Papers by Author: Heinz Günter Brokmeier

Abstract: The orientation changes during heating of extruded AZ31 were investigated using synchrotron Xrays by in-situ experiments. The as-extruded sample shows a strong <10.0>-fiber texture which is generally observed after round extrusion. The initial <10.0>-fiber texture, in which the <10.0> direction of the hexagonal crystallites is parallel to extrusion direction, starts to change to <11.0>- fiber component at 300 °C. The orientation change rate shows an exponential relation to the heating temperature and the soaking time. The microstructure observations, prior and post heat treatment, indicate that the texture changes occur mainly during grain growth.

Abstract: Dissimilar welded components joined with any kind of welding technologies gain an increasing interest due to significant improvements in engineering structures by using new materials (alloys) or new materials combinations. The present paper deals with laser welding of Al5083-H111 and Al6013-T6 and the characterization of the crystallographic texture. Fine grained Al5083 was joined with coarser grained Al6013.Whereas, Al6013 is strongly oriented dominated by a strong cube component and a much lower Goss component, the finer grained Al5083 shows a week deformation texture. The welding seam itself has a moderate cube texture with a minor <100> fiber texture in welding direction. A small texture variation about the texture strength and the volume fraction of the fiber component was observed along the weld. Results were obtained by neutron, hard X-ray and electron diffraction.

Abstract: ZWK510 (Mg-5.0wt%Zn-0.9wt%Y-0.2wt%Zr) magnesium alloy containing Mg3YZn6 quasicrystal phase was prepared by conventional permanent mold casting. Part of the cast ingot was subjected to equal channel angular pressing (ECAP) directly; another part of the cast ingot was extruded initially, then ECAP was applied to the extruded alloy. After 4-pass ECAP, the fraction of coarse grains of the as-cast alloy was decreased to about 30%, and the grain size of fine grain was decreased to about 2 μm. Both strength and ductility of the as-cast ZWK510 alloy were significantly improved with increasing ECAP passes, which was resulted from broken and dispersed I-phase, and fine grains formed due to recrystallization. The as-extruded ZWK510 had an initial grain size of about 2 μm and bands of quasicrystal phase parallel to the extrusion direction. After the extruded alloy was subjected to ECAP, the grain size of the extruded alloy was further refined, the grain size was refined to below 0.5 um after 8-pass ECAP; and the quasicrystal phase was further broken and dispersed in the matrix. After ECAP, the elongation to failure of the extruded alloy was improved. However, both yield strength and ultimate tensile strength were decreased, which is considered to be resulted from the texture modification during ECAP.

Abstract: The technical aluminum alloy AA 5109 with a strong cube rolling texture has been deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. Samples for ECAP have been cut parallel and at 45° with respect to the rolling direction yielding different starting textures. The local texture after ECAP has been investigated by highenergy synchrotron radiation. It is characterized by typical shear components of face-centred cubic (fcc) metals which deviate from their ideal positions. The texture with respect to intensity and deviation from ideal positions of the components depends on the distance from the top of the extruded billet and changes from pass to pass. It is also strongly influenced by the starting texture. The texture gradient has been discussed in the light of Tóth’s flow line model. The texture results have also been compared with those of other fcc metals with different stacking fault energy.

Abstract: Cu-Nb composites are characterized by some special properties, which were discussed since a long time by many different authors [1, 2, 3, and 4]. For manufacturing linear accelerator units it is a great advantage that Cu-Nb don’t form intermetallic compounds. One of the basic questions during application is the influence of the thermal expansion of copper and niobium. Thermal expansion of Cu-Nb was widely discussed by Nadeau and Ferrari [5]. Our research program consists of investigations on Cu50%-Nb50% composites and on Cu-Nb tubes, which on one hand have different textures and on the other hand the grain boundaries are much different in the composite with a curling microstructure and in co-extruded tubes. The present paper will concentrate on thermal stresses and the texture behavior in the temperature range 4K -1273K.

Abstract: In this study we present experimental investigations on the microscopic structure, constituent phases, and crystallographic textures of the exoskeleton of three types of decapod crustaceans, namely, lobster, crab, and horseshoe crab. The carapace of such animals is a biological multiphase nano-composite consisting of an organic matrix (crystalline chitin and non-crystalline proteins) and biominerals (calcite, phosphate). The synchrotron measurements of the crystalline chitin and of the biominerals which are embedded in the chitin-protein matrix (in case of lobster and crab) reveal strong textures. The horseshoe crab does not seem to contain notable amounts of crystalline minerals. The Debye-Scherrer images of the lobster specimen suggest that the biominerals form clusters of crystals with similar crystallographic orientation. TEM images support this suggestion. The crystallographic texture of the chitin is arranged with its longest cell axis parallel to the normal of the surface of the exoskeleton.

Abstract: The crystallographic response to deformation – texture evolution, internal elastic strain, and twin evolution – was measured for three load/orientation variants for AZ31 magnesium alloy extrudate tested in-situ in a synchrotron beamline. Specimens were loaded in tension parallel to the extrudate transverse direction, in compression along the same axis, and in compression parallel to the extrudate normal direction. The crystallographic responses are correlated with the mechanical behaviour of the extrudate.

Abstract: The texture influence on the mechanical behavior during uniaxial tension was studied in AZ31 (Mg – 3 Al – 1 Zn in wt.%), one of the common wrought Mg alloys. Since three tensile samples were cut in 0°, 45°, 90° to the extrusion direction, the initial bar texture influences on the mechanical behavior differently. In-situ texture measurements were carried out using hard X-rays under loading condition. According to the initial texture loading results in a variation of the mechanical behavior (yield strength, ultimate tensile strength and strain hardening rate) and in different final textures. The different texture development in each sample relates directly to the activation of different deformation systems, which is strongly influenced by the initial texture

Abstract: Silver of 3N purity was deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. The global and local texture were investigated by neutron diffraction and high-energy synchrotron radiation, respectively. The texture is characterized by typical simple shear components of fcc metals which differently deviate from their ideal positions. Local texture measurements reveal that the intensity and inclination of the texture components with respect to the extrusion direction depend on the distance from the top of the extruded bar and change from pass to pass. Reasons for the texture gradient are discussed. The texture of silver is compared with that of copper having a higher stacking fault energy.

Abstract: The crystal structure of R-phase in Ti50.75.Ni47.75.Fe1.50 shape memory alloy (SMA) has been studied at a temperature of (290 ± 7) K on cooling by combined synchrotron and neutron powder diffraction using Rietveld refinement with generalized spherical harmonic (GSH) description for preferred orientation (PO). The results showed that (i) no significant improvement in the crystallographic RWP-factor was found when the inversion center was removed from the 3 P model, suggesting that the space group was indeed 3 P and not lower symmetry 3 P neither m P31 and (ii) the refined atomic parameters were converging only when the 3 P space group was used in the refinement.