Laser modification of ceramic surfaces with micro- and nano-particles

Laser supported processes can be used to modify the electrical and thermal properties of ceramic substrates locally. These processes are characterised by a strong thermal interaction between the laser beam and the ceramic surface which leads to localised melting. During the dynamic melting process metal particles are introduced into the melt pool in order to modify the physical properties. Different alumina samples were treated with metal powders of tungsten, copper, and oxides of these metals. The interface between the metal and the ceramic can be designed by using selected combinations of metal- and metal-oxide-powders and also by a thermal post-processing. The application of nano-particles during the laser-dispersing process resulted in completely different characteristics of the micro-structure and the electrical properties compared to the conventional metal powders with an average grain size of 5 - 15 microns. The micron sized metal particles are embedded within the ceramic matrix as particle agglomerates or as distinct metal phase the nanoparticle phase covers the grain boundaries of the ceramics leading to network of nano-scaled electrically conducting "wires". The resulting resistance of the laser tracks can be adjusted from semi-conducting to metallic behavior with a resistivity down to 2-10(-6)W/m. The modified ceramic can be used for heating elements working at operation temperatures of up to 1000 degrees C, high current resistances which can be loaded with currents of up to 100 A.