain size was investigated. Cryogenic atmosphere rolling was confirmed to be smaller than normal temperature rolling. Electron back scatter diffraction (EBSD) confirmed the presence of oriented crystal grains in the material. The deformation, temperature, and stress generated during rolling were calculated using 3D simulation. Finite element analysis (FEM) modeling was used to analyze the trend of average grain size change during the heat treatment of the rolled samples.

The effect of microstructure and mechanical properties of submicro grained commercial pure titanium (CP–Ti) on the wear mechanism is still unclear. In the present work, CP-Ti samples were subjected to multi-axial forging (MAF) and low-temperature annealing treatment to prepare ultrafine-grained (UFG) material. The mechanical properties, microstructure, and tribological characterization between coarse-grained (CG) sample and UFG samples were comparatively studied. The results showed that the MAF sample could reach a grain size of 165 nm, while its grains coarsened slightly after low-temperature annealing. The MAF sample had the highest strength and hardness and the lowest coefficient of friction, but only a 7.3 % decrease in wear rate compared to the CG sample. The 400 °C annealed MAF sample possessed a good combination of tensile strength (814 MPa) and elongation (18.6 %), resulting in the lowest wear rate of 16.8 × 10−5mm3/(N∙m). The dominated wear mechanisms of the CG sample, MAF sample and 500 °C annealed MAF sample were abrasive wear, adhesive wear and delamination wear, while the primary mechanism of the 400 °C annealed MAF sample was abrasive wear and adhesive wear. It was found that the wear mechanism transforming, higher hardness and sufficient work hardening could be responsible for lower wear rate of the 400 °C annealed MAF sample. The 400 °C annealed MAF sample showed a thinner and more homogeneous deformation layer near the worn surface, and its thickness of deformation layer was about 8 μm.

Titanium and titanium alloys with a medium thickness of 5 to 12 mm are widely used for ocean platforms, military equipment and in other fields because of their light weight, appropriate strength and corrosion resistance. In this study, autogenous laser welding and narrow-gap laser welding processes were researched and compared, and the welding characteristics, weld microstructure and joint strength were analyzed. The results showed that autogenous laser welding had higher efficiency, narrower weld width and higher microstructure uniformity. Autogenous laser welding can achieve the single pass weld penetration at laser keyhole mode. The weld width of narrow-gap laser welded joint was 12.5 mm, which was nearly three times than that of autogenous laser welding. The grain size of autogenous laser welding was obviously smaller and more uniform in depth than that of narrow-gap laser welding. In the weld zone, the coarse columnar α grains grew from the fusion line, while in the heat-affected zone, equiaxed α grains with needle and sawtooth α morphologies were presented. The microhardness of the heat-affected zone was higher than in the weld zone and the base metal due to the denser needle microstructure. The tensile samples all fractured at the base metal, indicating the welded joint strength efficiency was greater than 1.

This study investigates the impact of hard coatings on the fatigue properties of pure titanium. A specialized fatigue test which ensured machine equivalence was conducted to compare the fatigue behavior of coated and uncoated metals. The findings reveal that the application of coatings adversely affects the fatigue properties of pure titanium due to stress concentration from the coating, which accelerates fatigue crack propagation within the substrate material. Notably, zigzag fatigue cracks at the interface between the coating and substrate and multiple micro-cracks initiated within the coating are found. [ABSTRACT FROM AUTHOR]

In this study, crystal grain refinement of pure titanium manufactured by electron beam melting through cryogenic rolling was performed. The effect of rolling in a cryogenic atmosphere on average grain size was investigated. Cryogenic atmosphere rolling was confirmed to be smaller than normal temperature rolling. Electron back scatter diffraction (EBSD) confirmed the presence of oriented crystal grains in the material. The deformation, temperature, and stress generated during rolling were calculated using 3D simulation. Finite element analysis (FEM) modeling was used to analyze the trend of average grain size change during the heat treatment of the rolled samples. [ABSTRACT FROM AUTHOR]

Re-endothelialization has been recognized as a promising strategy to address the tissue hyperplasia and subsequent restenosis which are major complications associated with vascular implant/interventional titanium devices. However, the uncontrollable over-proliferation of smooth muscle cells (SMCs) limits the clinical application of numerous modified strategies. Herein, a novel modified strategy involving with a two-step anodic oxidation and annealing treatment was proposed to achieve rapid re-endothelialization function regulated by regular honeycomb nanotexture and specific anatase phase on the titanium surface. Theoretical calculation revealed that the presence of nanotexture reduced the polar component of surface energy, while the generation of anatase significantly enhanced the polar component and total surface energy. Meanwhile, the modified surface with regular nanotexture and anatase phase produced positive effect on the expression of CD31, VE-Cadherin and down-regulated α-SMA proteins expression, indicating excellent capacity of pro-endothelial regeneration and inhibition of SMCs proliferation and migration. One-month in vivo implantation in rabbit carotid arteries further confirmed that modified tube implant surface effectively accelerated confluent endothelial monolayer formation and promoted native-like endothelium tissue regeneration. By contrast, original titanium tube implant induced a disorganized tissue proliferation in the lumen with a high risk of restenosis. Collectively, this study opens us an alternative route to achieve the function that selectively promotes endothelial cells (ECs) growth and suppresses SMCs on the medical titanium surface, which has a great potential in facilitating re-endothelialization on the surface of blood-contacting titanium implant.

Modeling concurrent nucleation and growth in the phase-field framework on experimentally relevant length scales remains a significant challenge due to spatial resolution and driving force limitations. This work proposes a modeling framework that overcomes these challenges by integrating the explicit nucleation method within the recently developed high-driving force phase-field model to investigate the influence of the cooling rate on solid-state nucleation and growth. The model accurately captures the growth behavior of individual nuclei across varying length scales, and allows efficient one grid point nucleation without modifying the high driving force equation. To accommodate nanoscale nucleation within a mesoscale phase-field framework, the model incorporates an analytical subscale step accounting for critical nucleus growth to one grid point. The model was applied to the β to α transformation in extra pure titanium, for which a material-specific input parameter study was performed. Simulation results were compared to experimental results on the cooling rate dependence of transformation temperatures and mean grain sizes obtained through an Electron Backscatter Diffraction analysis of furnace-, air-, and water-cooled samples. The model's significance lies in extending the phase-field method's applicability to simulate nucleation on much larger length-scales than previously achievable, bridging the gap between simulation and experimental length-scales.

For improving the biocompatibility of TA2 pure titanium surface，micro-arc oxidation technology was used to prepare four kinds of titanium oxide coatings with different microstructures on TA2 pure titanium substrate by setting different electrolytes and electrical parameters.XRD， SEM， step profiler， and contact angle measuring instrument were employed to analyze the phase composition， micro morphology， roughness and hydrophilicity of coatings.Furthermore，MC3T3-E1 (mouse osteoblasts) were co-cultured with the titanium oxide coatings with different microstructures to observe the adhesion status between cells and the surface of the sample.Results showed that titanium oxide coatings with structural morphology of smooth macropores and rough macropores could be prepared in phosphate system electrolyte.By observing the adhesion state of cells using SEM， it was found that filopodia were generated on the surface of titanium oxide coatings with these two structural morphology， and cell secretions could be seen on the surface， indicating that the coating surface had certain biological activity.Moreover， the titanium oxide coatings with structural morphology of smooth pores and small rough pores were prepared in NaOH system electrolyte.On the surface of the titanium oxide coating with these two structural morphology， the adhesion area of cells was significantly increased， lamellipodia and filopodia were abundant， and the biological activity was greatly enhanced.The further comparative analysis suggested that the titanium oxide coating could guide the migration direction of cells when the roughness was high， and could improve the adhesion ability of the coating surface to cells when the roughness was low.Besides，the coatings with micro and nano dual-order structure had an integration effect on the two kinds of abilities.

Pure titanium is a preferred material for medical applications due to its outstanding properties, and the fabrication of its surface microtexture proves to be an effective method for further improving its surface-related functional properties, albeit imposing high demands on the processing accuracy of surface microtexture. Currently, we investigate the fabrication of precise microtextures on pure titanium surfaces with different grid depths using precision-cutting methods, as well as assess its impact on surface wettability through a combination of experiments and finite element simulations. Specifically, a finite element model is established for pure titanium precision cutting, which can predict the surface formation behavior during the cutting process and further reveal its dependence on cutting parameters. Based on this, precision-cutting experiments were performed to explore the effect of cutting parameters on the morphology of microtextured pure titanium with which optimized cutting parameters for high-precision microtextures and uniform feature size were obtained. Subsequent surface wettability measurement experiments demonstrated from a macroscopic perspective that the increase in the grid depth of the microtexture increases the surface roughness, thereby enhancing the hydrophilicity. Corresponding fluid–solid coupling finite-element simulation is carried out to demonstrate from a microscopic perspective that the increase in the grid depth of the microtexture decreases the cohesive force inside the droplet, thereby enhancing the hydrophilicity.

In this work, TA2 pure titanium was treated by borocarburizing (BC), boriding first and then carburizing (B + C), and carburizing first and then boriding (C + B), and morphology and wear and corrosion properties of these layers were investigated. The results show that the BC layer and B + C layer are composed of TiB, TiB2, and TiC phases, while the C + B layer consists of TiC and TiB2 phases. The wear type of these treated samples is abrasive wear, and wear resistance is in the sequence of B + C layer > BC layer > C + B layer. In 3.5 wt.% NaCl solution, corrosion resistance is in the order of B + C layer > C + B layer > BC layer > TA2. In 5.0 vol.% H2SO4 solution, corrosion resistance is in the order of C + B layer > B + C layer > BC layer > TA2. The B + C treatment can form a layer with gentle hardness gradient, excellent wear properties, and good corrosion resistance, which is most conducive to the bonding between layer and matrix.

Pure titanium is gaining increasing interest due to its potential use in dental and orthopedic applications. Due to its relatively weak mechanical parameters, a limited number of components manufactured from pure titanium are available on the market. In order to improve the mechanical parameters of pure titanium, manufacturers use alloys containing cytotoxic vanadium and aluminum. This paper presents unique explosive hardening technology that can be used to strengthen pure titanium parameters. The analysis confirms that explosive induced α-ω martensitic transformation and crystallographic anisotropy occurred due to the explosive pressure. The mechanical properties related to residual stresses are very nonuniform. The corrosion properties of the explosive hardened pure titanium test do not change significantly compared to nonhardened titanium. The biocompatibility of all the analyzed samples was confirmed in several tests. The morphology of bone cells does not depend on the titanium surface phase composition and crystallographic orientation. [ABSTRACT FROM AUTHOR]

The micro-arc oxidation process was used to apply a ceramic oxide coating on a pure titanium substrate using calcium acetate and sodium dihydrogen phosphate as an electrolyte. The influence of the current frequency and duty ratio on the surface morphology, phase composition, wear behavior, and corrosion resistance were analyzed by employing a scanning electron microscope, X-ray diffractometer, ball-on-disk apparatus, and potentiodynamic polarization, respectively. Analyses of the surface and cross-sectional morphologies revealed that the MAO films prepared via a low current frequency (100 Hz) and a high duty ratio (60%) had a lower porosity and were more compact. The medium (500 Hz) and high (1000 Hz) frequencies at the higher duty ratios presented with better wear resistance. The highest film thickness (11.25 µm) was achieved at 100 Hz and a 20% duty ratio. A negligible current density was observed when the frequency was fixed at 500 Hz and 1000 Hz and the duty cycle was 20%. [ABSTRACT FROM AUTHOR]

In this study, we investigated the anisotropy in tensile deformation behaviour of CP-Ti plate in the rolling (RD) and transverse direction (TD), using in-situ SEM-EBSD testing and stress-relaxation method. The EBSD-assisted slip trace analysis was conducted to examine the slip systems activated within individual grains. It was found that the prismatic slip is dominant in the RD sample, whilst the activity of non-prismatic slip systems is higher in the TD sample. The slip transfer significantly occurred in the TD sample, thereby promoting the activity of multiple slips and dislocation interactions at the grain interiors. However, the limited occurrence of slip transfer in the RD sample indicates the strong dislocation pinning at the grain boundaries (GBs). Combined with the EBSD analysis, the SEM observations revealed that the GBs with ledge character are formed in the slip-favourable and -unfavourable grain pairs, and the GBs with sink character are created in the grain pairs whose c-axes are equally inclined to the loading direction, but the sign of c-axis inclination angles is opposite with each other. The formation of GB ledges and GB sinks was pronounced in the RD and TD sample, respectively. The GB-dislocation interactions and GB-mediated deformation arising from the orientation relationship between the particular grain pairs led to the anisotropy in strain-hardening behaviour of polycrystalline α-Ti.

Pure titanium is widely used in clinical implants, but its bioinert properties (poor strength and mediocre effect on bone healing) limit its use under load‐bearing conditions. Modeling on the structure of collagen fibrils and specific nanocrystal plane arrangement of hydroxyapatite in the natural bone, a new type of titanium (Ti) with a highly aligned fibrous‐grained (FG) microstructure is constructed. The improved attributes of FG Ti include high strength (≈950 MPa), outstanding affinity to new bone growth, and tight bone‐implant contact. The bone‐mimicking fibrous grains induce an aligned surface topological structure conducive to forming close contact with osteoblasts and promotes the expression of osteogenic genes. Concurrently, the predominant Ti(0002) crystal plane of FG Ti induces the formation of hydrophilic anatase titanium oxide layers, which accelerate biomineralization. In conclusion, this bioinspired FG Ti not only proves to show mechanical and bone‐regenerative improvements but it also provides a new strategy for the future design of metallic biomaterials. [ABSTRACT FROM AUTHOR]

The effect of hydrogen ion irradiation on the formation of hydride and vacancy-type defects in pure titanium was investigated by X-ray diffraction (XRD), Doppler broadening spectrum (DBS), and coincidence Doppler broadening spectrum (CDB) based on slow positron beam. The XRD results showed that γ-TiH was observed in single hydrogen ion-irradiated and hydrogen + deuterium (H + D) sequentially irradiated specimens but not in the single deuterium plasma-implanted sample. This finding indicates that the vacancy-type defects caused by H ion irradiation greatly promoted the formation of γ-TiH. The DBS results showed that for the single D plasma-implanted sample, the damage peak was closer to the surface region and lower compared to the other two samples containing γ-TiH, indicating that vacancy generated by lattice distortion didn't diffuse to the depth of the matrix, and the concentration of that was smaller, which was not conducive to the deuteride formation. For the H + D sequentially irradiated sample, the number of hydrogen-vacancy complexes (HmVn) further increased compared with the single H ion-irradiated sample. Thus, the effective volume of vacancy defects was reduced, which led to the decrease in the S parameter.

In this work, the corrosion behaviors and mechanisms of the pure titanium by pack boronizing with different Nd 2 O 3 contents in 3.5 wt% NaCl and 5.0 vol% H 2 SO 4 solutions were characterized and analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), electron probe microanalyzer (EPMA), and electrochemical tests. The results showed that the sample boronized with 4 wt% Nd 2 O 3 has the smoothest surface, the densest ceramic coating with a thickness of 52 μm, and the best corrosion resistance. Nd 2 O 3 can react with B to generate Nd–B active group, which promotes ceramic coating growth and turns local corrosion into uniform corrosion. [ABSTRACT FROM AUTHOR]

Abstract Pure titanium is widely used in clinical implants, but its bioinert properties (poor strength and mediocre effect on bone healing) limit its use under load‐bearing conditions. Modeling on the structure of collagen fibrils and specific nanocrystal plane arrangement of hydroxyapatite in the natural bone, a new type of titanium (Ti) with a highly aligned fibrous‐grained (FG) microstructure is constructed. The improved attributes of FG Ti include high strength (≈950 MPa), outstanding affinity to new bone growth, and tight bone‐implant contact. The bone‐mimicking fibrous grains induce an aligned surface topological structure conducive to forming close contact with osteoblasts and promotes the expression of osteogenic genes. Concurrently, the predominant Ti(0002) crystal plane of FG Ti induces the formation of hydrophilic anatase titanium oxide layers, which accelerate biomineralization. In conclusion, this bioinspired FG Ti not only proves to show mechanical and bone‐regenerative improvements but it also provides a new strategy for the future design of metallic biomaterials.

This study investigates the impact of hard coatings on the fatigue properties of pure titanium. A specialized fatigue test which ensured machine equivalence was conducted to compare the fatigue behavior of coated and uncoated metals. The findings reveal that the application of coatings adversely affects the fatigue properties of pure titanium due to stress concentration from the coating, which accelerates fatigue crack propagation within the substrate material. Notably, zigzag fatigue cracks at the interface between the coating and substrate and multiple micro-cracks initiated within the coating are found.

The carbon-supersaturated SKD11 punch was proposed as a green, or, a galling-free, long-life and low energy-consuming forging tool of pure titanium and β-titanium alloy that works with low friction and less work hardening and without galling. The reduction in thickness was increased up to 50% to investigate the friction process on the contact interface and the work-hardening behavior. The nitrogen-supersaturated SKD11 punch was utilized as a reference tool for this forging experiment. Three-dimensional finite element analysis was employed to derive the regression curve between the contact interface width and the friction coefficient. The friction coefficient was estimated in forging the pure titanium wires by using the regression curves. The work-hardening process was analyzed by the hardness mapping on the cross-section of forged wires. The SEM-EDX analysis on the contact interface proved that no adhesion of fresh metallic titanium and titanium oxide debris was seen on the interface between the carbon-supersaturated SKD11 punch and the titanium work. In particular, the work hardening is suppressed without shear localization in forging the β-titanium. Finally, the uniform carbon layer was derived from the supersaturated carbon solute from the punch matrix and wrought as a friction film on the contact interface to reduce the friction and the work hardening as well as suppress the chemical galling. This in situ carbon lubrication must be essential in green forging to highly qualify the titanium and titanium alloy products and to prolong the punch-and-die lives in practical operation.

Pure metals tend to have a superior malleability compared to alloys. However, the applicability of pure metals is limited by their low strengths and hardness properties. In this study, strong and ductile pure Ti was synthesized via an approach involving powder modification and additive manufacturing (AM) under a reactive atmosphere. Specifically, pure Ti was processed by laser powder bed fusion in an environment containing a mixture of argon and nitrogen gases. In-situ high-energy synchrotron X-ray diffraction analysis reveals that in-situ nitrogen strengthening of the pure Ti occurs during the reactive AM of Ti. Furthermore, the presence of a nitrogen solid solution leads to the formation of high-strength pure Ti (yield strength of ∼979 MPa and ultimate tensile strength of ∼1058 MPa, respectively). This material exhibits excellent uniform elongation (11%) due to strong work hardening caused by the interaction of interstitial elements and submicrostructure. The proposed reactive AM approach paves the way for in-situ strengthening of pure metals and alloys.

The 'plainification of materials' has been conceptualized to promote the sustainable development of materials. This perspective, for the first time in the field of biomaterials, proposes and defines 'plain metallic biomaterials (PMBs)' with demonstrated research and application case studies of pure titanium with high strength and toughness, and biodegradable, fine-grained and high-purity magnesium. Then, after discussing the features, benefits and opportunities of PMBs, the challenges are analyzed from both technical and regulatory aspects. Regulatory perspectives on PMB-based medical devices are also provided for the benefit of future research, development and commercialization. [ABSTRACT FROM AUTHOR]

The nitriding process of the coarse-grained and fine-grained pure titanium proceeded by multidirectional forging technique has been investigated at temperatures of 623, 673, and 723 K. The process was carried out by high-density radiofrequency-direct current plasma combined with a rectangular hollow cathode device. The result obtained is a significant increase in surface hardness with increasing holding temperature. The surface hardness increases due to forming a surface layer composed of δ-Ti2N, ε-Ti2N and TixNx observed from x-ray diffraction results. This paper explains the mechanism of surface layer formation. We also observed anisotropic phase transformation of titanium nitride through the right shift of the x-ray diffraction peaks. Diffused nitrogen atoms during the nitriding process cause a change in crystal orientation through structural transformation of the metastable δ-Ti2N to the stable ε-Ti2N. The structural reconstruction will continue by forming TixNx to achieve stoichiometric equilibrium. More compacting of the surface microstructure is also obtained by increasing nitriding temperature.

Improving uniform elongation in metals typically involves enhancing the work hardening rate, as elevated work hardening can delay necking and fracture. However, our investigation into commercial pure titanium reveals a counterintuitive relationship between these properties. We find that high uniform elongation correlates with low work hardening capability, while a high work hardening rate results in reduced ductility. Two types of ultrafine-grained pure titanium, prepared by rotary swaging, subsequent rolling, and annealing, exhibit different mechanical properties. Microstructural and deformation mechanism analyses reveal that the difference arise from variations in texture. Specifically, extensive activation of dislocations in the former sample leads to premature, intense work hardening that is quickly exhausted, while the latter sample shows a steady, uniform work hardening progression that delays necking. Our findings challenge the conventional understanding that high work hardening rates ensure high uniform elongation. Instead, we propose that optimizing ductility requires a strategic allocation of work hardening throughout the tensile deformation to delay necking. This study reveals the intrinsic relationship between work hardening and ductility, offering new strategies for designing stronger and tougher materials. [Display omitted] • Rotary swaging significantly enhances the work hardening ability of pure titanium compared to rolling. • Contrary to conventional wisdom, increased work hardening does not equate to higher ductility in this work. • High work hardening is attributed to the concurrent activation of multiple slip systems. • Optimizing ductility requires a strategic allocation of work hardening throughout the tensile deformation. [ABSTRACT FROM AUTHOR]

Pure titanium is gaining increasing interest due to its potential use in dental and orthopedic applications. Due to its relatively weak mechanical parameters, a limited number of components manufactured from pure titanium are available on the market. In order to improve the mechanical parameters of pure titanium, manufacturers use alloys containing cytotoxic vanadium and aluminum. This paper presents unique explosive hardening technology that can be used to strengthen pure titanium parameters. The analysis confirms that explosive induced α-ω martensitic transformation and crystallographic anisotropy occurred due to the explosive pressure. The mechanical properties related to residual stresses are very nonuniform. The corrosion properties of the explosive hardened pure titanium test do not change significantly compared to nonhardened titanium. The biocompatibility of all the analyzed samples was confirmed in several tests. The morphology of bone cells does not depend on the titanium surface phase composition and crystallographic orientation.

The micro-arc oxidation process was used to apply a ceramic oxide coating on a pure titanium substrate using calcium acetate and sodium dihydrogen phosphate as an electrolyte. The influence of the current frequency and duty ratio on the surface morphology, phase composition, wear behavior, and corrosion resistance were analyzed by employing a scanning electron microscope, X-ray diffractometer, ball-on-disk apparatus, and potentiodynamic polarization, respectively. Analyses of the surface and cross-sectional morphologies revealed that the MAO films prepared via a low current frequency (100 Hz) and a high duty ratio (60%) had a lower porosity and were more compact. The medium (500 Hz) and high (1000 Hz) frequencies at the higher duty ratios presented with better wear resistance. The highest film thickness (11.25 µm) was achieved at 100 Hz and a 20% duty ratio. A negligible current density was observed when the frequency was fixed at 500 Hz and 1000 Hz and the duty cycle was 20%.

Punch force is the main factor in the success of making holes using the punching process. However, the punching process cannot make a hole when the punch force in the machine is smaller than the punch force in the material. Preheating can be used to reduce the punch force in the material. This research aims to develop the preheating method with low current electricity for reducing the punch force in the material. The preheating method is used two tubular type heating elements with an electric current of about 0.9 A. This method can be heating the material below recrystallization temperature (100 and 150 °C). Preheating at 100 and 150 °C can reduce the punch force by 4 and 11% compared to without preheating. These results can be concluded the material heating below recrystallization temperature is effectively enough to reduce the punch force. Thus, the punching process is able to make a hole even though the punch force in the machine is smaller than the punch force in the material.

Micro deep drawing (MDD) is a fundamental process in microforming which has wide applications in micro electromechanical system (MEMS) and biological engineering. Titanium possesses excellent mechanical properties and biocompatibility, which makes it a preferred material in micromanufacturing. In this study, eco-friendly and low-cost water-based TiO2 nanolubricants were developed and applied in the MDD with 40 μm-thick pure titanium foils. The lubricants consisting of TiO2 nanoparticles (NPs), 10 wt% glycerol, 0.1 wt% sodium dodecyl-benzene sulfonate (SDBS) and balanced water were synthesised in a facile process. The MDD with 40 μm-thick pure titanium was carried out using the lubricants with varying concentrations of 0.5, 1.0 and 2.0 wt%. The results show that the formability of micro cups could be significantly improved when the nanolubricants are applied. Especially, the use of 1.0 wt% TiO2 nanolubricant demonstrates the best lubrication performance by significantly reducing the final drawing forces, and surface roughness, and the wrinkles by up to 24.2%, 12.55% and 4.82%, respectively. The lubrication mechanisms including the ball bearing and mending effects of NPs on open lubricant pockets (OLPs) and close lubricant pockets (CLPs) areas were then revealed through microstructure observation. [ABSTRACT FROM AUTHOR]

The present work dealt with the development of a protective and functional oxide layer via one-step plasma electrolytic oxidation (PEO) on pure titanium by employing highly concentrated aluminate solution in a short processing time. A compositional analysis showed that Al2TiO5 active compound was formed successfully by means of Al2O3 incorporation when TiO2 was spontaneously developed with the aid of plasma swarms. The electrochemical performance showed the protective and functional capabilities of the layer, which was attributed to the respective amounts of Al2O3 and Al2TiO5. Such capabilities were achieved in a short processing time, thus reducing the total production cost. [ABSTRACT FROM AUTHOR]

The carbon-supersaturated SKD11 punch was proposed as a green, or, a galling-free, long-life and low energy-consuming forging tool of pure titanium and β-titanium alloy that works with low friction and less work hardening and without galling. The reduction in thickness was increased up to 50% to investigate the friction process on the contact interface and the work-hardening behavior. The nitrogen-supersaturated SKD11 punch was utilized as a reference tool for this forging experiment. Three-dimensional finite element analysis was employed to derive the regression curve between the contact interface width and the friction coefficient. The friction coefficient was estimated in forging the pure titanium wires by using the regression curves. The work-hardening process was analyzed by the hardness mapping on the cross-section of forged wires. The SEM-EDX analysis on the contact interface proved that no adhesion of fresh metallic titanium and titanium oxide debris was seen on the interface between the carbon-supersaturated SKD11 punch and the titanium work. In particular, the work hardening is suppressed without shear localization in forging the β-titanium. Finally, the uniform carbon layer was derived from the supersaturated carbon solute from the punch matrix and wrought as a friction film on the contact interface to reduce the friction and the work hardening as well as suppress the chemical galling. This in situ carbon lubrication must be essential in green forging to highly qualify the titanium and titanium alloy products and to prolong the punch-and-die lives in practical operation. [ABSTRACT FROM AUTHOR]

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When it comes to using bio-metals, the chemical and biocompatibility properties of titanium led to its widespread use in biomedical implants. However, pure titanium possesses lower mechanical properties than Ti alloys containing cytotoxic elements. Severe plastic deformation (SPD) techniques were able to cause a significant strength increase, corrosion behavior improvement, and the release of the alloying elements. In this study, the ECAP process was performed on commercially pure titanium with a square cross-section at two and four passes, which resulted in a finer grain size and a more uniform microstructure. In order to improve cell behaviors, etch treatment was performed to produce nano-rough and nano-texture surfaces for all Ti samples. The effect of surface etching on corrosion, surface roughness, and cell behaviors on ECAP and untreated samples was also investigated. Optical/Field Emission Scanning Electron Microscopy, Atomic Force Microscopy, and X-Ray Diffraction were used to study the microstructural characterizations of samples. In addition, the impact of grain structure on the contact angle, electrochemical corrosion behavior, osteoblast response, and cell viability was investigated. The titanium that was ECAPed four times provided finer grains (200 nm) than the unprocessed sample (25 µm). The potentiodynamic polarization test revealed that corrosion resistance of ECAPed samples was enhanced, which was associated with grain refinement, affecting the passive film formation. Corrosion resistance and wettability experienced an apparent increase after each ECAP pass. In conclusion, improvement of grain size and surface roughness was due to the simultaneous effect of ECAP and etching treatment that led to the osteoblast response and cellular activity of samples. [ABSTRACT FROM AUTHOR]

Commercially pure titanium (CP-Ti) has seen major applications in biomedical equipment. The use of selective laser melting (SLM) has become more common concerning the fabrication of CP-Ti components with a complicated shape in biomedical implants, where high strength and ductility are required. However, SLM manufactured CP-Ti often exhibits high strength and low ductility, as well as mechanical anisotropy because SLM process typically results in the formation of long columnar grains comprising of fine acicular α′ martensite. Heat treatment must be preceded to transform the acicular α′ to equiaxed α grain. This study demonstrated that annealing at 650 °C of SLM CP-Ti can create an equiaxed structure, resulting in a weakened texture. The formation of equiaxed grains occurred at two types of microstructural features, acicular α′ and irregular massive (α′m) martensite, which exhibited different sizes, morphologies, and contained different types of substructures under SLM as-fabricated condition. The formation mechanism of equiaxed grains in the α′ region is dominated by the coalescence of acicular α′ of the same variant and the dissolution of α′ into the matrix, whereas the formation mechanism in the α′m region is primarily dominated by the growth of the preexisting subgrains. A small number of equiaxed grains with new orientations were formed in the α′m region. The majority of equiaxed grains were formed in the acicular α′ region and inherited the grain orientations of the preexisting α′ or matrix. Therefore, a similar but weakened texture was inherited from the microstructure of the SLM CP-Ti after annealing.

A boriding and aluminizing two-step method was used to fabricate a B–Al composite layer on the surface of pure titanium. The composite layer was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoindentation, wear tests, and electrochemical experiments. For comparison, single boriding and single aluminizing treatments were performed on pure titanium. The results show that the surface morphology characteristics from the single boriding and single aluminizing treatments were transferred to the composite sample. The XRD pattern reveals that the B–Al composite layer also has XRD peaks of Al 3 Ti+TiB 2 +TiB. The SEM results revealed that the B–Al composite layer is composed of an outermost TiB 2 layer, a TiB+Al 3 Ti sublayer, an Al 3 Ti layer, and an internal diffusion layer. The corrosion resistance of the composite sample is slightly better than that of the matrix, and the hardness is approximately 3 times higher than that of the matrix. The wear type is mainly abrasive wear, and the wear resistance is improved; with increasing temperature, the wear on the surface of the sample is intensified, and the wear resistance is reduced. [ABSTRACT FROM AUTHOR]

While pure titanium is a material of choice for medical applications for its excellent mechanical and chemical properties, further improving its surface-related functionalities by surface texturing is also promising. In the present work, we experimentally investigate the fabrication, as well as the resulting functionalities of surface wettability and biocompatibility, of precise mesh-type surface textures on pure titanium by picosecond pulsed laser ablation operating at 1064 nm wavelength. Specifically, the dependence of microgroove morphology on average power and scanning speed is evaluated to yield optimized laser processing parameters, which are utilized to fabricate high precision mesh-type surface textures with uniform feature size and limited thermal effects on pure titanium. Subsequent performance evaluation tests demonstrate that the mesh-type surface textures induce a beneficial effect on the biocompatibility with respect to BMSC cells due to the enhanced hydrophilicity. [ABSTRACT FROM AUTHOR]

Electrolytic hydrogen charging experiments on cold-deformed and well-annealed (annealing at 700 °C for 2 h) pure titanium samples were carried out, respectively. Positron annihilation spectroscopy and X-ray diffraction were used to characterize all experimental samples to explore the formation of vacancy defects and the storage form of hydrogen in pure titanium after charging. Results showed that hydrides formed in well-annealed samples after electrolytic hydrogen charging, but a new phase in the cold-deformed samples was not observed. The annealed samples formed vacancy-type defects in the process of electrolytic hydrogen charging, and the excess hydrogen atoms were easily trapped by vacancies to form a hydrogen vacancy complex (HmVn). The defects formed in the cold-deformed hindered the diffusion of hydrogen atoms and inhibited the formation of vacancies. Compared with the well-annealed electrolytic hydrogen charging samples, the S parameters of the deformed electrolytic hydrogen charging samples hardly changed. The coincidence Doppler broadening spectrum results showed that wide peaks related to hydrogen vacancy complexes were found in electrolytic hydrogen charging samples. The formation of hydride in titanium affected the positron annihilation environment in the low-momentum region. The hydride-related peak was observed only in the electrolytic hydrogen-charged samples after being well annealed. [ABSTRACT FROM AUTHOR]

In the present study, a porous Ti layer was deposited on the surface of a Co–Cr alloy using the directed energy deposition process, and the effects of the laser power and scan speed on the porosity, coating layer thickness, melt pool depth, contact (bonded) area fraction, and fatigue life of the built components were studied. To fabricate an ideal porous Ti layer on the substrate, a high coating thickness and a high porosity are important for effective bonding between bone tissue and porous structures. Furthermore, a high contact area fraction is desired because as this fraction increases, the resistance to peeling and separation of the porous layer increases, and a high fatigue life is important for long-term reliable use of the components. As the laser power increased, the fatigue life and porosity decreased, but the coating layer thickness and the contact area fraction increased. Therefore, the laser power should be optimized to provide a good balance between the fatigue life/porosity and layer thickness/fraction of contact area. For a given laser power, a decrease in the scan speed increased the coating layer thickness, but it decreased the contact area fraction. Therefore, the scan speed also needs to be optimized. The heat treatment after deposition of the Ti layer greatly increased the fatigue life because it decreased the thickness of the intermetallic compound layer formed at the interfaces and increased the blending of the elements through enhanced atomic diffusion, which reduced the probability of crack nucleation and decreased the crack size upon nucleation during fatigue testing.

The nitriding process of the coarse-grained and fine-grained pure titanium proceeded by multidirectional forging technique has been investigated at temperatures of 623, 673, and 723 K. The process was carried out by high-density radiofrequency-direct current plasma combined with a rectangular hollow cathode device. The result obtained is a significant increase in surface hardness with increasing holding temperature. The surface hardness increases due to forming a surface layer composed of δ-Ti2N, ε-Ti2N, and TixNx observed from x-ray diffraction results. This paper explains the mechanism of surface layer formation. We also observed anisotropic phase transformation of titanium nitride through the right shift of the x-ray diffraction peaks. Diffused nitrogen atoms during the nitriding process cause a change in crystal orientation through structural transformation of the metastable ε-Ti2N to the stable δ-Ti2N. The structural reconstruction will continue by forming TixNx to achieve stoichiometric equilibrium. More compacting of the surface microstructure is also obtained by increasing nitriding temperature. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure characteristics and microhardness distribution of titanium alloy joints by narrow gap fiber laser welding were studied. High-quality welded joints in 40-mm-thick TA2 have been successfully manufactured using the laser multi-pass narrow gap welding process. The welds were found to be free of lack of fusion defects. The size of grains, microstructure, dislocations, Kernel average misorientation (KAM), texture and microhardness of joint in upper and middle were investigated by optical microscope (OM), transmission electron microscope (TEM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and microhardness Vicker. Results indicate that the upper joint has great different from middle joint on microstructure. In addition, the microhardness of the weld metal center is the highest, and the fusion zone is higher than the base metal and lower than the weld metal. The microhardness of the upper weld metal is higher than that of the middle weld metal. The strength of weld metal is not lower than that of the base metal, and impact toughness KV2 of joint is lower than that of base metal. [ABSTRACT FROM AUTHOR]

Ag-carrying micro-arc oxidation ceramic film was prepared on the surface of pure titanium by combining micro-arc oxidation and hydrothermal treatment to improve its wettability, corrosion resistance and impart antibacterial properties. The MAO film was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The hydrophilicity of the film was evaluated by contact angle test. The corrosion resistance of the film was evaluated by electrochemical test, and the antibacterial property was analyzed by the antibacterial property test. The results show that the surface morphology of Ag-carrying MAO film remains volcanic porous structure. Nano-scale Ag particles are evenly distributed around the pores. The surface of Ag-carrying MAO film is mainly TiO2 and nano-Ag particles. The hydrophilicity of the Ag-carrying MAO film is 77.0% higher than that of pure titanium, and 68.2% higher than that of MAO film. The self-corrosion potential of Ag-carrying MAO film increases by 0.44 V and 0.31 V compared with pure titanium and MAO film. The antibacterial rate of MAO film is 32.2%. The antibacterial rate of Ag-carrying micro-arc oxidation MAO film is more than 99.9% and has excellent antibacterial property.

Ultrasonic vibration (UV) assisted plastic forming technology is an ideal way to improve the formability of titanium and its alloys at room temperature, due to the softening effect which is more effective than thermal input. Thus, UV assisted compression test of commercially pure titanium is carried out and the deformation behavior is focused in this study. For an accurate prediction of the flow behavior and further application in UV forming process, the original Johnson–Cook (JC) model and its modified formulae have been adopted to construct the constitutive relation of pure titanium deformed with high-frequency oscillation. The yield stress reduction is related to both the amplitude and its square. The other material constants in JC model are established as the function of the amplitude. The comparative analysis of the predicted stress through the built JC model with the measured one is performed, showing the improved JC model can precisely describe the stress-strain relation in a large deformation range at different vibration amplitudes and strain rates.

Selective laser melting (SLM), which is an additive manufacturing technology, is attractive due to its ability to freely form shapes. SLM forms a 3D material by building it layer-by-layer from a metal powder. However, some issues have yet to be resolved, including dimensional accuracy, surface finish, processing time, and mechanical properties such as surface roughness, hardness, and crystal orientation. We demonstrate that pure titanium (Ti), which is clinically used for artificial bone and hard tissue implants because it is lightweight and biocompatible, can be fabricated by the SLM process in vacuum to develop a spatter-less process. The amount of spatter was dependent on the laser scanning rate; at 10 mm/s and an output power of 200 W, the spatter was minimized so that the surface roughness was reduced to 4.2 µm from 50 µm with a laser scanning rate of 50 mm/s. Defects such as pores, voids and delamination were found to be caused with an increase in the amount of spatter.

Designing a gradient nanostructure is regarded as an effective strategy for strengthening commercial pure Ti without seriously sacrificing ductility. However, the corrosion behavior of the gradient nanostructured (GNS) pure Ti is far from clear, especially in reducing acid in which pure Ti shows poor corrosion resistance. The present paper aims at investigating the corrosion behavior of GNS pure Ti in hydrochloric acid by electrochemical method. The GNS surface layer is produced by a recently developed method called ultrasonic severe surface rolling. The GNS pure Ti exhibits spontaneous passivation behavior as well as the coarse-grained one in 1 M HCl. Due to the GNS surface layer, the corrosion current density and passive current density decrease by 70% and 54%, respectively, giving rise to significantly enhanced corrosion resistance and passivation ability. The better corrosion resistance is believed to be ascribed to the high-density grain boundaries and dislocations induced by the surface nano-grained structure as well as the smooth surface with few surface defects. The USSR processing also enlarges the static water contact angle of the pure Ti to 61.0 ± 0.3°.

Micro deep drawing (MDD) is a fundamental process in microforming which has wide applications in micro electromechanical system (MEMS) and biological engineering. Titanium possesses excellent mechanical properties and biocompatibility, which makes it a preferred material in micromanufacturing. In this study, eco-friendly and low-cost water-based TiO2 nanolubricants were developed and applied in the MDD with 40 μm-thick pure titanium foils. The lubricants consisting of TiO2 nanoparticles (NPs), 10 wt% glycerol, 0.1 wt% sodium dodecyl-benzene sulfonate (SDBS) and balanced water were synthesised in a facile process. The MDD with 40 μm-thick pure titanium was carried out using the lubricants with varying concentrations of 0.5, 1.0 and 2.0 wt%. The results show that the formability of micro cups could be significantly improved when the nanolubricants are applied. Especially, the use of 1.0 wt% TiO2 nanolubricant demonstrates the best lubrication performance by significantly reducing the final drawing forces, and surface roughness, and the wrinkles by up to 24.2%, 12.55% and 4.82%, respectively. The lubrication mechanisms including the ball bearing and mending effects of NPs on open lubricant pockets (OLPs) and close lubricant pockets (CLPs) areas were then revealed through microstructure observation.

The present work dealt with the development of a protective and functional oxide layer via one-step plasma electrolytic oxidation (PEO) on pure titanium by employing highly concentrated aluminate solution in a short processing time. A compositional analysis showed that Al2TiO5 active compound was formed successfully by means of Al2O3 incorporation when TiO2 was spontaneously developed with the aid of plasma swarms. The electrochemical performance showed the protective and functional capabilities of the layer, which was attributed to the respective amounts of Al2O3 and Al2TiO5. Such capabilities were achieved in a short processing time, thus reducing the total production cost.

Modeling concurrent nucleation and growth in the phase-field framework on experimentally relevant length scales remains a significant challenge due to spatial resolution and driving force limitations. This work proposes a modeling framework that overcomes these challenges by integrating the explicit nucleation method within the recently developed high-driving force phase-field model to investigate the influence of the cooling rate on solid-state nucleation and growth. The model accurately captures the growth behavior of individual nuclei across varying length scales, and allows efficient one grid point nucleation without modifying the high driving force equation. To accommodate nanoscale nucleation within a mesoscale phase-field framework, the model incorporates an analytical subscale step accounting for critical nucleus growth to one grid point. The model was applied to the β to α transformation in extra pure titanium, for which a material-specific input parameter study was performed. Simulation results were compared to experimental results on the cooling rate dependence of transformation temperatures and mean grain sizes obtained through an Electron Backscatter Diffraction analysis of furnace-, air-, and water-cooled samples. The model's significance lies in extending the phase-field method's applicability to simulate nucleation on much larger length-scales than previously achievable, bridging the gap between simulation and experimental length-scales. • The high driving force phase-field model was extended by incorporating a nucleation submodel, allowing efficient one-gridpoint nucleation. • Single and multiple nuclei growth was successfully validated by benchmarking with analytical solutions and JMAK theory, demonstrating quantitative results. • The simulation of nucleation at the nanoscale within a mesoscale phase-field framework surpasses limitations inherent in the classical phase-field approach. • Direct comparison between simulations and experimental data on transformation temperatures and mean grain size were conducted for extra pure titanium. • Simulation results highlight the influence of interfacial energy, interfacial mobility, and cooling rate on the transformation temperatures and grain size. [ABSTRACT FROM AUTHOR]