bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Beam Welding of TZM Sheets
Authors: Stütz Markus , Oliveira Diogo , Rüttinger Matthias , Reheis Nikolaus , Kestler Heinrich , Enzinger Norbert
Published: November 2016

In the scope of this work, 2 mm thick TZM sheet metal is butt welded by electron beam welding (EBW) without filler material and a systematic investigation of the most relevant welding parameters to improve the weld quality is conducted. With the aid of design of experiment (DoE), it is shown that with careful selection of the welding parameters it is possible to considerably reduce the size of the fusion zone and the heat affected zone and the grain size of both. Furthermore, the influence of the parameters on the quality of the weld and the characterizing values ultimate tensile strength and hardness of fusion zone is presented. It is concluded, which parameters influence the quality of the weld and suppress pores and cracks.
Systematic Investigation of the Temperature Field in Atmospheric Plasma Processing (APP)
Authors: Stummer M. , Stögmüller P. , Eichinger T. , Enzinger Norbert
Published: November 2016

The application of functional layers has increased constantly over the last decades [1]. Coating processes like plasma spraying allow efficient processing of metal or oxide particles, and have already found their application in various sectors of industries. Ultra fine cleaning, surface activation or surface modification with the plasma arc are currently also under investigation. In the scope of this work the influence of four different main parameters - current, working distance, feed speed and gas flow - on the arc temperature field was investigated. Due to the complex and different interactions of these parameters on the temperature field, the temperature distribution in steel and aluminium sheets was systematically examined. Furthermore, the relationship between the measured surface temperatures and the wettability of the substrates is being discussed.
To generate the required data, two different experimental setups were used. First, the spatial heat distribution of the plasma arc was measured with a special arrangement of thermocouples. Second, the temperature fields during the plasma surface treatment of DC01 and Al 6082 substrates was measured. In addition to measurements with NiCr-Ni thermocouples an investigation with an IR-Camera was performed. After the plasma surface treatment, the resulting wettability was determined by contact angle measurement.
The obtained results and especially the measured temperature fields will be used in a next step to validate numerical simulations with SYSWELD and ANSYS CFX, which will be used for process optimization.
Effect of the Interfacial Thermal Resistance on Effective Thermal Conductivity of Al/SiC Particle-Dispersed Composites
Authors: Sugio Kenjiro , Yamada Rio , Choi Yong Bum , Sasaki Gen
Published: November 2016

Steady state thermal conductivity measuring device was designed to measure the effective thermal conductivity of composites. Computer simulations of thermal conduction revealed that the designed device over estimates the effective thermal conductivity, and the correction coefficient was suggested. With this designed device, the effective thermal conductivities of Al/SiC particle-dispersed composites were measured by changing the size of SiC particles from 0.3 μm to 3 μm. The critical element size which could determine the optimal size of reinforcements have been suggested, and validity of the critical element size for Al/SiC composites was confirmed. The thermal conductivity of the composites including small SiC particles was degraded by the interfacial thermal resistance between the matrix and the reinforcement. On the other hand, the thermal conductivity of the composites including large SiC particles was not affected by the interfacial thermal resistance. These results suggest that consideration of the critical element size is valid.
Progress in the Understanding of the Microstructure Evolution of Direct Laser Fabricated TiAl
Authors: Thomas Marc
Published: November 2016

With the introduction of TiAl in aircraft jet engines, there is an increasing demand for the evaluation of novel processing routes for gamma titanium aluminides such as additive manufacturing (AM). A Ti-47Al-2Cr-2Nb powder material has been used as feedstock for laser fabrication of 3D samples by means of “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD). A number of processing parameters including laser power, laser scan rate, powder feed rate, have been varied to evaluate their effects on the material soundness. Optimised conditions can significantly reduce the crack sensitivity for this relatively low ductility material. In particular, crack-free experimental conditions have been identified by using additional heating strategies, thus limiting built-up residual stresses during fast cooling. The different samples have been examined using optical and scanning electron microscopy in the as-built condition. The non-equilibrium cooling conditions generate ultra-fine and metastable structures exhibiting high microhardness values. A range of post-heat treatments have been performed to relieve the residual stresses and to tailor more uniform microstructures. Conventional heat treatments in the α+γ two-phase domain or in the α single phase domain have been successfully used to fully restore homogeneous microstructures either duplex or fully lamellar. A comparison is made with microstructures of both laser treated materials and of conventionally processed materials.
Effect of SPD Processing Technique on Grain Refinement and Properties of an Austenitic Stainless Steel
Authors: Tikhonova Marina , Shakhova Iaroslava , Kaibyshev Rustam , Belyakov Andrey
Published: November 2016

The formation of nanocrystalline structures and mechanical properties were studied in a nitrogen-bearing 304-type stainless steel subjected to severe plastic deformation (SPD). The steel samples were processed at ambient temperature using three different methods, i.e., caliber rolling, multidirectional forging and high pressure torsion. All these techniques resulted in pronounced grain refinement. The microstructures consisting of austenite/ferrite crystallites with transverse dimensions of 50 and 30 nm evolved in the rolled and forged samples, respectively. The austenite fractions comprised approximately 0.4. In contrast, the microstructure consisted mainly of austenite with an average grain size of about 25 nm evolved after high pressure torsion. All samples of the stainless steel subjected to severe plastic deformation demonstrated significant strengthening. The ultimate tensile strengths of 2065 MPa and 1950 MPa, were obtained after rolling and high pressure torsion, respectively. The ultimate tensile strength of samples subjected to multidirectional forging was 1540 MPa.
Fabrication of High Porosity Mullite Foams and their Thermal Properties
Authors: Shimizu Toru , Matsuzakaki Kunio
Published: November 2016

Already, we developed a high porosity alumina foam. However, alumina has high thermal conductivity about 36W/mK at room temperature, and it need to achieve to high porosity to decrease thermal conductivity to for application of refractory bricks. Therefore, high porosity mullite refractory brick is developed using GS (Gelation of Slurry) method that is already developed for production of high porosity metal foam. Appling this method to production of mullite foams, the ceramics foams from 93 to 97% porosity can be produced. Also, their thermal conductivities are proportional to densities and obey to Ashby-Glicksman model. Its thermal conductivity is about 0.07W/mK when density is 0.1 g/cm3. The high porosity mullite foams achieved enough thermal insulating properties for refractory brick.
Nonlinear Optimization Methods for the Determination of Heat Source Model Parameters
Authors: Hartel Udo , Ilin Alexander , Sonntag Steffen , Michailov Vesselin
Published: November 2016

In this paper the technique of parameter identification is investigated to reconstruct the 3D transient temperature field for the simulation of laser beam welding. The reconstruction bases on volume heat source models and makes use of experimental data. The parameter identification leads to an inverse heat conduction problem which cannot be solved exactly but in terms of an optimal alignment of the simulation and experimental data. To solve the inverse problem, methods of nonlinear optimization are applied to minimize a problem dependent objective function.In particular the objective function is generated based on the Response Surface Model (RSM) technique. Sampling points on the RSM are determined by means of Finite-Element-Analysis (FEA). The scope of this research paper is the evaluation and comparison of gradient based and stochastic optimization algorithms. The proposed parameter identification makes it possible to determine the heat source model parameters in an automated way. The methodology is applied on welds of dissimilar material joints.
High-Temperature Mechanical Properties and Constitutive Modelling of Ti6Al4V Sheets
Authors: Valoppi Beatrice , Bruschi Stefania , Ghiotti Andrea
Published: November 2016

In this paper, tensile tests were performed at elevated temperature and strain rate in order to investigate the plastic flow behavior, anisotropic characteristics and microstructural evolution of Ti6Al4V sheets under testing conditions similar to the ones experienced during hot stamping operations. It is shown that the Ti6Al4V anisotropic characteristics under the investigated forming conditions, different from the ones of the superplastic regime, are influenced by the variation of the material texture as a function of the testing temperature. The Ti6Al4V flow stress behavior was analyzed as a function of the deformation temperature and strain rate. Afterwards, the Arrhenius constitutive model was proposed to predict the flow behavior of Ti6Al4V sheets at elevated temperature and strain rate. The statistical analysis of its predictive capabilities suggests that the Arrhenius model guarantees a good accuracy in reproducing the flow behavior of Ti6Al4V sheets.
Innovative Experimental Approaches and Physical Measurement Methods for Fatigue Monitoring and Life Assessment
Authors: Beck Tilmann , Klein Marcus , Smaga Marek , Balle Frank , Eifler Dietmar
Published: November 2016

The present contribution gives an overview on innovative methods to characterize cyclic deformation and lifetime behavior of metallic materials and hybrid joints based on high precision measurement of electrical resistance, temperature and magnetic properties during fatigue testing. General aim is to minimize the number of fatigue tests for reliable S-N curve calculation. Moreover, instrumented cyclic hardness tests allow short-time assessment of cyclic hardening in case of limited availability of test material. The methods are applied to a wide range of materials, from carbon steels, over cast iron and metastable austenitic steels to ultrasonically welded Al-alloy/polymer matrix composites.
Effects of Microalloy Additions and Thermomechanical Processing on Austenite Grain Size Control in Induction-Hardenable Medium Carbon Steel Bar Rolling
Authors: Whitley B.M. , Speer John G. , Cryderman R.L. , Goldstein R.C. , Findley K.O. , Matlock David K.
Published: November 2016

Three AISI 1045 steels: a base steel, one modified with vanadium (V), and one modified with V and niobium (Nb) were studied to evaluate microstructural conditioning prior to induction hardening. Simulated bar rolling histories were evaluated using fixed-end hot torsion tests with a Gleeble® 3500. The effects of chemical composition and thermomechanical treatment on final microstructures were examined through analysis of laboratory simulations of steel bar rolling and induction hardening processes in order to provide additional insights into the morphological evolution of austenite of microalloyed steels. Analysis of prior austenite grain size (PAGS) is complemented with analysis of austenite recrystallization and pancaking during rolling. The potential for utilizing TMP, in conjunction with microalloy additions, to enhance bar steel microstructures and subsequent performance is assessed by evaluating the induction hardening response of each steel systematically processed with different preconditioning treatments.
Influence of NbC-Precipitation on Hot Ductility in Microalloyed Steel - TEM Study and Thermokinetic Modeling
Authors: Wojcik Tomasz , Kozeschnik Ernst
Published: November 2016

One of the main challenges during continuous casting of microalloyed steel is to avoid the formation of transverse surface cracks on the steel slabs. These cracks occur due to severe mechanical and thermal stresses in the strand during the straightening operation. The reason for this phenomenon is a ductility loss of austenite in a typical temperature range of 700°C - 1100°C. One of the main mechanisms reducing the ductility is the precipitation of carbides and nitrides. In this work, we correlate ductility loss and precipitation state accompanying two model cooling strategies in a microalloyed steel grade. Continuously cooled samples show a minimum of ductility at temperatures around 750°C. With increasing temperature, deformability recovers again to reach full ductility again at 950°C. In contrast, samples treated with a fast intermediate cooling and reheating show constant low ductility in this entire temperature range. A transmission electron microscopy (TEM) investigation shows nanometer-sized NbC precipitates in the low ductility states. In contrast, in the samples with high ductility, larger NbC precipitates with lower number densities are observed. The experimental results show a good accordance with corresponding precipitation kinetics simulations carried out with the MatCalc software package.
Defects and Charging Processes in Li-Ion Battery Cathodes Studied by Operando Magnetometry and Positron Annihilation
Authors: Würschum Roland , Topolovec Stefan , Klinser Gregor , Sprengel Wolfgang , Kren Harald , Koller Stefan , Krenn Heinz , Hugenschmidt Christoph , Reiner Markus , Gigl Thomas , Berkemeier Frank , Fiedler Martin
Published: November 2016

A brief report is given on recent studies of the atomistic processes during charging of battery cathode material LixCoO2 by means of magnetometry and positron annihilation. A set-up for operando magnetometry is implemented which, for the first time, allowed to continuously monitor the distinct variation of the magnetic susceptibility χ of LixCoO2 which occurs during consecutive charging and discharging cycles. The variation of χ with Li+ content in the concentration range 1>x≥0.77 arises from a variation of the electronic density of states and from electronic correlation effects. The χ (x)-behaviour for x<0.77 shows that oxygen is involved in the charging process. Positron annihilation reveals vacancy-type defects on the Li-sublattice, the size of which increases with Li-extraction. Indication for Li-reordering at the reversibility limit of Li extraction is found which correlates with χ (x)-variations in this concentration regime. First measurements on LixCoO2 thin-films performed at the positron beam line NEPOMUC of FRM II at the Heinz Maier-Leibnitz neutron source will be presented.
Effect of Continuous Annealing Temperature on Microstructure and Mechanical Properties of a High Strength Cold-Rolled DP980 Steel
Authors: Zhou Kai , Zou Ying , Xu Yun Bo , Hu Zhi Ping , Tan Xiao Dong , Yang Xiao Long , Yu Yong Mei , Zhan Hua
Published: November 2016

Continuous annealing processes were applied to a 980MPa cold-rolled dual phase steel (Fe-0.11C-2.5Mn-0.5Si-0.4Cr) and the effect of continuous annealing temperature on microstructure and mechanical properties was investigated. The microstructures were observed and analyzed by optical microscopy (OM), scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM). The mechanical properties were measured by uniaxial tensile tests. The results revealed that the steel is composed of a certain percentage of ferrite, martensite and perhaps a small amount of retained austenite as well. As the annealing temperature increased, the volume fraction of martensite reached to 67% from 48% and the morphology translated to lath-like from M/A island. As a consequence, the ultimate tensile strength (UTS) and yield strength had a moderate increase from 1070 to 1110 MPa and 580 to 640 MPa, respectively. Meanwhile, the fracture elongation rose to the maximum 12.6% firstly and then decreased to about 9.0%. The optimizing mechanical properties with UTS up to 1090 MPa, yield ratio about 0.54 and fracture elongation about 13% could be obtained at the annealing temperature of 790°C for 120s.
Crystallographic Features of Electronic States in the Highly-Correlated Electronic System Sr1-xSmxMnO3 around x = 0.50
Authors: Yamagata Misato , Inoue Yasuhide , Koyama Yasumasa
Published: November 2016

The highly-correlated electron system Sr1-xSmxMnO3 (SSMO) with the simple-perovskite structure has been found to exhibit fascinating electronic states accompanying antiferromagnetic and ferromagnetic orderings. It was, in particular, reported that the electronic state for 0.46 ≤ x ≤ 0.54 was characterized by the coexistence state consisting of the A-type antiferromagnetic and ferromagnetic states. However, the features of the coexistence state in this Sm-content range have not been understood yet. We have thus investigated the crystallographic features of prepared SSMO samples with 0.46 ≤ x ≤ 0.55, mainly by transmission electron microscopy. As a result, all prepared SSMO samples were first confirmed to have the orthorhombic-Pnma structure at 300 K. When the temperature was lowered from 300 K, in the case of x=0.47, the disordered-Pnma state was found to be transformed into an orbital-modulated (OM) state accompanying an incommensurate modulation. The notable feature of the OM state is that the state becomes unstable with increasing Sm contents at 100 K. In other words, the OM state was never changed into the CE-type state with the orbital and charge modulations. In addition, no orbital-ordered state for the A-type antiferromagnetic ordering was also found for 0.46 ≤ x ≤ 0.55.
Crystal Structure, Microstructure and Martensitic Transformation Path in Ni-Mn-In Alloys
Authors: Yan Hai Le , Zhang Yu Dong , Yang Bo , Esling Claude , Zhao Xiang , Zuo Liang
Published: November 2016

In the present work, the crystal structure, microstructure and martensitic transformation path in Ni-Mn-In alloys were systematically studied. Results show that the austenite has a highly ordered cubic L21 structure. The martensite phase possesses a 6M incommensurate monoclinic modulated structure. The microstructure of martensite is in plate shape and self-organized in colonies. The maximum of 6 distinct martensite colonies and 24 kinds of variants in one parent grain are observed. Both of K-S and Pitsch orientation relations are found to be appropriate to describe the lattice correspondence between the parent and product phase. However, the transformation path related to Pitsch relation should be the real one that governs the transformation process in Ni-Mn-In alloys. With the determined martensitic transformation path, the formation mechanism of the microstructure of martensite phase is revealed. The 6 distinct martensite colonies are respectively generated by the six (110) planes of the cubic austenite phase during martensitic transformation. Each (110) plane transforms into four twin-related variants by changing the directions of the transformation plane and direction.
Mg-Zn-Y Alloys with Long-Period Stacking Ordered Phases: Deformation, Creep, Solute Segregation and Strengthening Mechanisms at Elevated Temperatures
Authors: Yang Zhi Qing , Hu Wei Wei , Ye Heng Qiang
Published: November 2016

Mg-Zn-Y alloys with long-period stacking ordered (LPSO) phases have superior strength at elevated temperatures. We studied plastic deformation and creep behavior of a Mg97Zn1Y2 (at.%) alloy. Deformation kinking of the LPSO phase plays an important role in strengthening the alloy during compression at elevated temperatures. Growth stacking faults with Zn/Y segregation can act as obstacles to non-basal slip and deformation twinning in Mg matrix. The tensile creep strain was only about 0.01% under a tensile stress of 70MPa for 100h at 200 °C, demonstrating excellent creep resistance of this alloy. Generation and motion of basal dislocations led to bending of LPSO phase during tensile creep of the Mg97Zn1Y2 (at.%) alloy. Plastic deformation in Mg grains was mostly achieved through basal slip during creep at temperatures below 200 °C, while non-basal slip through the generation and motion of “a + c” dislocations was activated with increasing the temperature to 200 °C and above. Dissociation of dislocations and Suzuki segregation on basal planes occurred widely in Mg matrix, which hindered dislocation motion and thus played an important role in preventing Mg grains from softening during deformation at elevated temperatures. In addition, Cottrell atmospheres were observed along dislocations in plastically deformed LPSO phase, impeding motion of dislocations. The superior strength and creep resistance of the Mg97Zn1Y2 (at.%) alloy at elevated temperatures are thus associated with the LPSO phase, stacking faults in Mg grains, formation of Cottrell atmospheres in LPSO and occurrence of Suzuki segregation in Mg.
Crystallographic Features of the State Appearing in the Multiferroic Material Bi1-xLaxFeO3 around x = 0.20
Authors: Yoshida Haruka , Nomoto Masashi , Inoshita Takumi , Inoue Yasuhide , Horibe Yoichi , Koyama Yasumasa
Published: November 2016

The simple-perovskite system Bi1-xLaxFeO3 (BLFO) is one of mixed-oxide systems having the multiferroic BiFeO3 as an end material, which shows the ferroelectric and antiferromagnetic orders in its ground state. Because of the paraelectric nature of LaFeO3 as another end material, the ferroelectric-to-paraelectric state change can be expected to occur in the mixed-oxide system BLFO. The interesting feature of BLFO is that there are both the PbZrO3-type and incommensurately modulated (IM) states in the intermediate La-content range between the ferroelectric-R3c and paraelectric-Pnma states. Although the detailed features of these two states have not been understood sufficiently, in this study, we focus on the IM state around x = 0.20, and have investigated the crystallographic features of prepared BLFO samples with 0.15 ≤ x ≤ 0.35, mainly by transmission electron microscopy. It was found that six kinds of superlattice reflections were, for instance, present in the reciprocal lattice of the state at 300 K for x = 0.20, in addition to fundamental reflections due to the cubic simple-perovskite structure. To understand the appearance of these superlattice reflections, we regarded the state as a modulated-structure state in this study. Concretely, the modulated structure was assumed to be characterized by the appearance of both the incommensurate wave with qI = <1/(4+δ) 1/(4+δ) 0>c and the commensurate wave with qII = <1/4 0 0>c in the normal-Imma structure. In addition, the appearance of the two modulation waves could also produce the superlattice reflections at the <1/4 1/4 1/4>c-, <1/2 0 0>c-, and <1/2 1/2 0>c-type positions in the reciprocal lattice. From the comparison with the experimental data obtained in this study, our modulated-structure model seems to be appropriate for the IM state in the vicinity of the PbZrO3-type/IM state boundary.
Comparison of Self-Annealing Behaviors in (001)- and (111)-Oriented Electrodeposited Silver Films by In Situ EBSP Analysis
Authors: Yumi Hayashi , Shohji Ikuo , Miyazawa Hiroshi
Published: November 2016

Self-annealing behaviors of the electrodeposited silver films which preferentially orient in (001) and (111) directions were investigated by in situ EBSP analysis. In the (001)-oriented film, self-annealing starts in storage for a few hours at R. T. and is almost complete after storage for 6 h at R. T. (001)- and (212)-oriented recrystallized grains mainly nucleate, and (001)-oriented grains mainly grow up. In the (111)-oriented film, self-annealing starts in storage for 15 min at R. T. and is almost complete after storage for 1 h at R. T. (111)-, (001)- and (212)-oriented recrystallized grains mainly nucleate, and (111)-oriented grains mainly grow up. The size of recrystallized grains induced in the (111)-oriented film by self-annealing is approximately half that in the (001)-oriented film although the rate of recrystallization in the (111)-oriented film is faster than that in the (001)-oriented one. The area fraction of the preferential orientation after completion of recrystallization saturates in approximately 70% and 50% in the (001)- and (111)-oriented films, respectively.
The Portevin-Le Chatelier Effect and Kinematics of Deformation Bands in an Al-Mg-Sc Alloy: Effect of Grain Size
Authors: Zhemchuzhnikova Daria , Lebyodkin Mikhail , Lebedkina Tatiana , Kaibyshev Rustam
Published: November 2016

Stress serration patterns and kinematics of deformation bands associated with the Portevin-Le Chatelier (PLC) effect were examined for an Al–6%Mg–0.35%Mn–0.2%Sc–0.08%Zr–0.07%Cr (in wt.%) alloy with two grain sizes: 22 μm and 0.7 μm. The fine-grained structure of the alloy was obtained using equal-channel angular pressing (ECAP) at 320°C up to a total strain of ~12. Tensile tests were carried out at room temperature and strain rate ranging from 10-5 s-1 to 10-2 s-1. In addition, high-frequency local extensometry technique was applied to monitor the evolution of the axial strain distribution during deformation. Depending on the strain rate, conventional A, B, C, or mixed types of serrations were observed on the stress-strain curves. These types of behavior usually correspond to different kinematics of the PLC bands, including band propagation and localization. However, the propagation regime was found to dominate in the investigated alloy in the entire strain-rate range. This unusual behavior of deformation bands and their features depending on the grain size are discussed.
Characterization of Phase Transitions Occurring in Solution Treated Ti-15Mo during Heating by Thermal Expansion and Electrical Resistance Measurements
Authors: Zháňal Pavel , Harcuba Petr , Hájek Michal , Šmilauerová Jana , Veselý Jozef , Janeček Miloš
Published: November 2016

Metastable β titanium alloy Ti-15Mo was investigated in this study. In-situ electrical resistance and thermal expansion measurements conducted on solution treated material revealed influence of ongoing phase transitions on measured properties. The monotonicity of the dependence of electrical resistance on temperature changes at 225, 365 and 560 °C The thermal expansion deviates from linearity between 305 and 580 °C.
Microstructure and Creep Properties of Silicon- and/or Germanium-Bearing Near-α Titanium Alloys
Authors: Kitashima Tomonori , Suresh K.S. , Hara T. , Yamabe-Mitarai Yoko , Toda Y.
Published: November 2016

The effects of Si and/or Ge addition on the microstructure and creep properties at 650°C and 137 MPa were investigated in near-α Ti–Al–Sn–Zr–Mo alloys. Si and/or Ge addition decreased the minimum creep strain rate owing to the solid solution of Si and Ge in the matrix and the precipitation of silicide, germanide, and their solid solutions. The decrease in the minimum creep strain rate in the alloy with 1 wt% Ge without Si was the most significant because of the formation of very fine germanide precipitates. In addition, a marked shift in the lattice parameters of the α and β phases was detected for the alloy with 4 wt% Ge. The Moiré fringe patterns at the α/β interfaces in the alloys were investigated using high-resolution transmission electron micrographs to discuss the alloying effect on the structure of the interfaces.
Near Infrared Device for Tissue Inflammation Evaluation
Authors: Staderini Enrico M. , Junior Branco David , Mugnaini Stefano , Gentili Sandro
Published: November 2016

A photoplethysmographic (PPG) near infrared (850nm) system has been developed for the non-invasive assessment of superficial tissues’ (skin) swelling and redness. The PPG signal is treated to avoid ambient light and to extract the DC (direct current) and AC (alternate current) components. These components are then subtracted from the same components acquired on a reference site on the same subject. The resulting measures are used in a model able to classify different states of inflammation of the tissues. Numerical results permit to follow the inflammation state and to evaluate possible medical and physiotherapy interventions. To avoid artefacts due to compression of the skin by the instrument, a pressure sensor has been also embedded on the optical sensing head of the system, so that the measures are considered as valid only if they are taken within the same range of applied pressure on the skin. This is important to get comparable PPG measures. Heart rate and hemoglobin oxygen saturation measures are a by-product out of the system and they can be exploited for other purposes or they can be taken into account for a better evaluation of the inflammation state. Although the system is still a research prototype and no real model is available about how inflammation affects the optical properties of the skin, the very first qualitative results show a strong sensibility of the system to skin alterations due to acute inflammation.
Complex Nano-Scale Structures for Unprecedented Properties in Steels
Authors: Caballero Francisca G. , Poplawsky Jonathan D. , Yen Hung Wei , Rementeria Rosalia , Morales-Rivas Lucia , Yang Jer Ren , Garcia-Mateo Carlos
Published: November 2016

Processing bulk nanoscrystalline materials for structural applications still poses a significant challenge, particularly in achieving an industrially viable process. In this context, recent work has proved that complex nanoscale steel structures can be formed by solid reaction at low temperatures. These nanocrystalline bainitic steels present the highest strength ever recorded, unprecedented ductility, fatigue on par with commercial bearing steels and exceptional rolling-sliding wear performances. A description of the characteristics and significance of these remarkable structures in the context of the atomic mechanism of transformation is provided.
Recrystallization Twinning in Stable Single Crystals of Cu-2%Al and Al-1%Mn Alloys
Authors: Paul Henryk , Miszczyk Magdalena M. , Driver Julian H. , Drzymała Piotr
Published: November 2016

The crystallographic aspects of recrystallization twinning have been characterized in {110}<001> and {110}<112>-oriented single crystals of Cu-2%wt.Al and Al-1%wt.Mn alloys. The samples were plane strain compressed to logarithmic strain of 0.52 and then lightly annealed. SEM/EBSD local orientation measurements on partly recrystallized samples demonstrate the appearance of a specific number of new orientation groups of recrystallized grains, which resulted from rotation of the deformed crystal orientations around axes lying near (but rarely at) selected the <111> directions. Then the primary nucleus can transform through the formation of a first generation recrystallization twin. The most frequent situation was that the twinning plane normal was situated near the rotation axis, around which the crystal lattice of the ‘primary nuclei’ rotates. Based on new algorithm to identify coherent and incoherent twin boundaries the influence of free surface on the intensity of annealing twinning was analyzed.
Revealing the Individual Hardening Effects of Twins, Dislocations, Grain Boundaries and Solid Solution in a Twinning-Induced Plasticity Steel
Authors: Liang Zhi Yuan , Liu Ying Zhuang , Wang Xu , Liu Ren Dong , Huang Ming Xin
Published: November 2016

Manganese-rich austenitic twinning-induced plasticity (TWIP) steels with high strength and superior ductility have received much attention in the past two decades. Tremendous efforts have been made to explore their unusual hardening behaviour which includes contributions from twins, dislocations, grain boundaries and solid solution. Nevertheless, the individual hardening effects of twins, dislocations, grain boundaries and solid solution on the high strength of TWIP steels are still unclear. In the present work, the flow stress of a TWIP steel was experimentally decomposed into the respective contributions of twins, dislocations, grain boundaries and solid solution. For the forest hardening, synchrotron X-ray diffraction experiments with line profile analysis were carried out to measure the dislocation density. It is found that the yield stress of the present TWIP steel is controlled by solid solution and grain boundary hardening, which contribute to 238.3 and 238.5 MPa, respectively. After yielding, the work-hardening rate is dominated by dislocation multiplication which accounts for up to 922 MPa at a true strain of 0.4, equal to about 60% of the flow stress. In comparison, twins contribute to only 118 MPa at the same true strain, equal to about 8% of the flow stress. In other words, twins have minor effect on the flow stress, in contrast to the current understandings in the literature.
Dissimilar Metal Joining of A5052 Aluminum Alloy and AZ31 Magnesium Alloy Using Laser Brazing
Authors: Ogura Tomo , Netsu Syunsuke , Yokochi Tetsuya , Saida Kazuyoshi
Published: November 2016

The microstructure and mechanical properties of a joint produced by laser brazing between A5052 and AZ31 with AZ61, AZ91 and AZ125 filler metal was investigated. The effects of filler metals on joint characteristics are also discussed. Measurement of microstructural factors in the laser brazed joint revealed that increasing the laser power results in a decrease in the weld toe angle and an increase in the bead width, which indicates superior wettability. A high strength laser brazed joint can be achieved through the combination of good wettability and a thin intermetallic layer produced by a laser power of 590 W in a brazed joint with AZ125 filler metal Any further increase in power, however, results in a rapid increase in the thickness of the intermetallic compound (IMC) reaction layer. The superiority of the brazed joint with AZ125 filler metal is due to its lower melting point than that of AZ61 and AZ91 filler metal.
Phase Constitution and Martensitic Transformation Behavior of Au-51Ti-18Co Biomedical Shape Memory Alloy Heat-Treated at 1173K to 1373K
Authors: Buasri Taywin , Shim Hyun Bo , Tahara Masaki , Inamura Tomonari , Goto Kenji , Kanetaka Hiroyasu , Yamabe-Mitarai Yoko , Hosoda Hideki
Published: November 2016

Phase constitution and martensitic transformation behavior were investigated for a Au–51Ti–18Co alloy heat-treated at 1173 K to 1373 K for 3.6 ks. The Au–51Ti–18Co alloy was fabricated by Ar arc-melting technique and subsequently by hot-forging at 1423 K for 10.8 ks. X-ray diffraction analysis revealed that B2 parent phase, B19 martensite phase and AuTi3 simultaneously appeared regardless of the heat-treatment temperatures. By increasing the heat-treatment temperature, the volume fraction of AuTi3 was slightly reduced. Besides, the lattice transformation strain which was calculated from the precisely-determined lattice parameters was evaluated to be 7 % in the Au–51Ti–18Co alloy in all the heat-treated conditions. This value is comparable to that of NiTi practical alloys. From differential scanning calorimetry (DSC) analysis, reverse martensitic transformation temperature was slightly increased with the heat-treatment temperature. From the lattice transformation strain point of views, the Au–51Ti–18Co has a large potential for novel biomedical shape memory alloy.
Development of Al-Mg-Si-(Cu) Alloys for Automotive Body Panels and the Related Ageing Behaviours
Authors: Zhong Hao , Liao Bin , Wu Xiao Dong , Cao Ling Fei , Rometsch Paul A.
Published: November 2016

In this work, Al-Mg-Si-Cu alloys for automotive body panels were designed and the related ageing behaviours were discussed in detail to help understand natural ageing and pre-ageing, as well as their influence on the subsequent paint-bake response. The clustering behavior of these Al-Mg-Si-Cu alloys in different ageing conditions was investigated by hardness / yield strength and electrical conductivity testing. The microstructure was investigated by using Electron Backscattered Diffraction (EBSD) technique, along with Scanning Electron Microscopy with Backscattered Electron Detector (BSE). The results show that the paint bake response is strongly influenced by the pre-ageing and natural ageing conditions. Both alloys show serrated yielding in a short natural ageing condition. Immediate high-temperature pre-ageing treatments were found to give a promising hardening response during the subsequent artificial ageing/ paint baking at 170oC.
Gold Recovery from PCBs with Thiosulfate as Complexing Agent
Authors: Cerchier Pietrogiovanni , Dabalà Manuele , Brunelli Katya
Published: November 2016

Waste of electrical and electronic equipment (WEEE) is the fastest growing advanced type of solid waste streams in the urban environment worldwide and contains interesting amounts of precious metals. Hydrometallurgical technique is fast emerging as preferred process for the recovery of a variety of metals due to its lower energy consume and lower smelter emissions than conventional pyrometallurgical processes. In this work, a hydrometallurgical process for the recovery of gold and silver from electronic scraps was studied. In place of cyanide, thiosulfate was chosen as complexing agent for gold. Thiosulfate leaching can be considered a non-toxic process and the gold dissolution rates can be faster than conventional cyanidation. The electronic scraps, obtained from “end of life” mobile phones, were crushed and pre-treated with nitric acid before the leaching. Different parameters were studied: concentration of thiosulfate, temperature and reaction time. Moreover, the use of ultrasound to assist the hydrometallurgical gold extraction was investigated, as its application in ores leaching shows a greater metals release in shorter time and the advantage of working at lower concentration of reagents and at lower temperature. In this work, the use of ultrasound allowed a higher recovery of the precious metals than conventional leaching in all the conditions studied (different concentrations of reagents, temperature and reaction time). Moreover, the studied process allowed also the recovery of the other metals present in the waste (Cu, Sn and Ag).
Fatigue Life Extension by Crack Repair Using Double Stop-Hole Technique
Authors: Ayatollahi Majid Reza , Razavi Nima , Sommitsch Christof , Moser Christian
Published: November 2016

Drilling holes in the vicinity of the crack tip turns the crack into a notch and reduces the crack tip stress intensity factor. In this paper, a new idea is used in which instead of a single hole, two symmetric and interconnected holes are drilled at the crack tip. The main concept of double stop-hole method is to reduce the stress concentration at the edge of stop-holes in the cracked structural elements. The double stop drill hole method can be used to increase the fatigue life of the cracked components. The fatigue crack growth retardation is examined using an experimental investigation coupled with a stress analysis on the efficiency of proposed double stop-holes. The distance between the hole centers is considered as the main parameter affecting the efficiency of this method. The results show that the fatigue life extension caused by the double stop-hole method is significantly more than the conventional single stop-hole method.
Effects of Laser Power on Track Profile and Structure Formation during Selective Laser Melting of CoCrMo Alloy
Authors: Chen Zhan W. , Darvish Kourosh , Pasang Timotous
Published: November 2016

A strong research effort has continued to determine how selective laser melting (SLM) process parameters relate to the amount of defects present in SLM products. However, how these parameters affect the track profiles which should geometrically affect the amount of lack of fusion (LOF) during SLM has not been studied. This study is needed as severe LOF should be a severe quality and property issue. In this work, how laser power (P) and thus energy, as other build rate related parameters are kept unchanged, affects the size of SLM tracks and the formation of LOF during SLM of CoCrMo alloy has been studied. Through examining the track profiles, track sizes have been geometrically demonstrated to insufficiently overlay and overlap for LOF free when the recommended condition (P = 180W) was used. A further contributing factor for LOF is the irregularity of track shape. Increasing P increased the sizes and improved the stability of the melt and the shape regularity of the tracks, reducing the amount of LOF. It will be shown that there is a rapid decay in the amount of LOF as P increases from 180 W, predominantly as the result of geometrical effect of the track profile on track coverage.
The Role of Microstructure in Creep Strength of 9-12%Cr Steels
Authors: Kaibyshev Rustam , Mishnev Roman , Fedoseeva Alexandra , Dudova Nadezhda
Published: November 2016

Tempered martensite lath structure (TMLS) plays a vital role in creep resistance of high chromium martensitic steels. Under creep conditions the TMLS could be stabilized by three agents: (i) a dispersion of boundary M23C6 carbides and Laves phase; (ii) a dispersion of M(C,N) carbonitrides, which are homogeneously distributed within ferritic matrix; (iii) substitutional alloying element within ferritic matrix. The boundary particles exert a large Zener drag force which effectively hinders migration of low-and high-angle boundaries. A dispersion of M(C,N) carbonitrides both within ferritic matrix and lath boundaries provides the pinning of mobile dislocations. This process is responsible for reliving long-range elastic stress field originated from lath boundaries. In addition, M(C,N) carbonitrides provide high threshold stress. Substitutional elements as W and Mo effectively slowing down diffusion in ferritic matrix retard climb of lattice dislocation that also prevents the aforementioned knitting reaction. The suppression of knitting reaction between lattice dislocation and low-angle boundaries prevents their transformation to subboundaries by concurrent operation of all three agent types.
Depletion of W and Mo from solid solution leads to the occurrence of static recovery and precipitation of Laves phase at boundaries under long-term aging. This process is responsible for creep strength breakdown. The strain-induced formation of Z-phase at the expense of V-rich M(C,N) carbonitrides highly facilitates this process. However, slow strain-induced coarsening of M23C6 carbides and M(C,N) carbonitrides provides the suppression of the knitting reaction between mobile lattice dislocations and intrinsic dislocations of lath boundaries and replacement of TMLS by subgrain structure. Ostwald ripening of boundary M23C6 carbides and Laves phase leads to rapid creep rate increase with strain in tertiary creep and premature rupture owing to the formation of subgrain structure replaced TMLS and further subgrain growth.
Comparative Study of Optimization in Pultrusion with Pre-Heating and Die-Cooler Temperature for Improved Cure
Authors: Costa Rita de Cassia Dias , de Sousa Santos Lizandro , Schledjewski Ralf
Published: November 2016

Pultrusion is a composite manufacturing technique for processing continuous composite profiles with a constant cross section. In such system, energy and mass balances are used to model the thermal and kinetic behavior of the material during processing. This work aims to compare the results obtained in the recent literature, regarding thermal optimization of pultrusion. In the present analysis, an alternative thermal configuration has been suggested, with the objective of maximizing the mean degree of cure. A general-purpose FE software, ANSYS-CFX®, has been used to perform a three-dimensional (3D) conductive heat transfer analysis. Several case studies were conducted where the degree of cure was analyzed for varying heating scenarios. Results have shown that it is possible to get a higher cure in less process time if the die is isolated from the environment.
Relationship between the Yield Strength-Fracture Toughness Balance and the Multiscale Microstructure of a Maraging Stainless Steel for Aircraft Applications
Authors: Le Nué Charline , Cloué Jean Marc , Mathon Marie Hélène , Puech Sylvain , Béchet Denis , Delagnes Denis
Published: November 2016

Two grades of Fe-Cr-Ni-Al-Ti-Mo maraging steels, with a different titanium content, were investigated. Particular attention was given to the correlation between the precipitated phases and the yield strength. Synchrotron X-ray diffraction, small-angle neutron scattering and atom probe experiments were performed to determine the crystal structure, shape, size distribution, chemical composition, particle number density and volume fraction of precipitates. Both alloys show a strong increase in strength after an aging treatment, which is attributed to the co-precipitation of two different intermetallic phases. Strengthening by a single precipitation of β-Ni (Al,Ti) particles induces a saturation of yield strength around 1600 MPa above a volume fraction of 6 %. The improvement of yield strength is then obtained by introducing a nanoscale co-precipitation of η-Ni3(Ti,Al) phase.
Micro-Mechanical Responses of Ultrafine-Grained Materials Processed through High-Pressure Torsion
Authors: Kawasaki Megumi , Jang Jae Il , Ahn Byung Min , Langdon Terence G.
Published: November 2016

The processing of metals through the application of high-pressure torsion (HPT) provides the potential for achieving exceptional grain refinement in bulk metal solids. These ultrafine grains in the bulk metals usually show superior mechanical and physical properties. Especially, the development of micro-mechanical behavior is observed after significant changes in microstructure through processing and it is of great importance for obtaining practical future applications of these ultrafine-grained metals. Accordingly, this presentation demonstrates the evolution of small-scale deformation behavior through nanoindentation experiments after HPT on various metallic alloys including a ZK60 magnesium alloy, a Zn-22% Al eutectoid alloy and a high entropy alloy. Special emphasis is placed on demonstrating the essential microstructural changes of these materials with increased straining by HPT and the evolution of the micro-mechanical responses in these materials by measuring the strain rate sensitivity.
Mechanical Behaviour of Materials during Creep with Changing Loads
Authors: Angella Giuliano , Donnini Riccardo , Ripamonti Dario , Maldini Maurizio
Published: November 2016

A component in service experiences stress conditions that change continuously with time. Since service conditions are usually difficult and expensive to reproduce in laboratory, the creep behaviour of alloys in service has to be extrapolated from a limited number of creep tests at constant loads and temperatures. Empirical rules have been proposed to forecast the effects of variable load and temperature both on the time to rupture, as the life fraction rule (LFR), and on the accumulation of creep strain with time, as the strain hardening rule (SHR). Two directionally solidified (DS) nickel based superalloys have been investigated with creep tests at constant and variable loads and constant temperature. Nickel based superalloys, for the typical stresses experienced in service, are often characterised by a small negligible primary, a minimum of strain rate with no secondary state, and a dominant accelerating creep caused by dislocation multiplication. The damage mechanisms causing the final rupture appear only in the very last percentage of life. In the present work, simulation results are reported to show that the physical-sounded model used to describe the accelerating creep due to dislocation multiplication can be employed to better predict the times to rupture and the creep curves of the two DS nickel based super-alloys with step-like variable stress than the empirical LF and SH rules.