Eulerian Cradle Research Articles

On the effect of detwinning during compressive deformation of martensitic NiTi: in situ neutron diffraction and micromechanical modeling

A combined experimental and computational effort was undertaken to provide insight into the microscopic deformation behavior of B19′ martensitic NiTi during compressive loading–unloading. In situ neutron diffraction experiment was performed under quasi-static compression on a modified Eulerian cradle, where orientations rotated 50° away from the loading axis were selected to capture the hkl reflections all the way during compression. A domino detwinning scheme was deducted and implemented in an elastic–viscoplastic self-consistent (EVPSC) model in order to interpret the experimental data and elucidate the deformation mechanisms. Predictions of the model adequately fit the in situ load–unload stress–strain curve and lattice strains. Validity of the model was also confirmed by validation against deformed texture and evolution of individual microstrains from published work. Effects of domino detwinning on the intergranular stresses were analyzed. Possible deformation systems during compressive load and unload processes, including detwinning, slip and deformation twinning, were thoroughly discussed by comparisons between simulations and experiments.

Nondestructive Texture Measurement of As-Received Ti Alloy Tubing via Simultaneous Shaping and Tilting Defocusing Correction

During the traditional process of texture testing, the sample to be tested must be flat. Generally, it is quite complicated and difficult to prepare the texture sample for the x-ray diffraction examination since it usually adopts time-consuming corrosion flattening or slice sticking for tubing. In this work, a new method is proposed to measure the texture of curved tube directly by using Eulerian Cradle installed on the x-ray diffractometer. This nondestructive method is favorable for a special defocusing correction sample composed of pure Ti powders with the same curvature radius as that of the tested Ti alloy tubing, and can be used to correct the strength loss caused by the elongated x-ray spot during the tube testing. It is verified that this nondestructive testing method is valid and feasible as compared to the traditional corrosion flattening method of tubing texture measurement. Moreover, this nondestructive testing method is highly effective, more accurate, and time-saving, which can be used for the rapid texture measurement for Ti alloy tubes.

Omega–Phi compensated GID in side inclination mode for measurement of residual stress in polycrystalline thin films

The grazing incidence diffraction (GID) method in side inclination mode, described by Ma et al. in 2002, of polycrystalline thin-film residual stress was revisited and explained using simple geometric relations. To overcome the issue of decreasing peak intensity of this method, which is induced by the decreasing incident angle because of the Eulerian cradle Chi-tilt, an improvement of Omega (ω)–Phi (φ) compensation was devised and applied to a NiFe thin-film sample. The geometry of this improved ω–φ compensated GID method in side inclination mode is detailed in this paper. This improvement guarantees a constant incident angle on the sample surface and a fixed sample illumination volume during measurement. The measured data were analysed using parametric refinement in DIFFRAC.TOPAS v6 software in Launch Mode, and details of the input file (.INP) are explained in this paper. The tensile stress of the NiFe thin-film sample was measured to be 1181 ± 85 MPa using this improved method.

Texture evolution in metals under mechanical stress: Application of a tensile stage on a laboratory X-ray system

ABSTRACTThe evolution of texture in copper has been studied in situ as a function of the applied mechanical stress. A uniaxial tensile stage was integrated onto a Eulerian cradle in a laboratory X-ray diffraction system, providing a platform for pole figure measurements on samples under an externally applied mechanical load. Thin strips of rolled copper were investigated at various stages of elongation. The pole figures were of good quality such that the orientation distribution function could be well determined. Changes in the orientation distribution function as a function of strain along the β-fiber could be clearly observed; the initial main component S is replaced by the Copper component at higher stages of elongation.

Texture gradient studies of a Cu‐tube by the robot at STRESS‐SPEC

The handling of larger samples for texture studies is limited when we using the Eulerian cradle. The robot Stäubli RX160 installed at STRESS‐SPEC offers much more freedom in sample manipulation on one hand to perform pole figure scanning and on the other hand to position the sample for a texture mapping. A key problem is that slit systems cannot be positioned close to large samples due to safety reasons which makes corrections more important. A very simple solution was tested to correct the scattered intensity for each pole figure point for constant volume and anisotropic absorption. A simple method to make these corrections is needed because engineering samples such as semi‐finished products have a large variety of shapes and weights and an ideal slit system is only seldomly available. The test sample was a Cu‐tube of 140 mm in diameter with an average wall thickness of 10 mm. To compare the corrections three kind of samples were measured, first a cube of 10 × 10 × 11 mm³ without any correction, second an 11 mm long tube segment and third a tube segment of 250 mm (12 kg weight) in length. Orientation Distribution Function (ODF) analysis of the average texture over the tube wall by the iterative series expansion method has shown that sufficient intensity corrections can be done to describe the texture gradient around the circumference of the Cu‐tube related to low ovality and eccentricity of the Cu‐tube.

Neutron diffraction on functional materials under electric field or mech. load

In this contribution neutron diffraction studies on functional materials under special environmenal conditions will be presented. In particular, studies of ferroelectric ceramics under high electric fields as well as shape memory alloys under mechanical load will be highlighted. The investigations were carried out at the high-resolution neutron powder diffractometer SPODI (FRM II / Garching n. Munich) which offers special sample environmenal tools for electric fields, mechanical load etc. In-situ studies on ferroelectrics under the influence of high electric fields enable to establish correlations between the macroscopic poling behaviour and corresponding structural changes. The investigations were carried out on technologically applied lead zirconate titanate based samples and on a bismuth sodium titanate based system. A self-designed device allows the investigation of large bulk samples under different orientations of the electric field. This method allows to analyze the poling mechanisms in technical ferroelectrics, such as piezoelectric effect, domain reorientation and phase transformations. In the system Bi0.5Na0.5TiO3 - BaTiO3 – K0.5Na0.5NbO3 the large recoverable field-induced strain could be attributed to a reversible field-induced phase transition from an almost non-polar, pseudocubic tetragonal phase to a distorted, ferroelectric active phase [1]. Polycristalline monoclinic nickel-titanium shape memory alloys have been investigated under mechanical load to analyze their stress-strain behaviour and to derive the elastic constants. A novel tensile rig allows to orient the load axis in a Eulerian cradle like manner. The elastic constants tensor could be calculated based on a series of diffraction patterns under different sample orientations in the initial state and under 0.6 % strain. Furthermore the contributions of elastic deformation (lattice dilatation) and inelastic deformation (orentation of twins) to the total strain could be separated.

Alignment of a ¼-Circle Cradle for Reliable Residual Stress Measurements

The alignment of a ¼-circle Eulerian cradle is discussed. The method is based on diffraction and uses a special alignment tool and a stress-free powder sample. A new profile shape function is introduced to describe better distorted diffraction peaks.

Rotatable multifunctional load frames for neutron diffractometers at FRM II—design, specifications and applications

Novel tensile rigs have been designed and manufactured at the research reactor Heinz Maier-Leibnitz (FRM II, Garching near Munich). Besides tensile and compressive stress, also torsion can be applied. The unique Eulerian cradle type design (ω, χ, and φ axis) allows orienting the stress axis with respect to the scattering vector. Applications of these tensile rigs at our neutron diffractometers enable various investigations of structural changes under mechanical load, e.g. crystallographic texture evolution, stress-induced phase transformations or lattice expansion, and the anisotropy of mechanical response.

Investigation of Texture Gradients of Semi-Finished Products by Neutrons and Photons

Texture gradients are present in most samples, which are due to materials processing. Standard methods to evaluate texture gradients are based on the cut of samples, such as the X-ray investigation of surface textures against the texture inside a sheet. Bulk textures itself averaging over the whole sheet thickness are analysed by thermal neutrons. Both thermal neutrons and photons with high energies allow investigations non-destructively. The beam port Stress-Spec at the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) at Garching/Germany is equipped with a robot system based on a RX160 Stäubli robot, a Laser Tracker and a heavy basement. Samples up to 30kg can be investigated. Main restrictions are the available neutron flux, the detector efficiency and the detector size. Thus, the gauge volume is restricted to 1x1x1mm for ideal scattering conditions to measure in acceptable time scale. Photons with up to 200keV are known as high brilliant and high intense beam with similar penetration power than thermal neutrons. A typical set up of a high energy beamline for texture gradient investigations works without an Eulerian cradle so that restrictions in handling large sample are of less importance. The HZG materials science beamlines at Doris III and Petra III (Harwi-II@DorisIII and HEMS@PetraIII) are equipped with massif units for sample rotation and x-, y- and z- scanning for samples and additional equipments up to 200kg. Compared to thermal neutrons, which work with wavelengths between 1Å-2.5Å, the wavelength of high energy photons is small (0.05Å – 0.20Å). That leads on one hand to low scattering angles (1° - 10°) and on the other hand to an anisotropic ellipsoidal gauge volume. The local resolution of the synchrotron beam is much better than for thermal neutrons. In both methods corrections for constant gauge volume during pole figure scanning and for anisotropic absorption are of great importance.

Burgers vector types and the dislocation structures in sputter-deposited Cu–Nb multilayers

The dislocation density and the Burgers vector population are determined within the Cu and Nb layers in highly textured sputter-deposited Cu–Nb multilayers by X-ray line profile analysis. The measurements are conducted with films on and off the substrates and by orienting the films in the Eulerian cradle for acquiring the h k l reflections corresponding to planes of the major texture component. The analysis reveals a nearly constant total dislocation density in the Cu layers in all the samples measured where the layer thickness varies from 20 nm to 75 nm, whereas in the Nb layers the dislocation density decreases slightly with increasing layer thickness. The overwhelming majority of the prevailing Burgers vectors of dislocations are oriented parallel to the interface planes of the multilayers.

Texture analysis at neutron diffractometer STRESS-SPEC

In response to the development of new materials and the application of materials and components in advanced technologies, non-destructive measurement methods of textures and residual stresses have gained worldwide significance in recent years. The materials science neutron diffractometer STRESS-SPEC at FRM II (Garching, Germany) is designed to be applied equally to texture and residual stress analyses by virtue of its very flexible configuration. Due to the high penetration capabilities of neutrons and the high neutron flux of STRESS-SPEC it allows a combined analysis of global texture, local texture, strain pole figure and FWHM pole figure in a wide variety of materials including metals, alloys, composites, ceramics and geological materials. Especially, the analysis of texture gradients in bulk materials using neutron diffraction has advantages over laboratory X-rays and EBSD for many scientific cases. Moreover, neutron diffraction is favourable for coarse-grained materials, where bulk information averaged over texture inhomogeneities is needed, and also stands out due to easy sample preparation. In future, the newly developed robot system for STRESS-SPEC will allow much more flexibility than an Eulerian cradle as on standard instruments. Five recent measurements are shown to demonstrate the wide range of possible texture applications at STRESS-SPEC diffractometer.

Construction and testing of the instrument for neutron holographic study at the Budapest Research Reactor

Neutron scattering device dedicated to neutron holography experiments is described. The device is operating at a constant wavelength prepared by a double focusing monochromator. It is equipped by highly efficient shielding, proper collimator, Eulerian cradle, monitor detector, gamma-ray, and neutron detectors as well. Relevant software serves as control for the measurement and data collection. The harmonized application of the components enumerated above makes our device extremely efficient and unparalleled. Two atomic resolution neutron holographic experiments carried out illustrate the efficiency and power of the instrument.

A versatile automated sample changer for texture measurements on the high pressure-preferred orientation neutron diffractometer

An automated sample changer with an Eulerian cradle for neutron texture measurements is described. This device has been measuring over 2300 texture and almost 400 powder samples at ambient conditions since it became operational in 2002 for use in the high pressure-preferred orientation diffractometer at the LANSCE neutron scattering facility. Operation for almost a decade resulted in sustained enhancements of mechanics, electronics, and software which significantly improved reliability and resiliency. We also describe in this paper our platform independent computer program POD2K which we use to create publication quality pole figure plots for texture samples.

Fast, micrometer scale characterization of group-III nitrides with laboratory X-ray diffraction

We have designed a convergent beam, concurrent detection X-ray diffractometer. The instrument was built by Bruker AXS and is equipped with a rotating anode generator, a Johannson monochromator crystal for beam focusing, and a Soller slit arrangement in combination with a knife edge in front of the sample which defines the illuminated area on the sample. Samples up to 12 in. can be mounted on the sample stage of a D8 Eulerian cradle. A large area detector enables rapid simultaneous detection of the diffracted intensity. The instruments allow for a fast evaluation of large samples at high lateral resolution. In favourable cases lateral resolution down to 1 μm is possible. Furthermore a grazing incidence diffractometer has been developed which allows for depth-dependent measurements at high intensity.

Inelastic neutron scattering facilities at the Budapest Neutron Center

Two Triple Axis spectrometers are commissioned now at the Budapest Neutron Center. The Thermal Triple Axis Spectrometer (TAST) is installed on the 8-th beam (60 mm diameter) and supplied with a 120 mm-long sapphire crystal placed inside the channel (2 m far from monochromator) to filter fast neutrons. The Eulerian cradle can be placed at the sample position to carry out holographic measurements. Otherwise a normal goniometer (carrying up to 100 kg weight for orientation, e.g. Cryostat/magnet/heavy sample) is used. This spectrometer's resolution was modeled by VITESS program package. The second (cold) neutron spectrometer (ATHOS) on a curved (4200m) neutron guide is mounted at the 19m-position from the cold source. The neutron guide 1.5Θc, made of boron glass, is coated with NiTi multilayer. This instrument, developed into the RITA-type spectrometer, is supplied with a 190 × 190 mm2 position sensitive detector and a polarization option (stacked polarizer). In addition it has the optional COMPACT Neutron Spin Echo setup, based on Larmor precession, for energy analysis with the resolution of 10 µeV. The test measurements are presented. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Light-weight steels based on iron-aluminium - influence of micro alloying elements (B, Ti, Nb) on microstructures, textures and mechanical properties

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Texture analysis with high-energy synchrotron radiation

Texture measurement with short-wave X-ray synchrotron radiation in the range of λ ≃ 0.1 Å is described. The measurements were carried out with the multipurpose diffraction instrument at the high-field wiggler, high-energy beamline BW5 at HASYLAB. The instrument was equipped with an on-line image-plate area detector for diffraction-image registration and a Eulerian cradle for sample orientation. The particular features of texture measurement with the BW5 instrument are: good resolution in the Bragg angle, extremely high angular resolution in crystal orientation (pole-figure angles) and particularly high penetration depth of several millimetres to centimetres, comparable with that of neutrons but at high spatial resolution. Several examples illustrate the particular advantages of this method for texture studies using large or encased samples (in situstudies in complicated environments, such as cryostats, furnaces, vacuum or pressure chambers, with no serious window problems). This allows, among others, non-destructive texture analysis in technological parts and whole components. Because of the extremely high beam intensity (short exposure times) compared with all other methods of texture measurement, the new technique is particularly suited for the study of large sample series (as is often necessary in industrial applications).

放射光高エネルギーＸ線を用いた入射角一定法による表面下深部の残留応力分布の非破壊評価

A new method is proposed to estimate nondestructively the distribution of the equibiaxial residual stress beneath the surface by using an Eulerian cradle type goniometer. By maintaining a constant value of the X-ray incident angle, the probing depth of X-rays is kept nearly constant, even though sin2ψ is changed. From the slope of the linear relation between the diffraction angle and sin2ψ, the stress value is calculated for a given probing depth. This new method is applied to estimate the residual stress of a shot-peened steel sample, whose compressive zone extended about 150μm below the surface. High energy X-rays of 72keV from synchrotron radiation source, SPring-8, was used for stress measurements. The residual stress distribution estimated by the new method agreed well with that determined by the conventional sin2ψ method with Cr-Kα radiation combined with the method of the successive removal of the surface layer by electropolishing.

On the generation of microstrains during the plastic deformation of Waspaloy

Neutron diffraction has been used to characterize the development of microstrains during the plastic deformation of the polycrystalline nickel-base alloy, Waspaloy. Two types of experiment were performed: (i) in situ tensile testing on the diffractometer to determine the response parallel and perpendicular to the loading direction and (ii) measurement of the orientation dependence of the microstrain accumulation using a Eulerian cradle. Large residual microstrains are shown to develop. Along the loading direction, these are typically tensile in the γ′ phase and compressive in the γ phase; however, the values are sensitive to both the orientation of the diffracting crystallite and the amount of plastic deformation of the material. The behaviour is due to the differential deformation between grains in differing orientations (intergranular microstresses) and the two phases (interphase microstresses). It is shown that at low bulk plastic strains, intergranular microstresses develop rapidly, whilst at larger plastic strains the microstresses arising from interphase interactions become dominant. These effects have implications for the determination of residual stresses using diffraction-based techniques and these are discussed.

The multicrystal modular spectrometer for x-ray diffraction studies using SR

We suggest a set of elements united in the modular x-ray spectrometer to easily implement multiaxis, multipurpose x-ray diffraction schemes, multiple-diffraction layouts with two-dimensional collimation of the incident beam, surface diffraction schemes, and experiments with various modifications of the x-ray standing wave method. The main elements of the spectrometer are: the one-circle goniometer with the vertical axis, the multicircle research goniometer, and different slit systems. All units except the multicircle goniometer can be mounted on two parallel optical guides. The multicircle goniometer is a stand-alone unit consisting of an Eulerian cradle mounted on a two-circle goniometer. All rotations are driven by stepping motors via worm gears. On axes where fine (to 0.1 arc sec or less) angular positioning is desirable, torsion-element-based rotation is used; it is driven via piezo drivers. A program package was developed to control the experiments. The software is based on the modular principle providing for fast implementation of application programs suited for specific x-ray diffraction methods. The results of multiple-diffraction studies with the use of the instrument are presented.