Preparation and characterization of ceramics laser alloyed with WO3 and CuO nanopowders

A surface layer of a ceramic substrate can be modified by introducing a second phase into a melt pool generated locally by a laser beam. CuO, WO3 powders with nanosized particles were used to alloy alumina and a glass ceramic LTCC (Low Temperature Co-fired Ceramic). Depending on the process parameters the nano-particles were melted during the laser process and solidified during cooling in the ceramic matrix. As a result a composite with complex multiphase micro-structure was developed with particle agglomerates, small crystals as well as grains covered with reaction phase, in parts with typical length scales down to the submicron range. Also the geometry of the modified area could be controlled by the process parameters. A significant change of properties could be established for the laser alloyed tracks. Especially the thermal and elec-trical properties were changed in comparison to that of the ceramic substrate. The developed composites showed a measurable electrical conductivity with a negative temperature coefficient for the resistivity. Therefore, the resistivity decreases with increasing temperature, which is typical for a thermally activated conduction mechanism as in semiconductors. The thermal conductivity could be increased to about 20% for CuOand up to 70% for WO3-powder compared to the unmodified LTCC-substrate.