Single Roll Research Articles

Attempt to develop Ti-based amorphous alloys for biomaterials

The purpose of the present study is to develop a biocompatible Ti-based amorphous alloy. We examined mechanical and chemical properties of newly developed Ti-based amorphous alloys in comparison with pure Ti metal and Ti–6Al–4V alloy which have been used at present for biomaterials. Ti-based multi-component alloys do not contain Al and Ni elements which are the origin for cytotoxicity and neurotoxicity. The amorphous alloy ribbons were prepared by the single roll melt-spinning method. The Ti-based amorphous ribbons exhibited good bend ductility, higher strength and lower Young's modulus than pure Ti and Ti–6Al–4V alloy. In addition, Ti-based amorphous alloys had an excellent potentiality of corrosion resistance that was passivated in wide passive range and at the lower passive current density of approximately 10 −2 A m −2 in 1 mass% lactic acid, 3 mass% NaCl and PBS(−) solutions at 310 K.

Transformation behaviour of Ti–Ni and Ti–Ni–Cu alloy ribbons with nano Ti 2Ni particles

Ti–Ni and Ti–Ni–Cu alloy ribbons have been prepared by single roll melt spinning, and then martensitic transformation behaviours were investigated by means of transmission electron microscopy, differential scanning calorimetry and X-ray diffraction. In 51Ti–49Ni(at.%) alloy ribbons, Ti 2Ni particles of a size less than 50 nm with the coherent interface with the matrix were found, while they were not found in 50Ti–50Ni alloy ribbons. In 49Ti–46Ni–5Cu and 50Ti–45Ni–5Cu alloy ribbons, Ti 2Ni particles of size less than 30 nm with coherent interface with the matrix were found. Coherent Ti 2Ni particles induced the R phase transformation in Ti–Ni alloys, and consequently transformation occurred in two-stages, i.e., B2–R–B19. Coherent Ti 2Ni particles induced the B19 martensite in a Ti–45Ni–5Cu alloy, and consequently transformation occurred in two-stages, i.e., B2–B19–B19′. The change in transformation behaviour was ascribed to strain fields developed around coherent Ti 2Ni particles.

Experimental Measurement of the Deformation in Hot Rolling of Aluminium 1% Mn: The Grid Technique

The grid technique is an experimental method for measuring the deformation in hot rolling. An AA3004 sample -fitted with an insert - was rolled in a single hot rolling pass at 400 oC. The insert was hand engraved with a 1x1 mm grid and the analysis of the image of the deformed grid enabled the calculation of the components of the deformation gradient tensor. In order to prevent relative motion between the insert and the work-piece, four steel pins were used; after the test no detachment was observed between insert and sample. The temperature was monitored during rolling using two embedded thermocouples, one close to the surface and the other on the centre-line of the slab. The commercial finite element (FE) code ABAQUS was used to build a threedimensional model of the rolling process. The recorded temperature was compared with the FE values evaluated after tuning the heat transfer coefficient. The FE model was run several times with different friction coefficients and the deformation gradient checked against the experimental measurement of the deformed grid in order to obtain the optimum friction coefficient. The experimentally determined deformation gradient and the measured temperature agreed well with the numerical values.

A Monte Carlo approach to rolling leukocyte tracking in vivo

Tracking the movement of rolling leukocytes in vivo contributes to the understanding of the mechanism of the inflammatory process and to the development of anti-inflammatory drugs. Several roadblocks exist that hinder successful automated tracking including the moving background, the severe image noise and clutter, the occlusion of the target leukocyte by other leukocytes and structures, the jitter caused by the breathing movement of the living animal, and the weak image contrast. In this paper, a Monte Carlo tracker is developed for automatically tracking a single rolling leukocyte in vivo. Based on the leukocyte movement information and the image intensity features, a specialized sample-weighting criterion is tailored to the application. In comparison with a snake-based tracker, our experiments show that, as the noise intensity level increases, the performance of the snake tracker degrades more than that of the Monte Carlo tracker. In cases, where the leukocyte is observed in contact with the vessel wall, the Monte Carlo tracker is less affected by the image clutter. From tracking within 99 intravital microscopic video sequences, the Monte Carlo tracker exhibits superior performance in the reduced localization error and the increased number of frames tracked when compared with the centroid tracker, the correlation tracker and the GVF snake tracker.

An isolated cloud band around a typhoon in the western tropical Pacific

Satellite imagery and C‐band radar on the R/V Mirai detected an isolated convective cloud band over the western tropical Pacific, and dropsondes observed the surrounding atmospheric environment. The reasonable development mechanism of this unusual cloud band is investigated using observational and numerical simulation data. Although theoretically, the surrounding atmospheric profile supported convective rolls, only a single cloud band was developed. Numerical simulations revealed a single cloud band and roll structure without condensate in the boundary layer. A westerly jet just above the cloud band influenced the environment with strong vertical shear supporting convective rolls; this was maintained by a typhoon at a distance of 1500 km away. A large‐scale convergence in the meridional wind was also accompanied with this westerly jet. This special environment made by a typhoon could develop the unusual single cloud band.

Magnetic Nanoparticles as Pinning Center in Bi-Sr-Ca-Cu-O/Ag Superconductor Tapes

This paper reports on the effectiveness of magnetic nanoparticles as pinning center in the Bi-based superconductor tapes. Nanosize γ-Fe2O3 and ultrafine Fe3O4 have been employed to enhance the transport current density of Ag-sheathed-(Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor tapes prepared by the powder-in-tube technique. The transport critical current density, Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(γ-Fe2O3)0.01, sintered at the optimum temperature of 845 oC is 6490 A/cm2 when measured at 77 K. A further single intermediate rolling step increases Jc to 9560 A/cm2. Samples without γ-Fe2O3 prepared under the same condition showed a lower Jc with a maximum of 1560 A/cm2. Similar results are also obtained for ultrafine Fe3O4. Magnetic impurities generally suppress superconductivity. However, our study shows great promise of magnetic nanorod γ-Fe2O3 and ultrafine Fe3O4 as novel pinning centers in enhancing the transport critical density of Ag sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is in line with previous calculations on frozen flux superconductor with magnetic nanoparticle as pinning centers.

Quantum corrections to slow roll inflation and new scaling of superhorizon fluctuations

Precise cosmological data from WMAP and forthcoming cosmic microwave background experiments motivate the study of the quantum corrections to the slow roll inflationary parameters. We find the quantum (loop) corrections to the equations of motion of the classical inflaton, to those for the fluctuations and to the Friedmann equation in general single field slow roll inflation. We implement a renormalized effective field theory (EFT) approach based on an expansion in ( H / M Pl ) 2 and slow roll parameters ϵ V , η V , σ V , ξ V . We find that the leading order quantum corrections to the inflaton effective potential and its equation of motion are determined by the power spectrum of scalar fluctuations. Its near scale invariance introduces a strong infrared behavior naturally regularized by the slow roll parameter Δ = η V − ϵ V = 1 2 ( n s − 1 ) + r / 8 . To leading order in the (EFT) and slow roll expansions we find V eff ( Φ 0 ) = V R ( Φ 0 ) [ 1 + Δ T 2 32 n s − 1 + 3 8 r n s − 1 + 1 4 r + higher orders ] where n s and r = Δ T 2 / Δ R 2 are the CMB observables that depend implicitly on Φ 0 and V R ( Φ 0 ) is the renormalized classical inflaton potential. This effective potential during slow roll inflation is strikingly different from the usual Minkowski space–time result. We also obtain the quantum corrections to the slow roll parameters in leading order. Superhorizon scalar field fluctuations grow for late times η → 0 − as | η | − 1 + Δ − d − where d − is a novel quantum correction to the scaling exponent related to the self-decay of superhorizon inflaton fluctuations φ → φ φ and η is the conformal time. We find to leading order − d − = Δ R 2 σ V ( η V − ϵ V ) + 6 ξ V 2 4 ( η V − ϵ V ) 2 in terms of the CMB observables. These results are generalized to the case of the inflaton interacting with a light scalar field σ and we obtain the decay rate Γ φ → σ σ . These quantum corrections arising from interactions will compete with higher order slow-roll corrections in the Gaussian approximation and must be taken into account for the precision determination of inflationary parameters extracted from CMB observations.

Fabrication and Properties of High Strength Al-8Fe-2Mo-2V-1Zr Alloy Produced by Melt Spinning Techniques

High strength Al-8Fe-2Mo-2V-1Zr (wt.%) alloys fabricated by a melt spinning and a hot extrusion process were produced to correlate the microstructure and mechanical property. Melt spun ribbon prepared by single roll melt spinner showed a cellular structure with an average size of 10nm and Al-Fe based intermetallic dispersoid of less than 10nm in particle size. The melt spun ribbon obtained was then pulverized to make a powder shape followed by hot extrusion at 648K, 673K, 723K and 773K in extrusion ratio of 5 to 1, respectively. Equiaxed grain structure containing Al-Fe based intermetallic phase was observed in all extruded specimens. According to increasing extrusion temperature, the grain size increased and particle size of intermetallic dispersoid. The lattice parameter increased from 0.4051nm to 0.4059 nm with increasing extrusion temperature from 648K to 773K, those values were larger than that obtained in pure Al (0.4049nm). Yield strength of the specimen extruded at 648K measured to 956MPa at room temperature, 501MPa at 573K and 83MPa at 773K, respectively. With increasing extrusion temperature yield strength decreased significantly at room temperature and even in the intermediate temperature range, while no noticeable difference in yield strength was observed at 773K.

Aspect-ratio dependence of heat transport by turbulent Rayleigh–Bénard convection

We have studied the heat transport by steady circulating flows in two-dimensional rectangular cells of different values of the aspect ratio Γ. The cells are heated from below and cooled on top with a fixed temperature difference. These steady circulating flows mimic the mean large-scale circulating wind observed in turbulent Rayleigh–Bénard convection. When the heat transport is dominated by that carried by the mean large-scale wind and when the mean circulating wind is a single roll, we have found the following dependence of the Nusselt number (Nu) and the Reynolds number (Re) on the Rayleigh number (Ra), the Prandtl number (Pr) and the aspect ratio Γ: Nu = B(Pr) N 0 (Γ)Ra 1/4 and Re = C(Pr) R 0 (Γ)Ra 1/2, where N 0(Γ) decreases and R 0(Γ) increases with Γ.

Martensitic Transformation Behavior and Shape Memory Properties of Ti–Ni–Pt Melt-Spun Ribbons

Martensitic transformation behavior and shape memory properties of a Ti 50 Ni 40 Pt 10 (TiNiPt) melt-spun ribbon fabricated by a single roll melt-spinning technique were characterized. The constituent phases of the as-spun ribbon were B2 (parent phase) and B 19 (martensite phase) at room temperature. The B2-B19 martensitic transformation temperatures of the as-spun ribbon were 100 K higher than those of the bulk-material with the same chemical composition. The martensitic transformation temperatures of the as-spun ribbon were decreased with increasing the temperature of the heat-treatment made after the melt-spinning. The as-spun ribbon and the heat-treated ribbons exhibited shape recovery by heating and/or pseudoelasticity. The martensitic transformation temperatures determined from the temperature dependence of the 0.2% flow stress of the pseudoelastic deformation were in good agreement with those of B2-B19 martensitic transformation determined by DSC. It was confirmed that the observed shape recovery and pseudoelasticity are shape memory effect and superelasticity due to the B2-B19 martensitic transformation. Shape memory effect and superelasticity of melt-spun TiNiPt alloy were found to appear at higher temperatures compared to those of Bulk-material with the same composition.

NUMERICAL SIMULATION OF COUPLED FLUID FLOW AND SOLIDIFICATION IN A SINGLE ROLL CASTER

A mathematical model was developed to study fluid flow and solidification in a single roll casting system. Fluid flow coupled with energy equations were solved numerically using a finite volume method. A body fitted coordinate (BFC) transformation technique was adopted to handle the irregularly shaped domain. In order to couple the continuity and momentum equations, a SIMPLEC algorithm was used. A fixed grid enthalpy method was considered to model the solidification in the system. The turbulence effect on flow field was modelled using a low Re k- model. The model developed in this work was further run under various conditions to optimize the process parameters of the process.On a développé un modèle mathématique pour étudier l’écoulement de fluide et la solidification dans un système de coulée à cylindre unique. On a résous numériquement l’écoulement de fluide couplé aux équations d’énergie en utilisant une méthode de volume fini. On a adopté une technique de transformation de coordonnée ajustée au corps (BFC) pour manier le domaine de forme irrégulière. Afin de coupler la continuité et les équations de quantité de mouvement, on a utilisé un algorithme SIMPLEC. On a considéré une méthode d’enthalpie à grille fixe pour modéliser la solidification dans le système. On a modélisé l’effet de turbulence sur le champ d’écoulement en utilisant un modèle à faible Re k-e. On a également opéré le modèle, développé dans ce travail, sous des conditions variées pour optimiser les paramètres du procédé.

Single Roll Drive Equal Channel Angular Process –a Potential Severe Plastic Deformation (SPD) Process for Industrial Application

Single roll drive equal channel angular process (SRD-ECAP) is derived from classical equal channel angular pressing (ECAP). It overcomes the drawbacks of ECAP, which is a discontinuous process and can only process short billets with invariable square or round section. SRD-ECAP, however, can process long billets continuously. In addition, it can also process sheet or strip. Another merit is that diameter or thickness of billets processed is adjustable. The structure of SRD-ECAP is quite simple and easy to be realized. In this paper, stress analysis has also been carried out. It is believed that SRD-ECAP can be a potential severe plastic deformation (SPD) process for Industrial Application.

Measurement of deformation gradients in hot rolling of AA3004

In this paper we describe an experimental technique developed to measure the deformation gradients and temperature in a single hot rolling pass of an AA3004 sample that was fitted with an insert. The insert had been previously hand engraved with a 1×1 mm grid pitch, and the analysis of the data digitally captured from the image of the deformed grid enabled the calculation of the components of the deformation gradient tensor. Four steel pins prevented relative motion between the insert and the rest of the sample. No detachment was observed between insert and sample after rolling. The temperature was measured during rolling using two embedded thermocouples, one close to the surface and the other in the centerline. The commercial finite element code ABAQUS was used to create a three-dimensional model of the rolling process. The recorded temperature was compared to the numerical values evaluated after tuning the heat transfer coefficient. The shape of the grid after rolling was checked against the deformed mesh using different fricition coefficients in order to obtain the optimum match. The unusually large length of the insert enabled the rolling process to be stopped halfway so that a picture of the roll-gap area could be obtained. This provided a partially deformed grid that represented the transient state during rolling. The experimentaily determined deformation gradient in this area as well as in the steady-state area agreed well with the finite element oredictions.

Void initiation close to a macro-inclusion during single pass reductions in the hot rolling of steel slabs: A numerical study

The work is focussed on the start of void formation close to a hypothetical single macro-inclusion in the hot rolling of steel slabs. The inclusion is chosen to be either three times harder or three times softer than the surrounding matrix. A commercial FE-code LS-Dyna3D has been utilized for the numerical analysis. Process data from the Swedish company “SSAB Tunnplåt AB” are used. The initial inclusion geometry is assumed to be cylindrical with an extension through the entire width of the slab. Different distances from the slab surface, on the vertical symmetry plane in rolling direction, are chosen as locations for the enclosure. Influence of different single pass reductions and roll radii are analysed. The only boundary force used on the matrix/inclusion interface is referred to friction. By treating a very big inclusion and neglecting bonding forces in radial direction, a worst-case scenario means to be studied. Two indices, one describing the deformation of the inclusion and one the surrounding matrix are used to estimate the likelihood for start of void formation. If the matrix index is bigger than that of the inclusion, voids are assumed to be initiated. This hypothesis gives trusty results. Near the hard particle, voids are likely to be formed. It became clear that the risk is smaller when large rolls are used. Furthermore, the threat for start of void formation turned out to be slighter for high reductions and in the vicinity of the slab surface. Soft particles were just elongated and no risk for void formation could be predicted.

Microstructural features of rolled Mg-3Al-1Zn

The microstructures of hot- and cold-rolled Mg-3Al-1Zn (AZ31) are examined using scanning electron and optical microscopy. It is shown that the microstructures following multipass hot rolling and annealing are more uniform than those formed by heavy single pass rolling and annealing. The importance of twins in producing intragranular recrystallization is evident, although the most dominant nucleation site is grain boundaries. The cold-rolled structure after a rolling reduction of 15 pct is dominated by the presence of deformation twins. Twin trace analysis suggests that approximately two thirds of the twins are a form of “c-axis compression” twin. A number of “c-axis tension” twins were also observed and additional in-situ scanning electron microscopy experiments were performed to confirm earlier observations that suggest these twins can form after deformation, during unloading.

Development of industrial production of ultrafine grained steel in tandem hot strip mill

Based on a model of microstructure evolution, an appropriate rolling schedule has been worked out to produce ultrafine grained steel (2 to 5 μm) on the hot strip mill. This rolling schedule is characterized by a large reduction in the finishers followed by strong cooling. Implementing such a rolling schedule on a conventional HSM raises major problems: increased rolling torque and force, lowered crown and shape control, disturbed looper control, accelerated roll damage, increased slip between strip and roll, insufficient cooling efficiency. These problems have been solved on the new Nakayama HSM by introducing innovative processes such as: single roll drive with different diameter and a new CVC, curtain wall cooling in the finisher, low inertia hydraulic looper, new high-speed steel rolls with solid lubrication.

Mean Wind in Convective Turbulence of Mercury

The large-scale circulation, often called "wind," in the confined thermal turbulence of mercury is studied experimentally. The instantaneous velocity profile at 128 points is directly measured using ultrasonic velocimetry. The periodic velocity oscillation is observed in the case of the aspect-ratio Gamma = 1,2 but not in Gamma = 0.5. Its peak frequency is scaled by f(c) proportional Ra(gamma(c)), where Ra is the Rayleigh number and gamma(c) = 0.43,0.45 for Gamma = 1,2. f(c) is close to the wind circulation frequency f(p), and has the same order of transit time from the bottom to the top of the convection cell. A single roll circulation is expected in Gamma = 1; however, axisymmetric toroidal rings may exist near the upper and lower plate for Gamma = 0.5, which are stable up to Ra = 7 x 10 (10).

Effect of Rolling Conditions on Microstructure and Mechanical Properties of AZ31 Mg Alloy

The effect of warm rolling under various conditions on the microstructure and mechanical property was investigated using an AZ31 Mg alloy sheet. Several processing parameters such as initial thickness, thickness reduction by a single pass rolling, rolling temperature, roll speed, and roll temperature were varied to elicit an optimum condition for the warm rolling process of AZ31 Mg alloy. Microstructure and mechanical properties were measured for specimens subjected to rolling experiments of various conditions. Warm rolling of 30% thickness reduction per pass was possible without any side-crack at temperatures as low as 200oC under the roll speed of 30 m/min. The initial microstructure before rolling was the mixed one consisting of partially recrystallized and cast structures. Grain refinement was found to occur actively during the warm rolling, producing a very fine grain size of 7 µm after 50% reduction in single pass rolling at 200oC. Yield strength of 204MPa, tensile strength of 330MPa and uniform elongation of 32% have been obtained in warm rolled sheets.

Multiplicity of nonlinear thermal convection in a spherical shell

Linear and weakly nonlinear thermal convection in a moderately thin spherical shell in the presence of a spherically symmetric gravity subject to a spherically symmetric boundary condition is systematically investigated through fully three-dimensional numerical simulations. The convection problem is self-adjoint and the linear convective stability is characterized by l, the degree of a spherical harmonics Yml (theta,phi). While the radial structure of the linear convection is determined by the stability analysis, there exists a (2l + 1)-fold degeneracy in the horizontal structure of the spherical convection. When l = O(10) , i.e., in a moderately thin spherical shell, the removal or partial removal of the degeneracy represents a mathematically difficult, physically not well-understood problem. By starting with carefully chosen initial conditions, we are able to obtain a variety of nonlinear convective flows at exactly the same parameters near the onset of convection, including steady axisymmetric convection, steady azimuthally periodic convection, steady azimuthally nonperiodic convection, equatorially asymmetric convection, and steady convection in the form of a single giant spiral roll covering the whole spherical shell which is stable and robust for a wide range of the Prandtl number.

Transport critical current density of Bi–Sr–Ca–Cu–O/Ag superconductor tapes with addition of magnetic nanopowder γ-Fe2O3

The effect of sintering temperature on the transport properties of Ag-sheathed-(Bi1.6Pb0.4)Sr2Ca2Cu3O10–(γ-Fe2O3)0.01 superconductor tapes prepared by the powder-in-tube technique with sintering time fixed at 50 h has been investigated. The maximum transport critical current density, Jc of 6490 A/cm2 at 77 K, was observed at sintering temperature of 845 °C. A further single intermediate rolling step increases Jc to 9560 A/cm2. Sintering temperature from 830 to 845 °C increases the 2223 phase content and resulted in improved Jc. At 850 °C, the content of 2223 phase decreased resulting in a corresponding decrease in Jc. X-ray diffraction patterns suggest that the 2212 phase reacts with non-superconducting phase such as CaCuO2, (SrCa)2CuO3, CaO, and CuO to form the 2223 phase. Samples without γ-Fe2O3 prepared under the same condition showed a lower Jc with maximum at 1560 A/cm2. Our results show that nanomagnetic γ-Fe2O3 addition improved Jc which supports previous calculations on the possibility of frozen flux superconductor with nanomagnetic addition in this class of materials.