Vortrag (20 Min. Vortrag, 5 Min. Diskussion, 5 Min. Raumwechsel)
In the production of cast parts with a low fatigue, the removal of non-metallic inclusions from the metallic melt during the casting process plays a crucial role. For the filtration, functionalized ceramic foam filters with active and/or reactive surface coatings are utilized. A prerequisite for a targeted functionalization of the filter surface is the knowledge about the chemical reactions occurring at the interface between the metallic melt and the filter materials, and about the interactions between the inclusions and the functionalized filter surface.
In this study, the chemical reactions between molten aluminum alloys and functional surface coatings were investigated with the aid of in situ high-temperature X-ray diffraction (XRD). The XRD phase analyses were performed on thin (<10 µm) metal layers of Al and AlMg1 that were deposited on polished ceramic substrates (SiO2, Al2O3 and MgAl2O4) via magnetron sputtering. The samples were placed inside a high temperature chamber (MTC Hightemp+, Bruker AXS) mounted on a theta/theta-diffractometer (D8 Advance, Bruker AXS). The diffraction patterns were collected during the heat treatment up to 1473 K. Post mortem electron micrographs disclosed the distribution of the reaction products in the interface region.
For MgAl2O4, no considerable reaction with Al or AlMg1 was found. Al2O3 reacted with AlMg1 to magnesium spinel (MgAl2O4). However, the interesting reaction was observed between amorphous silica and aluminum. Already below the melting temperature of Al, the formation of metastable alumina and crystalline Si was observed. At temperatures above 1273 K, the metastable alumina transformed into the thermodynamically stable corundum.
The reaction kinetics and the microstructural changes at the interface regions will be discussed with respect to their relevance for the metal melt filtration.