IOP Conference Series Materials Science and Engineering

A central parameter to describe the formation of porosity and macrosegregation during casting processes is the permeability of the dendritic mushy zone. To determine this specific feature for a binary Al-18wt.%Cu alloy, flow simulations based on the Lattice Boltzmann (LB) method were performed. The LB method allows an efficient solving of fluid flow problems dealing with complex shapes within an acceptable period of time. The 3D structure required as input for the simulations was captured with X-ray microtomography, which enables the generation of representative geometries for permeability investigations. Removing the eutectic phase from the measured dataset generated a remaining network of solid primary dendrites. In the simulations, a pressure gradient was applied to force the liquid through the free interdendritic channels. The permeability of the structure was then calculated from the resulting flow velocity pattern using Darcy’s law. To examine the influence of different boundary conditions on the results obtained, several simulations were conducted.

We have recently described a novel method for the construction of a solid-state optical frequency reference based on doping $^{229}$Th into high energy band-gap crystals. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we have argued that the $^{229}$Th optical nuclear transition may be driven inside a host crystal resulting in an optical frequency reference with a short-term stability of $3\times10^{-17}<\Delta f/f <1\times10^{-15}$ at 1 s and a systematic-limited repeatability of $\Delta f/f \sim 2 \times 10^{-16}$. Improvement by $10^2-10^3$ of the constraints on the variability of several important fundamental constants also appears possible. Here we present the results of the first phase of these experiments. Specifically, we have evaluated several high energy band-gap crystals (Th:NaYF, Th:YLF, Th:LiCAF, Na$_2$ThF$_6$, LiSAF) for their suitability as a crystal host by a combination of electron beam microprobe measurements, Rutherford Backscattering, and synchrotron excitation/fluorescence measurements. These measurements have shown LiCAF to be the most promising host crystal, and using a $^{232}$Th doped LiCAF crystal, we have performed a mock run of the actual experiment that will be used to search for the isomeric transition in $^{229}$Th. This data indicates that a measurement of the transition energy with a signal to noise ratio (SNR) greater than 30:1 can be achieved at the lowest expected fluorescence rate. Comment: Eurodim Conference Proceedings

The uranium mononitride (UN) is a material considered as a promising candidate for Generation-IV nuclear reactor fuels. Unfortunately, oxygen in air affects UN fuel performance and stability. Therefore, it is necessary to understand the mechanism of oxygen adsorption and further UN oxidation in the bulk and at surface. Recently, we performed a detailed study on oxygen interaction with UN surface using density functional theory (DFT) calculations. We were able to identify an atomistic mechanism of UN surface oxidation consisting of several important steps, starting with the oxygen molecule dissociation and finishing with oxygen atom incorporation into vacancies on the surface. However, in reality most of processes occur at the interfaces and on UN grain boundaries. In this study, we present the results of first DFT calculations on O behaviour inside UN grain boundaries performed using GGA exchange-correlation functional PW91 as implemented into the VASP computer code. We consider a simple interface (310)[001](36.8{\deg}) tilt grain boundary. The N vacancy formation energies and energies of O incorporation into pre-existing vacancies in the grain boundaries as well as O solution energies were compared with those obtained for the UN (001) and (110) surfaces.

Ternary eutectics provide a unique opportunity for studying the eects of complex microstructure formation, as three distinct phases must be formed simultaneously from the melt. In order to produce fully coupled three-phase growth, Al-Ag-Cu at the ternary eutectic composition was directionally solidied in a constant temperature gradient of 3 K/mm at velocities between 0.2 and 5.0 m/sec. Under these conditions, the two intermetallic phases appear to grow as closely coupled rods in an (Al) matrix, with the solidication velocity aecting the specic morphologies chosen by the rods and the general degree of alignment of the structure. Crystal orientations were examined by EBSD to determine if variations in morphology within a single sample are due to specic orientation relationships. Although no conclusive connection to morphology has yet been found, two dierent sets of orientation relationships between the three phases have thus far been identied.

The precipitation of Mn-rich intermetallics in AlSiMn alloys during solidification ahead of the mushy zone affects the solidification microstructure, especially if fluid flow is present. Recently Steinbach and Ratke reported a barrier effect of -AlMnSi, meaning these intermetallics prevent fluid flow to enter the mush. To investigate this effect further we studied the solidification of AlSi7Mn1 with a fluid flow field induced by a traveling magnetic field (TMF). Samples were molten and directionally solidified within a silica aerogel crucible at various constant solidification velocities between 0.03 and 0.24 mm/s. The application of two separate heaters allowed the fixation of constant temperature gradients in the solid and liquid parts of the samples, the use of a transparent aerogel as crucible material permitted direct optical verification of the desired solidification velocity using an infrared line camera. Three collinear coils induced a TMF of approximately 5 mT strength, traveling either up or downward in the direction of the sample axis. The microstructures of the processed samples were studied using light microscopy and SEM-EDX and characterised by the primary and secondary dendrite arm spacing, the distribution of intermetallic phases as well as the radial segregation of primary phase and eutectic. Results are presented which show differences between samples with and without TMF-induced fluid flow. We noticed a radial macro-segregation dependent on the orientation of the TMF and the effects of the induced fluid flow on the primary and secondary dendrite arm spacing are examined.

In secondary AlSi alloys, the presence of small amounts of Fe causes the formation of intermetallic phases, which have a negative effect on mechanical and physical properties of castings. To understand the effect of fluid flow on the microstructure and intermetallic phases, Al-5/7/9 wt pct Si 0.2/0.5/1.0 wt pct Fe alloys have been directionally solidified under defined thermal (gradient 3 K/mm, solidification velocity 0.04 mm/s) and fluid flow (rotating magnetic field 6 mT) conditions. The primary α-Al phase and intermetallic phases were studied using light microscopy and SEM with EDX. The influence of fluid flow and intermetallic phases (β- Al5FeSi) on microstructure was characterized by changes of primary and secondary dendrite arm spacing and specific surface area of the dendrites. We observe a pronounced effect of flow on the length of the intermetallic precipitates, a macro-segregation Fe and Si and even small amounts of iron and thus intermetallics reduce possible effects of flow on microstructural parameters.

Rapid slurry formation is a semi-solid metal forming technique, which is based on a so-called solid enthalpy exchange material (EEM). It is a fascinating technology offering the opportunity to manufacture net-shaped metal components of complex geometry in a single forming operation. At the same time, high mechanical properties can be achieved due to the unique microstructure and flow behaviour. The major process parameters used in the RSF process are rotation speed of the EEM, melt superheat, amount of EEM added (determining fs), and holding time. The process parameters can be well controlled with clear effects on the microstructure. There is a lack of theoretical modelling of the morphological evolution in these two-phase slurries.

Simple casting experiments were set up to solve the question, if heterogeneous nucleation of the liquid-liquid decomposition in monotectic systems is possible. Al{Pb alloys with dierent inoculants were solidied, and the resulting microstructure was analysed by SEM and X-ray microtomography. Pronounced changes in the distribution of the lead precipitations indicate that it is possible to trigger the nucleation.

The days of the lone astronomer with his optical telescope and photographic plates are long gone: Astronomy in 2025 will not only be multi-wavelength, but multi-messenger, and dominated by huge data sets and matching data rates. Catalogues listing detailed properties of billions of objects will in themselves require a new industrial-scale approach to scientific discovery, requiring the latest techniques of advanced data analytics and an early engagement with the first generation of cognitive computing systems. Astronomers have the opportunity to be early adopters of these new technologies and methodologies: the impact can be profound and highly beneficial to effecting rapid progress in the field. Areas such as SETI research might favourably benefit from cognitive intelligence that does not rely on human bias and preconceptions.

We report here the magnetic properties of electron-doped Sm1-xCaxMnO3 manganites with the doping level of x=0.91. Exchange bias effect has been observed in Sm0.09Ca0.91MnO3 nanomanagnites system and can be tuned by the strength of cooling magnetic field (Hcool). The values of exchange bias parameter i.e. exchange bias fields (HE), coercivity (HC), remanence asymmetry (ME) and magnetic coercivity (MC) are found to strongly depend on Hcool. The larger effective magnetic moments and deviation of inverse susceptibility (\c{hi}-1) from Curie-Weiss law indicate the possible existence of Griffiths phase (GP). A rigorous measurement of linear and nonlinear ac and dc magnetic susceptibility in nanomanganites proves the existence of Griffiths phase (GP) in the temperature range TC<T<TG (Griffiths temperature). The effect of size reduction on exchange bias effect and GP is addressed here. The enhancement of exchange bias effect and GP has been argued to be due to the modification of the phase separated state on size reduction.

We discuss the consistency of the D=11 supermembranes with non zero central charge arising from a nontrivial winding CSNW. The spectrum of its regularized Hamiltonian is discrete and its heat kernel in terms of a Feynman formula may be rigorously constructed. The $N\to\infty$ limit is discussed. Since CSNW is equivalent to a noncommutative supersymmetric gauge theory on a general Riemann surface, its consistency provides a proof that all of them are well defined quantum theories. We interpret the supermembrane with central charge $n$, in the type IIA picture, as a bundle of D2 branes with $n$ units of D0 charge induced by a nonconstant magnetic flux.

The overwhelmingly increasing amount of stored data has spurred researchers seeking different methods in order to optimally take advantage of it which mostly have faced a response time problem as a result of this enormous size of data. Most of solutions have suggested materialization as a favourite solution. However, such a solution cannot attain Real- Time answers anyhow. In this paper we propose a framework illustrating the barriers and suggested solutions in the way of achieving Real-Time OLAP answers that are significantly used in decision support systems and data warehouses.

We propose a framework for indexing of grain and sub-grain structures in electron backscatter diffraction (EBSD) images of polycrystalline materials. The framework is based on a previously introduced physics-based forward model by Callahan and De Graef (2013) relating measured patterns to grain orientations (Euler angle). The forward model is tuned to the microscope and the sample symmetry group. We discretize the domain of the forward model onto a dense grid of Euler angles and for each measured pattern we identify the most similar patterns in the dictionary. These patterns are used to identify boundaries, detect anomalies, and index crystal orientations. The statistical distribution of these closest matches is used in an unsupervised binary decision tree (DT) classifier to identify grain boundaries and anomalous regions. The DT classifies a pattern as an anomaly if it has an abnormally low similarity to any pattern in the dictionary. It classifies a pixel as being near a grain boundary if the highly ranked patterns in the dictionary differ significantly over the pixels 3x3 neighborhood. Indexing is accomplished by computing the mean orientation of the closest dictionary matches to each pattern. The mean orientation is estimated using a maximum likelihood approach that models the orientation distribution as a mixture of Von Mises-Fisher distributions over the quaternionic 3-sphere. The proposed dictionary matching approach permits segmentation, anomaly detection, and indexing to be performed in a unified manner with the additional benefit of uncertainty quantification. We demonstrate the proposed dictionary-based approach on a Ni-base IN100 alloy.

Effect of an electric field along [100] direction on diffuse phase transitions in a relaxor ferroelectric 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 (PZN-0.045PT) crystal is studied through dielectric properties and a longitudinal acoustic (LA) phonon. Compared with the diffuse phase transition observed in zero-field cooling in PZN-0.045PT, it shows two sharp phase transitions under field cooling. This result indicates that inhomogeneity is reduced by the electric field in the way that electric field grows the static polar nanoregions and microdomains into larger ferroelectric domains. From a thermodynamic point of view, the electric field enhances the relaxation from the nonequilibrium polymorphic states to the equilibrium homogeneous state. At the same time, ferroelectric tetragonal phase is stabilized with increasing an electric field along [100].

The structure of [Rb0.92(NH4)0.08]2TeCl4Br2 has been determined from conventional X-ray powder diffraction data, by Rietveld method, in P4/mnc tetragonal space group (a = 7.315 (2) Å, c = 10.354(4) Å, Z = 2). The refinement of the structure led to final factor χ2 = 4.20%. The structure is considered as isolated octahedred TeCl4Br22-. These anions show a 4° rotation around the fourfold axis against the cubic arrangement of the K2PtCl6 type structure. The monovalent cations (Rb+/NH4+) are located between the octahedra ensuring the stability of the structure by ionic and hydrogen bonding contacts: Rb....Cl/Br and N-H...Cl/Br. At low temperature a second order transition phase was detected at 213K by DSC.

Pb-based complex perovskites with Fe3+ like Pb(Fe2/3W1/3)O3 (PFW) were found to be interesting because of their unique properties such as relaxor and magnetoelectric behavior. PFW is ferroelectric with ferroelectric Curie temperature TC between 150 and 200 K and at the same time is antiferromagnetic with magnetic Neel temperature about 400 K. BiFeO3 is a well known perovskite compound which exhibits ferroelectric (TC = 1103 K) and antiferromagnetic (TN = 643 K) ordering simultaneously. The polycrystalline sample of 0.1Bi0.95Dy0.05FeO3 – 0.9Pb(Fe2/3W1/3)O3 were synthesized using standard sintering procedure. Magnetization vs. magnetic field (at 4.2 K) curves was measured. Magnetoelectric properties of the sample were obtained.

Multiferroics which are simultaneously ferroelectric and magnetically ordered are of great importance both for fundamental solid state physics and for modern technology. The polycrystalline sample of 0.1Bi0.95Dy0.05FeO3 – 0.9Pb(Fe2/3W1/3)O3 were synthesized using standard sintering procedure. Crystal phase purity and crystal structure were determined using XRD method. The obtained crystal structure of the compound is a tetragonally distorted perovskite like structure (P4mm) with lattice parameters a = b = 3.987 Å, c = 3.990 Å. Mössbauer Effect (ME) studies were performed on 57Fe nuclei at 77K. The obtained spectra are composed of three Zeeman sextets. In the middle part of the obtained spectra there is observed paramagnetic dublet, which could be designated to impurity phase, which wasn't reveled on XRD pattern. The hyperfine interaction parameters for the all subspectra components confirm existence iron Fe3+ only in the investigated material.

We present here a comparative study of sol-gel-derived 0.9Pb(Mg1/3Nb2/3)O3−0.1PbTiO3 (PMNT) thin films about 120 nm in thickness that were, respectively, deposited directly on a platinized Si substrate and on a Pb(Zr,Ti)O3 (PZT)-buffered one, but were both annealed at 750 °C in ambient air. It was found that the PZT buffer layer plays an important role in the enhancement of crystallographic and electrical properties of PMNT thin films. The PMNT film grown on PZT-buffered platinized Si substrate showed a nearly pure perovskite structure, while the film without buffer layer contained a big amount of pyrochlore phase. Also, the PZT buffer layer changed the preferred orientation of PMNT thin films from (111) to mainly (110) orientation, and helped to improve the films' densification and microstructural evolution. Coherent with what was observed comparatively in structural characterization, enhanced dielectric and leakage current characteristics were observed in the film with buffer layer. For the PMNT film grown directly on Pt-coated Si substrate, the dielectric permittivity is as low as 570, whereas the value is enhanced to 1200 for the PMNT film with PZT buffer layer. Moreover, the leakage current density of PMNT thin films is reduced remarkably, roughly 4-5 orders of magnitude lower, by introducing the PZT buffer layer.

PET foils have a high potential as a material for biomedical and electrical industries. PET foils were irradiated by ions for variable irradiation time. The effects of low (2.5, 0.2 keV) energy argon ion flux irradiation on the surfaces of polyethylene terephthalate thin foils (PET) were studied. The source of ions was an ECR Ion Gun with settable acceleration voltages. The modified foils were investigated by in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Fourier transform infrared spectroscopy (FTIR). The significant changes in the chemical composition of the surface layer were quantitatively studied by XPS. The scission of the chains in the surface layer of PET foil was induced by ion flux interaction with PET surface. The strong selective sputtering of oxygen atoms in PET film was observed. The atomic ratio O/C was decreased by 0.2keV and 2.5keV argon ion flux from 0.40 to 0.25 and 0.04 respectively. The oxygen atoms in ester bonds are detached first. This phenomenon is responsible for the creation of carbon-rich surface layer. The FTIR analyses identified changes in chemical composition but with no obvious correlation to surface changes. PET volume changes in the spectra were probably results of photons from the ion source influence on PET foils.

A systematic study of the deformation microstructures over 3 perpendicular surfaces was carried out in the present work in order to correlate better the substructure with slip patterns, initial and final crystal orientation, and the macroscopic coordinate system. The microstructure and texture evolution of high purity Al-0.3 wt% Mn alloy of initial near brass {110}<112> (or Bs) orientation, channel-die compressed to the strain level of 1.5, were studied by TEM (including TEM orientation mapping) and high-resolution FEG-SEM/EBSD techniques to observe crystal subdivision deformation patterns at the microscopic scale. The grain orientation dependent structures were analyzed in terms of active slip systems focussing on the crystallography of extended planar boundaries. It was concluded that the type of dislocation structure (one or two sets of microbands) in {110}<112> oriented crystallites, at moderate strains (< 1.5) depended strongly on the crystallographic grain orientation. In this non-ideal initial crystal orientation the applied deformation mode activates a double slip, of which one system predominates and leads to further rotation away from Bs. A general rotation combined with a wide orientation spread is observed after a strain up to 1.5. The microband boundary alignment corresponds very well to the traces of crystallographic {111} planes, on which most of the slip occurs.

We have investigated nanoscale domain structures of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ((1-x)PMN-xPT) single crystal with x~0.32 around a morphotropic phase boundary (MPB) by a transmission electron microscopy (TEM). We found domain structures with multiple inhomogeneities in the so-called monoclinic phase near the MPB region around x~0.32 at room temperature. In addition to the large banded domains with the 100~200 nm width, there exist nanoscale lamella-type domain structures with ~10 nm width inside the large banded domains. In-situ TEM observation revealed that these nanoscale domain structures are inherent to the monoclinic phase. These domain structures with multiple inhomogeneities in the monoclinic phase should be responsible for the giant piezoelectric response to the external electric field.

The maximum strain and strain rate experienced during friction stir welding/processing (FSW/P) has remained quite unclear, despite various efforts. Knowledge of strain and strain rate is important for understanding the subsequent evolution of grain structure, and serves as a basis for verification of various models as well. In the present study, we facilitated the breaking and embedding of the pin into the workpiece of cast Al-Si-Mg alloy during FS to obtain "frozen" samples for analysis. Metallographic evidence has indicated that in the leading transitional zone the strain gradient increased rapidly before entering into the thread space. Analysis of the deformed dendrites has suggested that the strain was ~ 3.5 and the strain rate was ~ 85 s-1 when the deforming material entered the thread space. The heavily deformed material then formed a rotational zone confined within thread spaces rotating largely with the pin, depositing a large part on the trailing side of the pin. Thus, once into the thread spaces, further strain is low and strain rate should decrease considerably.

Polycrystalline samples of the delafossite Cr oxide Cu1−xAgxCrO2 were investigated to clarify its transport properties. The synthetized phases are found to contain a slight oxygen excess (δ = 0.06). The valence state of the Cr ions in the Cu1−xAgxCrO2 samples was identified as >3+ by analysing their TGA spectra, their lattice parameters and their electrical properties. The temperature dependence of zerofield-cooling magnetization was measured. All samples exhibits paramagnetic behaviour at high temperature. At low temperature they exhibit a clear ferromagnetic (FM) transition around 130 K. For x = 0.10 the samples exhibit an AFM transition at 25K. Clear hysteresis loops indicate that FM order exists in the Ag-doped samples at 2 K. All samples behave like semiconductors.

The morphology and growth of interfacial intermetallic compound (IMC) between Sn-3.0Ag-0.5Cu solder alloy and Cu substrate metal of solder joint is reported. The IMC morphology and IMC thickness layer were observed at three different porosities of porous Cu interlayer. The results revealed that during soldering process, Cu6Sn5 compound with scallop like morphology was formed at the interface of both the solder alloy and Cu substrate and at solder alloy and porous Cu interlayer. By adding porous Cu interlayer at the solder joint, the IMC thickness increased with increasing soldering temperature and the number of pores in porous Cu interlayer. The effect of porosity on increasing the IMC layer was also due to the slower cooling rate during solidification of molten solder.

High purity Nd2O3-doped (1−x)BaTiO3-xBi0.5(Na, K)0.5TiO3 (x = 0.00-0.08) were synthesized by a composite-hydroxide-mediated approach at 200°C using a hydrothermal reaction apparatus with a rolling system. The powders with an average size of 100 nm in diameter were produced and were sintered to almost full theoretical density at low temperature such as 1200°C for 2 h. Although (1−-x)BaTiO3-xBi0.5(Na, K)0.5TiO3 could not be poled, Nd2O3 additive was useful to proceed the polarization of (1−x)BaTiO3-xBi0.5(Na, K)0.5TiO3 ceramics.