bluuebunny/crossref_metadata_2025 huggingface dataset:
The transport mechanism of P4 ATPase lipid flippases
Authors: López-Marqués Rosa L. , Gourdon Pontus , Günther Pomorski Thomas , Palmgren Michael
Published: October 2020

P4 ATPase lipid flippases are ATP-driven transporters that translocate specific lipids from the exoplasmic to the cytosolic leaflet of biological membranes, thus establishing a lipid gradient between the two leaflets that is essential for many cellular processes. While substrate specificity, subcellular and tissue-specific expression, and physiological functions have been assigned to a number of these transporters in several organisms, the mechanism of lipid transport has been a topic of intense debate in the field. The recent publication of a series of structural models based on X-ray crystallography and cryo-EM studies has provided the first glimpse into how P4 ATPases have adapted the transport mechanism used by the cation-pumping family members to accommodate a substrate that is at least an order of magnitude larger than cations.
Understanding the impact of COVID-19 on early career molecular bioscientists
Authors: Gruszka Dominika
Published: October 2020

The COVID-19 pandemic has affected scientific research across the world, emphasizing old entrenched problems as well as bringing new challenges and even some opportunities. In May 2020, the Biochemical Society conducted a survey of 469 researchers, across all career stages, to assess the impact of the pandemic on the molecular bioscience community. The survey results indicated that researchers early in their careers are the most adversely affected by the ongoing circumstances.
Titanium in France: research activities, industrial developments and applications
Authors: Louvigné P.-F.
Published: October 2020

The French titanium community has been very active in the past four years for developing new applicative opportunities in all traditional sectors: aerospace, industrial, medical, defence etc. Thanks to good connections between academia and industry, the research activities are supporting the main priorities: improvement of efficiency, reduction of cost and control of the quality. This presentation will give an overview of the most significant progress made in France during the period.
Recent Studies and Developments in Titanium Biomaterials
Authors: Ikedaa M. , Ueda M. , Ninomi M.
Published: October 2020

Titanium and its alloys have a high specific strength, excellent corrosion resistance, and good biocompatibility. Therefore, these alloys are adopted as raw materials for artificial bones and joints. Furthermore, these alloys are used as materials for dental surgery. In the development of alloy design, beta-type titanium alloys that possess a lower Young’s modulus than other types of titanium alloys, e.g., Ti-6Al-4V alpha-beta-type alloys, are being actively investigated worldwide. Based on these studies, titanium-niobium-tantalum and zirconium system alloys were developed. For example, Ti-29Nb-13Ta-4.6Zr alloy has a low Young’s modulus, excellent biocompatibility, and improved mechanical properties. Many researchers are actively investigating surface modifications and surface treatments. Additive manufacturing, namely 3D printing, wherein metal powders are piled up layer by layer to produce goods without a mold, has attracted attention in many fields, including manufacture of implants, especially porous structural implants with a low Young’s modulus. It is very important that titanium and its alloys be applied to health-care goods, e.g., wheelchairs and prostheses. Therefore, we herein consider four topics: alloy development, coating and surface modification, additive manufacturing, and health care applications.
The influence of microstructure on mechanical properties of SLM 3D printed Ti-6Al-4V
Authors: Funch Cecilie V. , Somlo Kinga , Poulios Konstantinos , Mohanty Sankhya , Somers Marcel A.J. , Christiansen Thomas L.
Published: October 2020

This research focuses on establishing the relationship between the SLM process parameters, microstructure and mechanical properties in 3D printed ti-6Al-4V. To this end modelling of the thermal history, reflecting the applied process parameters, is linked to the as-printed microstructure, which, in turn, is linked to experimentally determined mechanical properties. The very high cooling rates in the centre of the specimen, as predicted by modelling, lead to a fine, martensitic microstructure, while the slower cooling rates close to the support structure lead to a fine lamellar α+β microstructure. The tensile properties, in particular the ductility, were found to depend on the printing orientation and surface finish.
Microstructure development in Laser Metal Deposition of Ti-5553
Authors: Hicks C. , Konkova T. , Blackwell P.
Published: October 2020

Laser Metal Deposition (LMD) is promoting increased interest with regard to manufacturing parts of complex geometry. It is especially important with respect to manufacturing cost reductions for relatively expensive Titanium alloys. The rapid and directional cooling processes inherent with LMD produce nonhomogeneous microstructures and large residual stresses. Knowledge of the LMD process to optimise deposited microstructures is in high demand. The high-strength β-Titanium alloy, Ti-5Al-5Mo-5V-3Cr (Ti-5553), was deposited using LMD on to a heat-treated substrate of the same alloy. Two blocks of 15 x 15 x 6.4 mm3 were made with different laser power to powder feed rate ratios followed by microstructural analyses. Both blocks have almost identical geometry and density. Low ratios of laser power to powder feed rate resulted in pure β phase in the deposited layers and the re-melted material in the substrate. High ratios resulted in larger columnar β grains, the precipitation of nano-scaled α, and a pronounced increase in microhardness ≈1 mm above and below the substrate interface. This could be detrimental to the mechanical properties of the substrate and highlights the importance of the optimisation of LMD parameters.
An innovative method to assess and manage residual stresses in additively manufactured titanium
Authors: Germain A. , Freiherr von Thüngen I. , Piellard M. , Metton C.
Published: October 2020

A simple method for residual stresses (RS) evaluation in additively manufactured titanium samples is described in this study. This method allows to obtain samples that are separated from the build plate but still include building’s RS. Thanks to these samples, the influence of time and temperature on thermal stress relieving performance and microstructural evolution for Ti64 alloy processed by LBM have been analysed. Additionally, the obtained data allowed to compare the thermal stress relief behaviour of additively manufactured parts to conventional wrought alloy. Process simulations have also been undertaken to predict RS fields and check this method accuracy.
Safety Evaluation for Pure Titanium by Lock-in Infrared Thermography
Authors: Matsunaga T. , Nagashima N. , Nojima T. , Sugimoto S.
Published: October 2020

The lock-in infrared thermography has been applied to an estimation of fatigue limits at several stress ratios, i.e., R=-1, 0.05, and 0.5, for commercially pure titanium (CP-Ti JIS grade 2) at room temperature. In the present study, frequencies were1 Hz and 4 Hz at R=-1, and 7 Hz at R=0.05 and 0.5. Tests at R=-1 showed a negligible frequency dependency of a fatigue limit of 250 MPa. Other tests at R=0.05 and 0.5 showed respective fatigue limits of 123 MPa and 48 MPa. Tensile tests were performed to obtain a tensile strength and a proof stress. A fatigue limit diagram of the sample was plotted using the above values, showing a violation of the mod. Goodman line and the Soderberg line. Next, the diagram was revised using a stress starting plastic deformation shown by creep tests. It revealed a safety area of the new diagram is 35% smaller than that of the conventional safety standards.
Superplastic Behaviour of Ti54M and Ti64
Authors: Mandal Paranjayee , Gomez-Gallegos Ares , Gonzalez Diego , Elrakayby Hosam , Blackwell Paul
Published: October 2020

Even though TIMETAL-54M (Ti-5Al-4V-0.6Mo-0.4Fe or Ti54M) has been commercially available for over 10 years, further study of its superplastic properties is still required in order to assess its applicability within the aerospace industry as a potential replacement for other commercial titanium alloys such as Ti-6Al-4V (Ti64). Ti54M is expected to obtain superplastic characteristics at a lower temperature than Ti64 due to its lower beta-transus temperature. The superplastic forming (SPF) capability of alloys that can be formed at lower temperatures has always attracted the interest of industry as it reduces the grain growth and alpha-case formation, leading to longer life for costly high temperature resistant forming tools.

In this work, the SPF characteristics of both Ti54M and Ti64 have been examined by conducting tensile tests according to the ASTM E2448 standard within a range of temperatures and strain values at a fixed strain rate of 1 × 10-4/S. A high strain rate sensitivity and uniform deformation at high strains are key indicators in selecting the optimum superplastic temperature. This was observed at 815˚C and 925˚C for Ti54M and Ti64 respectively. The tensile samples were water quenched to freeze their respective microstructure evolution following superplastic deformation and SEM images were captured for grain size and volume fraction of alpha-phase analyses. A slightly higher alpha-grain growth rate was observed during superplastic deformation of Ti64. The initial fine-grain microstructure of Ti54M (~1.6 micron) resulted in a final microstructure with an average grain size of ~3.4 micron and optimum the alpha/beta ratio. Both the fine-grained microstructure and increased amount of beta-volume fraction promotes the superplastic behaviour of Ti54M by grain boundary sliding (GBS). Thus superplastic properties were observed for Ti54M at a lower temperature (~100˚C) than for Ti64.
“Microstructure and mechanical characterisation of titanium alloy linear friction welds”
Authors: Flipo Bertrand , Beamish Kathryn , Humphreys Bryan , Wood Martin
Published: October 2020

The increasing use of composite materials in new aircraft builds leads to a significant demand for titanium alloy structural parts. The increasing costs and popularity of this material, together with restrictions in supply and processing, are driving the aerospace industry to make increasingly efficient use of available material.

Linear Friction Welding (LFW) is a rapid, high integrity, solid-state forging process that has the potential to decrease the buy-to-fly ratio, production time and time to market of aerostructure components. Its dependability has already been proven for the production of key components in some of the latest generation aero engines.

The LFW process is yet to be used for aerostructures. This is primarily due to the LFW process not being widely known, but also due to a lack of performance data on aerostructures manufactured by LFW being available to the supply chain and design community.

To address this issue, a large series of titanium alloy weldments was produced and assessed via metallographic examinations and mechanical testing in both as-welded and post-weld heat-treated condition. The matrix of experiments was able to capture the LFW process window of this titanium alloy, and to measure the impact of the parametric conditions.

Metallographic examination revealed a high integrity weld free from contaminants and oxides at the weld interface; with a characteristic recrystallised Widmanstätten martensitic Beta weld centre zone microstructure, in as welded condition, and a finegrained equiaxed recrystallised to alpha-beta microstructure in post-weld heat-treated condition.

As-welded joints were tested under tensile and alternating fatigue conditions to provide an extended set of joint performance data. Joints demonstrated tensile performance equivalent to that of the parent material in all cases, with near-parent fatigue properties and improved (reduced) fatigue scatter in the post-weld heat-treated condition.
Development of α+β-type biomedical Ti–Nb alloys with high oxygen content
Authors: Ueda K. , Omiya M. , Hirose Y. , Narushima T.
Published: October 2020

Ti-(5–20)Nb-(0.5–1)O alloys (mass%) were investigated for developing low-cost biomedical α+β-type Ti alloy. Ti-(5, 10, 15, 20)Nb-(0.5, 0.75, 1)O alloys (mass%) were arc-melted and forged into bars. The forged alloy bars were heat-treated at 873 to 1373 K for 3.6 ks in an Ar atmosphere and quenched in iced water. β transus (Tβ) of the Ti-Nb-O alloys decreased with increasing Nb content. An increase in the oxygen content led to an increase in Tβ. After quenching, the formation of α′ martensite was observed in Ti-5Nb-yO alloys. An increase in the Nb content to 10 mass% led to the formation of α′ and α″ martensites. A further increase in the Nb content to 15 and 20mass% resulted in the formation of more α″ martensites. The boundary temperature for the formation of α′ and α″ martensite in the Ti-10Nb-yO alloys increased with increasing oxygen content, because oxygen enhances the Nb distribution to the β phase. The ultimate tensile strength of the Ti-xNb-0.75O alloys heattreated to obtain the α-phase fraction (fα) of 0.5 was over 1000 MPa, except for the Ti-15Nb-0.75O alloy. The total elongation decreased with increasing Nb content. The Ti-5Nb-0.75O alloy exhibited excellent strength-ductility balance as a low-cost α+β-type biomedical Ti alloy.
Fabrication and bioresorbability of Ag- and Ta-containing amorphous calcium phosphate films formed on titanium substrates by RF magnetron sputtering
Authors: Wu Jun , Ueda Kyosuke , Narushima Takayuki
Published: October 2020

Silver (Ag)- and tantalum (Ta)-containing amorphous calcium phosphate (ACP) coating films were fabricated on titanium substrates by radiofrequency magnetron sputtering for biomedical applications. The sputtering targets were hot-pressed into 10 mol% Ag-containing ß-tricalcium phosphate sintered compacts with and without 8 mol% Ta. The fabricated ACP coating films were dense and smooth, with all elements distributed homogeneously along the depth direction. In addition, Ag existed as ions in the ACP regardless of the presence of Ta. The resorbability of the Ag-containing ACP coating films in simulated body fluids was suppressed by the addition of Ta. The concentration of detected Ag ions was higher in diluted nutrient broth solution than in Tris-HCl solution.
Effect of Thermo-mechanical Treatment on Microstructure and Mechanical Properties of Two-phase TiNbO Alloy
Authors: Junshuai Wang , Chaoli Ma , Wenlong Xiao
Published: October 2020

We designed the composition of alloy with Ti-8Nb-0.5O (at. %) and fabricated in high vacuum arc-melting furnace. This work was focused on the effect of thermomechanical treatment on microstructure and mechanical properties. Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), X-ray Diffraction analysis (XRD), Micro Vickers Hardness Tests and Tensile Tests were utilized to characterize the alloys. The annealing temperature has a significant effect on the microstructure and mechanical properties of TiNbO alloy. When the alloy was annealed at 300℃, 400℃ or at hot-rolled state, there were just α and β phases in the alloy. When the alloy was annealed at 500℃, 600℃, the alloy recrystallized and harmful ω phase appeared, which increased the modulus and strength of the alloy greatly. When the alloy is annealed at 700℃, the alloy recrystallized completely without ω phase. When we accelerated the cooling rate after annealed, the martensitic transformation appeared, which restrained the appearance of ω phase and reduced the modulus.
Mechanical and electrochemical response in Surface treated low modulus biomedical alloy Ti-Nb-Ta-O
Authors: Acharya Srijan , Dabas Shaurya Singh , Suwas Satyam , Chatterjee Kaushik
Published: October 2020

Surface modification of metallic biomedical implants are often performed using chemical or mechanical methods in order to make them more bio-active or resistant against surface-induced phenomena such as wear, corrosion or corrosion fatigue. In the present study, one such method, known as Surface Mechanical Attrition Treatment (SMAT), has been studied in terms of its effects on the mechanical and functional response of a newly developed low modulus metastable β Ti-Nb-Ta-O alloy. The hardness of the surface was found to increase up to a certain duration of SMAT, due to increased degree of deformation on the surface. This was also supported by an increase in the peak broadening with respect to SMAT duration. Apart from surface hardening, SMAT also resulted in improvement of corrosion resistance of the Ti-Nb-Ta-O alloy due to formation of a more stable passive film.
Corrosion Resistance of Ultrafine-grained Titanium Alloys in Different Corrosive Environments
Authors: Dong Yuecheng , Li Xin , Yu Zequn , Alexandrov Igor , Chang Hui , Zhou Lian
Published: October 2020

Corrosion Resistance of ultrafine-grained (UFG) titanium alloys fabricated by equal channel angular pressing (ECAP) was investigated in this study. Electrochemical measurements of pure Ti and Ti-6Al-7Nb alloy were conducted in 3.5 wt.% NaCl and Ringer’s solution separately. Results indicated that both ultrafine-grained pure Ti and Ti-6Al-7Nb alloy had much lower corrosion current density than annealed coarse-grained counterparts in the specified corrosive environment.
Modelling the high temperature oxidation of titanium alloys: review of analytical models and development of a new numerical tool PyTiOx
Authors: Ciszak C. , Monceau D. , Desgranges C.
Published: October 2020

In order to limit the ecological impact of air traffic and its operating costs, the aeronautical industry is looking for improving engines efficiencies and substitutes to high density Ni-based superalloys. Thus, a wider use of Ti-alloys operating at higher temperatures is one of the developed solutions. Being able to predict as accurately as possible the oxidation behavior of Ti-based components at high temperatures appears therefore crucial to improve their sizing and durability. Analytical models based on the solid-state diffusion laws can be found in the litterature. They are fairly accurate in most cases, but they reveal some intrinsic limitations in specific cases such as temperature transients or thin components. Numerical models were later developed to break down these limitations. First results from a new numerical tool called “PyTiOx” (still under development are presented here. They confirm the intrinsic limitations of analytical models. In the case of thin samples, the numerical model predicts an increase of scaling kinetic when metal becomes O-saturated, whereas analytical models do not.
Manufacturing of High Quality Titanium Thin Foil by Electrodeposition Route
Authors: Suzuki Daisuke , Yamamoto Haruka , Horikawa Matsuhide , Fujii Hideki
Published: October 2020

To challenge the significant reduction of manufacturing cost of Ti thin sheet or foil in the future, manufacturing of Ti foil by electrodeposition route was studied with emphasizing on factors affecting quality of the foil and separability from Mo cathode. Current density was one of the strong factors affecting soundness of deposited Ti foil and its separability from the cathode. Electrolyte bath temperature also affected soundness and separability of deposited Ti foil. Separability was closely related to interdiffusion distance of Ti and Mo, that is, shorter diffusion distance, which was brought by low temperature and low current density, led to good separability as well as good surface quality. By reflecting above knowledge, post card size Ti foil of around 0.1 mm in thickness was successfully obtained. It had good quality and could be separated from the cathode by hand. O and Fe contents were drastically decreased by this process.
Kinetic Study of Selective Chlorination of Iron in Ilmenite Ore
Authors: Lee So-Yeong , Park Sung-Hun , Sohn Ho-Sang
Published: October 2020

The selective chlorination of ilmenite with coke and chlorine gas was conducted in the fixed bed reactor and effects of coke content and reaction temperature on reaction rate were investigated. In particular, the chlorination rate of iron in ilmenite was simulated by the unreacted shrinking core model. The reaction rate was simulated by calculating the chlorine gas consumption rate as the unreacted core shrinks. In addition, each of reaction resistances that chemical reaction at the reaction interface, diffusion through the product layer, and boundary film mass transfer resistances were calculated. The simulated reaction rates were in good agreement with the experimental results and the rate controlling step changed as the chlorination reaction progressed. Furthermore, the diffusion resistance through the product layer was dominant at lower reaction temperature, whereas the chemical reaction was dominant as the reaction temperature increased. It is because the diffusion of chlorine gas through the product layer could be hindered at lower reaction temperatures.

Key words: Ilmenite, Selective chlorination, Synthetic rutile, Shrinking core model
A Method for the Production of Titanium-Tantalum Binary Alloys Using the Metalysis-FFC Process
Authors: Howell Robert J. , Benson Marshall Luke A. , Jackson Martin , Wynne Brad P.
Published: October 2020

Titanium-tantalum alloys have historically been difficult to produce using conventional techniques due to the large difference in melting point and poor interdiffusivity rates of the two elements, leading to large levels of segregation. In this work we have investigated using the Metalysis-FFC process to overcome this problem. The Metalysis-FFC process is an electrochemical process where metal oxides are reduced by acting as a cathode in an electrolytic cell combined typically with a graphite anode and molten calcium chloride electrolyte. Previous work has proven that the process works when applied to mixed oxides to produce alloys. The reduction process is performed in the solid state and so negates the problems associated with traditional melting practices such as segregation and evaporation losses. In this work we have been able to successfully produce a range of Ti-Ta alloy powders from pure titanium to pure tantalum in 10 wt% increments using the Metalysis-FFC process. Moreover, energy dispersive spectroscopy analysis of the powders suggests uniform distribution of titanium and tantalum within all compositional ranges, suggesting the Metalysis-FFC process has the potential to be a transformative manufacturing methodology for producing titanium-tantalum alloys.
Hydrogen absorption and hydride formation in pure titanium T40 (grade 2) and TA6V ELI (grade 23) under cathodic polarization in artificial seawater
Authors: POLONI Alexandre , OUDRISS Abdelali , CREUS Juan , BERZIOU Cyril , CONFORTO Egle , SAVALL Catherine , FRAPPART Simon , MILLOT Thierry , MATHIS Aude , FEAUGAS Xavier
Published: October 2020

Different kinetics of hydrogen absorption in T40 (grade 2) and TA6V ELI (grade 23) under cathodic polarization in artificial seawater have been highlighted. These polarizations were made by applying potentials from -0.8 to -1.8V/SCE in artificial seawater and NaCl solution. Four stages were identified and related in term of hydrogen ingress, hydrides formation and calcareous deposit growth. The formation of γ and δ-hydrides have been observed, localized and characterized using several techniques. On T40, hydrides form as a layer that increases the surface roughness and clusters form in the bulk after first moments of hydrogen absorption. Whereas in TA6V ELI, hydrogen is absorbed by β-phase leading to a volume expansion of this phase. Then after reaching the hydrogen solubility limit of β-phase, hydrides form on interfaces α/β or α/α and in α grains. For long durations, the hydrogen ingress is limited by the subsurface hydrides and the stabilized calcareous deposit. These different steps are time depend on processes which need to be tacked into account to improve knowledge of hydrogen embrittlement in titanium alloys.
Improving fatigue performance of surface-damaged Ti-6Al-4V alloy via ultrasonic surface rolling process
Authors: Ao Ni , Liu Daoxin , Zhang Xiaohua
Published: October 2020

Surface damages caused by markings, like laser marking and mechanical marking are detrimental to the fatigue performance of the components. To improve the fatigue performance of laser marked or mechanical marked Ti-6Al-4V alloy, ultrasonic surface rolling process (USRP) was performed on Ti-6Al-4V alloy prior to marking. The results showed that laser marking induced a porous and loose oxidized layer which severely decreased the fatigue performance of the substrate. And the mechanical marking slightly decreased the fatigue performance of the substrate due to the local stress concentration at the bottom of the pits. After USRP pretreatment, the detrimental effect of laser marking on the fatigue performance of the substrate was eliminated while the fatigue performance of mechanical marking sample was significantly improved by a factor of 3. That was because the USRP-induced residual compressive stress suppressed the crack early propagation.

Key words: Titanium alloy; Fatigue; Ultrasonic surface rolling process; Surface damage; Residual compressive stress; Laser marking, Mechanical marking
Influence of hydrogen on mechanical properties of pure titanium T40 (grade 2) and TA6V ELI (grade 23): a local approach of fracture
Authors: POLONI Alexandre , OUDRISS Abdelali , CREUS Juan , COHENDOZ Stéphane , Bouhattate Jamaa , FRAPPART Simon , MILLOT Thierry , MATHIS Aude , FEAUGAS Xavier
Published: October 2020

The effect of hydrogen charging by cathodic polarization on T40 (grade 2) and TA6V ELI (grade 23) in artificial seawater appeared to be dependent on the metallurgical structure of the alloys. Mechanical tensile tests were performed on smooth samples and with different notches without and with hydrogen charging. Evolution of the fracture mode has been studied and the impact of hydrides was questioned. FEM calculation offers the opportunity to associate the local hydrostatic stress σmand equivalent plastic strain εpeqleading to the fracture and to illustrate the evolution of these conditions with hydrogen absorption and hydrides formation. Hydrogen charged by cathodic polarization appeared to have a small impact on grade 2 reducing its A%, whereas it leads to a strong embrittlement of grade 23 when the solubility limit of β-phase is exceeded and hydrides formed.
Beta Fleck formation in Titanium Alloys
Authors: Kelkar K. , Mitchell A
Published: October 2020

Beta fleck is a troublesome segregation defect in many titanium alloys. It has previously been investigated by several authors and appears to have two formation mechanisms, one similar to that of “freckle” in steels and nickel-base alloys, the other arising in the “crystal rain” effect seen in conventional steel ingots. The freckle defect has been extensively studied and several theories developed to account for its formation in both remelted ingots and directional castings. In this work we compare the findings of investigations into the nickel-base freckle formation mechanism to similar conditions in the vacuum arc remelting of titanium alloys. We find that there are strong similarities between the beta fleck formation conditions and the parameters related to the Rayleigh Number criterion for freckle formation. In particular, the dendritic solidification parameters and the density dependence on segregation coefficients both fit well with the conditions proposed to characterise freckle formation. The second formation mechanism arises in the columnar to equiax transition in solidification. The condition for the avoidance of the defect in the two cases is the shown to be the same, namely the use of a very low VAR melting rate, but that it is unlikely to be 100% successful in preventing defect formation. We propose that the techniques presently in use for alloy development in the superalloy field through optimising the composition for minimum sensitivity to freckle formation should be applied to the formulation of future titanium alloys; also that attention should be paid to developing the PAM process to provide suitable solidification conditions for defect absence in a final ingot.
ELECTRON-BEAM MELTING OF INGOTS OF TiAl SYSTEM INTERMETALLICS
Authors: Akhonin S.V. , Berezos V.A. , Severyn A.Yu.
Published: October 2020

Performance of scientific-technical researches at the E. O. Paton Electric Welding Institute of the NAS of Ukraine have been directed on development of technology for manufacture of titanium aluminide –based alloys using the method of electron-beam melting (EBM). The mathematical models of heat state and evaporation of alloying elements in EBM were developed. The results of calculations of heat state using the mathematical model allowed determining a dependence of depth of liquid pool on different melting rates. The mathematical models of processes of evaporation in EBM of titanium aluminide ingots were used for plotting the nomograms, which help to determine the necessary content of alloying element of the alloy in the initial charge for acquiring the necessary concentration of this element in ingot at set technological parameters of melting.

In scopes of designed mathematical models there were investigated different technological modes of electron-beam melting of ingots based on titanium aluminide. The optimum EBM modes, at which a solidification front approaches to flat, were determined. At that, more uniform distribution of the additives on ingot section and volume is provided as well as level of stressed state is reduced.

The works were carried out on manufacture of titanium aluminide based-ingots with addition of refractory as well as volatile alloying elements. Composition and structure of produced ingots were examined. It is shown that electron-beam melting allows getting chemically homogeneous ingots based on titanium aluminide and is a perspective method for production of such class materials.
Mechanical behaviour and microstructural evolution in fine grain Ti-6Al-4V alloy under superplastic conditions
Authors: Despax Laurie , Vidal Vanessa , Delagnes Denis , Dehmas Moukrane , Matsumoto Hiroaki , Velay Vincent
Published: October 2020

Ti-6Al-4V is able to support high level of deformations like superplastic deformation for aeronautical structural applications. However, the applied temperature during forming induces changes in phase fraction, which may have an impact on the mechanisms of deformation involved and the final part. Mechanisms described in the literature, like dislocation glide, diffusional creep, Grain Boundary Sliding (GBS) accommodated by dislocation or diffusion, are still controversial as there are mainly based on post mortem analysis or on stress-strain data. The purpose of this work was to combine interrupted tensile tests and heat treatments to improve the understanding of the mechanisms of deformation on each stage of deformation. The chosen test temperatures were 750°C and 920°C which correspond to different β phase fractions. The microstructural features like grain size and phase fraction were studied by Scanning Electron Microscope (SEM) combined with image analysis. Moreover, EBSD was used to follow the change of crystalline orientation of α grains to distinguish the involved mechanisms as a function of the deformation. Indeed, it would appears that several mechanisms could be activated depending on the deformation stage and on the temperature.
Study on edge cracking of titanium cold rolled sheet
Authors: lee Hyunseok , Choi Miseon
Published: October 2020

In this study, to understand oxygen effects on workability of titanium, edge cracking and microstructure changes with the oxygen content variations in the cold rolled sheets were observed carefully and discussed. The higher oxygen content of titanium sheet, the more the edge cracks occurred after cold rolling deformation. While the specimen containing low oxygen became fine grained structures after the cold rolling, the other high oxygen sheets consisted of relatively coarse and elongated grains. The fine-grained structures was assumed to come from an active twinning behavior, meanwhile the other’s elongated structures were due to the twinning suppression by increasing oxygen contents. In addition, distinct shear bands were appeared in the high oxygen sheets after cold rolling. The high oxygen contents may multiply dislocation density by suppression of twinning and promoting dislocation slips. The increased dislocations can also produce a concentration of strain, slip bands thus appears during the cold rolling deformation. These slip bands cause the edge cracking in the higher oxygen sheets.
Vacuum superplastic deformation behavior of a near-alpha titanium alloy TA32
Authors: Cheng Chao , Zhang Weitang , Chen Zhiyong , Jin Liang , Wang Qingjiang
Published: October 2020

TA32 is a heat-resistant titanium alloy developed for superplastic forming in fabrication of near-space supersonic aerocraft. Clarification of superplastic deformation behavior is important to the optimization of forming parameters. Superplastic tensile test was conducted in vacuum to eliminate the effect of surface oxidation on experimental data, the test temperature and strain rate varied from 900oC to 960oC and 5.32×10-4 to 2.08×10-2s-1, respectively. It was observed that the size of equiaxed α grains exhibited a trend of coarsening with the increase of temperature and decrease of strain rate. Textures of deformed specimens exhibited random distribution with a decreased texture intensity compared with the as-received materials. The superplastic deformation mechanism of TA32 alloy was dominated by grain boundary sliding, which is accommodated by grain rotation and dynamic recrystallization.
Experimental study of the superplastic and hot deformation mechanisms of a Ti-6Al-2Sn-4Zr-2Mo Titanium Alloy
Authors: YAMANE Gen , AVOTRINIAINA Felantsoa , IMAI Hiroyuki , SONG Longqiu , VIDAL Vanessa , MATSUMOTO Hiroaki , VELAY Vincent
Published: October 2020

To clarify the hot deformation characteristics of Ti alloys, flow behaviour, micro structural evolution and deformation mechanisms were investigated in a Ti-6Al-2Sn-4Zr-2Mo alloy with two initial micro structure: an ultra-fine grained (UFG) and a fine-grained (FG) microstructure (dα=0,8 µm and dα=3 µm respectively) by isothermal interrupted tensile tests, SEM observations and through electron back scatter diffraction experiments.

Depending on the test conditions and on the initial α grain size, the flow behaviour can exhibit steady state flow and/or hardening and/or softening. The microstructure and texture evolutions have been studied mainly by using electron backscatter diffraction (EBSD) technique and SEM observations. They evidenced in particular the occurrence of α grains growth as well as dynamic recrystallization (DRX).

The different flow behaviour associated to the microstructure evolution is shown and discussed to clarify the main deformation mode that could be assume to occur depending on the microstructure, the temperature and the strain rate.
Early slip activity and fatigue crack initiation of a near alpha titanium alloy
Authors: Liu Conghui , Thomas Rhys , Quinta da Fonseca João , Preuss Michael
Published: October 2020

For titanium alloys, crack initiation as a result of plastic strain accumulation has been shown to govern fatigue life under the high cycle fatigue regime. In this study, the early plastic slip activity and fatigue crack initiation was studied using a cyclic four point bending test at 10 Hz with a load ratio of 0.1, up to 90% of the proof stress. The plastic slip in the high stress area was monitored by interrupting the test and performing optical microscopy. Following fatigue crack initiation, scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD) was used to identify the slip and crack initiation mode in a 600 x 600 μm2 area. Using slip trace analysis, it was shown that primary alpha grains offered dominant plastic deformation with basal slip activation. Cracking along basal planes was determined to be the dominant damage mode.
A Review of Hydride Precipitates in Titanium and Zirconium Alloys: Precipitation, Dissolution and Crystallographic Orientation Relationships
Authors: CONFORTO Egle , FEAUGAS Xavier
Published: October 2020

This work proposes a review of recent results on the formation and dissolution of hydrides in HCP alloys (Ti and Zr alloys) correlated to the nature of crystallographic hydride phases and their ORs. The crystallographic coherence observed between the surface hydride layer and the substrate is very important for many applications as for biomaterials devices. Five particular orientation relationships (OR) were identified between titanium/zirconium hydride precipitates and the oc-Ti and a-Zr substrates. In addition, the nature of hydrides have a large implication on the ductility, the strain hardening, and the local plastic strain accommodation in the Ti alloys. Our studies using XDR, TEM and SEM-EBSD have been demonstrating that the nature of the hydride phase precipitates depends on the hydrogen content. DSC has been used to obtain the hydride dissolution and precipitation energy values at the bulk scale, whose difference can be associated to misfit dislocations. Local in-situ TEM dissolution observations show the depinning of part of misfit dislocations during dissolution process. Hydride reprecipitation is thus possible only if hydrogen is not driven away during heating by misfit dislocations depinning.
Effect of Heat treatment on Microstructure and Mechanical Properties of Ti-6Al-2Zr-1Mo-1V Bar
Authors: Enen Xu , Yanwen Tian , Fang Hao , Linin Cu , Yuxuan Du , Jinwen Lei , Biao Ju
Published: October 2020

In this paper, the microstructure evolution and mechanical properties fluctuation of Ti-6Al-2Zr-1Mo-1V forging state bar after the first stage heat treatment at 950℃~955℃ and the second stage heat treatment at 760℃~840℃ were studied. In the first stage of heat treatment, the content of primary α and the tensile strength decreases with the increase of temperature, and the high temperature duration time is obviously prolonged. During the second stage of heat treatment, the metastable β phase precipitates third α phase, and with the increase of temperature, the tensile strength increases and the high temperature duration time prolongs.
Influence of Microstructures on Tensile Properties at 400℃ of TC4 Titanium Alloy
Authors: Yong Ren , Nan Yang , Jinwen Lei , Shaoqiang Li , Yuxuan Du
Published: October 2020

The effects of primary α phase volume fraction on the tensile properties at 400℃ of TC4 titanium alloy was studied by different solution temperature(Tβ-(10~80)℃). The effects of the thick of secondary α phase on the tensile properties at 400℃ of TC4 titanium alloy was studied by different cooling speed after solution treatment (water quench, air cooling, furnace cooling). The results show that with the decrease of primary α phase, the tensile and yield strength increase up, but the ductility has a little change. The thick of secondary α phase increases with the deceases of cooling speed after solution treatment, highest tensile and yield strength by water quench, the tensile strength of air cooling and furnace cooling were basically the same, but the yield strength of furnace cooling was 40MPa lower than air cooling. Therefore, the influence of the primary α phase volume fraction on the tensile strength at 400℃ was particularly obvious, we can control solution treatment and cooling way in combination with different requirements.
Strain-hardenability of new strengthened TRIP/TWIP titanium alloys
Authors: Danard Y. , Lilensten L. , Sun F. , Vermaut P. , Freiherr Von Thüngen I. , Martin G. , Bozzolo N. , Prima F.
Published: October 2020

A new Ti-Cr based alloy has been developed to reach a TWIP (TWinning Induced Plasticity) effect as the main deformation mechanism. This new composition, involving Fe addition, was derived from a classical TRIP/TWIP alloy Ti-8.5Cr-1.5Al (wt%) (TCA). The main objective is to achieve an optimized strength/hardenability combination by limiting the TRIP (TRansformation Induced Plasticity) effect whose critical resolved shear stress lowers the plasticity threshold. This new alloy Ti-7Cr-1Al-xFe (wt%) (TCAF) displays excellent mechanical properties, with an increased yield strength (with respect to TCA alloy), a very high work-hardening rate and an extremely high fracture strength (UTS=1415MPa), while maintaining an excellent ductility (ε=0.38 at fracture). Both mechanical (tensile tests) and microstructural characterization at different scales (EBSD, XRD) have been performed, evidencing a dense network of fine {332}<113> mechanical twins as well as the presence of stress-induced martensite plates at twins intersections, as a secondary mechanism.
Study on Microstructure and Mechanical Properties of Powder Metallurgy TA15 Titanium Alloy
Authors: Zhang Zhiyong , Ren Yafei , Shi Kun , Liu Hongyu , Liu Shibing , Zhao Jun
Published: October 2020

TA15 pre-alloyed powder chosen in this paper is made by plasma rotating electrode method. The powders were used to prepare fully dense TA15 alloy ingots by the means of hot isostatic pressing(HIP) forming technology. The optimum parameter of the HIP process is 900°C /120MPa/3h. After the process of hot isostatic pressing, the powders were pressed into a fully dense ingot. An optital microscope was used to observe the microstructure of the ingot specimen and its formation mechanism was analysized. The microstructure of the TA15 alloy prepared by hot isostatic pressing of pre-alloyed powder is composed of fine α-equiaxed grains along lamellar colony boundaries. The mechanical properties exceed that of the casting level, which is close to the forging level. A typical TA15 alloy component was finally produced by HIP-PM process.
The influence of ternary and quaternary alloy additions on the superelastic behaviour of metastable Ti-Nb based alloys
Authors: Jones N. G. , Hildyard E. M. , Connor L. D.
Published: October 2020

The superelastic behaviour of Ti-Nb alloys gives rise to properties that are attractive for specific applications in the biomedical and aerospace sectors. However, to date, industrial utilisation of these alloys has been limited due the inability to tailor the transformation conditions or achieve stable cyclic behaviour. Alloying is the primary method for modifying transformation conditions but significant variations exist between the results of different studies within the literature. Here, to try and provide increased clarity, the transformation behaviour of Ti-24Nb-(0-8)Ta and Zr (at.%) have been investigated using in situ synchrotron diffraction to directly assess the transformation behaviour of the alloys in response to both temperature and tensile loads. In contrast to previous reports, no evidence of the αʺ phase was found in any of the alloys when cooled from 350 to -196˚C. In addition, the β to αʺ transformation was observed to be reversible when loaded at both 30˚C and ‑196˚C. These observations suggest that β stability may be far greater than previously thought and requires a review of the current mechanistic understanding.
Yb: YAG laser welding of Ti6Al4V sheet using conventional and annular power density distribution: microstructure mechanical properties relationship
Authors: Béguin J.-D. , Balcaen Y. , Alexis J. , Gazagne V. , Andrieu E.
Published: October 2020

Development of high power laser beams with increasing beam quality and decreasing purchase cost lead to a strong development of laser welding techniques. Narrow weld beads, high welding speed, and low heat input are the main advantages of this reliable and repeatable joining process. The aim of this study is to investigate properties of weld seam obtained by Gaussian and annular power distribution, on butt joints of 0.9 mm annealed Ti6Al4V sheet by mean of an experimental design varying power level, spot size and shape, welding speed, and face gaseous protection flow. Examined characteristics of the weld seams are geometrical (Fusion Zone FZ and Heat Affected Zone HAZ shapes and dimensions, defects like porosities, undercut and underfill, distorsions of welded plates), microstructural (FZ and HAZ nature and morphology) and mechanical (tensile test, hardness filiations). Major features concerning the use an annular power distribution concern the flawless weld seam geometry and fair mechanical properties, with relatively low levels of distortions due to residual stresses.
Interactions between microstructure and fatigue crack growth in αβ titanium alloy
Authors: Renon Vincent , Henaff Gilbert , Larignon Céline , Perusin Simon , Villechaise Patrick
Published: October 2020

In a context of optimization of the crack propagation resistance properties in αβ titanium alloys, this work aim to explore interactions between microstructure and deformation at crack tip in lamellar titanium alloy, especially regarding to the differences between the two propagation regimes observed in these alloys. Analysis of crack path in these two propagation regimes will be performed with EBSD measurements at mid-thickness to characterize the crystallography contribution during propagation. This analysis indicates a strong propensity to cracking along crystallographic planes in the first propagation regime, followed by a reduction of this trend after the transition between the two regimes.
Machinability of cast titanium alloy Ti-6Al-4V with addition of boron
Authors: Cedergren Stefan , Pederson Robert
Published: October 2020

Cast titanium products generally have coarser microstructures compared to wrought, which explains their limited mechanical properties. However, instead of additional thermo-mechanical processing steps, as in the case of wrought components, the microstructure of castings can be refined by additions of boron. This enhances yield strength, tensile strength and ductility. In order to investigate the influence on machining of this microstructural refinement, cutting tests were performed in three different Ti-6Al-4V castings, having 0, 0.06 and 0.11 wt.% boron. Five machinability criteria were studied; cutting force, chip breakability, burr formation, surface roughness and tool wear. The results show anisotropic deformation behavior in chips when alpha colony size is on the same order of magnitude as the primary deformation zone, or larger. There was little or no influence on cutting forces and burr formation, however chip breakability and tool life was reduced when boron was added. Surface roughness showed a more complex behavior where 0.06 wt.% boron resulted in rougher surfaces compared to the other compositions at low feed rate.
Why titanium alloys withstand more strain under dwell-fatigue than under fatigue?
Authors: Hémery S. , Naït-Ali A. , Lavogiez C. , Villechaise P.
Published: October 2020

Experimental observations reveal that crack initiation proceeds at a reduced number of cycles if a load hold at maximum stress is introduced during cyclic testing. Although this feature was extensively investigated and stems from the occurrence of room temperature creep, other differences between fatigue and dwell-fatigue behaviors are still to be clarified. In particular, a higher plastic strain is cumulated prior to failure if the load hold is present. This observation highlights differences in the deformation behavior depending on the applied loading. The present article reports an investigation of this point using Fast-Fourier transforms based crystal plasticity simulations of the stress and strain field. Significant differences were evidenced and discussed in light of experimental results reported in the literature. In particular, the occurrence of crack initiation for different cumulated plastic strain depending on the loading conditions is elucidated.