Papers by Author: Helmut Klein

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Authors: Andrea Preusser, Helmut Klein, Lars Raue, Hans Joachim Bunge
Authors: Heidrun Sowa, Helmut Klein, Lars Raue
Abstract: In order to get information about the transition mechanism, the temperature-induced transformation in the binary com¬pound NiS was investigated. Above 379 °C, a single crystal of millerite -NiS transforms to polycrystalline NiAs type -NiS with a sharp texture. Pole figures of both phases in the same orientation were measured using synchrotron radiation and an imaging plate detector. The Rietveld texture analysis showed that there are at least three components of the high-temperature -NiS phase. The main component shows the following orientation relations: [001]NiAs type  [001]millerite, [100]NiAs type  [210]millerite, [210]NiAs type  [100]millerite. The broad peaks of the recovered polycrystalline millerite occur at the same positions as the reflections of the original single crystal.
Authors: M. Masimov, Helmut Klein
Abstract: Microstructure and texture formation in DP steels obtained by thermal treatment at temperatures of 780 °C i.e. between Ac1 and Ac3 and at 900 °C, i.e. above Ac3 and following different cooling techniques were studied by means of X-ray and electron diffraction techniques. The formation of the different structure constituents as well as substructure parameters such as blocks size and misorientation between them induced by thermal treatment was detailed analyzed. Various methods – conventional X-ray methods, high-energy synchrotron radiation and EBSD measuring – the texture of the bcc phase were applied in order to investigate their influence on the results. Beside texture heredity, a softening of the initial texture components induced by cold rolling and of related anisotropy of steels due to thermal treatment was estimated.
Authors: Helmut Klein, C. Heubeck, Hans Joachim Bunge
Authors: Lars Raue, Helmut Klein
Abstract: Dental enamel is the most highly mineralised and hardest biological tissue in human body [1]. Dental enamel is made of hydroxylapatite (HAP) - Ca5(PO4)3(OH), which is hexagonal (6/m). The lattice parameters are a = b = 0.9418 nm und c = 0.6875 nm [1]. Although HAP is a very hard mineral, it can be dissolved easily in a process which is known as enamel demineralization by lactic acid produced by bacteria. Also the direct consumption of acid (e.g. citric, lactic or phosphoric acid in soft drinks) can harm the dental enamel in a similar way. These processes can damage the dental enamel. It will be dissolved completely and a cavity occurs. The cavity must then be cleaned and filled. It exists a lot of dental fillings, like gold, amalgam, ceramics or polymeric materials. After filling other dangers can occur: The mechanical properties of the materials used to fill cavities can differ strongly from the ones of the dental enamel itself. In the worst case, the filling of a tooth can damage the enamel of the opposite tooth by chewing if the interaction of enamel and filling is not equivalent, so that the harder fillings can abrade the softer enamel of the healthy tooth at the opposite side. This could be avoided if the anisotropic mechanical properties of dental enamel would be known in detail, hence then another filling could be searched or fabricated as an equivalent opponent for the dental enamel with equal properties. To find such a material, one has to characterise the properties of dental enamel first in detail for the different types of teeth (incisor, canine, premolar and molar). This is here exemplary done for a human incisor tooth by texture analysis with the program MAUD from 2D synchrotron transmission images [2,3,4].
Authors: Helmut Klein
Authors: Helmut Klein, Andrea Preusser, Lars Raue, Hans Joachim Bunge
Abstract: The new developed “sweeping detector” techniques using high energy synchrotron radiation allow to measure textures and microstructures of materials and their change during heat treatment with high location and orientation resolution. Here we show these new methods applied to cold rolled and subsequently annealed nickel samples. The grain-resolved measurements show, impressively, many details of the recrystallization process which can otherwise not be seen. The results of these measurements can be the base for omprehensive recrystallization theories.
Authors: Helmut Klein, Hans Joachim Bunge
Authors: E. Dahlem-Klein, Helmut Klein, No Jin Park, Hans Joachim Bunge
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