bluuebunny/crossref_metadata_2025 huggingface dataset:
Sustained oscillations in interstellar chemistry models
Authors: Roueff Evelyne , Le Bourlot Jacques
Published: October 2020

Context. Nonlinear behavior in interstellar chemical models has been recognized for 25 years now. Different mechanisms account for the possibility of multiple fixed-points at steady-state, characterized by the ionization degree of the gas.

Aims. Chemical oscillations are also a natural behavior of nonlinear chemical models. We study under which conditions spontaneous sustained chemical oscillations are possible, and what kind of bifurcations lead to, or quench, the occurrence of such oscillations.

Methods. The well-known ordinary differential equations (ODE) integrator VODE was used to explore initial conditions and parameter space in a gas phase chemical model of a dark interstellar cloud.

Results. We recall that the time evolution of the various chemical abundances under fixed temperature conditions depends on the density over cosmic ionization rate nH∕ζ ratio. We also report the occurrence of naturally sustained oscillations for a limited but well-defined range of control parameters. The period of oscillations is within the range of characteristic timescales of interstellar processes and could lead to spectacular resonances in time-dependent models. Reservoir species (C, CO, NH3, ...) oscillation amplitudes are generally less than a factor two. However, these amplitudes reach a factor ten to thousand for low abundance species, e.g. HCN, ND3, that may play a key role for diagnostic purposes. The mechanism responsible for oscillations is tightly linked to the chemistry of nitrogen, and requires long chains of reactions such as found in multi-deuteration processes.
The best of both worlds: Combining LOFAR and Apertif to derive resolved radio spectral index images
Authors: Morganti R. , Oosterloo T. A. , Brienza M. , Jurlin N. , Prandoni I. , Orrù E. , Shabala S. S. , Adams E. A. K. , Adebahr B. , Best P. N. , Coolen A. H. W. M. , Damstra S. , de Blok W. J. G. , de Gasperin F. , Dénes H. , Hardcastle M. , Hess K. M. , Hut B. , Kondapally R. , Kutkin A. M. , Loose G. M. , Lucero D. M. , Maan Y. , Maccagni F. M. , Mingo B. , Moss V. A. , Mostert R. I. J. , Norden M. J. , Oostrum L. C. , Röttgering H. J. A. , Ruiter M. , Shimwell T. W. , Schulz R. , Vermaas N. J. , Vohl D. , van der Hulst J. M. , van Diepen G. M. , van Leeuwen J. , Ziemke J.
Published: October 2020

Super massive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei (AGN) is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination of the images at 1400 MHz produced by Apertif, the new phased-array feed receiver installed on the Westerbork Synthesis Radio Telescope, and images at 150 MHz provided by LOFAR, we have derived resolved spectral index images (at a resolution of ~15 arcsec) for all the sources within an approximately 6 deg2 area of the Lockman Hole region. In this way, we were able to select 15 extended radio sources with emission (partly or entirely) characterised by extremely steep spectral indices (steeper than 1.2). These objects represent cases of radio sources in the remnant or the restarted phases of their life cycle. Our findings confirm that these objects are not as rare as previously thought, suggesting a relatively fast cycle. They also show a variety of properties that can be relevant for modelling the evolution of radio galaxies. For example, the restarted activity can occur while the remnant structure from a previous phase of activity is still visible. This provides constraints on the duration of the “off” (dying) phase. In extended remnants with ultra-steep spectra at low frequencies, the activity likely stopped a few hundred megayears ago, and they correspond to the older tail of the age distribution of radio galaxies, in agreement with the results of simulations of radio source evolution. We find remnant radio sources with a variety of structures (from double-lobed to amorphous), possibly suggesting different types of progenitors. The present work sets the stage for exploiting the powerful tool of low-frequency spectral index studies of extended sources by taking advantage of the large areas common to the LOFAR and the Apertif surveys.
Application of Titanium and its Alloys for Automobile Parts
Authors: Takahashi Kazuhiro , Mori Kenichi , Takebe Hidenori
Published: October 2020

Titanium and its alloys have been applied to motorcycles and automobiles in order to reduce the weight of their component parts. In recent years, titanium exhaust systems, engine valves and connecting rods have been widely applied mainly to sports type or large motorcycles. In addition to Ti-6Al-4V, Ti-Al-Fe alloys which utilize Fe as an inexpensive and a common alloying element are used for engine valves and connecting rods. In exhaust systems, such as mufflers, at first, Gr.2 commercially pure titanium sheets have been mainly used because of their high cold formability. Furthermore, several titanium alloys to which Cu, Al, Si and Nb are added have been actively developed in order to improve strength, creep properties, oxidation resistance and so on at elevated temperatures, as service temperature becomes higher. Also, due to the development of processing technologies, the same methods and processes that are used for manufacturing steel parts have been applied to titanium ones, and the application of titanium has recently been expanded to fracture-split connecting rods and fuel tanks. Newly, titanium foil has been adopted as a separator of PEFC used in fuel cell vehicles from the viewpoints of excellent corrosion resistance and cold formability. As mentioned above, in this presentation, the technical contents of titanium products and parts developed for motorcycles and automobiles are reviewed.
Exploitation of field assisted sintering technology (FAST) for titanium alloys
Authors: Weston N. S. , Thomas B. , Jackson M.
Published: October 2020

Field assisted sintering technology (FAST), also known as spark plasma sintering (SPS), is increasingly utilised to process powders/particulates of engineering alloys and metal-based composite materials. FAST is currently extensively used at laboratory scale by research institutes and universities as a rapid and cost‑effective process to consolidate powders. This includes investigating new alloy compositions and material combinations, improving established materials’ properties, and consolidating materials considered challenging/impossible through conventional sintering techniques. FAST is gaining traction for industrial applications with possible benefits as an alternative to hot isostatic pressing or conventional melt-wrought processing. FAST preform complexity is improving and near-net-shape components are becoming a possibility. Demonstrator components for the aerospace and automotive sectors, including aeroengine blades, brake callipers and rocker arms, have been produced from titanium alloy powders. FAST has also been demonstrated as an effective intermediate step for consolidating a range of feedstocks, including recycled materials, into shaped billets that can be further processed to refine shape and/or properties. Hybrid processes such as FAST‑forge and FAST‑DB have been developed that can produce affordable titanium components with forged properties. This paper presents the current status, emerging developments, and challenges of FAST for titanium-based powders and particulates.
Study on the origins of residual stresses in Ti-6Al-4V processed by additive manufacturing
Authors: Dumontet Nathan , Malard Benoit , Viguier Bernard
Published: October 2020

In additive manufacturing processes using laser beam melting high thermal gradients are generated, inducing residual stresses within the parts that may lead to deformations and, in worst cases, cracks. One of the materials that is the most sensitive to residual stresses is the Ti-6Al-4V alloy. In the present study, we focus on the various parameters that may control the genesis and build-up of the residual stress states. Dwell time and thermal conductivity, both influencing the heat evacuation, were studied. Higher thermal evacuation was find to rises residual stresses within the part. Then, the reliability of the energy density as a comparison parameter was investigated. Samples with the same energy densities but different power and scanning speed were elaborated. Energy density was shown as a non-reliable parameter to compare different processed parts.
The uses and applications of hydrogen processing for titanium additive manufacturing
Authors: Dunstan Matthew K. , Paramore James D. , Butler Brady G. , Zak Fang Z.
Published: October 2020

Additive manufacturing has shown to be a promising method for reducing the cost and increasing the complexity of titanium components, with the majority of research focusing on beam-based methods (i.e. powder bed fusion and directed energy deposition). However, these processes produce highly complex thermal histories, which can result in highly anisotropic and otherwise undesirable microstructures and mechanical properties. In an effort to mitigate these challenges, the use of hydrogen as a temporary alloying element has been identified as a promising method to prevent unfavorable microstructures and isotropy in AM Ti-6Al-4V. Herein, the powder metallurgy process known as Hydrogen Sintering Phase Transformation (HSPT) used in conjunction with a solid state AM method known as fused filament fabrication (FFF) is discussed.
Hydride Approach in Blended Elemental Powder Metallurgy of Beta Titanium Alloys
Authors: Ivasishin O.M. , Savvakin D.G. , Oryshych D.V. , Stasiuk O.O. , Yuanyuan Li
Published: October 2020

The physical bases of hydrogenated titanium powders application in blended elemental powder metallurgy (BEPM) of titanium alloys were earlier developed. Hydrogen as temporary alloying addition for titanium strongly affects diffusion processes upon transformation of powder blends into alloys ensuring production of α+β and metastable β titanium alloys which mechanical properties meet standard requirements. At the same time, synthesis of metastable β alloys is complicated by a big amount of alloying elements which diffusion redistribution upon sintering has a strong impact on microstructure evolution.

In present study BEPM hydride approach was expanded for production of biocompatible low modulus Ti-Zr-Nb and Ti-Zr-Nb-Ta alloys having BCC structure which are attractive materials for medical application. The alloys of prescribed compositions were produced using various starting powders, including TiH2, ZrH2, hydrogenated niobium, tantalum and Ti-Nb master alloys. Peculiarities of volume changes of multicomponent powder blends on dehydrogenation were investigated. The specific volume changes of powder components during dehydrogenation affect densification kinetic of powder blends and microstructure of as-sintered alloys.
Recycling of titanium alloy swarf directly into wire using the ConformTM continuous extrusion process
Authors: Smythe Sarah A. , Thomas Ben , Suarez-Fernandez Daniel , Fang Xin , Marguet Benoit , Jackson Martin
Published: October 2020

ConformTM is an extrusion process, which has been in use since the 1970s. Although it is primarily used with aluminium or copper rod/powder feedstocks, work at the Univ. Sheffield over the last decade has involved the use of titanium feedstocks for various applications. This paper expands on this knowledge by utilising low cost, aerospace titanium alloy swarf, which is the largest waste product from the manufacturing of aerospace titanium components. Swarf is fed into a ConformTM extrusion machine at room temperature and is fully consolidated into round wire/rod profiles in one, solid-state step, using modified tooling for titanium. Such wire can be used for additive manufacture or welding wire. To date there has been numerous successful trials in this challenging process, including the production of both 10 mm commercially pure titanium rod (from powder) and, more importantly, the production of 5 mm diameter Ti-6Al-4V wire from swarf. The material produced has since been characterised using light and electron microscopy and mechanical properties determined using tensile testing and microhardness indenting.
X-ray Micro Tomography Study of Internal Defects of Electron Beam Melted Ti6Al4V and Their Effect on Fatigue Behavior
Authors: Sandell Viktor , Hansson Thomas , Forsberg Fredrik , Lycksam Henrik , Åkerfeldt Pia , Antti Marta-Lena
Published: October 2020

In this work, the fatigue behaviour of Ti6Al4V manufactured using electron beam melting, its dependency on porosity, distance from the base plate and build layer height were investigated. XCT scans of the fatigue sample gauge lengths were correlated to SEM investigations of the fracture surfaces. A comparison between the top and bottom halves of the builds in terms of defect population and fatigue behaviour was also made. Larger pores were detected in samples with a larger build layer height and lower position in the build chamber. Results also indicate that part geometry and pore location, specifically closeness to the surface, are important factors regarding the initiation location of fatigue fractures at 1 % strain. Furthermore, a fatigue critical lack of fusion defect was undetectable in the XCT scan.
Influence of wire arc additive manufacturing of Ti-6Al-4V on microstructure and mechanical properties for potential large-scale aviation parts
Authors: Elitzer D. , Höppel H.W. , Göken M. , Baier D. , Fuchs C. , Bähr H. , Meyer T. , Gallasch A.
Published: October 2020

As one of the most common Titanium alloys, Ti-6Al-4V faces new challenges concerning the ecological footprint. Due to the current processes, a high metal chip pollution leads to a Buy-to-Fly of 25:1.

In this study the parameter / microstructure relationship of Ti-64 on the mechanical properties are discussed. Wire Arc Additive Manufacturing (WAAM) was applied to build samples for microstructural analyses and compression tests. A stress relief (SR) and a solution treatment and annealing (STA) was performed. It was found that SR had no influence on multi-layered samples due to intrinsic heat-treatment. A STA heat-treatment led to a reduction in the mechanical strength. Helium as process gas resulted in an increased mechanical strength due to higher heat capacity compared to argon.
Effect of Microstructure on Fatigue Properties of Several Ti-Alloys for Aerospace Application
Authors: El-Chaikh A. , Danzig A. , Muenter D.
Published: October 2020

A wide range of available Ti-alloys is used atLiebherr-Aerospace Lindenberg GmbHfor several aeronautical applications in flight controls and landing gear systems. For these applications, the mechanical properties of conventionally manufactured Ti-alloys (α+β, near β) as well as additive manufactured Ti-alloy were optimized.

Modification of the heat treatment parameters of a near-β titanium alloy leads to optimization of the hardening process of large cross-sections. This modification allows the adjustment of an optimum volume fraction of the primary α-phase resulting in enhancing of the elongation, fracture toughness and fatigue properties.

For a fatigue critical forging part from (α+β)-alloy a slight modification of the chemical composition combined with an additional heat treatment step during the forging process was performed. The adjusted microstructure of the modified process exhibits better fatigue behavior when compared to the conventional microstructure.

Ti6Al4V parts produced by Additive Manufacturing, printed with optimized parameters and followed by heat treatment will result in reasonable fatigue properties in all printing directions, reducing the anisotropy of the printed parts.

These improvements bringLiebherr-Aerospace Lindenberg GmbHin the position to adapt the used titanium alloys for the needs in a wide range.

For the evaluation of the microstructure, light and scanning electron microscopes were used. Furthermore a model described in the “Metallic Materials Properties Development and Standardization” (MMPDS) was modified and used for the evaluation of the fatigue results.
Hot salt stress corrosion cracking by silver chloride in Ti-6Al-2Sn-4Zr-6Mo
Authors: Shi Yitong , Joseph Sudha , Lindley Trevor , Sandala Rebecca , Saunders Edward , Dye David
Published: October 2020

Hot salt stress-corrosion cracking (HSSCC) of titanium alloys has been found in the presence of chloride and other halide salts. Here, a series of AgCl HSSCC tests on Ti-6246 were conducted using a two-point bending rig at 380-500°C to determine the boundary conditions of stress and temperature. Rapid failure occurred after 24 hours above 440 °C, whilst the trigger stress of HSSCC was determined to be 400 MPa at 380 °C. Energy dispersive X-ray during scanning transmission electron microscopy (STEM-EDX) suggested the formation of metallic silver and chlorides of active alloying elements Al, Sn and Zr. The transgranular fracture surface is expected to be linked to an underlying hydrogen embrittlement via hydrogen charging from the corrosion reactions.
Sintering of Ti-based biomedical alloys with increased oxygen content from elemental powders
Authors: Stráský J. , Kozlík J. , Bartha K. , Preisler D. , Chráska T.
Published: October 2020

Revived interest for beta Ti alloys with increased oxygen content is motivated by the prospect of achieving material with low modulus and high strength simultaneously. Fine tuning of amount of oxygen and beta stabilizing elements is critical for achieving good mechanical properties. This study shows that powder metallurgy method of spark plasma sintering is capable of producing Ti-Nb-Zr-O alloys from elemental powders. This simple approach allows for quick sampling and production of several alloys with various chemical composition. Elemental powders were mixed with appropriate amount of titanium dioxide to achieve Ti-29Nb-7Zr-0.7O alloy. Sintering was performed at 1400 - 1500 °C for 15 – 30 minutes.
Research Progress and Trend of Plasma Metallurgy on Titanium Metallic Surface
Authors: Zhengxian Li , Wen Zhao , Shouchang Ji , Zhong Xu , Lian Zhou
Published: October 2020

By using vacuum plasma surface metallurgy technology, Chinese scientists have carried out comprehensive research on improving the wear resistance, corrosion resistance and flame retardancy of titanium metal. In this paper, the latest research results of alloy layer formation on titanium surface by plasma metallurgy technology and the development trend of plasma metallurgy technology on titanium surface are summarized.
Damage mechanisms and embrittlement kinetics in a β-rich Ti 17 alloy after long term aging
Authors: SASAKI Layla , HENAFF Gilbert , ARZAGHI Mandana , VILLECHAISE Patrick , HEMERY Samuel , DELFOSSE Jérôme
Published: October 2020

The Ti 17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) alloy is used in the first stages of engine compressors, at temperatures up to 450°C. However, its use in structural parts such as engine pylons is more prospective and raises the question of damage tolerance. As the engine pylon environment involves prolonged exposures to high temperatures, the impact of aging on mechanical properties has also to be taken in account.

In this work, the consequences of a long-term aging (up to 10 000 h at 450°C) on the mechanical resistance of a Ti 17 alloy are examined at different scales, from macroscopic fatigue crack growth tests to in-situ tensile tests performed on micro samples in a SEM. The detrimental effect of aging on the mechanical properties of the Ti 17 alloy was then discussed in the light of damage mechanisms analysis and embrittlement kinetics.
Titanium Production via Titanium Sulfide
Authors: Suzuki R. O. , Yashima Y. , Suzuki N. , Ahmadi E. , Natsui S. , Kikuchi T.
Published: October 2020

A new metallurgical process via titanium sulfide from ilmenite is proposed and experimentally approved: It consists of several stages; 1) The ilmenite ore is exposed to gaseous CS2 to selectively sulfurize to FeS, which is wet-chemically removed. 2) The residual oxide is again exposed to CS2 to form TiS2. 3) TiS2 is electrochemically reduced to metallic Ti using molten CaCl2-CaS as an application of OS process.

TiFeO3 was exposed to Ar-CS2 mixed gas flow at 1173 K to form the mixture of FeS+TiO2. FeS was easily separated by immersing in H2SO4 solution at 313 K. After recovery of TiO2, it was converted completely to TiS2 by the second sulfurization with CS2. TiS2 could be reduced to Ti powder by calciothermic reduction and simulteneous electrolysis in a CaS-CaCl2 melt for about 6 hours at 1173 K and 3.0 V. The impurity decreased to a low level such as 0.021 mass%S due to very small solubility of S in a-Ti. However, 1.06 mass%O remained because of wide solubility of oxygen in a-Ti and water contamination in initial CaCl2.
Electrochemical Deoxidation of Titanium in Molten MgCl2-HoCl3
Authors: Kong Lingxin , Ouchi Takanari , Okabe Toru H.
Published: October 2020

A new electrochemical deoxidation method is proposed for Ti, wherein a mixture of magnesium chloride and holmium chloride (MgCl2-HoCl3) is used as a flux. In the new process, Ti and C are used as the cathode and anode, respectively. Mg is deposited on the Ti cathode, which reduces the O in Ti to oxide ions (O2). The activity of the generated O2- (aO2-) in the system was effectively maintained at a low level by the formation of holmium oxychloride (HoOCl) and further decreased by the electrochemical oxidation reaction on the anode. By applying a voltage of 3.0 V between the cathode and anode at 1173 K, Ti was effectively deoxidized to approximately 1000 mass ppm O. Based on the results, in this study, an electrochemical cell, that simultaneously deoxidize Ti scrap or powders and recover HoOCl, is designed.
Deoxygenation of liquid titanium with aluminum addition
Authors: Matsuwaka Daisuke , Kudo Fumiaki , Ishida Hitoshi , Deura Tetsushi
Published: October 2020

To realize radical cost reduction of titanium, a process is needed which can directly make use of low quality material such as scrap, TiO2 or titanium ore. In this work, a highly efficient process has been developed to produce low oxygen titanium alloy using aluminum to rapidly reduce oxygen during melting. In this experiment titanium was prepared including 0.8 mass% oxygen. This titanium and aluminum in the range of 0 – 60 mass% was measured, mixed and melted by PAM (plasma arc melting) or ISM (induction skull melting). After melting, a small piece was taken and the aluminum and oxygen content was analyzed by ICP emission spectrometry and inert gas fusion-infrared absorption method respectively. A sample melted with CaO-CaF2 flux was analyzed as well after flux was mechanically taken off. As aluminum content increased, oxygen content decreased. For example, when 61.9 mass% aluminum was added, the oxygen content decreased to 0.028 mass% and Al2O3 was observed in the cross-section of the sample after melting. This was produced when the aluminum content increased and the oxygen solubility decreased in the metal. Flux addition was also clearly effective for deoxygenation.
Freckles pattern and microstructure feature of Nb-Ti alloy produced by vacuum arc remelting
Authors: Shang Jinjin , He Yongsheng , Yang Ce , Wu Ming , Luo Wenzhong , Wang Kaixuan
Published: October 2020

Nb-Ti alloys are normally produced by vacuum arc remelting process. Due to inadequate processing parameters, freckles can be observed in macroetched ingots. In the present work, visual, chemical, metallographic, and X-ray are presented which establish the appearance, composition, microstructure differences between freckle regions and normal regions. It has been observed that in freckles parallel to the ingot axis, the Ti content is up to 53wt%, 7wt% higher than normal regions. It is also shown that a lot of precipitation phases appeared in freckle regions, because of the thermosolutal convection in the mushy zone. The Rayleigh number, which recommended as a criterion for freckle initiation, has been calculated that using a VAR melting software. Based on the experimental results and simulation results, it is concluded that freckles can be influenced by processing parameters, and freckles in Nb-Ti alloy can be eliminated by matching appropriate processing parameters.
Surface engineering of titanium by multi-interstitial diffusion using plasma processing
Authors: Drouet M. , Pichon L. , Dubois J.B. , Le Bourhis E. , Christiansen T. L.
Published: October 2020

Titanium and its alloys possess a range of highly interesting properties such as excellent corrosion resistance, high specific strength and biocompatibility, but suffers from poor wear resistance. The present work addresses plasma assisted surface treatment of CP 2 titanium using various combinations of oxygen and nitrogen, i.e. mixed interstitials. The sequence of controlled plasma nitriding and oxidizing treatments plays a significant role for the evolution of the hardness depth profiles and the development of the surface compound layer and the underlying diffusion/transition zone. Composition profiles of oxygen and nitrogen are obtained by GDOES; Mixed interstitial solubility of nitrogen and oxygen is found in both h.c.p. α titanium and in the compound layer. The combination of interstitials leads to larger case depth, in particular for the diffusion zone (expanded h.c.p. α titanium). Therefore, it highlights the advantages of combined nitriding and oxidizing compared to single nitriding treatments on the mechanical properties.
Thermal Stability of Titanium Alloy VT8M-1 with Ultrafine-Grained Structure
Authors: Stotskiy A.G. , Polyakov A.V. , Dyakonov G.S. , Semenova I.P.
Published: October 2020

The paper considers the effect of a long-duration heating at a service temperature of 450oC on VT8M-1 with a coarse-grained (CG) and ultrafine-grained (UFG) microstructure. A duplex ultrafine-grained microstructure, composed of equiaxed grains of primary α-phase and an ultrafine constituent of α- and β-phases, was processed by thermal treatment and further rotary swaging. This type of a microstructure demonstrates a best combination of strength and ductility at room temperature in comparison with the CG structure. A thermal stability of an UFG state was studied at 450°C for 50, 100, 200, 300, 400, and 500 hours. The evolution of the alloy microstructure against the duration of heating was considered by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM). No increase in the alloy structural elements and strength decrease resulting from a long-term annealing (up to 500 hours) at T=450°C have been observed. This proves a high thermal stability of the UFG structure and mechanical properties of VT8M-1 processed via rotary swaging.
Comparison of different titanium alloys welded by Yb:YAG fibre laser for thin sheet applications used for T-ducts in bleed air systems
Authors: Riekehr Stefan , Ventzke Volker , Wagner Sabine , Beck Werner , Kashaev Nikolai
Published: October 2020

Research in aerospace applications includes the replacement of well-known materials by newly developed alloys or by new manufacturing methods for the existing materials. In the frame of TiB-Air project funded by the German Federal Ministry for Economic Affairs and Energy (BMWi) the development of a process chain consisting of deep drawing at elevated temperatures, chemical milling, contour machining by laser cutting and laser beam welding to produce pneumatic T-ducts used in bleed air systems is in focus. This production process of sheet metal parts could lower costs in terms of the process itself and the used materials: low alloyed Ti-alloys. Commercially pure titanium alloy (cp-Ti) is commonly used for these structures because of its balanced mechanical properties regarding tensile strength, yield strength, plastic strain and fatigue strength as well as good resistance against corrosion and oxidation. The possibility to substitute cp-Ti by low-alloyed Ti-alloys is examined in this work, by the comparison of two different low alloyed Ti-alloys, namely KS1.2ASN and Ti XT, with a cp-Ti alloy (Grade 4). Mechanical properties of the base materials, their weldability and the mechanical assessment of the laser beam welded butt joints in terms of static, cyclic and fracture mechanical behaviour is compared for sheet materials, with a thickness of 0.9 mm. Defect-free welding according to EN13919 acceptance criteria B was possible for all three alloys, no porosity problems occurred. The low strength alloy KS1.2ASN exhibited mechanical anisotropy between longitudinal direction and transverse direction in the tensile test, welded specimens of this alloy broke in the base material. Due to the tensile properties, both weld and base material of KS1.2ASN showed the least values for the fatigue strength and endurance limit strength. Ti XT and Grade 4 showed similar mechanical anisotropy and fractured in the base material, too. Fatigue strength of Ti XT is below Grade 4, but for the 50%-percentile the endurance limit strength is equal. Fracture mechanical testing showed that KS1.2ASN is a very promising alloy in the welded condition.
Towards work-hardenability of Ti-6Al-4V through a quenching and partitioning approach
Authors: Dumas O. , Hary B. , Martin G. , Sun F. , de Formanoir C. , Prima F. , Godet S.
Published: October 2020

In this work, the work-hardening ability of Ti-6Al-4V alloy was investigated using a quenching and partitioning strategy on dual-phase Ti-6Al-4V samples. As recently reported [1], it is known that a sub-transus thermal treatment followed by water quenching are able to generate a dual phaseα + α’ microstructure with a remarkable work-hardening coupled with an interesting balance between strength and ductility. Based on this statement, several heat treatments at various subtransus temperatures were performed on as-forged Ti-6Al-4V. In such a way, the respective volume fraction of each phase along with the size and the distance to the equilibrium composition of the quenched martensite are taken as microstructural variables to decompose the work hardenability of dual-phase Ti-6Al-4V alloys into respective contributions. Then, annealing of the metastable α + α’ microstructure was performed to trigger the α’ martensite decomposition, involving a partitioning of the alloying elements. The present investigation was carried out on wrought material.

The quenching and partitioning parameters led to a wide range of mechanical properties and associated work-hardening behaviour. The as-quenched and further annealed microstructures were characterized by Scanning Electron Microscopy (SEM). The resulting mechanical properties were discussed and compared to those of as-forged material.
The fracture behavior transitions in cold dwell fatigue of Ti-6Al-4V
Authors: Ozaki Tomomichi , Ota Yutaro , Kubushiro Keiji , Sano Kokichi
Published: October 2020

Ti-6Al-4V forged materials which had fine grain size and commercial billet which had moderate grain size and micro texture were prepared. Cold dwell fatigue tests were conducted using both materials, and dwell time condition was up to 1800s. Fracture cycles and elongation were almost same on each specimen. Number of cycle to failure decreased with increase of dwell time. Fracture elongation increased up to dwell time of 10s, and it was constant in over 10s. Fracture surface were observed. In short time dwell condition up to 2s, fracture surface showed fatigue type. Fracture surfaces changed to dimple in over 10s dwell. In billet material, facets were observed in inner area of fracture surface.
Observation of the microstructure of the metastable Ti15Mo alloy after ageing
Authors: Janeček M. , Bartha K. , Cieslar M. , Minárik P. , Stráský J.
Published: October 2020

Omega phase particles can be observed by conventional SEM. Metastable Ti15Mo alloy was annealed at 500 °C for 16 hours. During annealing, ω phase particles grew and got chemically stabilized by expelling Mo atoms. As the result, these ellipsoidal particles, approx. 100 nm long and 50 nm wide can be observed using back-scattered electrons signal in conventional SEM due to chemical contrast. TEM study proved that these particles indeed belong to ω phase. Co-existence of β, ω and α phases was observed. Thin α lamellae were observed along with distorted ω phase particles by TEM.
Flow modelling of Ti6Al4V under large strains
Authors: Katharina HOGREFE , Ricardo BUZOLIN , María Cecilia POLETTI
Published: October 2020

This work uses flow stresses obtained experimentally at different strain rates and temperatures to validate flow modelling results. Flow curves of Ti6Al4V are measured via torsion experiments with a Gleeble® 3800 up to effective strains of 8. A physically based model that describes the evolutions of microstructure and the flow stress in the β-phase field was developed. A model of continuous dynamic recrystallization (CDRX) based on the work of Gourdet and Montheillet [1] for aluminium alloys is combined in this work with elements taken from Kocks and Mecking [2]. The model consists of a detailed description of the microstructure, based on different dislocation density populations and grain boundaries. All these internal variables evolve according to a production and a recovery term correlated mathematically with the temperature and the strain rate. The modelled output variables besides the flow stress are the total, the interior and the wall dislocation densities as well as the subgrain and grain sizes developed by continuous dynamic recrystallization. The model describes the softening occurring during large strain deformations, which is partly produced by the formation of new high angle grain boundaries (HAGB). The fraction of HAGB was used to determine the recrystallization grade, validated with microstructural characterization.
Effect of oxygen addition on the formation of isothermal ω phase in Ti-Fe alloys
Authors: Kobayashi Sengo , Sasaki Shota , Kawano Sota , Sasaki Renta , Okano Satoshi
Published: October 2020

The effect of the addition of oxygen on the formation of microstructure cooled from the β phase of Ti-Fe alloy was examined. The alloy ingots of Ti-(4, 5, 6, 7, 8, 9 and 10) at.% Fe and Ti-8 at.% Fe-(1 and 3) at.% O were arc-melted. They were homogenized at 1200 °C for 3.6 ks and then hot-rolled at 850 °C into 1.5-mm thick sheets. The disk specimen was fabricated and then put in the differential thermal analysis (DTA) apparatus. The disk in the DTA was heated at 1000 °C for 0.6 ks in the β phase and then cooled to room temperature at a rate of 50 °C/min. The microstructure was examined by an optical microscope after the DTA experiment. In the Ti-(7 and 8) Fe alloys the ω phase formed during cooling. The addition of oxygen in the Ti-8Fe alloy promoted the β→α transformation. Furthermore, the addition of one at.% oxygen in the Ti-8Fe alloy promoted β→ωi transformation, while the addition of three at.% oxygen suppressed the β→ωi transformation during cooling.
The effect of plastic deformation on martensite decomposition process in Ti-6Al-4V alloy
Authors: Motyka Maciej , Ziaja Waldemar , Baran-Sadleja Anna , Slemp Karol
Published: October 2020

Microstructure and mechanical properties of heat treated martensitic two-phase α+β titanium alloys are in major perspective determined by results of martensite decomposition during tempering. The process of martensitic α’(α”) phase decomposition in titanium alloys, although utilized in industry for years, has not been sufficiently characterized in the scientific literature. Especially aspects of plastically deformed martensite decomposition is poorly described. Preliminary research results of water quenched Ti-6Al-4V alloy, subsequently cold deformed in compression and tempered at the temperature range of 600-900ºC for 1 and 2 h indicated that α’(α”) martensite undergoes strain hardening and deformed martensite laths exhibit tendency towards fragmentation and spheroidization during tempering at 900ºC. In the present paper, also α’(α”) martensite decomposition under compressive load applied at the temperature range of 600-900ºC is considered too. Based on light and scanning electron microscopy observations, thermal analyses and XRD measurements, the effect of plastic deformation on kinetics of martensite decomposition and morphology of α phase formed in the process is analysed.
Texture evolution during Isothermal compression process of Ti-22Al-25Nb alloy in B2 phase region
Authors: Ma Haoyuan , Zeng Weidong , Gao Xiongxiong , Zheng Youping
Published: October 2020

In the present work, the hot deformation behavior, dynamic recovery, dynamic recrystallization and texture evolution of Ti-22Al-25Nb alloy on the conditions of 1100°C with four different thickness reductions (35%, 50%, 65% and 80%) are investigated by isothermal compression testing on Gleeble-3500 thermo-mechanical simulator. The strain rate is 0.1mm/s-1. Subsequently, metallographic observation and EBSD analysis are carried out. The results show that during the hot deformation, the dynamic recovery (DRV) and dynamic recrystallization (DRX) strongly affect the microstructure and texture evolution. It is observed that with the strain increasing, the intensity of ηbcc-fiber increases firstly (crystallographic fiber axis <100> parallel to the compression direction). When the thickness reduction reaches to 80%, the intensity of <001> pole becomes stronger expectedly. Whereas the ηbcc-fiber transform into cube components ({100} <001>) unexpectedly. In addition, as the strain increases through 35%-80%, the fraction of large misorientation grain boundaries and fraction of DRX grains gradually increase due to continuous recrystallization. The evolution mechanism of grain orientations and texture during the DRX process will be discussed.
Analysis of the Development of Abnormal Grains Structures During Beta Annealing of Ti-64 Wrought Products
Authors: Byres Nicholas E. , Quinta da Fonseca João , Dod Benjamin , Donoghue Jack , Davis Alec , Prangnell Phillip B.
Published: October 2020

The ß-annealing of Titanium-6Al-4V (Ti64) wrought aerospace components can lead to the development of abnormal grain structures (AGS) that jeopardise material performance. Therefore, an in-depth understanding into the origins of AGS will help in the design of processing routes that can avoid the conditions that lead to their development. This research demonstrates the application of novel concurrent in-situ heating and electron back scatter diffraction (EBSD) techniques to help elucidate possible mechanisms for the development of AGS. It was found that primary-a (ap) may play a key role, acting as a second phase particle, in pinning the ß-phase grain boundaries during recrystallisation. The strengthening of a large area cube component texture macrozone, consisting of predominantly low angle grain boundaries, is also a prerequisite for the development of AGS.
The effect of Titanium Alloy Composition and Tool Coating on Drilling Machinability
Authors: Graves Alex , Teike Maria , Norgr Susanne , Crawforth Pete , Jackson Marun
Published: October 2020

Excessive tool wear and poor machinability is observed in the machining of high strength, near-β titanium alloys when compared to α + β titanium alloys such as Ti-64. Tooling suppliers want to better understand drilling machinability in terms of (1) why alloy composition influences tool wear behaviour, (2) how this impacts part integrity and (3) the effectiveness of tool coating. This paper presents a novel approach to investigating the mechanisms by which tool wear and microstructural deformation occur in a range of titanium alloys, through the manipulation of the force experienced by the tool and work piece. The investigation compares and contrasts the drilling machinability of three important aerospace titanium alloys. Force feedback, tool wear and microstructural damage results highlight key differences when drilling different titanium alloys. Such findings will contribute to tool design, providing a better understanding of wear and machinability in near-β titanium alloy drilling.
A linear programming technique to solve fuzzy multiple criteria decision making problems with an application
Authors: Sadabadi Seyed Ali , Hadi-Vencheh Abdollah , Jamshidi Ali , Jalali Mohammad
Published: October 2020

Generally, in real world multiple criteria decision making (MCDM) problems, we concern with inaccurate data. This paper transforms a fuzzy multiple criteria decision making (FMCDM) problem into two linear programming models based on simple additive weighting method (SAW). The new linear models calculate two scores for each alternative in optimistic and pessimistic viewpoints. To rank the alternatives, the numerical value of the arithmetic mean of good score and bad score is used as final score of each alternative. Finally, we illustrate the practical applications of the proposed method in selection an industrial zone for construct dairy products factory.
Soft tissue surgery as an initial treatment for hip displacement in spastic cerebral palsy
Authors: Angelo da Silva Luiz Antônio , Fucs Patricia Maria de Moraes Barros
Published: October 2020

Objective: To use the measurement of migration percentage (MP) to evaluate the long-term radiographic results of soft tissue surgery as the first treatment for hip displacement in spastic bilateral cerebral palsy. A secondary objective was to identify predictive factors of stability (i.e., less than 30% of MP in the long term), after surgical correction. Methods: In this longitudinal cohort study, we reviewed the electronic medical records and radiographs of all consecutive patients with cerebral palsy operated for the correction of hip displacement between 1984 and 2013 in a referral orthopedic public hospital in Brazil. Patients were included if they had received, as the first surgical procedure, soft-tissue release. All surgeries were bilateral and symmetrical. We used the available radiographs to evaluate the migration percentage (MP), acetabular index (AI), pelvic obliquity (PO) angle, head-shaft angle (HSA), congruence and femoral head sphericity, and function using the GMFCS (Gross Motor Function Classification System). Results: we included 93 patients, all operated before being 12 years old, with follow-up of 10 years in average, 73 (78%) of them with good results (MP < 30%). We found association between preoperative MP ≤ 40%, AI ≤ 25°, and postoperative symmetry with good results, with a cut-off value of 38% of MP and 27° of acetabular index being predictive. Discussion: The role of soft tissue releases remains controversial owing to small sample sizes, heterogeneity, variety range of ages, definitions used for outcome, and lack of statistical quality. Our results were better in combined tenotomies, in diparetic patients aged more than six years, and in patients with lower initial values of MP and AI. Radiographic variables had good correlation with each other and association with results, with cut-off values for MP and AI PRE.
Subtypes of Clinical High Risk for Psychosis that Predict Antipsychotic Effectiveness in Long-Term Remission
Authors: Zhang TianHong , Wang JunJie , Xu LiHua , Wei YanYan , Tang XiaoChen , Hu YeGang , Cui HuiRu , Tang YingYing , Hui Li , Li ChunBo , Wang JiJun
Published: October 2020

Introduction In a previous report, we used canonical correlation analysis to classify individuals with clinical high risk (CHR) of psychosis into the 3 subtypes: subtype-1, characterized by extensive negative symptoms and cognitive deficits, appeared to have the highest risk for conversion to psychosis; subtype-2, characterized by thought and behavioral disorganization, with moderate cognitive impairment; subtype-3, characterized by the mildest symptoms and cognitive deficits. The present study attempted to identify these subtypes’ response to antipsychotic (AP) treatment.

Methods A total of 289 individuals with CHR were identified and followed up for 2 years. Individuals with CHR were classified by subtype. Use of APs was examined at 2-month, 1-year, and 2-year follow-up interviews that inquired after the subjects’ medication history since the first visit. The main outcome was remission, determined according to global assessment of function (GAF) score (i. e., functional outcome) and SIPS positive symptom score (symptomatic outcome) at the follow-up points.

Results Among the 289 individuals with CHR included in the current analysis, 223 (77.2%) were treated using APs for at least 2 weeks during the follow-up period. Individuals with CHR tended to show significant improvement in both symptoms and function after 2 years, but subtypes exhibited significantly different trajectories. Subtype status can predict AP treatment outcome in terms of remission. The likelihood of remission differed significantly among the subtype groups. The remission rates for individuals with subtypes 1–3 treated using AP were 13.5%, 36.1%, and 67.0%, respectively.

Discussion These subtypes may be of clinical value in AP treatment decision-making in the CHR population.
ANIPE-Cu Catalyst Enables Highly Enantioselective Markovnikov Hydroboration of α-Olefins
Authors: Shi Shi-Liang , Cai Yuan
Published: October 2020

Asymmetric hydroboration of simple and unactivated terminal alkenes (α-olefins), feedstock chemicals derived from the petrochemical industry, has not been efficiently realized for past decades. Using a bulky ANIPE ligand, we achieved a rare example of highly enantioselective copper-catalyzed Markovnikov hydroboration of α-olefins. The chiral secondary alkylboronic ester products were obtained in moderate to good yields and regioselectivities with excellent enantioselectivities.

1 Introduction

2 Conditions Optimization

3 Substrate Scope

4 Application

5 Mechanistic Discussion

6 Conclusions and Future Directions
CuBr-Catalyzed One-Pot Three-Component Synthesis of Novel 2-(Carbazolyl)benzothiazoles
Authors: Meesala Ramu , Lee Yean Kee , Arshad Ahmad Saifuddin Mohamad , Abdullah Iskandar , Mordi Mohd Nizam , Abd Rahman Noorsaadah
Published: October 2020

A facile synthesis of various 2-(carbazolyl)benzothiazoles has been developed by one-pot CuBr-catalyzed three-component reactions of 2-iodoanilines, arylaldehydes, and elemental sulfur. Unlike traditional approach, this reaction exhibited a good functional group tolerance to produce the corresponding 2-(carbazolyl)benzothiazoles in good yields in the absence of any additive.
Asymmetric Synthesis of Isoxazol-5-ones and Isoxazolidin-5-ones
Authors: Brière Jean-François , Waser Mario , Massa Antonio , Macchia Antonio , Eitzinger Andreas
Published: October 2020

Isoxazol-5-ones and isoxazolidin-5-ones represent two important classes of heterocycles, with several applications as bioactive compounds and as versatile building blocks for further transformations. Unlike the parent aromatic isoxazoles, the presence of one or two stereocenters in the ring renders their asymmetric construction particularly important. In this review, starting from the description of general features and differences between these two related compound families, we present an overview on the most important enantioselective synthesis strategies to access these heterocycles. Both chiral metal catalysts and organocatalysts have recently been successfully employed for this task and some of the most promising approaches will be discussed.

1 Introduction

2 Isoxazol-5-ones as Nucleophiles

2.1 Isoxazol-5-ones as C-Nucleophiles

2.2 Isoxazol-5-ones as N-Nucleophiles

2.3 Isoxazol-5-ones as C-Nucleophiles in Cyclization Processes

3 Asymmetric Construction of Isoxazolidin-5-ones

3.1 Enantioselective α-Functionalizations of Isoxazolidin-5-ones

4 Arylideneisoxazol-5-ones in Conjugated Addition

5 Conclusions
Visible-Light-Driven Z-Selective Reaction of Methyl Ketones with DMSO: A Mild Synthetic Approach to Methylthio-Substituted 1,4-Enedione Promoted by Selectfluor™
Authors: Deb Mohit L. , Baruah Pranjal K. , Rastogi Gaurav K.
Published: October 2020

Here we disclose a simple, visible-light-driven Z-selective synthesis of methylthio-substituted 1,4-enedione in a single step promoted by Selectfluor. Dimethyl sulfoxide is used as both the ‘thio’ source and the solvent. Molecular iodine and potassium persulfate are used as catalyst and oxidant, respectively. White light (CFL-30W) is used as the light source. The proposed mechanism involves a Kornblum reaction followed by aldol reaction.