Papers by Author: André Eberhardt

Abstract: Ti-Nb based alloys are well known to their good mechanical properties, shape memory effect, superelasticity, as well as good biocompatibility. The Ti-24Nb (at%) binary alloy presents a shape memory behavior and low elastic modulus. Our study is focused on the improvement of their mechanical properties by adding a third alloying element (oxygen, nitrogen or silicon). Addition of 0.5 at% of N or O modifies drastically the mechanical behavior of Ti-24Nb alloy that exhibits superelastic behavior instead of shape memory one. On the other hand, addition of 0.5 at% of Si increased yield strength of the Ti-24Nb shape memory alloy.

Abstract: A Kossel microdiffraction experimental set up is under development inside a Scanning Electron Microscope (SEM) in order to determine the crystallographic orientation as well as the inter- and intragranular strains and stresses on the micron scale, using a one cubic micrometer spot. The experimental Kossel line patterns are obtained by way of a CCD camera and are then fully indexed using a home-made simulation program. The so-determined orientation is compared with Electron Back-Scattered Diffraction (EBSD) results, and in-situ tests are performed inside the SEM using a tensile/compressive machine. The aim is to verify a 50MPa stress sensitivity for this technique and to take advantage from this microscope environment to associate microstructure observations (slip lines, particle decohesion, crack initiation) with determined stress analyses.

Abstract: FCC metals with different stacking fault energy (SFE), namely Al, Ag and Cu have been investigated for the evolution of crystallographic texture during ECAE deformation using Route A. Different materials with different SFE result in their characteristic textures. The results have been analysed on the basis of microstructural features and related established concepts on texture evolution in FCC metals.

Abstract: FCC metals with different stacking fault energy (SFE), namely Al, Cu and Ag have been investigated for the evolution of crystallographic texture during ECAE deformation using Route A. Different materials with different SFE result in their characteristic textures. The results have been analysed on the basis of microstructural features and related established concepts on texture evolution in FCC metals during other deformation modes.

Abstract: We have developed a new convenient tool for local stress and strain analysis in the scanning electron microscope. It is based on the Kossel diffraction, physical phenomenon that is known for a long time because of its high accuracy for lattice constant determination in micron regions. The pattern is recorded on a CCD camera allowing a fast and reliable analysis. This technique has been applied to several materials. In-situ tensile tests were performed on a shape memory alloy. During loading, we observe clearly a shift of Kossel lines on the diagram, whose magnitude depends on the (hkl) crystallographic planes. The stress can be deduced from the diffracting plane strain measurement using a single crystal stress analysis.

Abstract: The amount of stored energy of cold work for the processing routes A and Bc of Equal Channel Angular Extrusion (ECAE) process has been measured using differential scanning calorimetry. The study is preceded by the effect of amount of ECAE deformation on materials of different stacking fault energies, namely Cu and Ag. The results indicate that the different processing routes have significant effect on the stored energy, which is likely to affect the grain refinement process.