High-Resolution Imaging of Texture and Microstructure by the Moving Detector Method

In order to describe texture and microstructure of a polycrystalline material completely, crystal orientation g={?1F?2} must be known in all points x={x1?x2?x3} 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.researc

Local texture measurements with high-energy synchrotron radiation on NiAl deformed in torsion

Plastic deformation leads to crystallographic preferred orientations (texture) of the grains in a polycrystalline sample. Therefore, the study of these textures gives informations about the slip systems activated during the deformation. In this study the deformation of polycrystalline NiAl was done by torsion under confining pressure leading to crack-free samples with a well-defined strain gradient. NiAl, an ordered intermetallic alloy with B2 structure, is a potential material candidate for high-temperature applications. Polycrystalline NiAl cylindrical samples with two different initial textures were deformed in torsion tests at 1000 K and 1273 K, respectively, in a Paterson-type rock deformation machine [1] under 400 MPa argon confining pressure. The diameter and height of the samples were 10 mm. The applied torsion leads to a simple shear in the tangential direction in a plane normal to the torsion axis. The shear strain and the shear strain rate in the samples increase linearly from zero at the torsion axis to a maximum ( ) at the sample edge. To investigate the local textures between the torsion axis and the edge, small pins with a diameter of 1 mm were prepared in the radial direction for each of the four deformed samples Quantitative texture measurements were performed with high-energy (100 keV) synchrotron radiation at the beamline BW5 [2], The incident monochromatic beam was defined by a slit system to 1 mm x 2 mm. The small pins were mounted in the Eulerian cradle parallel to the rotation axis ω. An image plate detector was positioned perpendicularly to the diffracted beam at a distance from the sample of about 1.3 m. Thus, the Debye-Scherrer rings with the indices (100), The texture was measured as a function of the shear strain at five different positions between γ = 0 and 3. The samples deformed at 1273 K showed a poor grain statistics due to a large grain size. The corresponding pole figures are not shown here. The torsion deformation at 1000 K leads to much smaller grains. The corresponding (100) pole figures are shown for γ = 1.5; 2.3 and 3 and two different initial texture

Inhomogeneity of Phase Transformations β→ω and β→α in the Quenched Cold-Rolled Alloy Zr-20 %Nb

The inhomogeneous character of phase transformations in the quenched cold-rolled alloy Zr - 20%Nb was investigated using new X-ray diffractometric procedures based on a position sensitive detector. It was shown that the distribution of strain hardening in β-grains with different orientations controls the development of phase transformation β→α and β→ω in the rolled alloy. Derivative phases inherit the substructure inhomogenity of the β-phase, i.e. their grains are most dispersive and/or have the most distorted crystalline lattice in texture minima, where both phase transformations develop primarily. To explain the obtained X-ray texture data a mechanism was suggested involving local formation of quasi-amorphous boundary interlayers by cold rolling and their crystallization by annealing