Melting Titanium Research Articles

Micro-/nano-topography of selective laser melting titanium enhances adhesion and proliferation and regulates adhesion-related gene expressions of human gingival fibroblasts and human gingival epithelial cells.

BackgroundSelective laser melting (SLM) titanium is an ideal option to manufacture customized implants with suitable surface modification to improve its bioactivity. The peri-implant soft tissues form a protective tissue barrier for the underlying osseointegration. Therefore, original microrough SLM surfaces should be treated for favorable attachment of surrounding soft tissues.Material and methodsIn this study, anodic oxidation (AO) was applied on the microrough SLM titanium substrate to form TiO2 nanotube arrays. After that, calcium phosphate (CaP) nanoparticles were embedded into the nanotubes or the interval of nanotubes by electrochemical deposition (AOC). These two samples were compared to untreated (SLM) samples and accepted mechanically polished (MP) SLM titanium samples. Scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, surface roughness, and water contact angle measurements were used for surface characterization. The primary human gingival epithelial cells (HGECs) and human gingival fibroblasts (HGFs) were cultured for cell assays to determine adhesion, proliferation, and adhesion-related gene expressions.ResultsFor HGECs, AOC samples showed significantly higher adhesion, proliferation, and adhesion-related gene expressions than AO and SLM samples (P<0.05) and similar exceptional ability in above aspects to MP samples. At the same time, AOC samples showed the highest adhesion, proliferation, and adhesion-related gene expressions for HGFs (P<0.05).ConclusionBy comparison between each sample, we could confirm that both anodic oxidation and CaP nanoparticles had improved bioactivity, and their combined utilization may likely be superior to mechanical polishing, which is most commonly used and widely accepted. Our results indicated that creating appropriate micro-/nano-topographies can be an effective method to affect cell behavior and increase the stability of the peri-implant mucosal barrier on SLM titanium surfaces, which contributes to its application in dental and other biomedical implants.

Structure and Phase Composition of a Ti Film–Al Substrate System Irradiated with an Intense Pulsed Electron Beam

Commercially pure A7 aluminum was exposed to surface modification in a single vacuum cycle which included vacuum arc evaporation and deposition of commercially pure titanium and intense electron beam irradiation and melting of the film–substrate system using a plasma-cathode pulsed electron source. The deposited Ti film thickness was 0.5 and 1 μm. The irradiated Ti–Al system revealed a multilayer multiphase structure consisting of submicro-and nanosized elements with intermetallic inclusions Al3Ti, Al2Ti, and TiAl3. The Ti film during irradiation broke up into fragments with their immersion in the molten Al surface layer to a depth of 20 μm. The modified material surpassed the initial aluminum in wear resistance by a factor of 2.4 and in microhardness by a factor larger than 4. The main cause for the high surface hardness and high wear resistance of the modified aluminum was likely the formation of both the intermetallic particles and the Ti-hardened transition layer.

Rapid mechanochemical synthesis of titanium and hafnium carbides

The mechanically triggered interactions in the Ti–C and Hf–C systems performed in a high-energy planetary ball mill are studied. The formation of carbides (TiC and HfC) in the course of mechanochemical synthesis at the different stages is followed by both conventional and synchrotron X-ray diffraction analyses and high-resolution scanning and transmission electron microscopy. The mechanism of the mechanochemically induced reactions in the Ti–C and Hf–C systems leading to the relatively rapid formation of TiC and HfC, respectively, is proposed. The interaction between metallic Ti (Hf) and C proceeds through the formation of mechanocomposites Ti/C (Hf/C) at the first stage, followed by the melting of titanium (hafnium), the spreading it over the carbon particle surface and the crystallization of titanium (hafnium) carbides. It is demonstrated that the mechanosynthesis of ultra-fine TiC and HfC is completed after 20 and 8 min of mechanical activation, respectively.

Enhanced antibacterial efficacy of selective laser melting titanium surface with nanophase calcium phosphate embedded to TiO2 nanotubes

Selective laser melting (SLM) has promising prospects in manufacturing customized implants, however the rough surface of SLM titanium specimen can facilitate bacterial adherence and biofilm formation, which is a risk to implant success. Therefore, surface modification is required to enhance its antibacterial efficacy. Sandblasting, anodization and electrochemical deposition were applied to construct a novel composite nanostructure of nanophase calcium phosphate embedded to TiO2 nanotubes on microrough SLM titanium substrates (NTN). NTN samples were compared with TiO2 nanotubes (NT) samples, mechanical polished (MP) samples and untreated SLM titanium samples. Surface characterization were analyzed using scanning electron microscope, energy dispersive spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, a three dimensional profilometer and a contact angle measuring device. Bacteria adhesion assay for bacteria colony counting and bacteria LIVE/DEAD staining was conducted using Streptococcus mutans and Streptococcus sanguinis. Both S. mutans and S. sanguinis adherence on SLM samples were significantly higher than on NTN, NT and MP samples. The antibacterial efficacy of NTN samples was superior compared to NT and had no significant difference with MP samples, despite the fact that NTN samples had much rougher surface than MP samples. This study elucidates an efficient method to enhance antibacterial efficacy on rough SLM surfaces, which contributes to its application in dental and other biomedical implants.

Dissolution of BaZrO3 refractory in titanium melt

AbstractAlthough numerous investigations have studied BaZrO3 as a crucible refractory for melting titanium alloys, the interaction mechanism between them has not been clarified. In this study, a set of three designed alloys with different Ti composition (TiNi, Ti1.5Ni, and Ti2Ni) were melted in the BaZrO3 crucibles. By using the X‐ray diffraction, optical, and scanning electron microscopy analysis, the interactions between the BaZrO3 crucibles and the titanium melts were investigated. It was found that dissolution of the BaZrO3 refractory into the titanium melts resulted in the crucible erosion and the melt contamination, the degree of which were both increased with the increasing of Ti content in the melts. The dissolution reaction could be determined as follows: . The oxygen content dissolved in TiNi, Ti1.5Ni, and Ti2Ni melts was thermodynamically calculated as 0.0055, 0.1922, and 0.2263 wt%, respectively, which were in agreement with the experimental results.

Titanium Melting Curve: Data Consistency Assessment, Problems and Achievements

Experimental data for the thermodynamic properties of titanium on the melting curve in the pressure range from atmospheric value to 90 GPa are analyzed and brought into correspondence. The problems that have been considered are (i) the lack of data for the solid β-phase density near the normal melting point and (ii) the formation probability of a triple point on the melting curve for the coexisting β-, ω-, and liquid phases of titanium. To estimate the change of the volume upon melting 3d elements from Mendeleev’s periodic system, a correlation between the change of the volume, ΔV m , and the change of the entropy, ΔS m , on the melting curve at atmospheric pressure is suggested and effectively used.

On the Mechanism of the Initial Stage of Titanium–Carbon Interaction

High-speed micro video recording and electron and atomic force microscopy have been used to obtain new experimental data at the initial stage of the titanium melt spreading along a carbon material (oriented pyrolytic graphite) and the formation of a reaction product. It has been shown that the melt spreading at the initial stages takes place along a framework of flat submicron crystalline grains of TiC with an open porosity. The grains form an island structure at the reagent contact boundary with gaps of about 100 nm in width between them, and these gaps are connected to each other to give a continuous network of channels along which the melt spreads. Thus, at the initial stage of the interaction, despite the formation of a solid product, direct contact of the reagents is retained, which ensures a high process speed.

Improved stability of BaZrO3 refractory with Y2O3 additive and its interaction with titanium melts

Two kinds of refractory (BaZrO3 and Y2O3 (Y)-doped BaZrO3) were prepared to melt two titanium alloys (TiNi and Ti2Ni), respectively. The influence of Y2O3 on the phase constitution and microstructure of BaZrO3, as well as the interaction between the refractory and the titanium alloys, were investigated using the XRD and SEM. The results revealed that the Y-doped BaZrO3 consisted of BaZr1-xYxO3 and Ba2YZrO6-d, no erosion phenomenon was observed for two kinds of refractory after melting TiNi alloys, however, a 275 μm thick reaction layer of BaZrO3 crucible was observed after melting Ti2Ni alloy, whereas, there existed only a 45 μm erosion layer for the Y-doped BaZrO3 crucible. The dissolution of BaZrO3 in the titanium melts was the main reason of the alloy-crucible interaction, and the dissolution equation was determined: TixNi(l)+x2BaZrO3(s)→TixNi[x2Zr,xO](l)+x2BaO(l), doping Y2O3 into BaZrO3 could reduce the dissolution amount of refractory in the titanium melts by improving its thermodynamic stability. This fact may imply that the Y-doped BaZrO3 was more suitable for induction melting of the titanium alloys.

Numerical study of titanium melting by high frequency inductive heating

High frequency induction heating process of titanium wire is investigated numerically and experimentally. The electromagnetic thermal and fluid fields during high frequency induction heating process are calculated. The effects of current frequency and current value of coil on the thermal and flow fields are numerically studied. The change of the applied current has profounder influence on the melting rate than the change of current frequency did. The simulation results are verified by experiments, and good agreement with simulation. With the ability to observe temperature distribution in titanium wire during high frequency induction heating, the numerical simulation method is demonstrated to be a cost-effective tool in predicting the process of high frequency induction heating of titanium wire.

Fabrication of Y2O3 doped BaZrO3 coating on Al2O3 applied to solidification of titanium alloy

The investment casting is one of the most versatile modern technique for metal forming, however, the high chemical stability of ceramic shell materials is required due to the high activity of titanium melt. The Al2O3 is one kind of the common refractory material, which can not be directly used for casting titanium alloys because of its reaction with the melt and contamination caused by this reaction. In this paper, the Y2O3 doped BaZrO3 coating was fabricated on the Al2O3 matrix in order to develop a novel casting and directional solidification technology. Using the Al2O3 as the matrix, the Y2O3 doped BaZrO3 coating was prepared by smearing the slurry, dusting the BaZrO3 powder and sintering them. The reaction between the Al2O3 matrix and the protective coating, the surface quality and chemical stability of the Y2O3 doped BaZrO3 coating were investigated using the optical microscope (OM), energy dispersive spectrometer (EDS) and scanning electronic microscope (SEM), respectively. Afterward, the interaction between Y2O3 doped BaZrO3 coating and titanium melt was discussed. Optical microscope and SEM results showed that the BaZrO3 coating possessed the good surface morphology and high chemical stability, and EDS results showed the thickness of interaction layer between the Al2O3 matrix and the protective coating did not vary with the sintering time and temperature (at 1500°C and 1600°C for 2, 4 and 6h). The thickness of diffusion layer was 10μm for the rod of Ti-46Al-8Nb with the directional solidification, the same was the counterpart for the casting part of Ti-6Al-4V alloy. This may imply that Y2O3 doped BaZrO3 is a promising coating for the solidification of titanium alloy.

Comparative study on electrocrystallization of calcium phosphate ceramics on commercially pure titanium and selective laser melting titanium

The present study investigates the electrocrystallization processes of calcium phosphate ceramics on commercially pure titanium (CP-Ti) and selective laser melting produced pure titanium (SLM-Ti) parts. The microstructure investigations show that SLM-Ti parts have martensitic α′ microstructure with more surface defects, whereas CP-Ti samples exhibit equiaxed α microstructure. The comparative electrochemical measurements reveal that the CaP depositions on both substrates exhibit the diffusion-controlled 3D instantaneous nucleation mechanism. However, the polarization potential recorded with SLM-Ti sample is obviously lower than that with CP-Ti sample at the initial stage of CaP deposition process, during which concentration polarization can be neglected. This result suggests that the overpotential caused by the slow electrocrystallization process was decreased on SLM-Ti samples since the SLM process develops more surface defects that can act as nucleation centers in the electrocrystallization process.

On the Modification of Hydration Resistance of CaO with ZrO2 Additive

Various ZrO2/CaO samples were fabricated by cold isostatic pressing and sintered at 1750°C for 4 h. It was observed that the sample with 12% ZrO2 additive possessed the good hydration resistance and had the lowest apparent porosity of about 0.75%; its weight additive stored after 56 days was less than 0.6 wt%, and it contributed to the occurrence of CaZrO3 on the surface of CaO. The CaO crucible with 12 mol% ZrO2 additive did not react with titanium melt during melting TiNi alloy. This provides a support for searching a new refractory with the good hydration resistance for induction melting titanium alloys.

Influence of Microarchitecture on Osteoconduction and Mechanics of Porous Titanium Scaffolds Generated by Selective Laser Melting

Bone regeneration is naturally based on bone forming cells, osteoinduction by diverse growth factors, and osteoconduction. The latter one used as term in this study is the ingrowth of bone in 3D structures, which leads to an optimal case in creeping substitution of the scaffold by newly formed bone. Autologous bone is still the gold standard for bone substitutes. In most cases, newly developed bone substitutes consist of calcium phosphate, since hydroxyapatite is the main component of bone and mimics cancellous bone in microstructure. In this study, we wanted to elucidate the optimal microarchitecture for osteoconduction and determine compression strength and Young's Modulus of the selected architectures. Selective laser melting of titanium was used as tool to generate diverse architectures in a repetitive and precise way. To link 3D scaffold architecture to biological readouts, bone ingrowth, bone to implant contact, and defect bridging of noncritical-sized defects in the calvarial bone of rabbits were determined. In this series, 5 different microarchitectures were tested with pore sizes ranging from 700 to 1300 μm and constrictions between 290 and 700 μm. To our surprise, all microstructures showed the same biological response of excellent osteoconduction. However, the mechanical yield strength of these structures differed by the factor of three and reached up to three times the strength of cancellous bone at a porosity of 72.3–88.4%. These results suggest that the microarchitecture of bone substitutes can be optimized toward mechanical strength in a wide range of constrictions and pore sizes without having a negative influence on osteoconduction.

Surface Modification of Ti-30Ta Alloy by Electrospun PCL Deposition

In this study, PCL electrospun fibers were deposited on the Ti-30Ta alloy for change the surface properties. Experimental Ti-30Ta alloy was obtained by melting titanium and tantalum in arc melting furnace with argon atmosphere. Ingots were homogenized and bars with 10 mm of diameter were obtained in rotative swagging. PCL fibers were deposited on disks of the alloy by electrospinning. Plasma treatment was carried out for change PCL electrospun superficial energy by using stainless steel plasma reactor. Samples were immersed in mineralization solution for apatite growth. Surfaces were evaluated by using SEM, X-rays diffraction and contact angle. Samples exhibited hydrophilic behavior after plasma treatment and mineralization. Results are very interesting for biomedical applications.

Thermodynamic evaluation of the BaO-ZrO2-YO1.5 system

Based upon the experimental data available in the literature and present measurements, thermodynamic reassessments were initially performed on the binary BaO-ZrO2, BaO-YO1.5 systems, and the resultant thermodynamic parameters were then merged in combination with that of the previous ZrO2-YO1.5 system to derive a self-consistent thermodynamic description for the ZrO2-BaO-YO1.5 ternary system with limited ternary thermodynamic parameters. The Gibbs energies of all the liquid and terminal solid solution phases were treated by the substitutional solution model, the BZ phase featured by second solid solution described by the compound energy formalism (CEF) model, and the stoichiometric compound BZY424 and Ba2YZrO6-d modeled following the Neumann-Kopp rule. The calculated results agree well with the isothermal sections at 1600°C and 1750°C (1873K and 1923K) from both of the previous and present measured phase diagrams. This demonstrates that the thermodynamic parameters derived in the present work could be applicable to compositional optimizations of novel refractories for melting titanium alloys on the basis of this ternary oxide system.

Improved bioactivity of selective laser melting titanium: Surface modification with micro-/nano-textured hierarchical topography and bone regeneration performance evaluation

Selective laser melting (SLM) titanium requires surface modification to improve its bioactivity. The microrough surface of it can be utilized as the micro primary substrate to create a micro-/nano-textured topography for improved bone regeneration. In this study, the microrough SLM titanium substrate was optimized by sandblasting, and nano-porous features of orderly arranged nanotubes and disorderly arranged nanonet were produced by anodization (SAN) and alkali-heat treatment (SAH), respectively. The results were compared with the control group of an untreated surface (native-SLM) and a microtopography only surface treated by acid etching (SLA). The effects of the different topographies on cell functions and bone formation performance were evaluated in vitro and in vivo. It was found that micro-/nano-textured topographies of SAN and SAH showed enhanced cell behaviour relative to the microtopography of SLA with significantly higher proliferation on the 1st, 3rd, 5th and 7th day (P<0.05) and higher total protein contents on the 14th day (P<0.05). In vivo, SAN and SAH formed more successively regenerated bone, which resulted in higher bone-implant contact (BIC%) and bone-bonding force than native-SLM and SLA. In addition, the three-dimensional nanonet of SAH was expected to be more similar to native extracellular matrix (ECM) and thus led to better bone formation. The alkaline phosphatase activity of SAH was significantly higher than the other three groups at an earlier stage of the 7th day (P<0.05) and the BIC% was nearly double that of native-SLM and SLA in the 8th week. In conclusion, the addition of nano-porous features on the microrough SLM titanium surface is effective in improving the bioactivity and bone regeneration performance, in which the ECM-like nanonet with a disorderly arranged biomimetic feature is suggested to be more efficient than nanotubes.

In situ elaboration of a binary Ti–26Nb alloy by selective laser melting of elemental titanium and niobium mixed powders

Ti–Nb alloys are excellent candidates for biomedical applications such as implantology and joint replacement because of their very low elastic modulus, their excellent biocompatibility and their high strength. A low elastic modulus, close to that of the cortical bone minimizes the stress shielding effect that appears subsequent to the insertion of an implant. The objective of this study is to investigate the microstructural and mechanical properties of a Ti–Nb alloy elaborated by selective laser melting on powder bed of a mixture of Ti and Nb elemental powders (26at.%). The influence of operating parameters on porosity of manufactured samples and on efficacy of dissolving Nb particles in Ti was studied. The results obtained by optical microscopy, SEM analysis and X-ray microtomography show that the laser energy has a significant effect on the compactness and homogeneity of the manufactured parts. Homogeneous and compact samples were obtained for high energy levels. Microstructure of these samples has been further characterized. Their mechanical properties were assessed by ultrasonic measures and the Young's modulus found is close to that of classically elaborated Ti–26Nb ingot.

Tribological, electrochemical and in vitro biocompatibility properties of SiC reinforced composite coatings

In this work, laser engineered net shaping (LENS™) technique was used to create SiC reinforced titanium matrix composite (TMC) on titanium surface. These composite coatings developed by injecting SiC powder into titanium melt pool, created using a high-power laser. The laser parameters strongly influenced the dissolution of SiC particles leading to formation of TiSi2, Ti5Si3, and TiC phases along with residual SiC in the composite layers. A graded microstructure, with high concentration of secondary phases on top compared to the bottom region was formed. The reinforcing ceramic phases in the TMC coatings enhanced the wear resistance of titanium by about 100 times. The wear resistance of the composite coatings in physiological environment found to increase with increase in the laser power and concentration of SiC particles injected into the melt pool. These composite coatings also showed better corrosion resistance than Ti. In vitro biocompatibility studies performed using osteoblast (MG63) and fibroblast cells (NIH3T3) demonstrated non-toxic nature of these composite coatings. It is envisioned that such coatings may find applications in articulating surfaces of load-bearing implants to enhance their in vivo lifetime with reduced metal ion release.

Review on manufacture by selective laser melting and properties of titanium based materials for biomedical applications

Titanium (Ti) based materials are deemed one type of the best metallic materials for biomedical application due to their good mechanical properties, high biocompatibility and corrosion resistance. Design and manufacture of complex shape Ti parts with good quality are highly demanded in biomedical areas. Selective laser melting (SLM), an additive manufacturing technology, is able to produce bulk structural parts almost without geometric constraints. This review paper briefly evaluates the work carried out on the significance of Ti materials, SLM technology and SLM manufacturing of Ti materials commonly used for biomedical applications including the microstructures and mechanical properties of resulting bulk dense parts (Ti, Ti–24Nb–4Zr–8Sn, Ti–6Al–4V, Ti–6Al–7Nb, Ti–TiC and Ti–TiB) as well as the porous structures successfully produced by SLM. This review indicates that SLM produced Ti materials are able to fulfill the biomechanical and biocompatibility requirements and can be considered as potential candidate for biomedical applications.

Hierarchical surface features for improved bonding and fracture toughness of metal–metal and metal–composite bonded joints

Structural adhesive joints involving Selective Laser Melting (SLM) titanium bonded to titanium or to a composite material have significant potential for weight and cost saving in aerospace and other industries. However, the bonding potential of as-manufactured SLM titanium is largely unknown, and the use of additional hierarchical surface features has not been explored or characterised. Here we demonstrate with the use of SLM that a hierarchy of two surface features at different length scales can improve the fracture toughness of metal–metal and metal–composite bonded joints. At one length scale (10–15μm), we established through fracture toughness testing that the intrinsic irregular roughness of the SLM surface maximises the bonding potential for both metal–metal adhesive joints (KIc=1.38kJ/m2) and hybrid metal–composite co-cured joints (KIc =1.20kJ/m2). We then combined this with surface features at a larger length scale (200μm). For metal–composite joints, the use of groove surface features was found to deflect the crack path, which increased the fracture toughness of the joint by up to 50% for outward protruding grooves to a value of KIc=1.65kJ/m2. We identified the rise in fracture toughness as a combination of an increase in the crack path length and a shift from pure mode I to a mixed-mode crack growth. We found that the relative contributions of these two factors were approximately equal. This work demonstrates that SLM-manufactured titanium can have significant advantages over conventional titanium for bonded joints. In comparison with conventional techniques, SLM surfaces can be used in adhesive bonds without the need for expensive and time-consuming surface preparation, and the design freedom allows for surface features that can significantly improve performance.