The evolution of ferroelectric domain structures inside a single grain embedded in a polycrystalline BaTiO3 ceramic was investigated under temperature and electric field using the three-dimensional X-ray diffraction (3D-XRD) method. The orientation of domains within the grain was studied during the phase transformation from the cubic to tetragonal crystal structure. The peak widths broadened from 0.10 ± 0.01∘ to 0.29±0.08∘ along the azimuthal direction during cooling. Four individual tetragonal domain structures were developed from the cubic grain. A twinning model based on {101} habit planes is discussed. While the twinning model predicts 89.47∘ misorientation between 90∘ domains and 1.049∘ misorientation between domain variants, the measured misorientations neither support the twinning model nor are the domain structures mutually orthogonal. The average misorientation of the domain structures at room temperature with respect to the cubic grain was about 0.3∘. Upon application of an electric field, the volume fractions of the domain structures changed systematically favoring growth of domain structures with small polarization angle with respect to applied field direction. No rotation of domain structures was observed upon application of an electric field which is consistent with domain boundary migration.
Crystallographic texture is described by pole figures. In this paper, we continue to study experimental pole figure errors. In other words it can be named pole figure measurement errors. These errors are connected with the experimental procedure and do not depend on any further computations. In our previous works it was shown that the qualitative behaviour of pole figure measurement errors is similar to peak width determination errors. To check this conclusion a set of diffraction spectra were measured for Mg + 4.5%Al + 1%Zn sample on the spectrometer for quantitative texture analysis (SKAT) at FLNP, JINR, Dubna. Then we simulated the individual spectra and used these spectra for the pole figure extraction and the pole figure error determination. Such simulation enabled to confirm conclusions concerning the main role of the peak width determination error in the pole figure error. Additionally, we simulated individual spectra using model pole figures and extracted pole figures and pole figures errors from those spectra. For this case we also confirmed the same qualitative behaviour of pole figure measurement errors and peak width determination errors. The model pole figures were calculated on the basis of normal distributions.
The effect of deposition environment conditions on the electrical and structural properties of deposited PbI2 layers were studied. The layers were deposited from solution under dark and room light illumination with and without applying magnetic field. XRD, electrical, and photo-electrical properties were measured at room temperature. An increase in the grain size versus the platelet area was noticed.The electrical properties revealed a dependence on deposition conditions. Dark conductivity increases from 1.7×10−10 to 5×10−9 (Ωcm)-1 when deposition was carried out in darkness. A gain factor (the ratio between photoconductivity and dark conductivity) of (23) was obtained. The results indicate that the increase in electrical conductivity is mainly due to the plane 001, where the average number of grain boundaries in this plane sharply decreases when deposition takes place in darkness. On the other hand, the increase in photoconductivity could be due to the decrease in the recombination of free carriers along the grain boundaries.
At the prospect of a lightening of the automobile structures, welded spots have been realized on a stacking of two sheets (a 6008 aluminum alloy on steel) Friction Stir Spot welding (FSSW). Different process parameters have been tested, but only the influence of the dwell time will be described in the present paper. The dwell time corresponds to the time during which the probe stays in rotation at its bottom location before extracting. A study of the microstructures and textures associated to mechanical tests (tensile shear tests) allowed determining the best set of welding parameters. The recrystallized area around the welding spot has been characterized by electron back-scattered diffraction (EBSD). A mechanism of continuous dynamic recrystallization has been identified since the misorientation of subboundaries increases close to the weld, and this is for all the dwell times tested. Elsewhere, the increase of the dwell time induced a larger recrystallized zone. It has also been found that a long dwell time induced a larger welded area but also a higher quantity of intermetallic compounds (especially FeAl, Fe2Al7, and FeAl2) with high-microhardness values (up to 800 Hv). Thus, the dwell time must not exceed a certain value, otherwise it can weaken the weld.
Methods of modern quantitative texture analysis are applied in order to characterize the crystallographic texture of various non-oriented electrical steel grades in view of their relation with the magnetic properties of the steel sheet. A texture parameter is defined which quantifies the density of ‹100› easy magnetic directions in the sheet planes. An extensive correlation study revealed the relation of this parameter with the hysteresis losses, determined at an induction of 1.5 T, and with the induction measured at an applied external field of 25 A/cm. It is shown that the latter magnetic property is the more texture dependent, whereas the former one is more sensitive to the grain size of the steel. Also various strategies for texture control are critically reviewed. It is shown that the conventional manufacturing process only provides poor tools for optimizing the texture of the final product. In order to obtain a quantum-leap improvement of the magnetic quality of the texture, in combination with other important microstructural features, nonstandard processing strategies are required, such as cross-rolling, two-stage cold rolling, or surface annealing.
1 Laboratoire d’Etude des Textures et Application aux Materiaux (LETAM), CNRS UMR 7078, University of Metz, Ile du Saulcy, 57045 Metz, France 2 Institut fur Metallkunde und Metallphysik, RWTH Aachen University, 52056 Aachen, Germany 3Laboratoire de Physico-Chimie de l’Etat Solide, UMR 8182, Bâtiment 410, Universte Paris-Sud XI, 15 rue Georges Clemenceau, 91405 Orsay Cedex, France 4 Institut fur Strukturphysik, Technische Universitat Dresden, 01062 Dresden, Germany
The texture of ultrafine-grained Al alloy AA6016 produced by accumulative roll bonding (ARB) has been measured by neutron diffraction. The starting texture consists of a strong cube component. During ARB, this texture breaks down and a texture typical for rolling of face-centered cubic metals with high stacking fault energy develops. The texture after 8 ARB cycles is characterised by the β-fiber with the Cu component dominating. Moreover, the rotated cube component is formed. This component is typical for simple shear, which takes place during rolling on the surfaces of the sheets. Based on the Taylor factor and calculated Lankford parameter, the mechanical anisotropy of the advanced metal sheets is discussed.
A 12 T magnetic field has been applied to the annealing process of a 0.81%C-Fe (wt.%). It is found that the magnetic field shifts the eutectoid carbon content from 0.77 wt.% to 0.83 wt.%. The statistical thermodynamic calculations were performed to calculate the eutectoid temperature change by the magnetic field. Calculation shows that the increase of the eutectoid temperature by a 12 T field is 29∘C. Synchrotron radiation measurements were performed to measure the pole figures of the samples and were analyzed by MAUD to determine the bulk texture of the ferrite phase In the field-treated and non field-treated samples. Results show that although there is no specific preferred orientation appearing by applying the magnetic field, slight enhancement of (001) fiber component occurs in both the sample normal direction (ND) and the transverse direction (TD). This effect might be related to the magnetic dipolar interaction between Fe atoms in the transverse field direction.
A newly developed laser powered heating stage for commercial SEMs in combination with automated established electron backscatter diffraction (EBSD) data acquisition is presented. This novel experimental setup can be used to achieve more information about microstructure and orientation changes during grain growth, recrystallization, recovery, and phase transformations. First results on the α−γ−α phase transformation in steel within 886∘C–900∘C are presented.
Diffraction with high-energy synchrotron radiation is a new experimental method to determine textures of materials, which due to the special properties of this radiation, in the future may have advantages in terms of accuracy of local texture measurements in comparison to established methods like Electron back scatter diffraction (EBSD). In the present study NiAl polycrystals with two different initial textures have been deformed in torsion at 727°C and 1000°C and their texture development has been measured with highenergy synchrotron radiation. Torsion enables the study of texture formation with strain as well as the exploration of large strains without changing the shape of the samples. The pole figures indicate the preferred alignment of ‹100› with the shear direction and {110} with the shear plane. High pressure torsion may also open new possibilities in terms of grain refinement and texture formation and thus ductilization of NiAl.
The present work is devoted to the study of the grain number influence on the quantitative texture analysis and on the values of averaged elastic properties. Number of grains does not influence mathematical definition of orientation distribution function (ODF) (Bunge, H.J. (1982). Texture Analysis in Material Science. Butterworths, London; Matthies, S., Vinel, G.W. and Helming, K. (1987). Standard Distributions in Texture Analysis. Akademie-Verlag, Berlin.); nevertheless, intuitively clear that, averaging procedure implies a ‘‘large’’ number of grains to make sense. In the present work we applied the already suggested procedure (Lychagina, T.A. and Nikolayev, D.I. (2003). Phys. Stat. Sol. (a), 195(N2), 322–334.) for the case of hexagonal symmetry to evaluate the influence of the grain number in the sample on the calculated elastic properties. This procedure was carried out for graphite that is one of the widespread, applicable and highly anisotropic materials.
Triaxial strain scanning has been performed on a 7mm thick 7150-aluminium alloy Variable Polarity Plasma Arc (VPPA) weld using synchrotron X-rays. It has been demonstrated that the use of specific advantageous ( hkl ) peaks that occur in this highly textured aerospace alloy plate permits fast deep measurements in reflection as well as in transmission. The sin2ψ method was also utilised to monitor the variation in deviatoric stress component (σ11−σ33) across the weld in both the test-piece and a comb like reference specimen used to map the changes in stress-free lattice spacings over the weld. The results suggest that microstresses have little effect on macrostress determination, particularly in the Heat Affected Zones (HAZ). Though small in magnitude, the macrostresses still present in the reference specimen can be allowed for to correct the stress tensor in the plate. Maximum tensile longitudinal stress values remain unchanged, whereas the stress condition in some parts of the HAZ is well described as biaxial after the proposed correction.
Physical mathematical model of sintering powders is suggested with respect to the influence of gravitation on sintering kinetics. Structure genesis and evolution in sintered glass‐based particulate bodies is investigated both in computer simulations and “ in situ ”.
Texture patterns of the starting ώ and transformed α structural phases were obtained from AISI 304 stainless steel sheets subjected to varying levels of tensile deformation using high energy X‐ray diffraction in combination with the texture enhanced Rietveld method. The use of this method allows the simultaneous determination of the orientation distribution functions (ODF) of both phases, even for small α ‐martensite fractions of the order of 5%. The texture patterns are analyzed in terms of the crystallographic orientation relation between the starting and transformed phases and the preferential formation of certain variants of this relation.
In this article, the powder metallurgy technique combined with flat hot‐extrusion and cold rolling processes was employed to fabricate 10 and 20vol.%Nb/Al metal–metal composite sheets. The hot‐extruded and coldrolled textures of the matrix aluminum in these metal–metal composite sheets were investigated by three dimensional orientation distribution functions (ODFs) analysis. The results show that the extrusion mode and large second phase particulate metal, Nb, have strong influence on the development of the extrusion and cold rolling textures in composites’ matrix. The matrix Al forms β ‐fiber textures after flat hot extrusion, where the components consist of B′‐{011} ‹322›, S′‐{124} ‹654› and C′‐{113}h332i. After cold rolling process, only B′‐{011} ‹322› changed to B‐{011} ‹211› while the other components remained the same. The large particles in composites affect the matrix deformation in such a way that separates the distorted or bound zones from the deformation zones, which resulted in the final cold rolling deformation textures.
High‐energy X‐rays from a synchrotron radiation source, SPring‐8, were applied to the stress measurements of thermal barrier coating (TBC). The specimen had a zirconia top coat on a bond coat of NiCoCrAlY sprayed on the substrate of Ni‐base super alloys. The stress in the bond coat was measured through the top coat using the diffraction of Ni3Al 311 by high‐energy X‐rays with an energy of 72 keV. The sin2ψ method was used to determine the stress value. A specially designed furnace with a wide beryllium window was developed to conduct in-situ measurements of the internal stress in the bond coating at the room temperature, 773, 1073, and 1373 K. The internal stress was tensile at the room temperature, and decreased with increasing temperature. At 1073K or higher, the internal stress in the bond coat was released due to softening of the bond coat. The normal stress perpendicular to the coating surface of TBC was evaluated by a new hybrid method. Since the penetration depth of low‐energy X‐ray is very small around a few micrometers for zirconia, the stress value measured by the sin2ψ method is the in‐plane stress, σ1, and the stress perpendicular to the surface was zero. On the other hand, the penetration depth of high‐energy X‐rays is very deep, so the measured stress value will be the in‐plane stress minus the out‐of‐plane stress, i.e. σ1 − σ3. The normal stress perpendicular to the surface, σ3, i.e. the spalling stress, was estimated from these two measurements. The specimens were exposed in air atmosphere at 1373 K for 500, 1000, and 2000 h. The distribution of the spalling stress in the top coat was estimated by the hybrid method. The spalling stress near the interface to the bond coat changed to a large tension after long‐time exposure.
In order to describe texture and microstructure of a polycrystalline material completely, crystal orientation g = { ϕ 1 Φ ϕ 2 } must be known in all points x = { x 1 x 2 x 3 } of the material. This can be achieved by locationresolved diffraction of high-energy, i.e. short-wave, X-rays from synchrotron sources. Highest resolution in the orientation- as well as the location-coordinates can be achieved by three variants of a detector “sweeping” technique in which an area detector is continuously moved during exposure. This technique results in two-dimensionally continuous images which are sections and projections of the six-dimensional “orientation– location” space. Further evaluation of these images depends on whether individual grains are resolved in them or not. Because of the high penetration depth of high-energy synchrotron radiation in matter, this technique is also, and particularly, suitable for the investigation of the interior of big samples.
The strain and phase distribution in a dissimilar friction stir weld of AA6082-T6 to AA2024-T3 is investigated non-destructively. The measurements are performed using a novel depth resolved strain and phase mapping technique. The technique is based on the use of a focussed high energy synchrotron beam, a novel spiral slit system, and an area detector system. Through thickness measurements of the residual strain along the weld centre show strong variations with changes of sign. The strain scans across the weld exhibit a strong asymmetry in particular for the longitudinal strain component. A depth resolved strain mapping across the weld shows for the dominant longitudinal strain component variations in depth, especially on the AA6082 side of the weld. Results from the strain measurements are related to the depth resolved map of the material distribution in the weld zone.
Sitepu et al. (Sitepu, H., Schmahl, W.W., Khalil Allafi, J., Eggeler, G., Dlouhy, A., Reinecke, T., Brokmeier, H.G., Tovar M. and Többens, D.M. (2002b). Texture and quantitative phase analysis of aged Ni‐rich NiTi using X‐ray and neutron diffractions. Materials Science Forum, 394‐395, 237‐240.) showed that Rietveld refinement with generalized spherical harmonic (GSH) description for neutron powder diffraction (ND) data of the aged (673 K, 20 h) Ni‐rich NiTi shape memory alloy (Sitepu H. (2002). Assessment of preferred orientation with neutron powder diffraction data. J. Appl. Cryst, 35, 274–277); of nominal composition 50.7 at.% Ni at 294K consists of four phases: precipitate (Ni4Ti3), R‐phase, monoclinic (B19′) and some residual cubic (B2). Therefore, they concluded that the differential scanning calorimetry (DSC) first peak, on cooling, (321 K) is not due to the formation of the R‐phase alone. The second, lower DSC peak (271 K) is due to the transformation of R‐phase and residual B2 phase to B19′ phase. The structural refinement of R‐phase problem, which was neglected in the previous study, was undertaken with great care in this study. The objective of the present article is to use the third generation synchrotron X‐ray source at the European Synchrotron Research Facility (ESRF) in Grenoble, which make available X‐ray beams of higher energy and much higher intensity than laboratory X‐ray sources, for describing crystal structure of the R‐phase in 50.75 at.% Ti–47.75 at.% Ni–1.50 at.% Fe ternary alloy. The synchrotron diffraction data of R‐phase were analyzed using the Rietveld refinement with GSH description. The results showed that no significant improvement in fit is found when the inversion center is removed from the model, suggesting that the space group is indeed and not P3.
High‐energy X‐rays between 30 keV and 1MeV, such as provided by modern synchrotron radiation sources as the ESRF and HASYLAB, bear the advantage of high penetration into most materials. Even heavy element compositions can be accessed in their volume. The range of applications is huge and spreads from nuclear spectroscopy to the characterization of metal extrusion under industrial conditions. This article compiles an overview over the most common instrumental diffraction techniques.Modern two‐dimensional detectors are used to obtain rapid overviews in reciprocal space. For example, diffuse scattering investigations benefit from the very flat Ewald sphere as compared to low energies, which allow mapping of several Brillouin zones within one single shot. Diffraction profiles from liquids or amorphous materials can be recorded easily. For materials science purposes, whole sets of Debye–Scherrer rings are registered onto the detector, their diameters and eccentricities or their intensity distribution along the rings relating to anisotropic strain or texture measurements, respectively. At this point we stress the resolution of this technique which has to be carefully taken into account when working on a second generation synchrotron source.Energy‐dispersive studies of local residual strain can be studied by a dedicated three‐circle diffractometer which allows accurately to adjust the scattering angle from a defined gauge volume.Triple axis diffractometry and reciprocal space mapping is introduced and can be employed for highest resolution purposes on single crystal characterization, even under heavy and dense sample environments. Thus, the perfection of single crystals can be mapped and strain fields and superstructures as introduced by the modulation from ultrasonic waves into crystals or epitaxially grown Si/Ge layers can be investigated in detail. Phase transitions as magnetic ordering can be studied directly or through its coupling to the crystal lattice. Time resolved studies are performed stroboscopically from a sub‐nanosecond to a second time scale.The combination of these techniques is a strong issue for the construction and development of future instruments.
