Papers by Author: Heinz Günter Brokmeier

Abstract: A new method to investigate thin wires has been tested, which is based on a special sample holder and on a high energy X-rays. Due to the high penetration power of high energy Xrays quantitative texture data will be obtained without any additional corrections such as constant volume correction and absorption correction. The measurements have been carried out at the high energy beam line BW5 at HASYLAB – DESY (Hamburg). In order to overcome grain statistics problems on the investigated Cu-wire of 122µm thickness a special scanning routine together with the sample preparation allows to average over a wire length between 1mm and up to 240 mm.

Abstract: Aluminum of 5N purity has been deformed at room temperature by equal channel angular pressing using three passes of route A. The microstructure and texture have been investigated by electron back-scattering and neutron diffraction. The microstructure from the first pass on is totally dynamically recrystallized. The recrystallization texture consists of an oblique cube component. The oblate grains and the cube texture are anticlockwise rotated about the transverse direction. The inclination with respect to the extrusion direction depends on the distance from the top of the extruded bar and changes from pass to pass. The mechanism of ormation of the recrystallization microstructure and texture is discussed.

Abstract: Copper of 4N purity was deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. The local microstructure and texture were investigated by orientation imaging microscopy and high-energy synchrotron radiation, respectively. The microstructure consists of elongated grains which are inclined to the extrusion direction. The texture is characterized by typical shear components of fcc metals which deviate from their ideal positions. The inclination of the grain long axis and the texture components with respect to the extrusion direction depends on the distance from the top of the extruded bar and changes from pass to pass. Reasons for the texture gradient are discussed.

Abstract: Ti-47Al-4(Cr, Nb, Mn, B) samples with different initial grain structures and fibre textures were deformed in torsion at 1000 °C under hydrostatic pressure of 400 MPa in a Paterson type rock deformation machine at a maximum constant strain rate of 2*10-4 s-1. The microstructure was investigated by transmission electron microscopy (TEM). Local texture measurements as a function of shear strain were done with high-energy synchrotron radiation. During shearing due to dynamic recrystallization the initially lamellar structure breaks down into a fine-grained globular structure with a g grain size in the order of 5 µm. The shear texture developed consists of <110> and {110} inclined to the shear direction and shear plane, respectively. The microstructure and texture development is discussed.

Abstract: The preferred crystallographic orientation (i.e. texture) and the non-transformed austenite can cause serious systematic errors in the structural study of the R-phase in 50.75at.%Ti- 47.75at.%Ni-1.50at.%Fe (hereafter referred to as Ti-Ni-Fe ternary) shape memory alloy. The crystal structure refinement of R-phase synchrotron high resolution powder diffraction (SRD) data using Rietveld refinement with generalized spherical harmonic (GSH) description for preferred orientation correction showed that the sample consists of minor cubic phase and the space group was 3 P [1]. The objective of the present paper is to study the crystallographic phase composition and crystal structure refinement of SRD data of trigonal R-phase martensite and monoclinic (B19¢) martensite in Ti-Ni-Fe ternary alloy during thermal cycling using the GSH description.

Abstract: The modelling and/or describing of texture (i.e. preferred crystallographic orientation (PO)) is of critical importance in powder diffraction analysis - for structural study and phase composition. In the present study, the GSAS Rietveld refinement with generalized spherical harmonic (GSH) was used for describing isostatically-pressed molybdite powders neutron powder diffraction data collected in the ILL D1A instrument. The results showed that for texture in a single ND data of molybdite the reasonable crystal structure parameters may be obtained when applying corrections to intensities using the GSH description. Furthermore, the WIMV method was used to extract the texture description directly from a simultaneous refinement with 1368 whole neutron diffraction patterns taken from the sample held in a variety of orientations in the ILL D1B texture goniometer. The results provided a quantitative description of the texture refined simultaneously with the crystal structure. Finally, the (002) molybdite pole-figures were measured using the GKSS TEX2 texture goniometer. The results showed that neutron diffraction is an excellent tool to investigate the texture in molybdite.

Abstract: Due to the high penetration power, the high photon flux and the excellent brilliance high energetic synchrotron radiations are a phantastic tool particular in fast experimentation. Therefore in-situ measurements under applied load or at various temperatures have been carried out to investigate the texture influence on the deformation of magnesium and aluminium. An upgraded loading device with a power up to 20 kN was installed at the hard wiggler beamline BW5. Magnesium samples with different initial textures show the strong influence on this texture on the activation of different glide systems and on the activation of twins. First experiments to study the phase transition in titanium were performed, which demonstrate the strong orientation correlation between the α- and the β-phase.

Abstract: The orientation distribution function (ODF) of the textured polycrystalline nickel titanium (NiTi) shape memory alloys (SMAs) was determined from the measured austenitic (B2)pole-figures by neutron diffraction. The texture results showed that neutron diffraction is an excellent tool to investigate the minor variation in the texture of NiTi alloys, which is very sensitive to the variation of the content of nickel in the materials. Moreover, the alloys crystallographic phase fraction and texture were calculated from Rietveld refinement with generalized spherical harmonic (GSH) description for the measured complete neutron powder diffraction (ND) spectrum, rather than a few isolated peaks, during in-situ temperature-induced martensitic transformation. The phase fraction results are consistent with the differential scanning calorimeter (DSC) curves.