The wettability of a liquid metal on a solid surface is of great technological interest for the industry (soldering, brazing, infiltration) as well as for fundamental research (diffusion, chemical reaction, intermetallic phases). The characterization of wetting is done by measuring the so-called contact angle at the triple line of the liquid on the solid. For this purpose a High Temperature Sessile Drop Device (HTSDD) was constructed and several tasks were performed with this device to test it's capability.
(i) a wettability study of a copper-based brazing alloy (Cu-ABA®) on TiN and TiC coatings with different stoichiometries was done. The data derived from the HTSDD show that the reduction of the nitrogen content in the TiN coating reduces the time for reaching the final contact angle. The N content was additionally quantified by Rutherford Backscattering (RBS).
Also for substoichiometric TiC a similar behavior is predicted in literature and measurement with the HTSDD on TiC coatings were done to confirm this statement.
(ii) The liquid surface energy of molten metals can be estimated from the curvature of flattened droplets due to the influence of gravity. Two models form the literature were used for the calculation of the liquid surface energy of different liquid metals (Cu, Pb, In, Al) and compared with literature values.
(iii) From the decrease of the contact angle (or increase of the droplet radius) vs. time curve it should be possible to distinguish between two different reactive wetting regimes – the diffusion and the reaction controlled reactive wetting. The beginning of this research topic will also be shortly discussed. |