CP Ti Research Articles

Laser Welding of Titanium Alloys with an Yb: YAG Disk Source

In this paper, the laser welding of thin titanium sheet in a butt joint configuration are investigated using a continuous Yb: YAG disk source, with high beam quality and a particular fiber configuration, enable to provide a broad range of beam diameters with different intensity distribution. The thermal efficiency of the laser process is discussed as a function of the fiber type. The weldability results for the CP Ti grade 2 and the Ti-6Al-4V titanium alloy are expressed in terms of full penetration, and correct bead geometry (NF L06-395-2000). Full penetration welds are easily achieved with the core fiber, but the outer fiber produces welds with limited geometric defects. Butt joints microstructure consists of an acicular α phase in the fusion zone for CP Ti, and a martensitic α’ phase for the Ti-6Al-4V alloy. Tensile test results confirm a similar or slightly higher joint strength for the full penetration welds, compared with the parent metal.

Experimental investigations and numerical prediction on the effect of shielding area and post flow time in the GTAW of CP Ti sheets

In this study, bead on plate (BoP) trials are conducted on 2-mm thick commercially pure titanium (CP Ti) sheets by gas tungsten arc welding (GTAW) process. Welding current (75–105 A) and joining speed (250–300 mm/min) are taken as the variables. In the weld samples’ appearance of the surface, colorizations are noticed for understanding the role of shielding gas. BoP trials are subjected to metallographic examination to measure weld profiles. These measured values are fed as input for the Goldak double ellipsoidal model to performing the GTAW process. For BoP trials, temperature profile and Iso-surface contours along the moving heat source direction are taken at various time intervals. From the temperature history, shielding area and post flow time are identified. A shielding arrangement is fabricated and implemented based on these bead profile and temperature profile history. After the successful fabrication of shielding arrangement, experimental butt joints are made by GTAW process to verify the efficiency of shielding arrangement. Bead profile of experimentally fabricated 1.6-mm and 2-mm butt joints are compared and verified against the finite element model results. Moreover, cupping test is conducted to analyze the ductility of the joints. The maximum elongation of 96.10% is measured for 1.6-mm face out joints from cupping test.

On the increase of the chemical reactivity of cp titanium and Ti6Al4V at low electrical current in a protein-rich medium

The aim of this study was to evaluate the effect of two electrical current intensities on titanium surface changes in a simulated physiological environment. Commercially pure titanium (cp Ti) grade IV and Ti6Al4V cylinders were coupled to a potentiostat and immersed in DMEM medium enriched with fetal bovine serum (FBS). Samples were divided into four groups: free of electrical stimulation at (C1) room environment or (C2) immersed in DMEM/FBS; and on 5 μA or 10 μA electrical stimulation in DMEM/FBS. After electrical stimulation, the protein adsorption was evaluated by Lowry method and FTIR. Additionally, titanium surfaces were studied by open circuit potencial (OCP), electrochemical impedance spectroscopy (EIS), optical profilometry, and scanning electron microscopy (SEM). FTIR analysis revealed energy bands indicating the presence of amide groups from proteins on all samples immersed in DMEM enriched with FBS. The highest amount of adsorbed total protein was noted on the control groups (p < 0.05). Regarding surface topography, the profilometric analyses showed higher Ra roughness values for cp Ti samples submitted to 10 μA (p < 0.05). Ti6Al4V surfaces had the highest Ra roughness values on 5 μA although no statistical difference within 10 μA group was noticed (p > 0.05). After electrochemical assays, test samples showed higher corrosion resistance than that recorded on control groups. The electrical stimulation increased the chemical reactivity between titanium-based surfaces resulting in a significant increase in roughness as well as on the thickness of the titanium oxide layer.

Microstructure, mechanical properties, and preliminary biocompatibility evaluation of binary Ti-Zr alloys for dental application.

The microstructure, mechanical properties, and in vitro biocompatibility of vacuum-sintered Ti-xZr binary alloys (x = 5, 15, 25, 35, 45 wt%) were investigated. The results indicated that α and α' phase existed in Ti-xZr alloys. The hardness of the Ti-Zr alloys increased as the contents increased and ranged from 473 HV (Ti-5Zr) to 525 HV (Ti-45Zr). Increasing Zr content could lead to an increase in compressive and bending strength. Additionally, the Ti-45Zr alloy exhibited the maximum bending strength of 867.1 MPa and the maximum compressive strength of 1599.8 MPa which were much larger than that of CP-Ti. Moreover, all Ti-Zr alloys showed a lower elastic modulus (ranging from 53.5 to 59.3 GPa) compared with CP-Ti (103 GPa). The in vitro cytotoxicity tests were carried out for biocompatibility evaluation. The alloys presented no cytotoxic effects and the surface of the alloys exhibited great growth conditions for MG-63 cells. The Ti-45Zr alloy exhibited better mechanical properties and biocompatibility. In conclusion, Ti-45Zr alloy is of great potential for dental applications.

Effect of Orientation of Weld Line on Formability of Electron Beam-Welded Dissimilar Thickness Titanium Sheets

Recently, manufacturing industries are looking forward to get insight into the influence of weld orientation on formability of tailor-welded blanks (TWBs) of titanium sheets for design and fabrication of lightweight components. Hence, commercially pure titanium (CP Ti) sheets of 1.0 and 1.2 mm thickness were joined together by electron beam welding process using accelerating voltage of 55 kV, beam current of 14.9 mA and welding speed of 865 mm/min. Two different types of TWBs with weld line perpendicular to the rolling direction (WL ⊥ RD) and weld line parallel to the rolling direction (WL || RD) were fabricated, and subsequently, the tensile test, microstructure and microhardness characterizations were conducted to ensure quality of weld. The limiting dome height (LDH) tests were carried out using laboratory-scale setup to evaluate forming behavior of both the above TWBs in terms of FLD, strain distribution, weld line movement and failure location. It was found that the tensile stress–strain response and formability performance of TWBs were significantly influenced by weld line orientation with lower ductility, ultimate tensile strength and LDH in TWB of WL || RD. Moreover, significant weld line movement and non-uniform strain distribution with necking and subsequently fracture were observed away from the weld line in thinner 1.0 mm CP Ti sheets depending on both sample geometry and weld line orientation.

Improvements in Welding Properties of Titanium Through the Use of Interlayers

This article presents some recent results from fusion welding of titanium alloys with interlayers. Without an interlayer, the CP Ti weld typically results in comparable hardness across the weld and base material (BM). However, for α alloys, near-α alloys and α + β alloys, the fusion zone (FZ) and heat-affected zone (HAZ) show high hardness compared with the BM. Inversely, β alloys have FZ and HAZ with lower hardness compared with BM. Under loading, the presence of areas with high or lower hardness could affect the load distribution across the weldments. Post-welding heat treatment (PWHT) is sometimes employed to minimise or avoid this situation. However, for large-size components, PWHT is not practical. In this investigation, we show that by selecting a proper interlayer the above issues can be minimised; hence, PWHT may not be necessary, leading to cost reduction and process efficiency.

Additive manufacturing of a novel alpha titanium alloy from commercially pure titanium with minor addition of Mo2C

In this study, a fully dense and crack-free alpha titanium alloy was fabricated using selective laser melting (SLM) of commercially pure titanium (CP Ti) blended with 1 vol.% micrometre-sized Mo2C powder. The microstructure and mechanical properties of the fabricated Ti alloy were systematically investigated. It was found that the fabricated Ti alloy consisted of both alpha (α) and beta (β) phases and exhibited a nest-like inhomogeneous microstructure with graded local phase formation, composition and crystallographic texture. This novel microstructure was formed through melting and rapid solidification of CP Ti and Mo2C during SLM, assisted by the high laser absorptivity and resultant high temperature rise of the Mo2C powder. The fabricated Ti alloy exhibited higher tensile strength (∼1250 ± 50 MPa) and improved ductility (elongation ∼17 ± 1%) when compared to CP Ti fabricated using the same SLM process. The underlying reasons were mainly attributed to (i) the nest-like inhomogeneous microstructure consisting of fine grained α-Ti and β-Ti, (ii) the overall solid solution strengthening of the Ti matrix by interstitial C, and (iii) the high dislocation density in the Ti matrix arising from the mismatch between α-Ti and β-Ti phases. This study not only provides a fundamental knowledge about the modification of CP Ti with minor addition of secondary particles through SLM but also provides insight into the fabrication of inhomogeneous Ti alloys with graded microstructure and local composition through SLM for enhanced mechanical properties.

Microstructure, mechanical and electrical properties of laser-welded overlap joint of CP Ti and AA2024

The study results of an overlap welded joint of Commercially Pure Titanium Grade 4 (CP Ti) and Aluminum-Copper Alloy 2XXX series (AA2024) obtained by laser welding without defects in the form of pores and cracks are presented. A microstructure using optical and scanning electron microscopes, a phase composition using X-Ray Diffraction, an electrical resistivity of welded joints were studied. It was found that at tensile shear strength (TSS) testing, failure occurs not only in the brittle intermetallic zone of the welded joint but also in the columnar heat affected zone (HAZ) of aluminum. A 1% of titanium does not have time to diffuse from the HAZ of aluminum at a higher welding speed (150 mm/s), whereas, at a speed of 20% less titanium is not observed in the HAZ of aluminum. The tensile shear strength of samples welded on the titanium side is in the range of 80–120 MPa, depending on the rate of input energy.

Corrosion of porous Ti35Zr28Nb in Hanks’ solution and 3.5 wt% NaCl

The present research examined the corrosion and crevice corrosion behavior of porous specimens of Ti35Zr28Nb and CP Ti in Hanks’ solution at 37 °C and in 3.5 wt% NaCl at 95 °C. The following conclusions can be drawn. There was no crevice corrosion for porous specimens of Ti35Zr28Nb and CP Ti in Hanks’ solution at 37 °C and in 3.5 wt% NaCl at 95 °C. Both alloys had low corrosion rates in both solutions, and both alloys were passive in both solutions.

Cytocompatibility evaluation of nano-sintered Ti-15Zr-4Nb-2Ta-0.2Pd alloy produced by spark plasma sintering technique

Nano-sintered Ti-15Zr-4Nb-2Ta-0.2Pd alloy made up of non-toxic elements was produced by mechanical alloying using high energy ball mill and synthesized by spark plasma sintering (SPS) hot furnace with an objective to develop cytocompatible metallic implant. These were done to develop an alloy capable of avoiding adverse body reaction and increase the longevity of human life by replacing the lost or diseased organs to restore form and function. Microstructure obtained shows well defined grain boundary lines for sintered CP Ti with no surface porosity. Sintered Ti-6Al-4V microstructure showed well defined sinter-bonding of grain matrix with white rings on grain boundary lines and sintered Ti-15Zr-4Nb-2Ta-0.2Pd alloy showed no definite orientation of grains on the surface and had obvious visible grain boundary lines with a few observable surface pores across the area of the specimen. Cytocompatibility test was conducted by culturing CP Ti, Ti-6Al-4V and Ti-15Zr-4Nb2Ta-0.2Pd alloys separately with murine fibroblast L929 at a concentration of 70 cells/well, and incubated for 7 days at a temperature of 37 °C. Amongst CP Ti, Ti-6Al-4V and Ti-15Zr-4Nb-2Ta-0.2Pd specimen surfaces, the murine fibroblast L929 cells were well attached, grew and formed more colonies on CP Ti and Ti-15Zr-4Nb-2Ta-0.2Pd and least attached to the Ti-6Al-4V surface.

Sintering Performance and Corrosion behavior of biomedical Ti-24Nb-4Zr-8Sn alloy produced using SPS in various simulated body solutions

In this study, the Ti-24Nb-4Zr-8Sn (Ti2448) alloy was produced using spark plasma sintering technique and its behaviour in 0.9% NaCl, Hank’s solution and cell culture medium were investigated using open circuit potential and potentiodynamic polarization techniques. The results were compared with that of CP Ti and Ti-6Al-4V alloy. Relative densities above 99.0% were achieved for all three systems. CP Ti and Ti64 had both 100% relative density, and Ti2448 showed a slightly lower density of 99.8%. Corrosion results showed that all three materials exhibited good corrosion resistance due to the formation of a protective passive film. In 0.9% NaCl Ti2448 had the highest current density (9.05 nA/cm2), implying that its corrosion resistance is relatively poor in comparison to Ti (6.41 nA/cm2) and Ti64 (5.43 nA/cm2), respectively. The same behaviour was observed in Hank’s solution. In cell culture medium, Ti2448 showed better corrosion resistance with the lowest current density of 2.96 nA/cm2 compared to 4.86 nA/cm2 and 5.62 nA/cm2 of Ti and Ti64 respectively. However, the current densities observed are quite low and insignificant that they lie within acceptable ranges for Ti2448 to be qualified as a biomaterial.

Effect of milling speed on the formation of Ti-6Al-4V via mechanical alloying

Ti-6Al-4V alloys are well known for good corrosion resistance, excellent surface oxide biocompatibility and high specific strength. This paper investigates the influence of milling parameters on the formation of Ti-6Al-4V alloy processed using mechanical alloying. A mixture of CP Ti and master alloy (60Al-40V) powder were milled using a high energy ball mill (HEBM) in order to produce a mechanically alloyed Ti-6Al-4V alloy powder. Milling was carried out at a constant milling time of 5 hours at varying speeds of 800, 900, 1000 and 1100 rpm in order to investigate the influence of speed on the formation of Ti-6Al-4V alloy. Scanning electron microscopy with energy dispersive analysis (EDX) and X-ray diffraction (XRD) were performed on the mechanically alloyed powder to investigate the chemical homogeneity and the formation of alpha (α) and beta (β) phase during the mechanical alloying of CP Ti and 60Al-40V.

Texture evolution, phase transformation and mechanical properties of selective laser melted Ti-13Nb-13Zr

The crystallographic texture and phase composition associated with the performance of materials have been well documented, but there are very few studies on their controlling strategies. In this work, the crystallographic texture orientation and phase transformation of Ti-13Nb-13Zr alloy were tailored for the first time by selective laser melting with different scanning strategies. 〈011〉 crystal orientation along the building direction is preferred in sample A (unidirectional scanning along one axis), while 〈001〉 is preferred in sample B (unidirectional scanning with a 90° rotation in each layer). The evolution of the volume fraction of α′ phase was investigated using X-ray photoelectron spectroscopy. The results indicated that sample B has the highest content of α′ phasein sample B. The hardness and wear resistance have been studied through nanoindentation and the results turn out that all samples show higher hardness and better wear resistance (hin sample B. The hardness and wear resistance have been studied through nanoindentation and the results turn out that all samples show higher hardness and better wear resistance (higher Hd/Er and Hd3/Er2 ratios) than widely used CP Ti. A simple micromechanical model was used to calculate the elastic moduli of α′ and β phases, which were determined to be 151 GPa and 64 GPa, respectively.

Strain rate sensitivity in commercial pure titanium: The competition between slip and deformation twinning

Titanium alloys are widely used in light weight applications such as jet engine fans, where their mechanical performance under a range of loading regimes is important. Titanium alloys are mechanically anisotropic with respect to crystallographic orientation, and remarkably titanium creeps at room temperature. This means that the strain rate sensitivity (SRS) and stress relaxation performance are critical in predicting component life. In this work, we focus on systematically exploring the macroscopic SRS of Grade 1 commercially pure titanium (CP Ti) with varying grain sizes and texture using uniaxial compression. Briefly, we find that Ti samples had positive SRS and samples compressed along the sheet rolling direction (RD) (i.e. soft grains dominant) were less rate sensitive than bars compressed along the sheet normal direction (ND) (i.e. hard grains dominant). We attribute this rate sensitivity to the relative activity of slip and twinning. Within the grain size range of ~317±7μm, we observe an increase in the rate sensitivity, where volume fraction of {101̅2}<101̅1>T1 tensile twins was low, and the twin width at different strain rates were similar. These observations imply that the macroscopic rate sensitivity is controlled by the ensemble behaviour of local deformation processes: the amount of slips accumulated at grain boundaries affects the SRS, which is grain size and texture dependent. We hope that this experimental study motivates mechanistic modelling studies using crystal plasticity, including strain rate sensitivity and twinning, to predict the performance of titanium alloys.

Ultrahigh-strength titanium gyroid scaffolds manufactured by selective laser melting (SLM) for bone implant applications

Commercially pure titanium (CP–Ti) gyroid scaffolds with interconnected pores and high porosities in the range of 68–73% and three different unit cell sizes of 2, 2.5, and 3 mm were manufactured by selective laser melting (SLM) for bone implant applications. The microstructure and mechanical properties of the scaffolds with different unit cell sizes and sample orientations were evaluated. The microstructure of as-built struts was dominated by massive martensite and the average microhardness of the struts was 2.27 GPa, which is ∼50% higher than that of dense cast CP–Ti. The elastic modulus and yield strength of the as-built scaffolds ranged from 1465 to 2676 MPa and from 44.9 to 56.5 MPa, respectively, values which are close to the elastic modulus of trabecular bone and presumably strong enough to bear the physiological loading of implants. The as-built scaffolds exhibited excellent ductility up to 50% strain and no sign of fracture up to 20–30% strain under compression. The dominant compressive response of the scaffolds was observed by formation of a plastic hinge which led to rotation of the struts about the plastic hinges followed by development of local shear bands in struts in the long plateau region. These SLM-manufactured gyroid CP–Ti scaffolds with significantly enhanced hardness and compressive strength exhibited an elastic modulus close to that of trabecular bone and offer a promising improvement on CP–Ti scaffolds for bone implant applications.

Influence of Cross-Section Design and Vertical Misfit on Stress Distribution in Overdenture Retaining System: 3-Dimensional Finite Element Analysis.

To evaluate by 3-dimensional (3-D) finite element analysis the stress generated on overdenture-retaining bar system with different cross sections (round, ovoid, or Hader) and misfit levels (50, 100, and 200 μm) manufactured with different metallic alloys (Au type IV, Ag-Pd, Ti cp, and Co-Cr). Three-dimensional finite element models were modeled using specific 3-D software (SolidWorks) and imported into mechanical simulation software (ANSYS). A displacement simulating the settlement of the screw was performed until the infrastructure was settled properly on the prosthetic platform. Higher misfit levels caused higher stress on the overdenture-retaining bar system components, where (1) Hader bar presented the highest values (bar = 730.71; screw = 59.66, and periimplant bone tissue = 42.96, in megapascal) and (2) round bars made with type IV Au alloy presented lower stress values on the bar framework (193.99 MPa) and screw (10.27 MPa). Higher vertical misfit increased the stress values on the overdenture-retaining bar system; complex cross-sectional designs increased stress values on the bar framework, prosthetic screw, and periimplant bone tissue; stiffer alloys caused higher stress values on all the studied conditions.

Synthesis and deposition of silver nanoparticles on cp Ti by laser ablation in open air for antibacterial effect in dental implants

Silver nanoparticles have been synthetized and deposited on cp Ti substrates in one-step process by the use of laser ablation in open air. The nanoparticles are produced by ablating Ag foil using two different lasers and an inert gas jet oriented into the interaction zone to prevent oxidation and to direct the ablated material to the substrate. The HRTEM images and FFT confirmed the crystalline nature of the obtained silver nanoparticles with the presence of oxidized ones, while FE-SEM revealed that the nanoparticles were uniformly distributed on Ti substrates. The Ag-containing Ti substrates showed good antibacterial activity against Lactobacillus salivarius.

How Close Is Too Close? Polymerization Behavior and Monomer-Dependent Reorganization of a Bimetallic Salphen Organotitanium Catalyst

The binuclear salphen Ti polymerization catalyst N,N′-1,2-phenylene[(salicylideneaminato)Ti(Cp*)Me2)]2 (2) is synthesized by reaction of salphen-H2 with Cp*TiMe3. Mononuclear [N-(2,6-diisopropyl)phenyl(salicylideneaminato)]Ti(Cp*)Me2 (1) serves as a control. Activation studies of 2 with cocatalyst Ph3C+B(C6F5)4– yield the cationic polymerization-inactive complex [N,N′-1,2-phenylene(salicylideneaminato)Ti(Cp*)]+B(C6F5)4– (4) and polymerization-active Cp*TiMe2+B(C6F5)4–. Polymerization studies comparing 2 with Cp*TiMe3 suggest that, within the catalytic time frame, while 2 retains bimetallic character under an ethylene atmosphere, it rapidly decomposes to 4 and Cp*TiMe2+ in the presence of 1-hexene. These monomer-dependent reorganization results highlight the importance of olefin polymerization activation mechanistic studies while providing insight for improved bimetallic catalyst design.

Molybdenum Disulfide Surface Modification of Ultrafine-Grained Titanium for Enhanced Cellular Growth and Antibacterial Effect

The commercially pure Ti (CP Ti) and equal-channel angular pressing (ECAP) processed Ti can contribute to the downsizing of medical devices with their superior mechanical properties and negligible toxicity. However, the ECAP-processed pure Ti has the risk of bacterial infection. Here, the coarse- and ultrafine-grained Ti substrates were surface-modified with molybdenum disulfide (MoS2) to improve the cell proliferation and growth with antibacterial effect for further dental applications. According to in vitro tests using the pre-osteoblast of MC3T3-E1 cell and a bacterial model of Escherichia coli (E. coli), MoS2 nanoflakes coated and ECAP-processed Ti substrates showed a significant increase in surface energy and singlet oxygen generation resulting in improved cell attachment and antibacterial effect. In addition, we confirmed the stability of the surface modified Ti substrates in a physiological solution and an artificial bone. Taken together, MoS2 modified and ECAP-processed Ti substrates might be successfully harnessed for various dental applications.

Wear Prediction of UHMWPE Acetabular Cup against CP Titanium Femoral Head in a Hip Joint Simulator

Ultra high molecular weight polyethylene (UHMWPE) is a biomaterial used for the human hip joint prosthesis bearings for decades. The main disadvantage is the wear resistant. The products should be in service in the lifetime of the patients. Tribological assessments by experiments and computations should be made to solve that problem. The aim of this research is to predict the UHMWPE acetabular cup wear volume sliding against commercially pure titanium (cp Ti) femoral head in a hip simulator. The cp Ti has the highest biocompatibility compared with other femoral head metals such as cobalt chrome, titanium alloy and 316L stainless steel. Computation processes use the Abaqus contact mechanics algorithm followed by a custom made Python script for the data extractions and Archard wear model calculations. Models were an assembly of the UHMWPE acetabular cup and 32 mm cp Ti femoral head in a biaxial rocking motion hip simulator. Sliding between the models was a 60 cycles per minute rotation. Calculations conducted for one million cycles cumulative polymer wear volume in five steps of 200,000 cycles. The geometries of the models were updated in every step. Experimental pin on disc tests conducted to obtain the wear factor and coefficient of friction. Those data support the input of computations. Wear volume verification use the experimental data from Röstlund. Results show a numerical error at 31.42 percents.