Embedding of Ceramic Particles in Metals Using Different Techniques for Undercooling of Metallic Melts

Metal Matrix Composites (MMCs) have great technical potential as they combine the ductility of metals with the hardness of ceramics: the reinforced material has improved mechanical properties. MMCs are interesting for the use in automotive or aerospace applications, e.g. in rolling bearings or turbine components. Recent manufacture is done by expensive methods like powder metallurgy to disperse the ceramic particles homogeneously in the metal matrix. In this contribution, we report on an approach to understand the basic mechanisms governing direct casting of MMCs. The basic problem is the particle-solid/liquid-interface interaction during dendritic solidification of metallic melts containing ceramic particles. The experimental idea is to deeply undercool the melt below its melting point. This results in a fast propagating solidification front when the solidification occurs. Due to the rapid solidification, the microstructure is frozen instantaneously and can be investigated post-mortem. It is expected that particles are incorporated in the material in the case of rapid solidification. Experimental techniques are electromagnetic levitation under terrestrial conditions and low gravity conditions during parabolic flight. With the electromagnetic levitation technique, samples were undercooled up to 150 K under its melting points despite the presence of particles. The experiments under low gravity show the importance of the reduction of melt convection on particle distribution within the rapidly solidified sample.