In order to develop a multifunctional material, a laser induced process was applied to change the properties of a glass-ceramic
by introducing a second phase into the surface. Localized melting of the ceramic and/or a melting of a preplaced
powder layer was achieved by the application of laser energy. After solidification a composite with new properties was
developed. The characteristic feature of the process is the option of a local modification, which is restricted to the
substrate surface and can be controlled by adjustment of the laser parameters. Accordingly modified areas with different
geometries and with a complex multiphase microstructure could be fabricated, while the ceramic bulk remains in its
original state.
Sintered LTCC-substrates (Low Temperature Co-fired Ceramic) were modified with powders metal-oxides (WO3, CuO)
with nanosized particles. Powders of metals (Cu, Ni) were used too. Cladding layers located at the top of the substrate or
layers with a thickness up to several hundred microns, which were embedded into the substrate surface, could be
fabricated. The properties of the laser modified regions differ significantly from that of the LTCC-substrate. The
obtained structures offer modified mechanical, thermophysical and electrical properties. In particular an enhanced
thermal conductivity could be detected. The electrical resistivity of the laser modified tracks widely varied depending on
the process parameters and the powder. Tracks made with CuO- and WO3-powders show a negative temperature
coefficient for electrical resistance, i.e. it decreases with increasing temperature, which is typical for semiconductors.
Laser supported processes can be used to modify the 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 second phase particles are
introduced into the melt pool in order to modify the physical properties. LTCC (Low Temperature Co-fired Ceramics)-substrates were laser alloyed and coated by laser cladding using nanoscaled powders of WO3 and CuO. Depending on the process parameters and the powders used modified areas with different geometries could be fabricated with a complex multiphase microstructure. Particle agglomerates, small crystals as well as grains covered with reaction phase could be found inside the microstructure, in parts with typical length scales in the submicron range. The properties of the laser modified tracks differ significantly from that of the substrate. In particular the thermal and electrical properties were changed. An enhanced thermal conductivity could be detected in laser tracks alloyed with the nano-scaled CuO- and WO3-powders. The electrical resistivity showed a semiconducting behaviour with a negative temperature coefficient, i.e. it decreases with increasing temperature.
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