bluuebunny/crossref_metadata_2025 huggingface dataset:
Wear Mechanisms of Ceramic Cutting Tool when Cutting Hardened Steel Rolls
Authors: Song Xin Yu , Du Guo Chen
Published: August 2016

Rolls are important tools in the steel industry. With the increase of the automobile and the mould, rolls are increasing rapidly. Hard rolls are very difficult to cut, almost all hard rolls are cut by only by grinding, and the grinding efficiency is relatively low, and it consumes a lot of cutting fluid. In this paper, the life and tool wear of ceramic tools in different cutting conditions were analyzed. Crack, chipping of cutting tools were analyzed. The experimental and theoretical analysis confirmed that the generation and expansion of the crack are the main wear mechanism of the tool failure, when the ceramic tools cutting cold rolls.
The Influence of Graphite Heat Conductor Technology on the Preparation and Crystal Structure of Single Crystal Blade
Authors: Li Yang , Zhao Yu Tao , Liang Xiang Feng , Jia Zhi Hong
Published: August 2016

Graphite heat conductor technology can effectively overcome the mixed crystal defect caused by geometric factors during the forming process of single crystal component. The simulation results show that, As for the component that uses heat conductor technology, the heat elimination condition in the corner of component is improved significantly. Before the melt body generating the supper-cold region at the platform end, the solidification interface will advance into the platform from the blade body with the relatively faster speed. According to the analysis of macro structure, the component with heat conductor, because of the diminution of supper-cold time and supper-cold region, the trend to generate mixed crystal on the platform reduces obviously, on one side near the wall of insulation heater, there is almost no mixed crystal on the platform.
Thermoelectric Properties of Silicon Germanium Alloy Nanocomposite Fabricated by Mechanical Alloying and Spark Plasma Sintering
Authors: Zhu Zhen Ye , Guo Shi Lei
Published: August 2016

High dense p-type Si95Ge5 doped with nanoSi70Ge30B5particles thermoelectric materials were firstly fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) method. The effects of different nanoSi70Ge30B5 doping content on the thermoelectric and phase properties were studied. A dimensionless thermoelectric figure-of-merit (ZT) of 0.47 at 710K in p-type nanocomposite bulk silicon germanium (SiGe) alloys is achieved. The enhancement of ZT is due to a large reduction of thermal conductivity caused by the increased grain boundaries of the numerous nanograins that effectively scatter long wavelength phonons.
Phase Field Simulation of the Lamellar Microstructure Formation in TiAl Alloys
Authors: Teng Chun Yu , Fu Yun , Ren Zhan Yong , Li Yong Hong , Wang Yun , Ouyang Wen Li
Published: August 2016

The details of the lamellar microstructure in TiAl intermetallic alloys, such as the lath thickness and interfaces type governs the strength, ductility, creep properties and the long term microstructure stability of the alloy. The lamellar microstructure coarsening may induce property degradation of materials when the working temperature is high especially for the aero-engine turbine blades. At the same time, the reliability of the structure will decreases dramatically during long term working. In order to customize highly stable microstructure in high temperature, the phenomenon of lamellar formation during the solid-solid α→α2+γ phase transformation in fully lamellar TiAl alloys was investigated by phase field simulations. The lamellar structure morphology obtained with simulation is coincides with the experimental results. It is found that the independent nuclei and twin-related nuclei co-exist in the nucleation stage for the random noise nucleation. During growth stage, the independent nuclei grow slowly or disappear for the interfacial energy and elastic energy minimization. While most twin-related nuclei survived. During the following coarsening stage, big nuclei swallow small nuclei for interfacial energy minimization. The statistical character of twin area fraction changes complicated during these processes and it will be analyzed in detail. These findings could shed light on the understanding of the lamellar formation and coarsening mechanisms during phase transformation in TiAl alloys.
Titanium Metal Injection Molding - A Commercial Overview
Authors: Scharvogel Matthias
Published: August 2016

Metal Injection Molding (MIM) of Titanium and its alloys has been the topic of many scientific research activities and presentations for many years. By now there are several companies that focus on applying the gained knowledge for producing Titanium MIM components in production quantities. This is only possible since Titanium powder in repeatable quality is available in production quantities and the specialized production equipment was developed over the recent years. Two ASTM standards for Titanium MIM implants have published and several Titanium MIM components have received approval around the globe, including approval by the Food and Drug Administration (FDA) for the United States. Based on this foundation, several large Medical Technology companies started developing next generation implants using MIM as the preferred production method in order to use the design advantages and / or reduce costs. The aerospace industry also started recognizing the advantages of Titanium MIM. There are several Titanium MIM parts that are already being used in commercial airplanes in production quantities. Additional applications in order to replace other materials, reduce costs or use the design advantages of MIM are currently being developed. The cost reduction related to Titanium MIM allows the usage of this great material in other industries like for sporting goods, outdoor equipment or luxury products. The Titanium MIM industry is slowly maturing and large companies started applying the great advantages into the product portfolio. It will be imperative that the relatively small Titanium MIM companies perform according to the high expectations of the large potential customers that would like to use the technology for future products.
Sintering Powder Metal Injection Molded (MIM) Titanium Alloys: In Vacuum or Argon?
Authors: Banerjee Satyajit , Joens Claus J.
Published: August 2016

Titanium alloys processed by the powder metallurgy route (PM) are sintered in vacuum, the higher the better. This philosophy is carried over to MIM titanium alloys. In the MIM process a large amount of out gassing of binders takes place, which affects the vacuum level and hence the interstitial element pick up in the titanium. In this paper the effect of gaseous material in vacuum is discussed and an alternate method of debinding and sintering in argon is proposed. Three processing conditions are applied to MIM tensile bars made from Ti-6-4 materials. First they are debound and sintered under high vacuum, second debound under argon and sintered in high vacuum and third debound and sintered in flowing argon. The physical properties and interstitial element contents are presented and the effects of the material structures due to different processing on the properties are discussed.
New Titanium Alloy Feedstock for High Performance Metal Injection Molding Parts
Authors: Tingskog Toby , Larouche Frederic , Lefebvre Louis Philippe
Published: August 2016

Ti 6-4 and other Titanium alloys have great potential for Metal Injection Molding of high performance parts. Markets like Automotive, Aerospace, 3C and sporting goods can benefit from the low density and high strength of Titanium. A new feedstock has been developed that incorporates pre-alloyed Ti 6-4 and discrete additions that simplify MIM processing and enhance properties. Processing and sintering parameters are presented together with mechanical and metallurgical properties of completed parts.
A MIM Route for Producing Ti6Al4V-TiC Composites
Authors: Pelletier Roger , Lefebvre Louis Philippe , Baril Eric
Published: August 2016

Discontinuous reinforced titanium matrix composites have generated significant interest due to their compelling properties such as their specific strength and wear resistance at room and elevated temperatures. For these reasons, these materials have been considered in various applications such as automotive (valve components), aerospace (engine components) and medical devices (implants). Metal injection molding (MIM) has proven to be an efficient near net-shape technology suitable for high volume manufacturing of parts having complex geometries. The MIM technology is particularly attractive for producing composites as the metallic matrix does not go through the liquid state. This helps minimizing the segregation of the hard particles. MIM also reduces the needs for machining. However, the production of titanium components with the MIM process has its own challenges and limitations, such as presence of porosities and coarser microstructures compared to wrought products. The present work introduces the results obtained during the development of a MIM route for producing Ti6Al4V-5wt%TiC composites. The feedstock developed is wax-based and incorporates a pre-alloyed metal powder. The microstructure, mechanical properties at room and elevated temperatures, the wear resistance and the thermal diffusivity of the composites have been characterised. Properties are compared with those of a Ti6Al4V MIM material produced with the same feedstock and process but without TiC as well as with those of wrought Ti6Al4V reported in the literature. The presence of a small amount of TiC promotes densification and grain size refinement and affects the surface finish of the sintered components. Tensile properties of the composites are comparable or better than those of wrought Ti6Al4V (ASTM F1472). Improved mechanical properties compared to unreinforced material are associated to the higher density, finer grain size as well as solution strengthening of the titanium matrix.
Increase of Fatigue Life of Titanium VT1-0 after Electron Beam Treatment
Authors: Konovalov Sergey V. , Panchenko Irina , Kosinov Dmitry , Ivanov Yurii F. , Gromov Victor , Semina Olga
Published: August 2016

The processing of commercially pure titanium VT1-0 with high intensity pulsed electron beam was carried out and the mode of irradiation allowing the increase in fatigue life of the material was revealed. Structure investigations of modified layer and fracture surface of commercially pure titanium samples subjected to fatigue multicycle tests were implemented. By methods of scanning electron microscopy the structural transformations responsible for increase in fatigue life of titanium irradiated with high intensity pulsed electron beam were revealed. It was shown that irradiation of commercially pure titanium of grade VT1-0 with high intensity electron beam (25 J/cm2, 150 μs, 3 pulses) resulted in the refinement of grain structure, formation of multilayer structure. Irradiation facilitated the formation of additional structural levels of micro and nanosize range in surface layer.
Identification of Contamination Levels and the Microstructure of Metal Injection Moulded Titanium
Authors: Ewart Paul , Jull Harrisson , Künnemeyer Rainer , Schaare Peter N.
Published: August 2016

The chemical elements used in the binder system for the injection moulding of titanium metal powders will change the final composition when not adequately controlled. Excess levels of carbon, hydrogen, nitrogen and oxygen adversly effect the mechanical properties by embrittlement. Before sintering debinding is done to remove the maximum possible amount binder thereby ensuring residual carbon levels are minimal. Testing the mechanical properties of samples can acknowledge deficiencies in the final part however, identification of the nature of the deficiencies is not so simple.In this work titanium-based metal parts were made using the metal injection moulding process and the microstructure was inspected. The investigation used scanning electron microscopy imaging, electron dispersion spectroscopy point and area mapping, LECO trace analysis and X-ray diffraction elemental mapping. Following this samples were ground and polished before immersing their surfaces in an etching solution to further expose the microstructure. Although the data collected from debinding indicated the binder had been removed prior to sintering contamination was still evident. This result showed that the traditional means of reporting binder levels in proportion to part mass after debinding is inaccurate. Subsequently laser induced breakdown spectroscopy was trialed as a method by which to determine the binder levels for parts in the green, grey, brown and sintered form.Interstitial carbon is a known alpha stabiliser however excess carbon on particle surfaces may impinge on particle coalesence limiting density levels. Comparison of the part mass method of binder determination with the laser induced breakdown spectroscopy results showed that the mass determination method was more accurate for the green and grey parts but the laser induced breakdown spectroscopy results were able to detect the residual binder more accurately for brown and sintered parts.
Metal Injection Moulding of Superelastic TiNi Parts
Authors: Bidaux J. Eric , Hidalgo Alexandra Amherd , Girard Hervé , Rodriguez-Arbaizar Mikel , Reynard Lionel , Chevallier Jacques , Aeby François , Giachetto Jean Charles , Carreño-Morelli Efrain
Published: August 2016

TiNi shape-memory properties are successfully used today for the fabrication of various technical devices. The limited machinability and high cost of TiNi encourage the use of near-net shape production techniques such as metal injection moulding. In this work TiNi alloys tensile test specimens are produced by metal injection moulding from pre-alloyed powders. A binder based on a mixture of polyethylene, paraffin wax and stearic acid is used. Parts with a density of about 96.6% of theoretical density are obtained. Scanning electron microscopy coupled with EDX measurements reveals a microstructure consisting of a TiNi matrix with small Ti4Ni2Ox and TiC inclusions. DSC and X-ray diffraction observations indicate the presence of additional Ni4Ti3 precipitates. The parts exhibit full superelasticity at room temperature even for strains of up to 4%, without the need for additional thermal post-treatments. Ultimate tensile strengths up to 980 MPa are obtained.
Microstructure of Ti-45Al-5Nb and Ti-45Al-10Nb Powders
Authors: Laipple Daniel , Stark Andreas , Schimansky Frank Peter , Schwebke Bernd , Pyczak Florian , Schreyer Andreas
Published: August 2016

Gas-atomised spherical powders of Ti-45Al-5Nb and Ti-45Al-10Nb alloys were produced using the plasma melting induction guided gas atomisation (PIGA) technique. The phase composition was determined by X-ray diffraction at the synchrotron beamline HEMS at PETRA III (DESY), as well as by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), two dimensional and focused ion beam (FIB) based three dimensional electron back scatter diffraction (EBSD) measurements. Due to the high cooling rates the alloy composition of both alloys consists of hexagonal-close-packed α- and body-centred-cubic β-phase. The α-phase is dominant in the larger powder size fractions. Considerable amounts of the β phase were only found in the powder particle size fractions smaller than 32 μm for the Ti-45Al-5Nballoy and smaller than 45 μm for the Ti-45Al-10Nb. A pronounced dendritic cauliflower-like structure was observed in bigger powder particles of the Ti-45Al-10Nb alloy. This gives proof that diffusion took place during the initial β-grain formation, even though there is no orientation relation between the final grain and the dendrite structure in the powder particles. The presence of dendritic structures showed that the cooling rate during powder atomization was still too low to reach the critical growth rate for a planar solidification. The absence of preferred misorientation angles between α-grains indicates that α-grains are not formed out of already solidified β-grains by a solid state phase transformation.
A Phase Field Approach for Modeling Melting and Re-Solidification of Ti-6Al-4V during Selective Laser Melting
Authors: Holfelder Peter , Lu Jin Ming , Krempaszky Christian , Werner Ewald A.
Published: August 2016

A Multi Phase Field model is proposed to describe the microstructure evolution induced by laser-material interaction in Selective Laser Melting (SLM). On the basis of the free enthalpy, the nucleation and growth processes occurring during the relevant phase transformations are explicitly taken into account. Within this contribution, the focus is laid on the SLM processing of the titanium alloy Ti-6Al-4V with special emphasis on the transition between β-titanium and melt. The results are discussed and compared to those of more conventional modelling approaches.
Corrosion and Tribocorrosion Behavior of Ti-Alumina Composites
Authors: Gordo Odériz Elena , das Neves Roberto G. , Ferrari Begoña , Jiménez-Morales Antonia , Lima Andreia , Alves Alexandra C. , Pinto Ana Maria Pires , Toptan Fatih
Published: August 2016

This work focuses in the corrosion and wear properties of titanium reinforced with 1% wt. alumina particles, produced by a combination of colloidal techniques and powder metallurgy. The alumina particles were added to control the grain growth of titanium during sintering, and simultaneously to increase hardness and wear resistance. Colloidal techniques permitted a homogeneous dispersion of alumina particles on the surface of fine Ti particles by the formulation of stable aqueous suspensions that were further processed by spray-dry to obtain spherical granules with improved compressibility. Ti-alumina samples were produced by uniaxial pressing of granules and vacuum sintering leading to materials with homogeneous microstructure, a reduction of grain size higher than 50 % with respect to pure titanium, and a sensible increase in hardness. But the addition of ceramic particles can also have an influence on the corrosion behavior that is one of the most interesting properties of titanium alloys, and on wear resistance, that is one of the drawbacks of Ti. Moreover, the study of simultaneous action of wear and corrosion (tribocorrosion) is an area of highest interest in applications like biomedical or automotive. The corrosion behavior was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PP) in NaCl at two concentrations (0.9 % and 3.5 %) and temperatures (37 oC, and room temperature). Tribocorrosion tests were performed using a reciprocating ball-on-plate tribometer where a 10 mm diameter alumina ball was used as counter material, and 10 N normal load was applied during 30 min in the same concentrations and temperatures of NaCl as in the static corrosion tests. The results showed a clear improvement of wear resistance on the composite without reducing the corrosion behavior in both conditions.
Spherical Ti-6Al-4V Powders Produced by Gas Atomization
Authors: Chen Gang , Tan Ping , Zhao Shao Yang , He Wei Wei , Tang Huiping
Published: August 2016

In this study, we fabricated spherical Ti-6Al-4V powders using gas atomization. Scanning electron microscope, optical microscope, X-ray diffraction and particle size distribution were extensively performed to investigate the properties of gas-atomized Ti-6Al-4V powders. The XRD analysis shows all the gas-atomized powders are with both α and β phases. The surface of coarse powders exhibited cellular structure with equiaxed grains. However, the fine powders achieved smooth surfaces and could not be observed any crystallization. Attributed to rapid solidification, both α cell and needle-like martensite α’ phase were observed in the internal area of coarse powders, while only honeycomb cellular structure was demonstrated with refined grains in fine powders.
Review of the Powder Metallurgical Production of Net-Shaped Titanium Implants
Authors: Laptev Alexander , Cysne Barbosa Ana Paula , Daudt Natália , Bram Martin
Published: August 2016

The paper gives a short review of P/M routes which were developed or adapted by the authors for the net-shape manufacturing of titanium implants. Special attention is paid to the production of highly porous bone implants, where the porosity is achieved by the application of temporary space holder particles, which are removed before or during sintering by decomposition or dissolution. In this case, shaping was done either by machining of powder compacts in the green and sintered state or by metal injection moulding (MIM). The challenges of these shaping technologies and current solutions are discussed. To complete the review, two promising new technologies for the net-shape production of highly porous titanium implants, the replica technique and additive manufacturing are briefly introduced.
Engineering Properties of Cellular Ti-6Al-4V Structures Fabricated by Electron Beam Melting
Authors: Smith Geoff , Brown Ian , Kirchner Alexander , Ryan Martin , McGavin Peter , Sharp Matt
Published: August 2016

Cellular Ti-6Al-4V materials with open-cell pore array structures have been fabricated by Electron Beam Melting (EBM) using an Arcam A2X system. The test samples were cylinders 20 mm diam. x 40 mm high, with pore diameters of 1.75 - 2.5 mm and porosities in the range of 61 - 83%. The structures were based on a simple cubic pore array.Sample stiffness and strength were both found to decrease with increasing porosity, exhibiting mean Young’s moduli of 3.5 – 15.6 GPa and mean yield stresses of 20.2 – 93.6 MPa. Finite element analysis (FEA) using ANSYS was performed to model the stress-strain curves for a representative volume, using measured bulk material properties. Stiffness and strength were significantly overestimated by this method, but better agreement with measured data was obtained when the representative volume was extended along the compression axis.
Design, Processing and Characterization of Materials with Controlled Radial Porosity for Biomedical and Nuclear Applications
Authors: Trueba Paloma , Chicardi Ernesto , Rodríguez-Ortiz José Antonio , Pavón Juan José , Cobos Joaquín , Torres Yadir
Published: August 2016

The manufacture of graded materials has gained an enormous interest during the last decade due to the diversity of industrial and biological materials systems that require or are actually designed to implement that criterion; those natural or artificial materials offer multiple possibilities of applications. In this work, a novel uniaxial and sequential compaction device has been successfully designed and fabricated, in order to obtain samples with three different layers; this new device is suitable for both conventional and non-conventional powder metallurgy (PM) techniques. In addition, this device allowed us to use different combinations of powders and space-holder particles, irrespective of their nature, sizes, morphologies and proportions. It has no restriction about applying different compaction pressures for every layer, which may result in increasing or decreasing porosity. This compaction device is especially powerful if the aim is obtaining samples with radial graded porosity for biomedical applications (replacement of cortical bone involved in different joints and dental restorations) and nuclear applications (mimicking burnt used nuclear fuel). Specifically in this work, different samples with radial graded porosity were fabricated and then microstructurally and mechanically characterized: i) Commercially pure titanium (CP Ti) samples, starting from blends CP Ti with 20 vol.%, 40 vol.% and 60 vol.% of Sodium Chloride (NaCl) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 800 MPa of compaction pressure and 1250 °C for 2h in high vacuum of sintering; and ii) CeO2 samples, starting from blends CeO2 with 0.5 vol.%, 3.0 vol.% and 7.5 vol.% of Ethylene Bis Stearamide (EBS) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 460 MPa in external layer and 700 MPa in core and intermediate layers of compaction pressure, and 1700 °C during 4h in static air of sintering. This new device has proved to have unique advantages for solving problems of structural integrity in conventional PM manufacturing in a simple, economic and reproducible way.
Press and Sintering of Titanium
Authors: Frykholm Robert , Brash Benjamin
Published: August 2016

Titanium based alloys show very high strength to density ratio, and could be the choice of material for a wide range of applications. By practicing press and sintering for production of Ti components, high materials utilization can be assured, and at the same time costly machining operations can be limited. Difficulties in processing and high cost for powders have been limiting factors for progress, but recent development indicates good possibilities on cost effective use of TiH2 powder in the press and sintering segment. In this paper, influence of processing parameters and powder properties on final sintered component properties are discussed.
Development of Low Cost PM Ti Alloys by Thermomechanical Processing of Powder Blends
Authors: Raynova Stiliana , Gabbitas Brian , Bolzoni Leandro , Yang Fei
Published: August 2016

This research focuses on the development of low cost powder metallurgy (PM) Ti alloys suitable for application in PM thermomechanical processing with mechanical properties comparable to those of wrought Ti6Al4V alloy. The alloy systems studied are Ti3Al2V, Ti5Fe and Ti3.2Fe1Cr0.6Ni0.1Mo (Ti5SS). The alloy mixtures were produced by blending Ti HDH powders with Al40V, 316SS master alloy powders or elemental Fe powder. The blended powders were further consolidated using various methods: high vacuum sintering (HVS), induction sintering (IS), powder compact forging (PCF) and powder compact extrusion (PCE). It is found that, PM Ti3Al2V and Ti5Fe alloy processed by PCE or PCF followed by recrystallization annealing (RA) achieved tensile properties comparable with wrought Ti6Al4V alloy. Tensile properties such as yield strength (YS) of 910MPa, UTS of 1010MPa and 15% elongation to fracture for Ti3Al2V alloy are reported. Ti5Fe alloy gives YS and UTS of 870MPa and 968MPa respectively, combined with 20.3% elongation to fracture. The tensile results are related to the microstructure developed during the consolidation processes. The oxygen contamination as a result of the high temperature processing is also reported.
Shaping Strategies for Porous Ti Fabrication throughout Colloidal Chemistry
Authors: Molero Esther , Sanchez-Herencia Antonio Javier , das Neves Roberto G. , Gordo Odériz Elena , Ferrari Begoña
Published: August 2016

Aimed by reducing the total cost of products, powder metallurgy (PM) processing of Ti is a subject of high interest. However, using of conventional PM techniques presents difficulties due to the intrinsic characteristics of Ti, like low strain ability, and high reactivity, which lead to low compressibility. Moreover, Ti powders with small particle size are difficult to process by conventional PM techniques as they present a lower compressibility and also a poor flowability. On the other hand, the colloidal processing has been used for long in ceramics to achieve green bodies with high densities, complex shapes and homogeneous microstructures, but they are rarely used to shape metal powders because of its high density and high surface reactivity. However, the possibility to process fine particles makes these techniques interesting for metals with low density like Ti.The colloid-chemistry control of metallic powders in aqueous slurries is proposed as a way to prepare Ti porous parts with small particle size, throughout the formulation of aqueous slurries with solid contents as high as 50 vol.%. The chemical and chemical-physic stability of Ti powders 10 μm in size was determined by measuring the zeta potential as a function of pH, and dispersant concentration, while the later optimization of Ti slurries and their adequation for the use of different colloidal techniques, were studied in terms of rheology and the addition of the processing additives, such as gel or foaming agents. Techniques such as thermal gelling, foaming, and impregnation of exo-templates or robocasting were used to build Ti parts with random and/or tailored macroporosity. The shaped pieces made on Ti were sintered in vacuum at 1100 oC for 30 minutes, and their microstructure and mechanical properties were determined and compared with dense materials shaped by combining PM and colloidal techniques in previous works
Processing, Microstructure and High Strain Rate Behaviour of Ti-6Al-4V Alloy Produced from a Blended Mixture Using Powder Compact Extrusion
Authors: Singh Ajit Pal , Gabbitas Brian , Yang Fei , Torrens Rob
Published: August 2016

Powder compact extrusion (PCE) is an innovative way of processing titanium and titanium alloys to produce good-quality material with a wide range of compositions, microstructures and mechanical properties. This paper explores PCE processing of Ti-6Al-4V alloy prepared from a blended powder mixture, containing elemental hydride-dehydride (HDH) titanium powder and master alloy (60Al-40V) powder. The warm pressed compacts of blended powders were sintered using a vacuum sintering furnace prior to β extrusion. The resulting material was used to measure the performance under high strain rate and tri-axial stress state using Charpy v-notch testing. A comparison was made of the microstructure after vacuum sintering and hot extrusion in addition to oxygen measurements to determine the degree of oxygen pickup during each processing stage. A comprehensive study of fracture surfaces in selected samples was carried out using optical microscopy and scanning electron microscopy. Based on the results, it is clear that certain samples picked up varying amounts of interstitial impurities during processing and as a consequence a significant number of micro-cracks were observed in lamellar type microstructures. The oxygen content of all as-extruded samples was between 0.34-0.44 wt.% with resultant impact toughness in the range of 10-14 J. The best impact toughness attained for the lowest oxygen as-extruded rods was 20% lower than the literature values for wrought material. In terms of fracture behaviour, ductile dimples, cleavage facets and cracks passing through lamellar structures were observed in all samples. However, the quantity of these fracture features varied significantly in each sample.
Fabrication of In Situ TiC Reinforced Ti Matrix Composites by Thermomechanical Consolidation of TiH2/CNTs Powder Mixtures
Authors: Zheng Yi Feng , Yao Xun , Su Yong Jun , Zhang De Liang
Published: August 2016

In this work, in-situ TiC reinforced Ti matrix composites (TMCs) have been fabricated via blending TiH2 powder and multi-walled carbon nanotubes (CNTs) followed by thermomechanical consolidation of the TiH2/CNTs powder mixture. The dehydrogenation, in situ reaction and consolidation occurred simultaneously and took less than 15 minutes in total. The effect of CNTs content (1 and 3 vol.% (0.56 and 1.69 wt.%)) on the evolution of microstructures and mechanical performances of the extruded samples has been investigated. The results showed that the extruded TMCs had a duplex microstructure consisting of coarse alpha titanium grains and ultrafine grained (UFG) regions, and the in-situ formed TiC particles had a near-spherical shape. The extruded sample with 1 vol.% (0.56 wt.%) CNTs reinforced exhibited a yield strength of 807.3 MPa, ultimate tensile strength of 1085.9 MPa and elongation to fracture of 3.3% at room temperature. The mechanism of microstructural evolution and material failure are discussed.e are discussed.
Preparation of Titanium Alloy Parts by Powder Compact Extrusion of a Powder Mixture and Scaled up Manufacture
Authors: Yang Fei , Gabbitas Brian , Singh Ajit Pal , Raynova Stiliana , Lu Hui Yang , Robinson Barry
Published: August 2016

Blended Elemental Powder Metallurgy (BE-PM) is a very attractive method for producing titanium alloys, which can be near-net shape formed with compositional freedom. However, a minimization of oxygen pick-up during processing into manufactured parts is a big challenge for powder metallurgy of titanium alloys. In this paper, different approaches for preparing titanium alloy parts by powder compact extrusion with 0.05-0.1wt.% of oxygen pick-up during manufacturing are discussed. The starting materials were a powder mixture of HDH titanium powder, other elemental powders and a master alloy powder. Different titanium alloys and composites, such as Ti-6Al-4V, Ti-4Al-4Sn-4Mo-0.5Si, Ti-5Al-5V-5Mo-3Cr, and Ti-5Al-5V-5Mo-3Cr-5vol%TiB, with different profiles such as round and rectangular bars, a wedge profile, wire and tubes have been successfully manufactured on a laboratory and pilot-plant scale. Furthermore, a possible route for scaling up the titanium processing capabilities in the University of Waikato has also been discussed.
Evaluation of Press-and-Sinter Processing Parameters in Titanium Hydride Powder Metallurgy
Authors: Petroni S.L.G. , Galvani Eduardo T. , Cairo Carlos Alberto Alves , Girotto C.C. , Henriques V.A.R.
Published: August 2016

The use of hydrogenated titanium powders combined with traditional PM techniques may lead to a significant reduction in the manufacturing costs of titanium components. In this work, the advantages and limitations of the use of TiH2 powder consolidated through the conventional press-and-sinter method were investigated. Processing parameters related to the compaction and sintering were studied for a TiH2 powder in the particle sizes <355 μm, <150 μm and <45 μm. Optimized compaction conditions were achieved by using admixed lubricant and compaction pressure of 800 MPa. The mechanisms involved in the compaction of powders were detailed through the fit of compressibility data to a theoretical model originally developed for titanium powders. Densification of samples was favored by the reduction in particle size and increase in sintering temperature up to 1300 °C. The positive effects of hydrogen release during dehydrogenation were verified through the results of sintered densities and the reduction of oxygen levels. Limitations were observed mainly regarding the flowability of powders and the difficulty to achieve full densification.
A joint data record of tropospheric ozone from Aura-TES and MetOp-IASI
Authors: Oetjen Hilke , Payne Vivienne H. , Neu Jessica L. , Kulawik Susan S. , Edwards David P. , Eldering Annmarie , Worden Helen M. , Worden John R.
Published: August 2016

Abstract. The Tropospheric Emission Spectrometer (TES) on Aura and Infrared Atmospheric Sounding Interferometer (IASI) on MetOp-A together provide a time series of 10 years of free-tropospheric ozone with an overlap of 3 years. We characterise the differences between TES and IASI ozone measurements and find that IASI's coarser vertical sensitivity leads to a small (< 5 ppb) low bias relative to TES for the free troposphere. The TES-IASI differences are not dependent on season or any other factor and hence the measurements from the two instruments can be merged, after correcting for the offset, in order to study decadal-scale changes in tropospheric ozone. We calculate time series of regional monthly mean ozone in the free troposphere over eastern Asia, the western United States (US), and Europe, carefully accounting for differences in spatial sampling between the instruments. We show that free-tropospheric ozone over Europe and the western US has remained relatively constant over the past decade but that, contrary to expectations, ozone over Asia in recent years does not continue the rapid rate of increase observed from 2004 to 2010.
How Does Downward Planetary Wave Coupling Affect Polar Stratospheric Ozone in the Arctic Winter Stratosphere?
Authors: Lubis Sandro W. , Silverman Vered , Matthes Katja , Harnik Nili , Omrani Nour-Eddine , Wahl Sebastian
Published: August 2016

Abstract. It is well established that variable wintertime planetary wave forcing in the stratosphere controls the variability of Arctic stratospheric ozone through changes in the strength of the polar vortex and the residual circulation. While previous studies focused on the variations in upward wave flux entering the lower stratosphere, here the impact of downward planetary wave coupling (DWC) on ozone is investigated for the first time. Utilizing the MERRA-2 reanalysis and a fully coupled chemistry-climate simulation with NCAR's Community Earth System Model (CESM1[WACCM]), we find two DWC effects on ozone: (1) the direct effect in which the residual circulation is modified and prevents the typical increase of ozone due to upward planetary wave events in winter, and (2) the indirect effect in which the modification of polar temperature during winter affects the amount of ozone destruction in spring. Winter seasons dominated by DWC events (i.e., reflective winters) are characterized by lower Arctic ozone concentration, while seasons dominated by increased upward wave events (i.e., absorptive winters) are characterized by relatively higher ozone concentration. This behavior is consistent with the cumulative effects of downward and upward planetary wave events on polar stratospheric ozone via the residual circulation and the polar temperature in winter. The results establish a new perspective on dynamical processes controlling stratospheric ozone variability in the Arctic.
The Acid-Catalyzed Hydrolysis of an α-Pinene-Derived Organic
Nitrate: Kinetics, Products, Reaction Mechanisms, and Atmospheric
Impact
Authors: Rindelaub Joel D. , Borca Carlos H. , Hostetler Matthew A. , Lipton Mark A. , Slipchenko Lyudmila V. , Shepson Paul B.
Published: August 2016

Abstract. The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate, due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO+NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still very uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically-derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, this study elucidated the hydrolysis mechanism and rate constants for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the APN lifetime ranging from 8.3 minutes at acidic pH (0.25) to 8.8 hours at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant data, the identification of the products campholenic aldehyde, pinol, and pinocamphone confirms a unimolecular specific acid-catalyzed mechanism is responsible for organic nitrate hydrolysis under acidic conditions, where carbocation rearrangement is favored for α-pinene-derived species. The free energies and enthalpies of the isobutyl nitrate hydrolysis intermediates and products were calculated using a hybrid density functional (ωB97X-V) to support the proposed mechanisms. These findings provide valuable insight into the organic nitrate hydrolysis mechanism and its contribution to the fate of atmospheric NOx, aerosol phase processing, and BSOA composition.
Simultaneous retrieval of water vapour and temperature profiles
and cirrus clouds properties from measurements of far infrared
spectral radiance over the Antarctic Plateau
Authors: Di Natale Gianluca , Palchetti Luca , Bianchini Giovanni , Del Guasta Massimo
Published: August 2016

Abstract. The possibility to discriminate the contribution of the atmosphere and ice clouds by using spectral infrared measurements is a fundamental step to quantify the cloud effect in the climate models. The simultaneous retrieval of clouds and atmospheric parameters allows to take into account the possible correlations between the variables. In this paper we describe the development of a routine able to perform the simultaneous retrieval and its application to the analysis of the spectral measurements acquired by the REFIR-PAD (Radiation Explorer Far Infrared – Prototype for Applications and Development) spectroradiometer, operative from Antarctic Plateau since 2012. This routine is able to operate the retrieval with reduced computing time comparable with the REFIR-PAD data acquisition time. The analysis allowed to retrieve the water vapour and temperature profiles and the clouds optical and micro-physical properties, such as the generalised effective diameter (Dge) and the ice water path (IWP), by exploiting the spectral band between 230–980 cm−1. To simulate the radiative transfer, the LBLRTM (Line By Line Radiative Transfer Model) was integrated with a specific code based on the delta-Eddington two-stream approximation, and further the cirrus clouds single scattering properties were derived from a database for hexagonal column habits. In order to identify the ice clouds a back-scattering and depolarisation lidar was available on the site and allowed to infer the position and the cloud thickness used in the simulations. A climatology of the vertical profiles of water vapour and temperature, was performed by using the daily radiosounding available at the base and it was used to build the a priori and initial guess profiles used in the fitting routine. An optimal estimation method with a Levenberg-Marquardt approach was applied to perform the retrieval. The comparison of results with radiosoundings demonstrates that the retrieved atmospheric state is not disturbed by the clouds presence. Finally, the retrieved clouds parameters were compared with the statistical correlation between the cloud temperature (Tc) and the optical depth measured in Antarctica at Dumond D'Urville and the effective diameters with the ice water content (IWC) obtained in the Arctic region finding a general agreement.
Development and evaluation of a suite of isotope reference gases for methane
in air
Authors: Sperlich Peter , Uitslag Nelly A. M. , Richter Jürgen M. , Rothe Michael , Geilmann Heike , van der Veen Carina , Röckmann Thomas , Blunier Thomas , Brand Willi A.
Published: August 2016

Abstract. Measurements from multiple laboratories have to be related to unifying and traceable reference material in order to be comparable. However, such fundamental reference materials are not available for isotope ratios in atmospheric methane, which led to misinterpretations of combined data sets in the past. We developed a method to produce a suite of synthetic CH4-in-air standard gases that can be used to unify methane isotope ratio measurements of laboratories in the atmospheric monitoring community. Therefore, we calibrated a suite of pure methane gases of different methanogenic origin against international referencing materials that define the VSMOW (Vienna Standard Mean Ocean Water) and VPDB (Vienna Pee Dee Belemnite) isotope scales. The isotope ratios of our pure methane gases range between −320 and +40 ‰ for δ2H–CH4 and between −70 and −40 ‰ for δ13C–CH4, enveloping the isotope ratios of tropospheric methane (about −85 and −47 ‰ for δ2H–CH4 and δ13C–CH4 respectively). Estimated uncertainties, including the full traceability chain, are < 1.5 ‰ and < 0.2 ‰ for δ2H and δ13C calibrations respectively. Aliquots of the calibrated pure methane gases have been diluted with methane-free air to atmospheric methane levels and filled into 5 L glass flasks. The synthetic CH4-in-air standards comprise atmospheric oxygen/nitrogen ratios as well as argon, krypton and nitrous oxide mole fractions to prevent gas-specific measurement artefacts. The resulting synthetic CH4-in-air standards are referred to as JRAS-M16 (Jena Reference Air Set – Methane 2016) and will be available to the atmospheric monitoring community. JRAS-M16 may be used as unifying isotope scale anchor for isotope ratio measurements in atmospheric methane, so that data sets can be merged into a consistent global data frame.
Distribution of Arctic and Pacific copepods and their habitat in the
northern Bering and Chukchi seas
Authors: Sasaki Hiroko , Matsuno Kohei , Fujiwara Amane , Onuka Misaki , Yamaguchi Atsushi , Ueno Hiromichi , Watanuki Yutaka , Kikuchi Takashi
Published: August 2016

Abstract. The advection of warm Pacific water and the reduction in sea ice in the western Arctic Ocean may influence the abundance and distribution of copepods, a key component of food webs. To quantify the factors affecting the abundance of copepods in the northern Bering and Chukchi seas, we constructed habitat models explaining the spatial patterns of large and small Arctic and Pacific copepods separately. Copepods were sampled using NORPAC (North Pacific Standard) nets. The structures of water masses indexed by principle component analysis scores, satellite-derived timing of sea ice retreat, bottom depth and chlorophyll a concentration were integrated into generalized additive models as explanatory variables. The adequate models for all copepods exhibited clear continuous relationships between the abundance of copepods and the indexed water masses. Large Arctic copepods were abundant at stations where the bottom layer was saline; however they were scarce at stations where warm fresh water formed the upper layer. Small Arctic copepods were abundant at stations where the upper layer was warm and saline and the bottom layer was cold and highly saline. In contrast, Pacific copepods were abundant at stations where the Pacific-origin water mass was predominant (i.e. a warm, saline upper layer and saline and a highly saline bottom layer). All copepod groups showed a positive relationship with early sea ice retreat. Early sea ice retreat has been reported to initiate spring blooms in open water, allowing copepods to utilize more food while maintaining their high activity in warm water without sea ice and cold water. This finding indicates that early sea ice retreat has positive effects on the abundance of all copepod groups in the northern Bering and Chukchi seas, suggesting a change from a pelagic–benthic-type ecosystem to a pelagic–pelagic type.