Neutron Diffraction Pole Figures Research Articles

Texture coefficients for the simulation of cordierite thermal expansion: A comparison of different approaches

The dependence of the coefficient of thermal expansion (CTE) from the texture description in porous ceramics is presented, in the example of cordierite. The texture description usually adopted for industrial ceramics, the I-ratio, is compared with the more rigorous approach of neutron diffraction (ND) pole figures. It is shown that the use of the I-ratio represents a coarse approximation of the complete materials texture and it yields different values of the texture coefficients used to model the CTE from lattice expansion data (according to the integrity function). For extruded and fired samples, it is shown that if for the transverse direction all approximations are equivalent, for the axial CTE the usual I-ratio values bring contradictory simulation results. On the contrary, the use of ND pole figures and of the Popa–Bruno method allows predicting sensible CTE values, consistent with other physical properties, such as Young's modulus.

The magnetic fabric in “undeformed clays”: AMS and neutron texture analyses from the Rif Chain (Morocco)

In this study we analyse the magnetic and mineral fabric of clay sediments that appear homogeneous and not deformed at the outcrop scale. We integrate low-field, high-field and low-temperature AMS analyses with neutron diffraction pole figures analysis as an alternative approach to studying the deformation mechanisms that drive the development of the magnetic lineation in these sediments. The studied sediments are Neogene claystones sampled from the Rif Chain (Morocco). High-field AMS measurements carried out on a large number of samples show that the relative percentage of the ferrimagnetic contribution is not significant (generally < 5%) and paramagnetic contribution prevails (generally > 95%). The principal axes of both components coincide with those of the low-field AMS at room and low temperatures. These results indicate that the magnetic anisotropy of the studied samples is predominantly carried by the paramagnetic phyllosilicates, i.e. chlorite, as deduced by X-ray diffraction. Neutron texture analysis confirms that the different AMS ellipsoids obtained with different magnetic methods reflect the spatial distribution of the basal planes of chlorite, demonstrating the great potential of the AMS to determine the mineral orientation fabric. The combination of these different approaches enables to establish a more accurate qualitative and quantitative correlation between the chlorite fabric and magnetic anisotropy and yields valuable information about the tectonic meaning of the magnetic fabric.

Determination of the morphological texture of the fibres in a composite material made from a textile of AISI 316L fibres using a mixed deconvolution/positivity method

The orientation distribution or `morphological texture function' (MTF) of the fibres is determined from measurements of the crystallographic texture of the fibres themselves. From neutron diffraction pole-figure measurements of the fibres in the composite and X-ray diffraction pole figures of the individual fibres, the MTF is determined by a deconvolution. To account for errors in the expansion coefficients due to measurement uncertainties, the deconvolution is performed simultaneously with a positivity criterion in the form of a set of linear equations which may be solved by a least-squares method. This approach is validated using a model system of AISI 316L stainless-steel fibres in an Al–13 wt% Si eutectic casting alloy. The fibres had been spun into yarns and subsequently woven to form a textile. The composite was made by infiltrating a `brick' containing several layers of the textile with the Al alloy. The results of the deconvolution procedure show that the method indeed yields the expected morphological texture. The so-determined MTF is resolved to an angular resolution not attainable by other methods. It also provides a very good estimate of the volume fractions of the different texture components.

Texture analyses of Sauropod dinosaur bones from Tendaguru

The apatite texture of fossil Brachiosaurus brancai and Barosaurus africanus sauropod bones from the excavation site at Tendaguru, Tanzania, was characterized by neutron diffraction pole figures. The results obtained reveal predominantly 〈0 0 0 1〉-fibre textures of the apatite; the fibre direction coincides with the longitudinal direction of the long bones of the skeletons. Neutron pole figures further indicate that other texture types may also be present. Texture strength is similar to dinosaur tendons and contemporary turkey tendon studied by others. Variations of texture strength across the bone wall cross-sections are not significantly large.

Texture of Al-Cu Alloys Deformed by ECAP

Materials of ultra-fine grained microstructure (sub-micrometer grain size) exhibit large strength, hardness and ductility and also the increased toughness in comparison with conventional coarse-grained ones. In these materials also the super-plastic flow at lower temperatures is observed. This behaviour may be interesting when aluminium alloys like AlCuZr, used in superplastic forming, are considered. In the paper, the methods of preparing such materials by equal-channel angular pressing (ECAP) is proposed and the texture analysis, based on neutron diffraction pole figure measurements and calculated orientation distribution function of two alloys AlCu4SiMn and AlCu5AgMgZr is discussed. The influence of short time recrystallization is discussed in relation with TEM and SEM observations.

Texture Investigations of Zircaloy-4 Tubes by Neutron Diffraction

This article presents the results of texture investigations of Zircaloy-4 tubes. Neutron diffraction and inversion pole figures were used to chracterize the texture of samples. The main interest is given to the analysis of texture changes under different tensile test conditions including tensile force direction, annealing temperature and tensile test temperature. Four different specimens of different orientation to the tube axis were tested.

On the increasing use of the Jülich texture diffractometer for geological projects

The diffractometer SV7-b at the FRJ-2 reactor is predominantly operated for texture investigations on geological samples and is thus attracting a novel community of users in neutron scattering. Neutron diffraction pole figures yield unique information on the mutual orientations of the mineral crystallites constituting multiphase rocks and provide a significant advance in reconstructing geological processes. Recent SV7-b geological projects, which involve a variety of about 200 samples from all continents, are presented discussing special aspects of the method.

On the Development of Copper Textures – Neutron Diffraction Control over a Period of 12 Years –

The longtime stability of copper textures has been periodically monitored over 12 years by neutron diffraction pole figure measurements on a cold rolled and a partially recrystallized copper specimen, always using the same diffractometer and the same procedure of data analysis. The texture component fractions of 'rolled' copper suffered a continuous decrease over about 8 years and seem to reverse since then. The decrease is accompanied by recrystallization from initial 3 to 34 vol. % at present. Texture changes in the partially recrystallized specimen are less pronounced. In this sample, the fraction of random orientations changed from initially 11 % to 31 % over the about first six years and followed by a decrease to 24 % at present.

Neutron and X-ray diffraction study of Al and Cu during ECA processing and subsequent recrystallization

The inhomogeneity of deformation in aluminium and copper, processed by Equal-Channel Angular (ECA) pressing, is discussed on the basis of X-ray as well as neutron diffraction pole figure measurements and calculated orientation distribution functions. The influence of short time recrystallization is considered. Structure observations by means of optical microscopy, Electron Back Scattered Diffraction (EBSD) and transmission electron microscopy were used to obtain complete information.

Determination of the Morphological Textures of Fibres in a Composite Material Made from a Textile of AISI 316L Fibres

The orientation distribution (morphological texture) of fibres in a composite is very important in determining the properties of the material. Therefore, methods which can provide quantitative descriptions of the morphological texture are essential. One approach to determining the morphological texture function (MTF) is to measure the orientation distribution of the crystals in the fibres. Since many types of fibres used for reinforcements are crystalline and textured (i.e. carbon fibres, steel fibres, etc.) this approach may be interesting for commercial/industrial applications. For this technique to be applied, the crystallographic texture intrinsic to the fibres must be determined and subsequently, measurements of the 'global' crystallographic texture should be made in the composite. The morphological texture can then be calculated by a deconvolution of the composite texture with the fibre's crystallographic texture. The deconvolution is most easily performed using the series expansion representation of texture functions. In this paper, the morphological texture was determined in a woven fabric made from bundle drawn AISI 316L stainless steel fibres embedded in an Al-13wt% Si alloy matrix. Straight fibres removed from the fabric serve as the reference material for the deconvolution. Neutron diffraction pole figures were used to determine the MTF's.

Neutron diffraction applied to geological texture and stress analysis

Texture is defined as preferred crystallographic orientation in a polycrystalline aggregate. The main mechanisms of geological texture formation are crystallization, sedimentation, plastic deformation, recrystallization and metamorphism. Textures of geomaterials are fingerprints of the earth's history. The complexity of geological texture analysis results mainly from the overprinting of different textures on several mineral components during different orogenic periods. Quantitative texture analysis, i.e., the calculation of a three-dimensional orientation distribution function of crystallites, is based on experimental pole figures which represent the orientation distributions of certain crystallographic directions and which can be obtained from X-ray or neutron-diffraction techniques. Due to the high penetration capability of neutrons, large specimens can be investigated resulting in global volume textures rather than local surface textures from X-rays. Neutron-diffraction pole figures are characterized by high grain statistics even on coarse-grained material. Individual pole figures can also be obtained from reflection-rich diffraction patterns of multiphase rocks and low-symmetry mineral constituents by using position-sensitive detectors and by pattern decomposition by means of profile-fitting methods. Neufron texture diffractometers are operated in the constant-wavelength mode at steady-state sources and using time-of-flight techniques at pulsed sources. Different experimental set-ups are discussed. Results of neutron-diffraction texture analyses on monomineralic and polymineralic rocks are presented, e.g., on calcite, quartzite, plagioclase, pyrrhotite ores, granite, and orthopyroxene-sillimanite-granulite. The wide application spectrum of neufron texture analysis includes objects of the outer solar system as in the low-temperature texture study on ice and the non-destructive investigations on rare pieces of meteorites. The application of neutron diffraction on strain measurements and residual stress analysis of geological material is discussed. Natural effects on rocks are orders of magnitude smaller than in technological material and drilling gives rise to stress relaxation. Experimental deformations can be observed during in situ measurements at various pressures and temperatures. Neutron strain diffractometers are described. Examples of recent results on the full strain/stress tensor in sandstone and on strain partitioning in polymineralic rocks are given. Future prospects of new high-intensity neutron sources are promising in performing combined structure, texture and stress analysis. New instruments are under construction and software packages on the basis of full-pattern Rietveld refinements are available.

Neutron diffraction pole figures of geological anorthosite textures

Texture investigations on geological anorthosite specimens with the triclinic plagioclase-type structure have been performed by neutron diffraction pole figure scanning. Representative pole figures of four specimens originating from different locations of the large massif-type Gruber anorthosite, Antarctica, are presented and discussed.

On the Longtime Stability of a Copper Rolling Texture Analysed by Neutron Diffraction Pole Figures

On the Longtime Stability of a Copper Rolling Texture Analysed by Neutron Diffraction Pole Figures

Estimation of the orientation distribution of short-fiber composites using ultrasonic velocities

A method for estimating the orientation distribution function (ODF) of short-fiber composites using measured ultrasonic velocities is presented. The method is based on the coupling of (i) a forward micromechanics model of the effective ultrasonic velocities of the textured composite in terms of the coefficients in an expansion of the ODF in generalized spherical harmonics, (ii) ultrasonic measurements of the velocities, and (iii) an inversion algorithm to obtain the coefficients of the ODF from the measured velocities and the forward model. The approach is used to determine the ODF coefficients for a transversely isotropic short-fiber SiC/Al metal-matrix composite. The ODF coefficients obtained by inversion of ultrasonic velocities agree reasonably with those obtained from neutron-diffraction pole figures. Corresponding elastic constants predicted with these coefficients also agree well with independently measured elastic constants.

Ergebnisse von Untersuchungen zur radialen Anisotropie und Textur in gezogenen Messingrohren

AbstractDie plastischen Eigenschaften von Rohren sind im allgemeinen anisotrop. Analog zur senkrechten Anisotropie von Blechen [1] kann das unterschiedliche Verhalten des Rohrwerstoffs in Umfangsrichtung und Wanddickenrichtung als radiale Anisotropie bezeichnet werden. Diese plastische Anisotropie resultiert aus kristallografischen Vorzugsorientierungen, d. h. der Textur, die sich während der Kaltumformung entwickelt hat. Im folgenden werden Ergebnisse der experimentellen Bestimmung der radialen Anisotropie im Zugversuch und von Texturmessungen an kaltgezogenen Messingrohren vorgestellt.

Texture study of MTG produced YBaCuO ceramic using X-ray and neutron diffraction

The X-ray and neutron diffraction pole figure technics were employed for studying the free surfaces and bulk textures of a MTG YBCO sample. We found a development and an enlargement of the texture from the free surfaces to the entire volume with {113}, {114} or {115} planes parallel to the surface. The 211 phase particulates are randomly oriented.

Measurement of stress in steel structures with SH wave EMATS: MacLauchlan, D.T.; Burns, L.R.; Alers, G.A. Review of progress in quantitative nondestructive evaluation, Williamsburg, Virginia (United States), 22–26 Jun. 1987. vol. 7B, pp. 1399–1404. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988

Theories have been developed by several authors to calculate velocities of bulk, guided and surface waves in polycrystalline aggregates of cubic metals. These theories can be used to predict the effect of texture on ultrasonic velocity in rolled aluminium and steel sheet, provided that the effects of dislocations, second-phase particles, inclusions, etc. can be ignored. The theories predict that ultrasonic velocities will will be influenced by three orientation distribution coefficients (ODCs). The ODCs are quantitative measures of the texture in the material; in general, more than three ODC are required to completely characterize texture. Neutron diffraction pole figures can also be used to obtain the ODCs. Neutron diffraction measurements of ODC can be compared against ultrasonic values to obtain an independent check on the validity of the ultrasonic theories. In this work, the texture of thin sheets of a commercial grade aluminium alloy was measured with both ultrasonics and neutron diffraction. Several ultrasonic techniques were employed, using bulk, guided and surface waves. Both piezoelectric and electromagnetic-acoustic transducers (EMATs) were used. Quantitative measurements of texture made with different ultrasonic techniques were in good agreement. These ultrasonic measurements also agreed with neutron diffraction measurements, indicating that the dominant features of the effect of texture on wave propagation have been modelled with sufficient accuracy. The extension of the ultrasonic technique to on-line (production) monitoring of texture is considered. In particular, it appears that EMATs are the transducer of choice for on-line texture measurement of rolled sheet, since they are non-contacting.

Advantages of Neutron Diffraction in Texture Analysis

Neutron diffraction texture analysis is based on pole figure measurement followed by pole figure inversion. Neutron diffraction pole figure measurement is quite similar to that by X‐rays. There are, however, several advantages in detail which are mainly due to the lower absorption coefficient. Besides these quantitative differences, there is one principle difference between the two methods. Neutron diffraction allows the magnetic texture to be measured which is not possible by X‐rays. The paper gives a survey on the advantages of neutron diffraction texture analysis which are only counteracted by the limited availability and higher costs of neutron diffraction.

Neutron diffraction pole figure measurements for the microstructure analysis of meteorites

Neutron diffraction pole figure measurements have been applied for meteoritic studies on hexahedritic and octahedritic iron-nickel meteorites. Two hexahedrite specimen have been proven to be monocrystals with twinning along {211}. An octahedrite originating from Gibeon has been characterized by α-iron-lamellae and γ-iron-rims. The orientation relationship is of the Nishiyama-Wassermann type with a preference of eight out of twelve possible variants.

Neutron diffraction pole figure measurements on iron meteorites

Neutron diffraction pole figures were measured on three iron-nickel meteorite samples, the hexahedrites Coahuila and Walker County, both belonging to group IIA, and the octahedrite Gibeon, group IVA. As expected, pole figure peaks of the hexahedrites can be assigned to reflections from a single crystal or to reflections due to twinning on {221}. Macroscopically visible fractures in Walker County sample can be recognized in the pole figures by peak splitting and broadening. Schreibersite pole figures of the Coahuila meteorite corroborate the orientation relationship between prismatic rhabdites and kamacite {110} Rh ' {210} α, <001> Rh ' <100> α). For the octahedritic specimen, taenite pole figures reveal that taenite rims have the orientation of the parent γ-phase crystal. By the kamacite pole figures we deduce the orientation between kamacite lamellae and taenite rims to be close to Nishiyama-Wassermann relationship ({110} α ' {111} γ, <001> α ' <1̄10> γ). Variant selection occurs with the kamacite crystals, and suggests the presence of strain during kamacite growth.