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The two-axis diffractometer SPN-100 at the Center of Accelerators and Nuclear Analytical Methods (CANAM) in Řež, is a neutron diffraction instrument dedicated to residual stress analyses in polycrystalline materials, it has recently been equipped with a new two-dimensional position sensitive detector (2D-PSD) and a six-axis robotic arm for sample positioning. Recent results of strain/stress distribution measurements with the upgraded tools are presented. The measured materials are made of C-Mn unalloyed steel used for spherical storage tank. Welding-induced residual stresses have direct influence on ductility and toughness of both weld metal and heat affected zone of the weld area, which affect the service life time of structures. Normal, transversal and longitudinal components of the stresses obtained in the vicinity of the butt weld from a spherical storage tank were measured by neutron diffraction at CANAM.

In this paper, two identical American Iron and Steel Institute 1008 steels sheets were welded together in a butt joint configuration, with the welding line direction parallel to the rolling direction. The sheets were welded using the electron-beam welding technique. Stress distribution was monitored in the surface and the bulk of the welded samples using X-ray Bragg–Brentano and neutron diffraction methods, respectively. Accordingly, surface and bulk magnetic properties, namely magnetic Barkhausen noise and quasi-dc permeability, were monitored in the same area. Both surface and bulk magnetic measurements exhibit good agreement with the surface and bulk stress measurements obtained by the diffraction methods, after a proper calibration procedure. Complementary measurements with scanning electron microscopy and Vicker’s microhardness tester provide similar good agreement between the microstructural characterization and the residual stress distribution. [ABSTRACT FROM AUTHOR]

Samples of highly conducting Bi12.5Lu1.5ReO24.5 and Bi12.5Er1.5ReO24.5 have been studied by neutron powder diffraction at room temperature for both phases and at 25°C≤T≤500°C in the case of Bi12.5Er1.5ReO24.5. Both materials crystallize in the cubic δ-Bi2O3 related system, space group Fm-3m. Changes in the oxygen sublattice at 25°C≤T≤500°C have been investigated by the Rietveld and maximum entropy methods. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure of fluorite-related Bi3ReO8 containing isolated ReO4 tetrahedra has been studied by powder X-ray and neutron diffraction at elevated temperatures. The phase is cubic and undergoes a phase transition between T ~150°C and 250°C passing from space group P213 at 25°C to I213 at higher temperature. The material is an oxide ion conductor and presents a sharp increase in conductivity at T ~450°C, with σ ~8×10−3 Scm−1 above 500°C. Two different long range oxide ion diffusion mechanisms involving vacancy and interstitial defects are proposed. Rotation of isolated ReO4 tetrahedra seem to facilitate the oxide ion conduction. [Copyright &y& Elsevier]

Abstract: The two crystallographically non-equivalent Co atoms of the quasi-one-dimensional crystal structure of Ca3Co2O6 form chains with alternating, face-sharing polyhedra of Co2O6 trigonal prisms and Co1O6 octahedra. This compound forms a substitutional solid-solution phase with Sc, in which the Sc atoms enter the Co2 sublattice exclusively. The homogeneity range of Ca3Co2− v Sc v O6 (more specifically Ca3Co1Co21− v Sc v O6) extends up to v≈0.55. The crystal structure belongs to space group R3¯c with lattice parameters (in hexagonal setting): 9.0846(3)⩽a⩽9.1300(2)Å and 10.3885(4)⩽c⩽10.4677(4)Å. The magnetic moment decreases rapidly with increasing amount of the non-magnetic Sc solute in the lattice. [Copyright &y& Elsevier]

Rietveld refinement of powder neutron diffraction data has been used to study the crystal structures of the four-layer Aurivillius-phase ferroelectrics Bi5Ti3FeO15 (at 25°C) and SrBi4Ti4O15 (at a series of temperatures up to 800°C). At 25°C both materials adopt the polar orthorhombic space group A21am, in common with two-layer analogues such as SrBi2Ta2O9. At temperatures well above the ferroelectric Curie temperature (i.e., at temperatures of 650°C and above, with Tc∼550°C) SrBi4Ti4O15 transforms to the centrosymmetric tetragonal space group I4/mmm. However, there is good evidence from the raw diffraction data of a very subtle intermediate paraelectric orthorhombic phase, of Amam symmetry, in the region 550>650°C. The distortion in the ferroelectric phase can be traced to displacements of the cations in the A site of the perovskite block, with cooperative tilting of the BO6 octahedra. The nature of the octahedral tilt system, cation disorder at the perovskite A and B sites, and the phase transition sequence in SrBi4Ti4O15, which parallels that found in SrBi2Ta2O9, are discussed. [ABSTRACT FROM AUTHOR]

Due to their superb mechanical properties and high specific mass, tungsten heavy alloys are used in demanding applications, such as kinetic penetrators, gyroscope rotors, or radiation shielding. However, their structure, consisting of hard tungsten particles embedded in a soft matrix, makes the deformation processing a challenging task. This study focused on the characterization of deformation behavior during thermomechanical processing of a WNiCo tungsten heavy alloy (THA) via the method of rotary swaging at various temperatures. Emphasis is given to microstrain development and determination of the activated slip systems and dislocation density via neutron diffraction. The analyses showed that the grains of the NiCo2W matrix refined significantly after the deformation treatments. The microstrain was higher in the cold swaged sample (44.2 × 10−4). Both the samples swaged at 20 °C and 900 °C exhibited the activation of edge dislocations with <111> {110} or <110> {111} slip systems, and/or screw dislocations with <110> slip system in the NiCo2W matrix. Dislocation densities were determined and the results were correlated with the final mechanical properties of the swaged bars. [ABSTRACT FROM AUTHOR]

Advanced thermomechanical hot rolling is becoming a widely used technology for the production of fine-grained spring steel. Different rapid phase transformations during the inductive heat treatment of such steel causes the inhomogeneous mixture of martensitic, bainitic, and austenitic phases that affects the service properties of the steel. An important task is to assess the amount of retained austenite and its distribution over the cross-section of the inductive quenched and tempered wire in order to evaluate the mechanical properties of the material. Three different analytical methods were used for the comparative quantitative assessment of the amount of retained austenite in both the core and rim areas of the sample cross-section: neutron diffraction—for the bulk of the material, Mössbauer spectroscopy—for measurement in a surface layer, and the metallographic investigations carried by the EBSD. The methods confirmed the excessive amount of retained austenite in the core area that could negatively affect the plasticity of the material. [ABSTRACT FROM AUTHOR]

The paper investigated the residual strain and stress distribution, microstructure, and macro-texture along the transverse direction of commercially pure titanium grade 2 samples prepared by the CONFORM ECAP technique. This method belongs to the severe plastic deformation methods; hence, it could be assumed that residual stress fields would be present in the work-pieces. Residual stresses cannot be directly measured; thus, neutron diffraction measurements, Electron back-scatter diffraction (EBSD) investigations, and local X-ray macro-texture measurements were performed in different regions of the sample to determine the data for the residual stress calculation. The calculation was based on the modified Kröner model. Neutron diffraction strain scans and residual stress calculations revealed that symmetrical residual strain and stress gradients with compression character were present in the axial and hoop direction after one and two passes. Asymmetric distribution of the residual strains and stresses remained after the third pass of the CONFORM ECAP. EBSD investigations showed that after the first pass, significant grain refinement occurred; however, further passes did not cause any dramatic grain refinement. X-ray texture measurements revealed that local macro-texture was dependent on the number of passes of the CONFORM ECAP and on the investigated area in the samples. [ABSTRACT FROM AUTHOR]