Papers by Author: Robert A. Schwarzer

Abstract: A high speed in acquisition of backscatter Kikuchi patterns (BKP) and solving the stored raw patterns offline has many advantages over online EBSD. No compromise is made between speed and reliability. Automated backscatter Kikuchi diffraction in the scanning electron microscope (SEM) is about to become a tool for process and quality control. Mandatory requirements for these applications are measures to enable re-examination of the results at any time and a high speed. Therefore, fast acquisition of pattern sequences and off¬line indexing will soon become standard. Online pattern solving is optional, but at the disadvantage of reduced speed and reliability.

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: The change of the deformation path leads to destabilization of the substructure and affects the texture of the deformed metal. The observed changes of texture and microstructure are, as a rule, significant and their characteristics depend on the geometry of the deformation process. Previous investigations on copper (and copper alloy) samples after deformation by rolling and channel-die compression were based on X-ray pole figure measurements and on observations in the light microscope. Hereby only global texture and structural characteristics have been obtained. The present study is mainly based on measurements of individual crystal orientations performed by ACOM (Automated Crystal Orientation Measurement, “Automated EBSD”) in the SEM which enables a precise local analysis of the investigated phenomena. For the channel-die experiments, (1 1 2)[1 1 -1] and (1 1 2)[1 -1 0] oriented copper single crystals have been used. After pre-deformation, a second deformation step has been carried out in transverse direction. The {1 1 2}<1 1 0> orientations are destabilized by channel-die compression, and clusters of layers develop which are composed of complementary {1 1 0}<1 1 2> components. The deformation process in polycrystalline sheets after rotating the rolling direction leads again to a distinct disintegration of the microstructure and destabilization of the b fiber. This process of microstructure reorganization after pre-deformation is fast and of high dynamics.

Abstract: The objectives of this investigation are structural effects in electrolytic copper sheets which are caused by the change of the direction of rolling. Unidirectional, reverse as well as cross-rolling at 90° respectively at 45° to the precedent rolling direction have been applied down to final deformations as low as 80% reduction in thickness. Texture has been determined by ACOM (Automated Crystal Orientation Measurement, “Automated EBSD”) in the SEM and by X-ray pole figure measurement. The main benefits of ACOM are a high spatial resolution which enables the investigation of texture gradients from the mid plane to the surface of the sheet, and the visualization of the microstructure by crystal orientation mapping. In addition to local texture, statistical distributions of misorientations across grain boundaries and of S grain boundaries have been derived from the individual grain orientation data. The change of the path of plastic deformation induces a destabilization of the substructure which is formed during the primary step of unidirectional rolling. A distinct change of texture is found depending on the deformation process. In cross rolling, the b fiber changes into the unstable b90 fiber which almost disappears with progressive deformation along the new rolling direction.

Abstract: The surface texture in fcc metals has been investigated after wear tests in a dry-running pin-on-disk test machine and after metallographic surface grinding. X-ray pole figures have been measured at a low angle of incidence of the primary beam, using an area detector for recording the diffraction patterns. SAD pole figures have been acquired on cross sections on-line in the TEM for examining the gradient of texture and microstructure beneath the surface. The XRD and SAD pole figures have been evaluated by ODF calculation. Wear and abrasion textures are distinctly different both for copper and bronze as well as for brass.

Abstract: In this work the textures of MgAl9Zn1, MgAl6Zn1, MgAl3Zn1 and MgAl2Mn alloys have been studied, using individual grain orientation measurement (“ACOM”) in the SEM. Hot extruded billets, unidirectional, reverse and cross-rolled sheet metals as well as laser welding seams have been investigated. In the shaft of a partial extrudate through a circular die orifice, a <0001> ring fiber texture has formed which continuously changes into a spiral fiber texture in the bottom neck. The unidirectional and the reverse hot rolled MgAl2Mn specimens show an R type <0001> texture with a small asymmetrical split whereby the basal poles are tilted by about ±12° from the sheet normal direction to the rolling direction. In the hot cross rolled specimens, the basal poles are slightly spread both in the first and second rolling directions. Texture in the laser welding seams is weak and distinctly different from that of the sheet material. There is almost no heat affected zone at the margins of the welding seams.