New titanium alloys for blended elemental powder processing

Six powder metallurgy titanium alloys based on commercial compositions were prepared using blended elemental titanium sponge and master alloy powders. The compositions were Ti-6Al-4V; Ti-6Al-4V + 0.5Fe; Ti-6Al-4V + 0.5Ni; Ti-6Al-6V-2Zr + 1Fe + 1Cu; Ti-6Al-6Zr-6Mo and Ti-10V-2Fe-3Al. The powders were cold isostatically pressed at 400 MPa and sintered at 1238 °C for 4 hours. The as-sintered samples had ～ 94% of the theoretical density, uniaxial yield strengths from 710 to 880 MPa and reductions in area from 0.5 to 8%. After a hot isostatic pressing cycle of 900 °C and 100 MPa for 2 h, the samples had ～ 99% of the theoretical density, yield strengths from 840 to 1035 MPa and reductions in area from 5 to 15%.     

Characterization of composite titanium nitride coatings prepared by reactive plasma spraying

Reactive plasma spraying (RPS) technology has been used to produce high thickness (>100 μm) films of composite Ti-TiN-Ti_xN_y coatings. Reactively sprayed coatings obtained from SP700 (Ti-4.5Al-3V-2Mo-2Fe) and Ti6242 (Ti-6Al-2Sn-4Zr-2Mo) powders, deposited onto flat substrates of Ti-6Al-4V, have been investigated. X-ray diffraction (XRD) and micro-hardness measurements have been used to characterize the crystallographic features and differences between the hardness of cross-section and surface. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques have been used to determine the morphology and surface chemical composition of the coatings. Back-scattered electron imaging has revealed the distribution of Ti and TiN in the composite material. Obtained results evidenced a sharp interface between the coating and substrate in terms of the profile of chemical composition. The presence of unmelted Ti particles as well as the formation of nitrides was observed.     

Al2O3/Cu-Sn-Ti+B钎料/Ti-6Al-4V合金连接的微观结构及力学性能

在Cu-21Sn-12Ti钎料中添加不同质量分数的B粉制备Cu-Sn-Ti＋B复合钎料,然后在钎焊温度910℃保温10 min条件下钎焊Al2O3与Ti-6Al-4V合金。研究了原位生成TiB对Al2O3/Ti-6Al-4V合金接头微观结构及力学性能的影响。接头中原位生成的TiB呈晶须状均匀分布在Ti2Cu上,当采用TiB体积分数低于40%的钎料钎焊Al2O3与Ti-6Al-4V合金时,均可获得连接良好且界面致密的钎焊接头。随接头中TiB的体积分数增加,Ⅱ区中的Ti2（Cu,Al）含量增加,并逐渐变得连续,TiB的分布区Ⅲ范围增宽,Ti-6Al-4V合金向钎料中的溶解量增加。接头的室温抗剪强度随TiB的体积分数增加先上升后下降,当接头中TiB体积分数增至20%时,接头抗剪强度达最大,为70.1MPa。     

Strength optimization of two-step-bonded Ti-6Al-4V/Si3N4 joint with Nb interlayer via transient-liquid-phase bonding and active-metal brazing

A novel two-step bonding of Ti-6Al-4V/Si₃N₄ joint was developed with Nb interlayer as residual-stress reliever via low-pressure transient-liquid-phase bonding (TLPB) of Ti-6Al-4V/Nb side prior to active-metal brazing of Nb/Si₃N₄ side. While 1.75 mass% of Ti in a 50-µm-thick CUSIL-ABA® filler was sufficient for sound bonding at Nb/Si₃N₄ side when brazed at 1103 K for 10 min, one-step-brazed joints with bonding area of 10 × 10 mm² were prone to failure at the Ti-6Al-4V/Nb side due to brittle Cu-Ti intermetallic compounds (IMCs). Replacing brazing of Ti-6Al-4V/Nb side with TLPB using pure Cu and Ni foils as filler at 1213 K for 180 min eliminated the formation of brittle IMCs via homogenization of (α + β)-Ti; bending strength increased to 193 MPa with residual-stress-induced failure from Si₃N₄ ceramics. Finally, effectiveness of stress-accommodation via Nb interlayer and filler’s plastic flow was quantitatively verified with reasonable fidelity by finite-element analysis incorporating temperature-dependent elasto-plastic properties.     

Corrosion behaviour of NiTi alloy

In the present work, the corrosion behaviour of NiTi in Hanks’ solution at 37 °C was assessed by the use of electrochemical methods. Pure titanium and pure nickel were included in the study in order to understand the contribution of each alloying element. The results were compared with Ti-6Al-4V alloy and 316L stainless steel, materials traditionally used as orthopaedic implants. Moreover, the susceptibility of NiTi to corrosion under different conditions was examined using other physiological solutions and different pH values.It was observed that the corrosion behaviour of NiTi is much closer to Ti than to Ni, as it may be seen on the polarization curve, where the high protective character of the passive oxide film formed on NiTi is similar to that of titanium. On the other hand, comparing the different implant materials, it was possible to establish the following relation for their corrosion resistances: 316L stainless steel < NiTi < Ti-6Al-4V.     

EVALUATION OF THE LONG-TERM DURABILITY OF HIGH-PERFORMANCE POLYIMIDE ADHESIVES FOR BONDING TITANIUM

This study was conducted to investigate the performance of the Ti-6Al-4V/FM-5 adhesive bonded system for potential applications on high-speed aircraft. The long-term environmental aging effects on Ti-6Al-4V/FM-5 bonded joints and neat FM-5 and PETI-5 resin specimens were investigated. Dynamic mechanical analysis (DMA) and uniaxial tensile testing using dogbone samples were performed on neat FM-5 and PETI-5 resin specimens before and after high-temperature aging in both ambient and reduced pressure environments. Mode I fracture testing was also performed on beam specimens fabricated with mat-scrim-cloth-supported films of FM-5 adhesive bonding titanium adherends prior to and after environmental aging. Experimental results revealed that both physical aging, which is reversible, and irreversible chemical aging took place simultaneously in the adhesive systems, and both types of aging could contribute to loss in adhesive bond performance. Furthermore, the properties of several different Ti–6Al-4V/FM-5 systems, prepared using different surface pretreatment methods and different supportive matrices of FM-5 resin, were compared in this study, and the effect of mode-mixity on the fracture toughness of the adhesive-bonded systems was also evaluated by conducting double cantilever beam (DCB), end-notched flexure (ENF), and mixed-mode flexure (MMF) tests. The creep behavior of the Ti/FM-5 bonded joint was also investigated by performing thick adherend shear tests.     

EVALUATION OF THE LONG-TERM DURABILITY OF HIGH-PERFORMANCE POLYIMIDE ADHESIVES FOR BONDING TITANIUM

This study was conducted to investigate the performance of the Ti-6Al-4V/FM-5 adhesive bonded system for potential applications on high-speed aircraft. The long-term environmental aging effects on Ti-6Al-4V/FM-5 bonded joints and neat FM-5 and PETI-5 resin specimens were investigated. Dynamic mechanical analysis (DMA) and uniaxial tensile testing using dogbone samples were performed on neat FM-5 and PETI-5 resin specimens before and after high-temperature aging in both ambient and reduced pressure environments. Mode I fracture testing was also performed on beam specimens fabricated with mat-scrim-cloth-supported films of FM-5 adhesive bonding titanium adherends prior to and after environmental aging. Experimental results revealed that both physical aging, which is reversible, and irreversible chemical aging took place simultaneously in the adhesive systems, and both types of aging could contribute to loss in adhesive bond performance. Furthermore, the properties of several different Ti-6Al-4V/FM-5 systems, prepared using different surface pretreatment methods and different supportive matrices of FM-5 resin, were compared in this study, and the effect of mode-mixity on the fracture toughness of the adhesive-bonded systems was also evaluated by conducting double cantilever beam (DCB), end-notched flexure (ENF), and mixed-mode flexure (MMF) tests. The creep behavior of the Ti/FM-5 bonded joint was also investigated by performing thick adherend shear tests.     

Effects of pH value and temperature on the corrosion behavior of a Ta2N nanoceramic coating in simulated polymer electrolyte membrane fuel cell environment

To improve the corrosion resistance and electrical conductivity of Ti-6Al-4V bipolar plates used in polymer electrolyte membrane fuel cells (PEMFCs), a novel electro-conductive Ta₂N nanoceramic coating was developed by reactive sputter-deposition using a double cathode glow discharge plasma technique. The microstructure of the coating consisted of fine equiaxed Ta₂N grains with an average grain size of ∼13 nm, which exhibited a strong (101) preferred orientation. To explore the influence of both pH values and temperatures on the corrosion resistance of the coating, the electrochemical behaviors and electronic properties of passive films grown on the Ta₂N coating were systematically investigated using different electrochemical techniques in simulated PEMFC operating environment. It was shown that either increasing the acidity or the temperatures of the solution, the corrosion potential (E_corr) decreased and the corrosion current density (i_corr) increased. At a given temperature or pH value, the Ta₂N coating had a higher E_corr and lower i_corr as compared with uncoated Ti-6Al-4V. The results of EIS measurements showed that with increasing temperature or acidity of the solution, the resistance of the passive film (R_p) formed on the Ta₂N coating decreased slightly, being of the order of magnitude of 10⁷ Ω cm², which was an order of magnitude higher than that of uncoated Ti-6Al-4V. The interfacial contact resistance (ICR) values were found to increase with increasing pH value or decreasing solution temperature, and the ICR values of the Ta₂N coating were markedly lower than that of uncoated Ti-6Al-4V, due to the thinner thickness of passive films. Furthermore, the Ta₂N-coated Ti-6Al-4V is more hydrophobic than bare Ti-6A1-4V, which was favorable for both the simplification of water management and improving corrosion resistance in PEMFC operating environment.     

Effects of Tool Electrode on EDM Performance of Ti-6Al-4V

Due to widespread application of Ti-6Al-4V especially in automotive, aerospace, defense, and biomedical industries; machinability of this alloy is of immense importance. Very low thermal conductivity of Ti-6Al-4V is mainly responsible for its poor machinability. During Electro-Discharge Machining (EDM), conductivity of the workpiece as well as electrode plays a vital role affecting process performance. In this context, choice of electrode also influences the machining efficiency. Therefore, selection of an appropriate electrode to enhance performance of EDM on Ti-6Al-4V alloy is indeed necessary. In the present reporting, an experimental work has been carried out to investigate ease of machining of titanium alloy (Ti-6Al-4V) for electro-discharge machining using Tungsten and Copper (normal and cryogenically treated) electrodes. Experiments have been performed at different values of peak discharge current to study EDM performance on Ti-6Al-4V in terms of material removal efficiency, surface roughness, surface crack density and white layer thickness observed for the EDMed end product prepared from Ti-6Al-4V work material. Influence of peak discharge current on topography of the EDMed work surface has been examined. EDS analysis followed by micro-indentation hardness test has been performed to examine the extent of carbon enrichment onto the machined surface during EDM operation. XRD tests have been carried out to comprehend metallurgical aspects of the EDMed work surface which are supposed to be affected by the thermo-electrical phenomenon of EDM operation. Results obtained thereof, have been analyzed in detail to understand effects of electrode in persuading machinability of Ti-6Al-4V while machining though EDM route. It has been found that among three tool electrodes selected (Tungsten, normal Copper and cryogenically treated Copper), cryogenically treated Copper electrode has been found the most superior in purview of EDM performance.

     

Influence of firing conditions and production methods on fracture strength of titanium-based metal ceramic crowns

Objectives: This study evaluated the effect of argon atmosphere compared with vacuum during porcelain firing on the fracture strength of crowns made of porcelain and electron beam melted (EBM) Ti-6Al-4 V, cast commercially pure titanium or milled commercially pure titanium. Methods: Sixty crown copings of c. p. titanium, Ti-6Al-4 V alloy and porcelain were fabricated using three production techniques. The copings were fired either under vacuum or in an argon gas atmosphere. Specimens were subdivided into groups of cast c. p. titanium, milled c. p. titanium and EBM Ti-6Al-4 V which were further subdivided according to firing modes employing either vacuum or argon gas. The 60 specimens were subjected to cyclic preloading and thermocycling, and were then individually loaded until interface fractured. Differences between the group mean values were calculated using the one-way ANOVA and Tukey’s range test. Two fractured samples from each group were cut with a diamond blade and examined using SEM and EDS for visualization and chemical composition analysis of the fractured interface. Results: The highest mean fracture strength values, though not significant, were recorded for the groups fired in argon atmosphere, and the lowest mean fracture strength values were recorded for the groups fired in vacuum, with one exception. Comparing the two main groups of firing atmosphere, no significant difference could be documented. SEM and EDS analysis indicated clear differences in composition and structure between the groups included in the study. Conclusions: Firing in argon atmosphere does not significantly improve the fracture strength of porcelain bonded to titanium.     

Effect of transition layer on the performance of hydroxyapatite/titanium nitride coating developed on Ti-6Al-4V alloy by magnetron sputtering

A gradient transition multilayer hydroxyapatite/titanium nitride (HA/TiN) coating was prepared on the Ti-6Al-4V alloy by magnetron sputtering. The composition, surface topography, microstructure, adhesion strength and electrochemical properties of the as-deposited coatings were characterized by SEM/EDS, AFM, XRD, FT-IR and electrochemical workstation. The experimental results showed that the single TiN coating deposited at a partial pressure of nitrogen (N₂) of 0.08?Pa had the best internal stress and tribological performance, and its volume loss was only 0.89% of that of Ti-6Al-4V alloy. The introduction of the TiN transition layer greatly improved the wear resistance of the Ti-6Al-4V alloy, and the adhesion strength of the HA layer to the substrate increased from 6.50?±?0.5?N to 11.70?±?1.2?N, an increase of 56%. The HA/TiN coating surface consisted of uniform hemispherical particles with dense structure and invisible defects (micro-cracks and pores). For the HA surface layer, the crystal structure and active hydroxyl (-OH) group was restored after heat treatment. Potentiodynamic polarization experiments indicated that the HA/TiN coating achieved the lowest corrosion current density and the most positive corrosion potential compared to the single TiN layer and Ti-6Al-4V alloy. In summary, it can be conclude that the gradient transition layer can well improve the mechanical properties and electrochemical behavior of the titanium alloy, and largely ensuring the stability of the surface bioactive coating.     

Corrosion behaviour of Ti-6Al-7Nb and Ti-6Al-4V ELI alloys in the simulated body fluid solution by electrochemical impedance spectroscopy

The corrosion behaviour of Ti-6Al-7Nb and Ti-6Al-4V ELI (extra low interstitial) was investigated as a function of immersion hours in simulated body fluid (SBF) condition, utilizing potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Polarisation experiments were conducted after 0, 120, 240 and 360 h of immersion in SBF solution. From the polarisation curves, very low current densities were obtained for Ti-6Al-7Nb alloy compared to Ti-6Al-4V ELI, indicating a formation of stable passive layer. Impedance spectra were represented in the form of Bode plots and it was fitted using a non-linear least square (NLLS) fitting procedure, in which it exhibited a two time constant system suggesting the formation of two layers. The surface morphology of the titanium alloys have been characterized by SEM and EDAX measurements.     

The influence of chloride and sulphate ions on the corrosion behavior of Ti and Ti-6Al-4V alloy in oxalic acid

The electrochemical behavior of pure Ti and Ti-6Al-4V alloy was investigated in oxalic acid solution using various electrochemical techniques, i.e. open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS) and surface examination via scanning electron microscope (SEM) technique. The influence of concentration and temperature on the electrochemical behavior of TI and its alloy were also studied. The results of polarization measurements showed that corrosion current density (i_corr) increases with increasing either temperature or oxalic acid concentration for both samples. Moreover, the value of i_corr for Ti was found to be lower than that for Ti-6Al-4 V alloy, where the corrosion resistance for titanium was always higher. The effect of additives as SO₄²⁻ and Cl⁻ ions was studied; results indicated that the oxide film resistance (R_ox) value decreases with increasing the concentration of SO₄²⁻ ion. However, for Cl⁻ ion, the value of R_ox decreases with increasing Cl⁻ ion concentration up to 1 mM before it starts to increase at higher concentrations. EIS and polarization results are in good agreement with each other. The obtained results were confirmed by surface examination.     

Pulsed laser deposition of hydroxyapatite-diamondlike carbon multilayer films and their adhesion aspects

We have developed a layered hydroxyapatite/diamondlike carbon/functionally gradient diamondlike carbon-silver/titanium carbide/titanium carbonitride/titanium nitride composite film using pulsed laser deposition. A diamondlike carbon interlayer between a hydroxyapatite coating and the Ti-6Al-4V alloy can serve several purposes, including preventing corrosion of Ti-6Al-4V alloy, overcoming poor adhesion between the hydroxyapatite coating and the titanium oxide surface, and reducing inflammation at the implant/tissue interface. Titanium nitride, titanium carbonitride (TiC _x N _y ), titanium carbide and functionally gradient diamondlike carbon-silver layers were used to improve the adhesion of diamondlike carbon films to Ti-6Al-4V alloy. We envision several potential medical applications for these multilayer materials, including use in orthopedic and dental devices.     

Antibacterial Activity and Drug Release of Ciprofloxacin Loaded PVA-nHAp Nanocomposite Coating on Ti-6Al-4 V

Journal of Inorganic and Organometallic Polymers and Materials - Here, a new composite coating was introduced for the Ti-6Al-4&nbsp;V implant, and the different properties were investigated...     

Laser Assisted Nitriding of Ti-6Al-4V Alloy: Metallurgical and Electrochemical Properties

The surface properties of Ti-6Al-4V alloy, such as wear resistance, are inadequate for many applications. To improve the surface properties of the alloy, many techniques have been considered. One of the promising techniques is to form a nitride layer on the surface of the workpiece by a laser beam. In the present study, laser assisted nitriding of the Ti-6Al-4V alloy surface is carried out under a nitrogen gas flow environment. A CO₂ laser is used to irradiate the Ti-6Al-4V alloy surface while nitrogen is introduced co-axially with the laser beam onto the workpiece surface. The resulting surface cross section is examined metallurgically. SEM and XRD were carried out for material characterization. The study is extended to include the electrochemical response of the resulting surfaces. The surface morphology of the electrochemically treated workpieces are examined. It is found that in the laser treated region dendritic structures occur and TiN forms in the surface vicinity. The density of pit formation at the surface of the treated region reduces considerably.     

Microstructural Study of the Brazed Joint between Alumina and Ti-6AI-4V Alloy

Alumina was joined to Ti-6AI-4V alloy by active brazing. High reactivity between the Cu-40Ag-5Ti braze alloy and these materials led to the formation of interfacial reaction products. These products were characterized by transmission electron microscopy and electron microprobe analysis. A continuous layer, identified as Cu₂(Ti, Al)₄O, was formed at the braze/Al₂O₃ interface. In addition, a series of Cu-Ti intermetallic phases ((Ti,Al)₃Cu, Ti₂Cu, TiCu, Ti₃Cu₄, and β-Ti(Cu, Al)₄), starting from the Ti-6Al-4V base metal was observed.     

Enhancement of the Ti-6Al-4V alloy corrosion resistance by applying CrN/CrAlN multilayer coating via Arc-PVD method

In this study, the Ti-6Al-4V substrate was coated by CrN-CrN/TiN-TiN and CrN/CrAlN multilayer coatings using the cathodic arc physical vapor deposition (Arc-PVD) method. The results of potentiodynamic polarization (PDP) have shown the lowest and highest corrosion current density belong to the double-layer (0.16 µA/Cm²) and TiN (0.51 µA/Cm²) samples, indicating the higher corrosion resistance of the double-layer coating. The field emission electron microscope (FESEM), X-ray diffraction pattern (XRD), open circuit potential (OCP), PDP, and electrochemical impedance spectroscopy (EIS) analysis were employed in order to characterize the coatings and evaluate their corrosion behavior. Finally, applying the double-layer coating resulted in the significant improvement of the protective behavior of the Ti-6Al-4V alloy, as compared to the sample coated with TiN in corrosive environments.     

Interfacial microstructure and mechanical properties of ultrasonic-assisted brazing joints between Ti–6Al–4V and ZrO2

Ultrasonic-assisted brazing (28.8 kHz, 180 W) was introduced to achieve high-quality joints between Ti–6Al–4V alloy and ZrO₂ ceramic with Al-5wt.%Si brazing filler in air. The interfacial microstructure of intermetallic compounds (IMCs) and the phase constitution of joints ultrasonic-assisted brazed at 700 °C for different ultrasonic time were investigated in detail using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer and X-ray diffractometer. When the ultrasonic time was 20s, the average shear strength of the joint reached a maximum value of 90.68MPa and two important types of IMCs Ti(Al,Si)₃ and Ti₇Al₅Si₁₂ formed at the interface between the Ti–6Al–4V and the filler. Ultrasonic played a vital role in the formation of Si segregation regions at the interface near the Ti–6Al–4V and in the centre of the joint. A change in the Ti molar fraction, resulting from the cavitation effect of ultrasonic on the surface of Ti–6Al–4V, increased the chemical potential gradient of Si across the joint. Meanwhile, driven by the ultrasonic standing wave field in the liquid Al-5wt.%Si filler, Si atoms moved to the ultrasonic antinode-plane spontaneously. Ultrasonic-assisted brazing proved to be an effective method of joining Ti–6Al–4V and ZrO₂ with Al-5wt.%Si filler.     

Microstructure evolution and bonding mechanism of ZrO2 ceramic and Ti-6Al-4V alloy joints brazed by Bi2O3-B2O3-ZnO glass paste

Ceramics and metal joinings have been widely employed in aerospace, dental implants, and the electronic packaging industry for fabricating multifunctional components. In this study, the 35Bi₂O₃-50B₂O₃-15ZnO (mol.%) glass has been employed for joining the ZrO₂ ceramic and Ti-6Al-4V alloy. The effect of brazing temperature on the microstructure evolution, mechanical properties, and bonding mechanism of brazed joints has been analyzed. The microstructure of the ZrO₂/glass/Ti-6Al-4V joints and the content of Bi₄B₂O₉, Bi₂O₃ and Bi₂₄B₂O₃₉ precipitated crystals in glass were found to be dependent on the brazing temperature. The reaction product of Bi₄Ti₃O₁₂ was identified in the glass/Ti-6Al-4V interface because of the chemical reaction between the oxidized layer of Ti-6Al-4V alloy and glass. A maximum shear strength as high as 48.8 ± 5.2 MPa was obtained. Our work, thus, demonstrates that the 35Bi₂O₃-50B₂O₃-15ZnO glass is an effective bonding material for joining ZrO₂ ceramic and Ti-6Al-4V alloy under low temperature in an ambient atmosphere.