Papers by Keyword: Neutron Diffraction

Abstract: A new Mg-RE (rare earth) alloy was previously developed by micro-alloying method (RE< 0.4 wt.%), which achieves a high ductility and good corrosion resistance. In-situ tensile test via neutron and synchrotron diffraction were performed to investigate first the deformation behaviour; and second the texture evolution which can be related to the deformation mechanism, and finally to understand why the as-cast Mg-RE alloys show such a high tensile ductility.Preliminary results showed that a dominated basal fibre texture was gradually developed with the increase of tensile strain. However, before the sample was broken a (10.0) fibre texture showed a similar intensity to that in (00.2), which means more activations of the non-basal slip planes during tensile deformation. This could also contribute to a relatively high elongation of this new Mg-RE alloy at room temperature. Further discussion will be showed together with the microstructures.

Abstract: With respect to residual stress analysis the inner gearing of an automotive sliding collar is a component with a challenging, complex geometry. The accessibility of the tooth root does not exist for conventional measuring approaches. However, the process steps like e.g. broaching and case hardening induce characteristic residual stress distributions, which must be known for the valuation of the mechanical integrity of the parts. For lab X-ray stress analysis approaches according to the sin2ψ-method [1] the ring like structure must be sectioned, which affects the process induced residual stress state. The tooth root is rather small, which further leads to shadowing effects during tilting of the sample. Standard mechanical approaches like incremental hole drilling can be excluded due to the narrow tooth root. Local neutron diffraction residual stress analysis in the tooth root by means of neutron through surface strain scanning at the STRESS-SPEC instrument at the research reactor FRM II, Garching (Germany) was successfully carried out for the inner gearing. A measuring and evaluation strategy is proposed, where special attention is paid to the compensation of the surface effect due to the incomplete immersion of the nominal gauge volume during through surface scanning and to the local variation of the D₀-value as a consequence of the case hardening process.

Abstract: Residual stresses are often introduced into aluminum alloys through quenching processes performed to generate the required microstructure. Such residual stresses are known to be deleterious to the integrity of the component. Methods to mitigate residual stresses in quenched components are therefore of great importance. Cold rolling has been proposed as an effective technique to remove residual stresses in large components. In this work, the effectiveness of cold rolling in reducing the residual stresses in quenched blocks AA7050 has been quantified using the neutron diffraction technique. Neutron diffraction measurements have been performed on two blocks one quenched and the other quenched & cold rolled block. Comparing the residual stress distributions pre and post rolling it has been found that cold rolling almost eliminates the tensile residual stresses in the core of the block, however it generates large tensile residual stresses d in a shallow region near the surface of the block.

Abstract: The hydrogenation of TbNi_0.4Co_0.6 was studied by means of neutron diffraction and calorimetric method with use of the differential heat-conducting Tian-Calvet type calorimeter. It was determined that TbNi_0.4Co_0.6H_3.8 crystallized in orthorhombic CrB-type structure (S.G. Cmcm). The hydride formation is accompanied with strong lattice expansion. In the structure TbNi_0.4Co_0.6D_3.4 deuterium atoms occupy tetrahedral 8f-intersices, trigonal bipyramidal 4c-interstices and octahedral 4b-interstices. Dependence of the differential molar enthalpy of absorption (ΔH_abs) vs. the hydrogen concentration in the metallic matrix was obtained at 50°C. It was ascertained that in the range of 0<X<2.0 (X=H/ TbNi_0.4Co_0.6) ΔH_abs =-102.0±2.3 kJ mol^-1H_2. The value of the integral enthalpy of hydrogen absorption by TbNi_0.4Co_0.6 equals -99.5kJ mol^-1H₂ for the composition TbNi_0.4Co_0.6H_3.8.

Abstract: We report on the magnetoelectric properties of Er₂CoMnO₆. This compound adopts the structure of a double perovskite with a strong monoclinic distortion. Our specimen exhibits a nearly perfect Co-Mn order. It undergoes a ferromagnetic transition at T_C~70 K due to the Co²⁺-O-Mn⁴⁺ ferromagnetic superexchange interaction. Below 30 K, the Er³⁺ moments start to order antiferromagnetically to the Co/Mn sublattice. Pyroelectric measurements reveal electrical polarization at low temperature but its strong dependence on the heating rate indicates the lack of a spontaneous ferroelectricity. Instead, electric polarization is derived from thermally stimulated depolarization currents.

Abstract: Neutron diffraction has been carried out to study temperature evolution of crystal and magnetic structure parameters of the multiferroic (0.9)BiFeO₃ + (0.1)BaTiO₃ over region (300 – 1000) K. Crystal structure is rhombohedral over whole temperature region and it is described by the R3c space group. The lattice parameters increase with temperature. The Ba ions are placed in the Bi sublattice and the Ti ions partly occupy the Fe sublattice. Assuming that the sample has a modulated magnetic structure with the propagation vector k = [0.0045, 0.0045, 0], we obtained a temperature dependence of the Fe-ion magnetic moment. The value of the moment is equaled to be μ = (3.46 ± 0.05) μ_B at 300 K and becomes zero at 600 K.

Abstract: In 2014, present-day scientists had the opportunity of marking the centennial of a discovery that triggered the development of a new field of research, which is now called Solid State Ionics.In their 1914 paper, Carl Tubandt and Erich Lorenz reported on the extraordinary properties of the alpha phase of silver iodide. Although α-AgI was a crystalline material, it resembled a molten salt with regard to the liquid-like value and weak temperature dependence of its ionic conductivity. With their transference measurements, Tubandt and Lorenz proved that the electric current in α-AgI was completely carried by the silver ions, while the iodide ions formed a rigid lattice. Up to the present day, α-AgI has been considered the fast ion conductor par excellence.In the mid-1930s, L.W. Strock was the first to use x-ray diffraction to investigate the crystal structure of α-AgI. The anion sublattice was found to be body centered cubic, but the arrangement of the silver ions remained a puzzling question. On the one hand, Strock could assign a large number of possible crystallographic sites to them. On the other hand, the state of the silver ions appeared to be rather ‘quasi-molten’ or ‘liquid-like’. This structural puzzle was resolved in 1977, when Cava, Reidinger and Wuensch used the results of a single-crystal neutron-diffraction experiment to construct contour plots for the probability density of the silver ions in α-AgI, which turned out to have broad maxima at the tetrahedral voids of the anion structure, with saddle points between them.A number of novel experimental approaches toward a better understanding of the ion dynamics in α-AgI were suggested by Wilhelm Jost in the 1960s and 1970s. These included high-accuracy specific heat measurements, measurements of the ionic conductivity in the microwave and far-infrared frequency regimes, and quasielastic neutron scattering. The results of the ensuing experiments, involving the present author, did not always provide immediate answers to the long-standing open questions, but rather created new puzzles instead. In this Chapter, an overview is given of the essential steps that were taken in experiment and modeling, eventually leading to the emergence of a self-consistent picture of the structure and dynamics of the mobile silver ions in α-AgI. Notably, that picture included both solid-like and liquid-like aspects. Strictly speaking, however, either category, ‘solid’ and ‘liquid’, had to be considered inappropriate for characterizing the actual state of the silver-ion sublattice.Recently, the transition to a more solid-like behavior of the mobile silver ions was observed in low-temperature α-AgI, which could be stabilized by confinement in glass, as first shown by Tatsumisago et al. Far below the regular phase transition temperature, 147 °C, measurements were performed of the frequency-dependent conductivity of α-AgI, yielding relevant information on the silver-ion dynamics. A conjecture put forward by Jost in 1937 could thus be corroborated by the present author and his coworkers. Below 147 °C, the ‘liquid-like’ activation energy for ionic transport was found to be replaced by a larger, more ‘solid-like’ value, although the anion structure and, therefore, the barriers for elementary displacements of the cations remained essentially unchanged. The underlying mechanism is sketched at the end of the Chapter.

Abstract: The purpose of this research was to investigate the changing patterns of the 3D rail residual stress as it accumulates on different portions of the rail manufacturing process. These patterns are of interest for manufacturers and railroad companies but also could serve as initial fields for various further numerical analyses of actual residual stress states in rails, wear and crack formation/development. Examined were four rail samples taken directly from manufacturing: 1. an air cooled rail; 2. an air cooled and roller straightened rail; 3. a head hardened rail; 4. a head hardened and roller straightened rail. An advanced experimental-numerical hybrid technique was developed and applied to perform all the required data reduction tasks. It comprises of an sectioning scheme called as the transverse/oblique slicing (T/O-S) technique and of a physically reasonable data reduction/smoothing procedure called as the global method (GM). Destructive experimental examinations were performed with the neutron diffraction method on thin rail slices at atomic reactor facility of US DOC, NIST Center for Neutron Research in Gaithersburg, MD. In the paper presented and discussed are results of the performed analyses.

Abstract: Synthesis of austenite stainless steel using extracted minerals from Indonesian mines has been carried out. It is namely A2 steel. The main raw material of making non standard steel A2 is granular scrap iron, nickel, iron-chromium, iron-manganese, and iron-silicon. It is obtained from non standards. A component of A2 steel consists of 15,42%Cr, 25,01%Ni, 0,32%Mn, 0,96%Si and 0,34%C with impurities of 0,039%V and 0,051%Cu. Characterization using neutron diffraction technique shows the first four Bragg peaks of (111), (200), (220) and (311). A machining process was performed to make a plat from ingot. After the machining process, intensities and FWHM of the first two Bragg peaks of (111) and (200) are quite the same. But the intensity of the peaks (220) and (311) changes. It is calculated that for (220)peak the decreasing intensity about 51.6% and increasing FWHM about 0.14%, whereas for (311) peak the intensity increase about 40.2% and the FWHM decrease about 3%. Furthermore, the material obtained from the machining process is used as a reference to the condition of the material without rolling. After being subjected to rolling up to 70% thickness reduction, crystal orientation changes from highest intensity with a sequence of (200), (111) and (220) to (220) (111) and (200) with highest increasing intensity about 2.25 times at (220). Quantitative analysis of texture after the rolling process is shown in pole figures of (111), (200) and (220). It is characterized that crystals are oriented mainly to {110} <113>, texture index is 1.0671.

Abstract: Multiferroic composites of (x)NiFe₂O₄ + (1-x)BaTiO₃ with x = 0.2, 0.3 and 0.4 and (x)CoFe₂O₄ + (1-x)BaTiO₃ with x = 0.2, and 0.4 have been synthesized by mixing NiFe₂O₄ (CoFe₂O₄) spinel and BaTiO₃ piezoelectric. Distribution of Ni (Co) ions on 8a and 16d positions of spinel lattice (space group F d-3m) is determined by neutron powder diffraction. Wave vector of magnetic structure of the spinel is k = 0. The dielectric permittivity of the composites was measured for the frequency range 10² – 10⁵ Hz. At low frequencies the dielectric permittivity decreased from ~940 for x = 0.2 to ~360 for 0.4.