Papers by Author: Matthias Merzkirch

Abstract: Ceramic freeze cast preforms based on alumina show an anisotropic behavior due to directional freezing during preform production. Beside the specific characteristics such as alumina content and lamellae spacing also the distribution of the so-called domains – regions with a relatively homogeneous orientation of alumina lamellae – play an important role considering stiffness and strength. The gas pressure infiltration process was used for infiltrating the freeze cast preforms with a eutectic aluminum/silicon alloy with a low melting point. Selected regions taken from the freeze cast preform have been analyzed via X-ray micro computed tomography (µCT) prior to the infiltration due to a higher contrast in comparison to the infiltrated preforms. The orientation of the lamellae has been determined from the three dimensional data with an algorithm which is based on the structure tensor. The mechanical stability - in terms of the strength - of the infiltrated preforms has been quantified via quasi static compression tests on cuboid samples. The results show a good agreement between the orientation of the lamellae distribution and the maximum strength of the preform which could also be verified using an analytical model.

Abstract: Properties of an interpenetrating metal–ceramic composite with freeze-cast preforms are investigated. For the estimation of elastic properties of the composite numerical homogenization approaches for 2D and 3D finite element models are implemented. The FE models are created based on micro-computed tomography (μCT) images. The results of the numerical 2D and 3D modeling coincide and are in good agreement with available experimental measurements of elastic properties.

Abstract: A possibility to increase both stiffness and strength of aluminium-based structures for the application in lightweight profiles for vehicle space frames is the use of composite extrusions in which high-strength metallic reinforcements are incorporated. Within the scope of the present investigations, composite-extruded profiles with wire-reinforcements made of austenitic spring steel 1.4310 (X10CrNi18-8), in an aluminium matrix AA6060 (AlMgSi0.5), which were exposed to different corrosive media for different times, were characterised in terms of the debonding shear strength using the push-out-technique. The formation of a galvanic couple could be conceived mathematically in regard of terms describing the formation of a shear-impeding layer and the corrosive attack. Thereby the parameters for the different media could be determined.